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N1548                    Committee Draft -- December 2, 2010          ISO/IEC 9899:201x




INTERNATIONAL STANDARD                         (C)ISO/IEC              ISO/IEC 9899:201x




Programming languages -- C


                                       ABSTRACT



                     (Cover sheet to be provided by ISO Secretariat.)

This International Standard specifies the form and establishes the interpretation of
programs expressed in the programming language C. Its purpose is to promote
portability, reliability, maintainability, and efficient execution of C language programs on
a variety of computing systems.

Clauses are included that detail the C language itself and the contents of the C language
execution library. Annexes summarize aspects of both of them, and enumerate factors
that influence the portability of C programs.

Although this International Standard is intended to guide knowledgeable C language
programmers as well as implementors of C language translation systems, the document
itself is not designed to serve as a tutorial.

Recipients of this draft are invited to submit, with their comments, notification of any
relevant patent rights of which they are aware and to provide supporting documentation.

Changes from the previous draft (N1256) are indicated by ''diff marks'' in the right
margin: deleted text is marked with ''*'', new or changed text with '' ''.




[page i]



[page ii]

Contents
Foreword       . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                                 xiii
Introduction    . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
1. Scope       . . . . . . . . . . . . . . . . . . . . . . . . . . . . .                                   1
2. Normative references     . . . . . . . . . . . . . . . . . . . . . . .                                  2
3. Terms, definitions, and symbols    . . . . . . . . . . . . . . . . . . .                                 3
4. Conformance       . . . . . . . . . . . . . . . . . . . . . . . . . .                                   8
5. Environment    . . . . . . . . . . .       . .   .   .   .   .   .   .   .    .   .   .   .   .   .    10
   5.1 Conceptual models       . . . . . .    . .   .   .   .   .   .   .   .    .   .   .   .   .   .    10
        5.1.1  Translation environment .      . .   .   .   .   .   .   .   .    .   .   .   .   .   .    10
        5.1.2  Execution environments     .   . .   .   .   .   .   .   .   .    .   .   .   .   .   .    12
   5.2 Environmental considerations    . .    . .   .   .   .   .   .   .   .    .   .   .   .   .   .    22
        5.2.1  Character sets    . . . . .    . .   .   .   .   .   .   .   .    .   .   .   .   .   .    22
        5.2.2  Character display semantics      .   .   .   .   .   .   .   .    .   .   .   .   .   .    24
        5.2.3  Signals and interrupts . .     . .   .   .   .   .   .   .   .    .   .   .   .   .   .    25
        5.2.4  Environmental limits    . .    . .   .   .   .   .   .   .   .    .   .   .   .   .   .    25
6. Language . . . . . . . . . . . . . . . .             .   .   .   .   .   .    .   .   .   .   .   .    35
   6.1 Notation . . . . . . . . . . . . . .             .   .   .   .   .   .    .   .   .   .   .   .    35
   6.2 Concepts       . . . . . . . . . . . . .         .   .   .   .   .   .    .   .   .   .   .   .    35
        6.2.1   Scopes of identifiers     . . . . .      .   .   .   .   .   .    .   .   .   .   .   .    35
        6.2.2   Linkages of identifiers . . . . .        .   .   .   .   .   .    .   .   .   .   .   .    36
        6.2.3   Name spaces of identifiers      . . .    .   .   .   .   .   .    .   .   .   .   .   .    37
        6.2.4   Storage durations of objects     . .    .   .   .   .   .   .    .   .   .   .   .   .    38
        6.2.5   Types       . . . . . . . . . . .       .   .   .   .   .   .    .   .   .   .   .   .    39
        6.2.6   Representations of types . . . .        .   .   .   .   .   .    .   .   .   .   .   .    44
        6.2.7   Compatible type and composite type          .   .   .   .   .    .   .   .   .   .   .    47
        6.2.8   Alignment of objects     . . . . .      .   .   .   .   .   .    .   .   .   .   .   .    48
   6.3 Conversions       . . . . . . . . . . . .        .   .   .   .   .   .    .   .   .   .   .   .    50
        6.3.1   Arithmetic operands      . . . . .      .   .   .   .   .   .    .   .   .   .   .   .    50
        6.3.2   Other operands       . . . . . . .      .   .   .   .   .   .    .   .   .   .   .   .    54
   6.4 Lexical elements       . . . . . . . . . .       .   .   .   .   .   .    .   .   .   .   .   .    57
        6.4.1   Keywords . . . . . . . . . .            .   .   .   .   .   .    .   .   .   .   .   .    58
        6.4.2   Identifiers . . . . . . . . . .          .   .   .   .   .   .    .   .   .   .   .   .    59
        6.4.3   Universal character names      . . .    .   .   .   .   .   .    .   .   .   .   .   .    61
        6.4.4   Constants . . . . . . . . . .           .   .   .   .   .   .    .   .   .   .   .   .    62
        6.4.5   String literals   . . . . . . . .       .   .   .   .   .   .    .   .   .   .   .   .    70
        6.4.6   Punctuators . . . . . . . . .           .   .   .   .   .   .    .   .   .   .   .   .    72
        6.4.7   Header names      . . . . . . . .       .   .   .   .   .   .    .   .   .   .   .   .    73
        6.4.8   Preprocessing numbers        . . . .    .   .   .   .   .   .    .   .   .   .   .   .    74
        6.4.9   Comments        . . . . . . . . .       .   .   .   .   .   .    .   .   .   .   .   .    75


[page iii]

     6.5  Expressions      . . . . . . . . . .     .   .   .   .   .   .   .   .   .   .   .   .   .   .    76
          6.5.1   Primary expressions      . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    78
          6.5.2   Postfix operators . . . . .       .   .   .   .   .   .   .   .   .   .   .   .   .   .    79
          6.5.3   Unary operators      . . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    88
          6.5.4   Cast operators . . . . . .       .   .   .   .   .   .   .   .   .   .   .   .   .   .    91
          6.5.5   Multiplicative operators   . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    92
          6.5.6   Additive operators     . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    92
          6.5.7   Bitwise shift operators . . .    .   .   .   .   .   .   .   .   .   .   .   .   .   .    94
          6.5.8   Relational operators . . . .     .   .   .   .   .   .   .   .   .   .   .   .   .   .    95
          6.5.9   Equality operators     . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    96
          6.5.10 Bitwise AND operator . . .        .   .   .   .   .   .   .   .   .   .   .   .   .   .    97
          6.5.11 Bitwise exclusive OR operator         .   .   .   .   .   .   .   .   .   .   .   .   .    98
          6.5.12 Bitwise inclusive OR operator     .   .   .   .   .   .   .   .   .   .   .   .   .   .    98
          6.5.13 Logical AND operator . . .        .   .   .   .   .   .   .   .   .   .   .   .   .   .    99
          6.5.14 Logical OR operator       . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .    99
          6.5.15 Conditional operator      . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   100
          6.5.16 Assignment operators . . .        .   .   .   .   .   .   .   .   .   .   .   .   .   .   101
          6.5.17 Comma operator . . . . .          .   .   .   .   .   .   .   .   .   .   .   .   .   .   104
     6.6 Constant expressions . . . . . . .        .   .   .   .   .   .   .   .   .   .   .   .   .   .   105
     6.7 Declarations      . . . . . . . . . .     .   .   .   .   .   .   .   .   .   .   .   .   .   .   107
          6.7.1   Storage-class specifiers    . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   108
          6.7.2   Type specifiers . . . . . .       .   .   .   .   .   .   .   .   .   .   .   .   .   .   109
          6.7.3   Type qualifiers . . . . . .       .   .   .   .   .   .   .   .   .   .   .   .   .   .   120
          6.7.4   Function specifiers     . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   124
          6.7.5   Alignment specifier . . . .       .   .   .   .   .   .   .   .   .   .   .   .   .   .   126
          6.7.6   Declarators     . . . . . . .    .   .   .   .   .   .   .   .   .   .   .   .   .   .   127
          6.7.7   Type names . . . . . . .         .   .   .   .   .   .   .   .   .   .   .   .   .   .   135
          6.7.8   Type definitions      . . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   136
          6.7.9   Initialization    . . . . . .    .   .   .   .   .   .   .   .   .   .   .   .   .   .   138
          6.7.10 Static assertions     . . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   144
     6.8 Statements and blocks      . . . . . .    .   .   .   .   .   .   .   .   .   .   .   .   .   .   145
          6.8.1   Labeled statements     . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   145
          6.8.2   Compound statement       . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   146
          6.8.3   Expression and null statements       .   .   .   .   .   .   .   .   .   .   .   .   .   146
          6.8.4   Selection statements     . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   147
          6.8.5   Iteration statements . . . .     .   .   .   .   .   .   .   .   .   .   .   .   .   .   149
          6.8.6   Jump statements      . . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   150
     6.9 External definitions      . . . . . . .    .   .   .   .   .   .   .   .   .   .   .   .   .   .   154
          6.9.1   Function definitions . . . .      .   .   .   .   .   .   .   .   .   .   .   .   .   .   155
          6.9.2   External object definitions   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   157
     6.10 Preprocessing directives     . . . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   159
          6.10.1 Conditional inclusion     . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   161
          6.10.2 Source file inclusion      . . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   163
          6.10.3 Macro replacement . . . .         .   .   .   .   .   .   .   .   .   .   .   .   .   .   165


[page iv]

       6.10.4 Line control . . . . . .        .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   172
       6.10.5 Error directive . . . . .       .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   173
       6.10.6 Pragma directive . . . .        .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   173
       6.10.7 Null directive      . . . . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   174
       6.10.8 Predefined macro names .         .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   174
       6.10.9 Pragma operator       . . . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   176
  6.11 Future language directions     . . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.1 Floating types      . . . . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.2 Linkages of identifiers . .      .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.3 External names        . . . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.4 Character escape sequences          .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.5 Storage-class specifiers     .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.6 Function declarators      . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.7 Function definitions . . .       .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.8 Pragma directives       . . .   .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
       6.11.9 Predefined macro names .         .   .   .   .   .   .   .   .   .    .   .   .   .   .   .   178
7. Library . . . . . . . . . . . . . . . . . .                .   .   .   .   .    .   .   .   .   .   .   179
   7.1 Introduction     . . . . . . . . . . . . .             .   .   .   .   .    .   .   .   .   .   .   179
         7.1.1 Definitions of terms . . . . . . .              .   .   .   .   .    .   .   .   .   .   .   179
         7.1.2 Standard headers . . . . . . . .               .   .   .   .   .    .   .   .   .   .   .   180
         7.1.3 Reserved identifiers . . . . . . .              .   .   .   .   .    .   .   .   .   .   .   181
         7.1.4 Use of library functions    . . . . .          .   .   .   .   .    .   .   .   .   .   .   182
   7.2 Diagnostics <assert.h>          . . . . . . .          .   .   .   .   .    .   .   .   .   .   .   185
         7.2.1 Program diagnostics       . . . . . .          .   .   .   .   .    .   .   .   .   .   .   185
   7.3 Complex arithmetic <complex.h>           . . .         .   .   .   .   .    .   .   .   .   .   .   187
         7.3.1 Introduction . . . . . . . . . .               .   .   .   .   .    .   .   .   .   .   .   187
         7.3.2 Conventions . . . . . . . . . .                .   .   .   .   .    .   .   .   .   .   .   188
         7.3.3 Branch cuts . . . . . . . . . .                .   .   .   .   .    .   .   .   .   .   .   188
         7.3.4 The CX_LIMITED_RANGE pragma                    .   .   .   .   .    .   .   .   .   .   .   188
         7.3.5 Trigonometric functions . . . . .              .   .   .   .   .    .   .   .   .   .   .   189
         7.3.6 Hyperbolic functions      . . . . . .          .   .   .   .   .    .   .   .   .   .   .   191
         7.3.7 Exponential and logarithmic functions              .   .   .   .    .   .   .   .   .   .   193
         7.3.8 Power and absolute-value functions             .   .   .   .   .    .   .   .   .   .   .   194
         7.3.9 Manipulation functions      . . . . .          .   .   .   .   .    .   .   .   .   .   .   195
   7.4 Character handling <ctype.h> . . . . .                 .   .   .   .   .    .   .   .   .   .   .   199
         7.4.1 Character classification functions    .         .   .   .   .   .    .   .   .   .   .   .   199
         7.4.2 Character case mapping functions     .         .   .   .   .   .    .   .   .   .   .   .   202
   7.5 Errors <errno.h>         . . . . . . . . . .           .   .   .   .   .    .   .   .   .   .   .   204
   7.6 Floating-point environment <fenv.h>        . .         .   .   .   .   .    .   .   .   .   .   .   205
         7.6.1 The FENV_ACCESS pragma           . . .         .   .   .   .   .    .   .   .   .   .   .   207
         7.6.2 Floating-point exceptions      . . . .         .   .   .   .   .    .   .   .   .   .   .   208
         7.6.3 Rounding . . . . . . . . . . .                 .   .   .   .   .    .   .   .   .   .   .   211
         7.6.4 Environment        . . . . . . . . .           .   .   .   .   .    .   .   .   .   .   .   212
   7.7 Characteristics of floating types <float.h>             .   .   .   .   .    .   .   .   .   .   .   215

[page v]

     7.8    Format conversion of integer types <inttypes.h> . . . .           .   .   .   .   216
            7.8.1    Macros for format specifiers      . . . . . . . . . .     .   .   .   .   216
            7.8.2    Functions for greatest-width integer types   . . . . .   .   .   .   .   217
     7.9    Alternative spellings <iso646.h> . . . . . . . . . . .            .   .   .   .   220
     7.10   Sizes of integer types <limits.h>         . . . . . . . . . .     .   .   .   .   221
     7.11   Localization <locale.h> . . . . . . . . . . . . . .               .   .   .   .   222
            7.11.1 Locale control . . . . . . . . . . . . . . . .             .   .   .   .   223
            7.11.2 Numeric formatting convention inquiry . . . . . .          .   .   .   .   224
     7.12   Mathematics <math.h> . . . . . . . . . . . . . . .                .   .   .   .   230
            7.12.1 Treatment of error conditions . . . . . . . . . .          .   .   .   .   232
            7.12.2 The FP_CONTRACT pragma             . . . . . . . . . .     .   .   .   .   234
            7.12.3 Classification macros       . . . . . . . . . . . . .       .   .   .   .   234
            7.12.4 Trigonometric functions . . . . . . . . . . . .            .   .   .   .   237
            7.12.5 Hyperbolic functions       . . . . . . . . . . . . .       .   .   .   .   239
            7.12.6 Exponential and logarithmic functions        . . . . . .   .   .   .   .   241
            7.12.7 Power and absolute-value functions         . . . . . . .   .   .   .   .   246
            7.12.8 Error and gamma functions . . . . . . . . . . .            .   .   .   .   248
            7.12.9 Nearest integer functions . . . . . . . . . . . .          .   .   .   .   250
            7.12.10 Remainder functions       . . . . . . . . . . . . .       .   .   .   .   253
            7.12.11 Manipulation functions       . . . . . . . . . . . .      .   .   .   .   254
            7.12.12 Maximum, minimum, and positive difference functions           .   .   .   256
            7.12.13 Floating multiply-add . . . . . . . . . . . . .           .   .   .   .   257
            7.12.14 Comparison macros . . . . . . . . . . . . . .             .   .   .   .   258
     7.13   Nonlocal jumps <setjmp.h>            . . . . . . . . . . . .      .   .   .   .   261
            7.13.1 Save calling environment         . . . . . . . . . . .     .   .   .   .   261
            7.13.2 Restore calling environment        . . . . . . . . . .     .   .   .   .   262
     7.14   Signal handling <signal.h> . . . . . . . . . . . . .              .   .   .   .   264
            7.14.1 Specify signal handling       . . . . . . . . . . . .      .   .   .   .   265
            7.14.2 Send signal      . . . . . . . . . . . . . . . . .         .   .   .   .   266
     7.15   Alignment <stdalign.h>            . . . . . . . . . . . . .       .   .   .   .   267
     7.16   Variable arguments <stdarg.h>           . . . . . . . . . . .     .   .   .   .   268
            7.16.1 Variable argument list access macros . . . . . . .         .   .   .   .   268
     7.17   Atomics <stdatomic.h> . . . . . . . . . . . . . .                 .   .   .   .   272
            7.17.1 Introduction . . . . . . . . . . . . . . . . .             .   .   .   .   272
            7.17.2 Initialization      . . . . . . . . . . . . . . . .        .   .   .   .   273
            7.17.3 Order and consistency . . . . . . . . . . . . .            .   .   .   .   274
            7.17.4 Fences . . . . . . . . . . . . . . . . . . .               .   .   .   .   277
            7.17.5 Lock-free property       . . . . . . . . . . . . . .       .   .   .   .   278
            7.17.6 Atomic integer and address types         . . . . . . . .   .   .   .   .   279
            7.17.7 Operations on atomic types . . . . . . . . . . .           .   .   .   .   281
            7.17.8 Atomic flag type and operations . . . . . . . . .           .   .   .   .   284
     7.18   Boolean type and values <stdbool.h>             . . . . . . . .   .   .   .   .   286
     7.19   Common definitions <stddef.h> . . . . . . . . . . .                .   .   .   .   287
     7.20   Integer types <stdint.h> . . . . . . . . . . . . . .              .   .   .   .   289


[page vi]

         7.20.1 Integer types      . . . . . . . . . . . .      .   .    .   .   .   .   .   .   289
         7.20.2 Limits of specified-width integer types    . .   .   .    .   .   .   .   .   .   291
         7.20.3 Limits of other integer types    . . . . . .    .   .    .   .   .   .   .   .   293
         7.20.4 Macros for integer constants     . . . . . .    .   .    .   .   .   .   .   .   294
  7.21   Input/output <stdio.h>         . . . . . . . . . .     .   .    .   .   .   .   .   .   296
         7.21.1 Introduction . . . . . . . . . . . . .          .   .    .   .   .   .   .   .   296
         7.21.2 Streams       . . . . . . . . . . . . . .       .   .    .   .   .   .   .   .   298
         7.21.3 Files . . . . . . . . . . . . . . . .           .   .    .   .   .   .   .   .   300
         7.21.4 Operations on files      . . . . . . . . . .     .   .    .   .   .   .   .   .   302
         7.21.5 File access functions     . . . . . . . . .     .   .    .   .   .   .   .   .   304
         7.21.6 Formatted input/output functions     . . . .    .   .    .   .   .   .   .   .   309
         7.21.7 Character input/output functions . . . . .      .   .    .   .   .   .   .   .   330
         7.21.8 Direct input/output functions    . . . . . .    .   .    .   .   .   .   .   .   334
         7.21.9 File positioning functions     . . . . . . .    .   .    .   .   .   .   .   .   335
         7.21.10 Error-handling functions . . . . . . . .       .   .    .   .   .   .   .   .   338
  7.22   General utilities <stdlib.h>        . . . . . . . .    .   .    .   .   .   .   .   .   340
         7.22.1 Numeric conversion functions . . . . . .        .   .    .   .   .   .   .   .   341
         7.22.2 Pseudo-random sequence generation functions         .    .   .   .   .   .   .   346
         7.22.3 Memory management functions . . . . .           .   .    .   .   .   .   .   .   347
         7.22.4 Communication with the environment        . .   .   .    .   .   .   .   .   .   349
         7.22.5 Searching and sorting utilities . . . . . .     .   .    .   .   .   .   .   .   353
         7.22.6 Integer arithmetic functions     . . . . . .    .   .    .   .   .   .   .   .   355
         7.22.7 Multibyte/wide character conversion functions       .    .   .   .   .   .   .   356
         7.22.8 Multibyte/wide string conversion functions      .   .    .   .   .   .   .   .   358
  7.23   String handling <string.h> . . . . . . . . .           .   .    .   .   .   .   .   .   360
         7.23.1 String function conventions . . . . . . .       .   .    .   .   .   .   .   .   360
         7.23.2 Copying functions       . . . . . . . . . .     .   .    .   .   .   .   .   .   360
         7.23.3 Concatenation functions . . . . . . . .         .   .    .   .   .   .   .   .   362
         7.23.4 Comparison functions . . . . . . . . .          .   .    .   .   .   .   .   .   363
         7.23.5 Search functions      . . . . . . . . . . .     .   .    .   .   .   .   .   .   365
         7.23.6 Miscellaneous functions . . . . . . . .         .   .    .   .   .   .   .   .   368
  7.24   Type-generic math <tgmath.h>          . . . . . . .    .   .    .   .   .   .   .   .   370
  7.25   Threads <threads.h>          . . . . . . . . . . .     .   .    .   .   .   .   .   .   373
         7.25.1 Introduction . . . . . . . . . . . . .          .   .    .   .   .   .   .   .   373
         7.25.2 Initialization functions . . . . . . . . .      .   .    .   .   .   .   .   .   375
         7.25.3 Condition variable functions     . . . . . .    .   .    .   .   .   .   .   .   375
         7.25.4 Mutex functions       . . . . . . . . . . .     .   .    .   .   .   .   .   .   377
         7.25.5 Thread functions . . . . . . . . . . .          .   .    .   .   .   .   .   .   380
         7.25.6 Thread-specific storage functions     . . . .    .   .    .   .   .   .   .   .   382
         7.25.7 Time functions . . . . . . . . . . . .          .   .    .   .   .   .   .   .   384
  7.26   Date and time <time.h>         . . . . . . . . . .     .   .    .   .   .   .   .   .   385
         7.26.1 Components of time        . . . . . . . . .     .   .    .   .   .   .   .   .   385
         7.26.2 Time manipulation functions      . . . . . .    .   .    .   .   .   .   .   .   386
         7.26.3 Time conversion functions      . . . . . . .    .   .    .   .   .   .   .   .   388


[page vii]

   7.27 Unicode utilities <uchar.h> . . . . . . . . . . . . . .               . .     .   395
        7.27.1 Restartable multibyte/wide character conversion functions        .     .   395
   7.28 Extended multibyte and wide character utilities <wchar.h> . .         . .     .   399
        7.28.1 Introduction . . . . . . . . . . . . . . . . . .               . .     .   399
        7.28.2 Formatted wide character input/output functions       . . .    . .     .   400
        7.28.3 Wide character input/output functions        . . . . . . .     . .     .   418
        7.28.4 General wide string utilities     . . . . . . . . . . .        . .     .   422
                 7.28.4.1 Wide string numeric conversion functions     . .    . .     .   423
                 7.28.4.2 Wide string copying functions . . . . . . .         . .     .   427
                 7.28.4.3 Wide string concatenation functions      . . . .    . .     .   429
                 7.28.4.4 Wide string comparison functions      . . . . .     . .     .   430
                 7.28.4.5 Wide string search functions      . . . . . . .     . .     .   432
                 7.28.4.6 Miscellaneous functions      . . . . . . . . .      . .     .   436
        7.28.5 Wide character time conversion functions       . . . . . .     . .     .   436
        7.28.6 Extended multibyte/wide character conversion utilities .       . .     .   437
                 7.28.6.1 Single-byte/wide character conversion functions     . .     .   438
                 7.28.6.2 Conversion state functions     . . . . . . . .      . .     .   438
                 7.28.6.3 Restartable multibyte/wide character conversion
                           functions   . . . . . . . . . . . . . . .          . . . 439
                 7.28.6.4 Restartable multibyte/wide string conversion
                           functions   . . . . . . . . . . . . . . .          .   .   .   441
   7.29 Wide character classification and mapping utilities <wctype.h>         .   .   .   444
        7.29.1 Introduction . . . . . . . . . . . . . . . . . .               .   .   .   444
        7.29.2 Wide character classification utilities . . . . . . . .         .   .   .   445
                 7.29.2.1 Wide character classification functions     . . .    .   .   .   445
                 7.29.2.2 Extensible wide character classification
                           functions   . . . . . . . . . . . . . . .          . . . 448
        7.29.3 Wide character case mapping utilities . . . . . . . .          . . . 450
                 7.29.3.1 Wide character case mapping functions      . . .    . . . 450
                 7.29.3.2 Extensible wide character case mapping
                           functions   . . . . . . . . . . . . . . .          .   .   .   450
   7.30 Future library directions    . . . . . . . . . . . . . . . .          .   .   .   452
        7.30.1 Complex arithmetic <complex.h> . . . . . . . .                 .   .   .   452
        7.30.2 Character handling <ctype.h>            . . . . . . . . .      .   .   .   452
        7.30.3 Errors <errno.h>           . . . . . . . . . . . . . .         .   .   .   452
        7.30.4 Format conversion of integer types <inttypes.h>            .   .   .   .   452
        7.30.5 Localization <locale.h>           . . . . . . . . . . .        .   .   .   452
        7.30.6 Signal handling <signal.h>           . . . . . . . . . .       .   .   .   452
        7.30.7 Boolean type and values <stdbool.h>            . . . . . .     .   .   .   452
        7.30.8 Integer types <stdint.h>          . . . . . . . . . . .        .   .   .   452
        7.30.9 Input/output <stdio.h>          . . . . . . . . . . . .        .   .   .   453
        7.30.10 General utilities <stdlib.h>        . . . . . . . . . .       .   .   .   453
        7.30.11 String handling <string.h>          . . . . . . . . . .       .   .   .   453



[page viii]

        7.30.12 Extended multibyte and wide character utilities
                <wchar.h>        . . . . . . . . . . . . . . . . . . . . 453
        7.30.13 Wide character classification and mapping utilities
                <wctype.h> . . . . . . . . . . . . . . . . . . . . 453
Annex A (informative) Language syntax summary   . .       .   .   .   .    .   .   .   .   .   .   454
  A.1 Lexical grammar       . . . . . . . . . . . .       .   .   .   .    .   .   .   .   .   .   454
  A.2 Phrase structure grammar . . . . . . . . .          .   .   .   .    .   .   .   .   .   .   461
  A.3 Preprocessing directives    . . . . . . . . .       .   .   .   .    .   .   .   .   .   .   469
Annex B (informative) Library summary     . . . . . . . . . . . . .                    .   .   .   471
  B.1 Diagnostics <assert.h>          . . . . . . . . . . . . . . .                    .   .   .   471
  B.2 Complex <complex.h> . . . . . . . . . . . . . . . .                              .   .   .   471
  B.3 Character handling <ctype.h> . . . . . . . . . . . . .                           .   .   .   473
  B.4 Errors <errno.h>         . . . . . . . . . . . . . . . . . .                     .   .   .   473
  B.5 Floating-point environment <fenv.h>          . . . . . . . . . .                 .   .   .   473
  B.6 Characteristics of floating types <float.h> . . . . . . . .                       .   .   .   474
  B.7 Format conversion of integer types <inttypes.h> . . . . .                        .   .   .   474
  B.8 Alternative spellings <iso646.h> . . . . . . . . . . . .                         .   .   .   475
  B.9 Sizes of integer types <limits.h>          . . . . . . . . . . .                 .   .   .   475
  B.10 Localization <locale.h> . . . . . . . . . . . . . . .                           .   .   .   475
  B.11 Mathematics <math.h> . . . . . . . . . . . . . . . .                            .   .   .   475
  B.12 Nonlocal jumps <setjmp.h>          . . . . . . . . . . . . .                    .   .   .   480
  B.13 Signal handling <signal.h> . . . . . . . . . . . . . .                          .   .   .   480
  B.14 Alignment <stdalign.h>           . . . . . . . . . . . . . .                    .   .   .   481
  B.15 Variable arguments <stdarg.h>         . . . . . . . . . . . .                   .   .   .   481
  B.16 Atomics <stdatomic.h> . . . . . . . . . . . . . . .                             .   .   .   481
  B.17 Boolean type and values <stdbool.h>           . . . . . . . . .                 .   .   .   483
  B.18 Common definitions <stddef.h> . . . . . . . . . . . .                            .   .   .   483
  B.19 Integer types <stdint.h> . . . . . . . . . . . . . . .                          .   .   .   483
  B.20 Input/output <stdio.h>         . . . . . . . . . . . . . . .                    .   .   .   484
  B.21 General utilities <stdlib.h>       . . . . . . . . . . . . .                    .   .   .   487
  B.22 String handling <string.h> . . . . . . . . . . . . . .                          .   .   .   489
  B.23 Type-generic math <tgmath.h>          . . . . . . . . . . . .                   .   .   .   491
  B.24 Threads <threads.h>          . . . . . . . . . . . . . . . .                    .   .   .   491
  B.25 Date and time <time.h>         . . . . . . . . . . . . . . .                    .   .   .   492
  B.26 Unicode utilities <uchar.h> . . . . . . . . . . . . . .                         .   .   .   493
  B.27 Extended multibyte/wide character utilities <wchar.h>     . . .                 .   .   .   493
  B.28 Wide character classification and mapping utilities <wctype.h>                   .   .   .   498
Annex C (informative) Sequence points     . . . . . . . . . . . . . . . . . 499
Annex D (normative) Universal character names for identifiers . . . . . . . 500
  D.1 Ranges of characters allowed       . . . . . . . . . . . . . . . . . 500
  D.2 Ranges of characters disallowed initially . . . . . . . . . . . . . 500
Annex E (informative) Implementation limits        . . . . . . . . . . . . . . 501

[page ix]

Annex F (normative) IEC 60559 floating-point arithmetic . . . . . .          . .     .   .   503
  F.1 Introduction      . . . . . . . . . . . . . . . . . . . .             . .     .   .   503
  F.2 Types . . . . . . . . . . . . . . . . . . . . . . .                   . .     .   .   503
  F.3 Operators and functions       . . . . . . . . . . . . . . .           . .     .   .   504
  F.4 Floating to integer conversion    . . . . . . . . . . . . .           . .     .   .   506
  F.5 Binary-decimal conversion       . . . . . . . . . . . . . .           . .     .   .   506
  F.6 The return statement . . . . . . . . . . . . . . . .                  . .     .   .   507
  F.7 Contracted expressions . . . . . . . . . . . . . . . .                . .     .   .   507
  F.8 Floating-point environment      . . . . . . . . . . . . . .           . .     .   .   507
  F.9 Optimization . . . . . . . . . . . . . . . . . . . .                  . .     .   .   510
  F.10 Mathematics <math.h> . . . . . . . . . . . . . . .                   . .     .   .   513
        F.10.1 Trigonometric functions . . . . . . . . . . . .              . .     .   .   514
        F.10.2 Hyperbolic functions     . . . . . . . . . . . . .           . .     .   .   516
        F.10.3 Exponential and logarithmic functions    . . . . . .         . .     .   .   516
        F.10.4 Power and absolute value functions     . . . . . . .         . .     .   .   520
        F.10.5 Error and gamma functions . . . . . . . . . . .              . .     .   .   521
        F.10.6 Nearest integer functions . . . . . . . . . . . .            . .     .   .   522
        F.10.7 Remainder functions      . . . . . . . . . . . . .           . .     .   .   524
        F.10.8 Manipulation functions     . . . . . . . . . . . .           . .     .   .   525
        F.10.9 Maximum, minimum, and positive difference functions            .     .   .   526
        F.10.10 Floating multiply-add . . . . . . . . . . . . .             . .     .   .   526
        F.10.11 Comparison macros . . . . . . . . . . . . . .               . .     .   .   527
Annex G (normative) IEC 60559-compatible complex arithmetic     .   .   .   .   .   .   .   528
  G.1 Introduction     . . . . . . . . . . . . . . . . .        .   .   .   .   .   .   .   528
  G.2 Types . . . . . . . . . . . . . . . . . . . .             .   .   .   .   .   .   .   528
  G.3 Conventions      . . . . . . . . . . . . . . . . .        .   .   .   .   .   .   .   528
  G.4 Conversions      . . . . . . . . . . . . . . . . .        .   .   .   .   .   .   .   529
       G.4.1 Imaginary types     . . . . . . . . . . . .        .   .   .   .   .   .   .   529
       G.4.2 Real and imaginary . . . . . . . . . . .           .   .   .   .   .   .   .   529
       G.4.3 Imaginary and complex       . . . . . . . . .      .   .   .   .   .   .   .   529
  G.5 Binary operators     . . . . . . . . . . . . . . .        .   .   .   .   .   .   .   529
       G.5.1 Multiplicative operators    . . . . . . . . .      .   .   .   .   .   .   .   530
       G.5.2 Additive operators     . . . . . . . . . . .       .   .   .   .   .   .   .   533
  G.6 Complex arithmetic <complex.h>         . . . . . . .      .   .   .   .   .   .   .   533
       G.6.1 Trigonometric functions . . . . . . . . .          .   .   .   .   .   .   .   535
       G.6.2 Hyperbolic functions     . . . . . . . . . .       .   .   .   .   .   .   .   535
       G.6.3 Exponential and logarithmic functions     . . .    .   .   .   .   .   .   .   539
       G.6.4 Power and absolute-value functions      . . . .    .   .   .   .   .   .   .   540
  G.7 Type-generic math <tgmath.h>         . . . . . . . .      .   .   .   .   .   .   .   541
Annex H (informative) Language independent arithmetic . .   .   .   .   .   .   .   .   .   542
  H.1 Introduction     . . . . . . . . . . . . . . . .      .   .   .   .   .   .   .   .   542
  H.2 Types . . . . . . . . . . . . . . . . . . .           .   .   .   .   .   .   .   .   542
  H.3 Notification      . . . . . . . . . . . . . . . .      .   .   .   .   .   .   .   .   546


[page x]

Annex I (informative) Common warnings         . . . . . . . . . . . . . . . . 548
Annex J (informative) Portability issues    . . . .   .   .   .   .   .   .   .    .   .   .   .   .   .   550
  J.1 Unspecified behavior . . . .           . . . .   .   .   .   .   .   .   .    .   .   .   .   .   .   550
  J.2 Undefined behavior          . . . .    . . . .   .   .   .   .   .   .   .    .   .   .   .   .   .   553
  J.3 Implementation-defined behavior          . . .   .   .   .   .   .   .   .    .   .   .   .   .   .   566
  J.4 Locale-specific behavior         . .   . . . .   .   .   .   .   .   .   .    .   .   .   .   .   .   574
  J.5 Common extensions          . . . .    . . . .   .   .   .   .   .   .   .    .   .   .   .   .   .   575
Annex K (normative) Bounds-checking interfaces . . . . . . . . . .                             .   .   .   578
  K.1 Background       . . . . . . . . . . . . . . . . . . . . .                               .   .   .   578
  K.2 Scope . . . . . . . . . . . . . . . . . . . . . . . .                                    .   .   .   579
  K.3 Library     . . . . . . . . . . . . . . . . . . . . . . .                                .   .   .   579
       K.3.1 Introduction . . . . . . . . . . . . . . . . . .                                  .   .   .   579
                K.3.1.1 Standard headers     . . . . . . . . . . . .                           .   .   .   579
                K.3.1.2 Reserved identifiers     . . . . . . . . . . .                          .   .   .   580
                K.3.1.3 Use of errno . . . . . . . . . . . . . .                               .   .   .   580
                K.3.1.4 Runtime-constraint violations     . . . . . . .                        .   .   .   580
       K.3.2 Errors <errno.h>           . . . . . . . . . . . . . .                            .   .   .   581
       K.3.3 Common definitions <stddef.h>               . . . . . . . .                        .   .   .   581
       K.3.4 Integer types <stdint.h>           . . . . . . . . . . .                          .   .   .   581
       K.3.5 Input/output <stdio.h>          . . . . . . . . . . . .                           .   .   .   582
                K.3.5.1 Operations on files      . . . . . . . . . . .                          .   .   .   582
                K.3.5.2 File access functions . . . . . . . . . . .                            .   .   .   584
                K.3.5.3 Formatted input/output functions . . . . . .                           .   .   .   587
                K.3.5.4 Character input/output functions . . . . . .                           .   .   .   598
       K.3.6 General utilities <stdlib.h>          . . . . . . . . . .                         .   .   .   600
                K.3.6.1 Runtime-constraint handling       . . . . . . .                        .   .   .   600
                K.3.6.2 Communication with the environment . . . .                             .   .   .   602
                K.3.6.3 Searching and sorting utilities . . . . . . .                          .   .   .   603
                K.3.6.4 Multibyte/wide character conversion functions                          .   .   .   606
                K.3.6.5 Multibyte/wide string conversion functions . .                         .   .   .   607
       K.3.7 String handling <string.h>            . . . . . . . . . .                         .   .   .   610
                K.3.7.1 Copying functions       . . . . . . . . . . .                          .   .   .   610
                K.3.7.2 Concatenation functions       . . . . . . . . .                        .   .   .   613
                K.3.7.3 Search functions     . . . . . . . . . . . .                           .   .   .   616
                K.3.7.4 Miscellaneous functions       . . . . . . . . .                        .   .   .   617
       K.3.8 Date and time <time.h>          . . . . . . . . . . . .                           .   .   .   620
                K.3.8.1 Components of time . . . . . . . . . . .                               .   .   .   620
                K.3.8.2 Time conversion functions       . . . . . . . .                        .   .   .   620
       K.3.9 Extended multibyte and wide character utilities
                <wchar.h>        . . . . . . . . . . . . . . . . .                             . . . 623
                K.3.9.1 Formatted wide character input/output functions                        . . . 624
                K.3.9.2 General wide string utilities . . . . . . . .                          . . . 635



[page xi]

               K.3.9.3 Extended multibyte/wide character conversion
                       utilities . . . . . . . . . . . . . . . . . . . 643
Annex L (normative) Analyzability . .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   648
  L.1 Scope . . . . . . . . . . .       .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   648
  L.2 Definitions . . . . . . . . .      .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   648
  L.3 Requirements . . . . . . . .      .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   .   649
Bibliography   . . . . . . . . . . . . . . . . . . . . . . . . . . . 650
Index    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 653




[page xii]

    Foreword
1   ISO (the International Organization for Standardization) and IEC (the International
    Electrotechnical Commission) form the specialized system for worldwide
    standardization. National bodies that are member of ISO or IEC participate in the
    development of International Standards through technical committees established by the
    respective organization to deal with particular fields of technical activity. ISO and IEC
    technical committees collaborate in fields of mutual interest. Other international
    organizations, governmental and non-governmental, in liaison with ISO and IEC, also
    take part in the work.
2   International Standards are drafted in accordance with the rules given in the ISO/IEC
    Directives, Part 2. This International Standard was drafted in accordance with the fifth
    edition (2004).
3   In the field of information technology, ISO and IEC have established a joint technical
    committee, ISO/IEC JTC 1. Draft International Standards adopted by the joint technical
    committee are circulated to national bodies for voting. Publication as an International
    Standard requires approval by at least 75% of the national bodies casting a vote.
4   Attention is drawn to the possibility that some of the elements of this document may be
    the subject of patent rights. ISO and IEC shall not be held responsible for identifying any
    or all such patent rights.
5   This International Standard was prepared by Joint Technical Committee ISO/IEC JTC 1,
    Information technology, Subcommittee SC 22, Programming languages, their
    environments and system software interfaces. The Working Group responsible for this
    standard (WG 14) maintains a site on the World Wide Web at http://www.open-
    std.org/JTC1/SC22/WG14/ containing additional information relevant to this
    standard such as a Rationale for many of the decisions made during its preparation and a
    log of Defect Reports and Responses.
6   This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as
    corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and
    ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:
    -- conditional (optional) features (including some that were previously mandatory)
    -- support for multiple threads of execution including an improved memory sequencing
      model, atomic objects, and thread-local storage (<stdatomic.h> and
      <threads.h>)
    -- additional floating-point characteristic macros (<float.h>)
    -- querying and specifying alignment of objects (<stdalign.h>, <stdlib.h>)
    -- Unicode characters and           strings   (<uchar.h>)       (originally   specified    in
      ISO/IEC TR 19769:2004)
    -- type-generic expressions


[page xiii]

    -- static assertions
    -- anonymous structures and unions
    -- no-return functions
    -- macros to create complex numbers (<complex.h>)
    -- support for opening files for exclusive access
    -- removed the gets function (<stdio.h>)
    -- added the aligned_alloc, at_quick_exit, and quick_exit functions
      (<stdlib.h>)
    -- (conditional) support for bounds-checking interfaces (originally specified in
      ISO/IEC TR 24731-1:2007)
    -- (conditional) support for analyzability
7   Major changes in the second edition included:
    -- restricted character set support via digraphs and <iso646.h> (originally specified
      in AMD1)
    -- wide character library support in <wchar.h> and <wctype.h> (originally
      specified in AMD1)
    -- more precise aliasing rules via effective type
    -- restricted pointers
    -- variable length arrays
    -- flexible array members
    -- static and type qualifiers in parameter array declarators
    -- complex (and imaginary) support in <complex.h>
    -- type-generic math macros in <tgmath.h>
    -- the long long int type and library functions
    -- increased minimum translation limits
    -- additional floating-point characteristics in <float.h>
    -- remove implicit int
    -- reliable integer division
    -- universal character names (\u and \U)
    -- extended identifiers
    -- hexadecimal floating-point constants and %a and %A printf/scanf conversion
      specifiers



[page xiv]

-- compound literals
-- designated initializers
-- // comments
-- extended integer types and library functions in <inttypes.h> and <stdint.h>
-- remove implicit function declaration
-- preprocessor arithmetic done in intmax_t/uintmax_t
-- mixed declarations and code
-- new block scopes for selection and iteration statements
-- integer constant type rules
-- integer promotion rules
-- macros with a variable number of arguments
-- the vscanf family of functions in <stdio.h> and <wchar.h>
-- additional math library functions in <math.h>
-- treatment of error conditions by math library functions (math_errhandling)
-- floating-point environment access in <fenv.h>
-- IEC 60559 (also known as IEC 559 or IEEE arithmetic) support
-- trailing comma allowed in enum declaration
-- %lf conversion specifier allowed in printf
-- inline functions
-- the snprintf family of functions in <stdio.h>
-- boolean type in <stdbool.h>
-- idempotent type qualifiers
-- empty macro arguments
-- new structure type compatibility rules (tag compatibility)
-- additional predefined macro names
-- _Pragma preprocessing operator
-- standard pragmas
-- __func__ predefined identifier
-- va_copy macro
-- additional strftime conversion specifiers
-- LIA compatibility annex


[page xv]

    -- deprecate ungetc at the beginning of a binary file
    -- remove deprecation of aliased array parameters
    -- conversion of array to pointer not limited to lvalues
    -- relaxed constraints on aggregate and union initialization
    -- relaxed restrictions on portable header names
    -- return without expression not permitted in function that returns a value (and vice
      versa)
8   Annexes D, F, G, K, and L form a normative part of this standard; annexes A, B, C, E, H, *
    I, J, the bibliography, and the index are for information only. In accordance with Part 2 of
    the ISO/IEC Directives, this foreword, the introduction, notes, footnotes, and examples
    are also for information only.




[page xvi]

    Introduction
1   With the introduction of new devices and extended character sets, new features may be
    added to this International Standard. Subclauses in the language and library clauses warn
    implementors and programmers of usages which, though valid in themselves, may
    conflict with future additions.
2   Certain features are obsolescent, which means that they may be considered for
    withdrawal in future revisions of this International Standard. They are retained because
    of their widespread use, but their use in new implementations (for implementation
    features) or new programs (for language [6.11] or library features [7.30]) is discouraged.
3   This International Standard is divided into four major subdivisions:
    -- preliminary elements (clauses 1-4);
    -- the characteristics of environments that translate and execute C programs (clause 5);
    -- the language syntax, constraints, and semantics (clause 6);
    -- the library facilities (clause 7).
4   Examples are provided to illustrate possible forms of the constructions described.
    Footnotes are provided to emphasize consequences of the rules described in that
    subclause or elsewhere in this International Standard. References are used to refer to
    other related subclauses. Recommendations are provided to give advice or guidance to
    implementors. Annexes provide additional information and summarize the information
    contained in this International Standard. A bibliography lists documents that were
    referred to during the preparation of the standard.
5   The language clause (clause 6) is derived from ''The C Reference Manual''.
6   The library clause (clause 7) is based on the 1984 /usr/group Standard.




[page xvii]



[page xviii]



    Programming languages -- C



    1. Scope
1   This International Standard specifies the form and establishes the interpretation of
    programs written in the C programming language.1) It specifies
    -- the representation of C programs;
    -- the syntax and constraints of the C language;
    -- the semantic rules for interpreting C programs;
    -- the representation of input data to be processed by C programs;
    -- the representation of output data produced by C programs;
    -- the restrictions and limits imposed by a conforming implementation of C.
2   This International Standard does not specify
    -- the mechanism by which C programs are transformed for use by a data-processing
      system;
    -- the mechanism by which C programs are invoked for use by a data-processing
      system;
    -- the mechanism by which input data are transformed for use by a C program;
    -- the mechanism by which output data are transformed after being produced by a C
      program;
    -- the size or complexity of a program and its data that will exceed the capacity of any
      specific data-processing system or the capacity of a particular processor;
    -- all minimal requirements of a data-processing system that is capable of supporting a
      conforming implementation.


    1)   This International Standard is designed to promote the portability of C programs among a variety of
         data-processing systems. It is intended for use by implementors and programmers.

[page 1]


    2. Normative references
1   The following referenced documents are indispensable for the application of this
    document. For dated references, only the edition cited applies. For undated references,
    the latest edition of the referenced document (including any amendments) applies.
2   ISO 31-11:1992, Quantities and units -- Part 11: Mathematical signs and symbols for
    use in the physical sciences and technology.
3   ISO/IEC 646, Information technology -- ISO 7-bit coded character set for information
    interchange.
4   ISO/IEC 2382-1:1993, Information technology -- Vocabulary -- Part 1: Fundamental
    terms.
5   ISO 4217, Codes for the representation of currencies and funds.
6   ISO 8601, Data elements and interchange formats -- Information interchange --
    Representation of dates and times.
7   ISO/IEC 10646 (all parts), Information technology -- Universal Multiple-Octet Coded
    Character Set (UCS).
8   IEC 60559:1989, Binary floating-point arithmetic for microprocessor systems (previously
    designated IEC 559:1989).




[page 2]


    3. Terms, definitions, and symbols
1   For the purposes of this International Standard, the following definitions apply. Other
    terms are defined where they appear in italic type or on the left side of a syntax rule.
    Terms explicitly defined in this International Standard are not to be presumed to refer
    implicitly to similar terms defined elsewhere. Terms not defined in this International
    Standard are to be interpreted according to ISO/IEC 2382-1. Mathematical symbols not
    defined in this International Standard are to be interpreted according to ISO 31-11.
    3.1
1   access
    <execution-time action> to read or modify the value of an object
2   NOTE 1   Where only one of these two actions is meant, ''read'' or ''modify'' is used.

3   NOTE 2   ''Modify'' includes the case where the new value being stored is the same as the previous value.

4   NOTE 3   Expressions that are not evaluated do not access objects.

    3.2
1   alignment
    requirement that objects of a particular type be located on storage boundaries with
    addresses that are particular multiples of a byte address
    3.3
1   argument
    actual argument
    actual parameter (deprecated)
    expression in the comma-separated list bounded by the parentheses in a function call
    expression, or a sequence of preprocessing tokens in the comma-separated list bounded
    by the parentheses in a function-like macro invocation
    3.4
1   behavior
    external appearance or action
    3.4.1
1   implementation-defined behavior
    unspecified behavior where each implementation documents how the choice is made
2   EXAMPLE An example of implementation-defined behavior is the propagation of the high-order bit
    when a signed integer is shifted right.

    3.4.2
1   locale-specific behavior
    behavior that depends on local conventions of nationality, culture, and language that each
    implementation documents


[page 3]

2   EXAMPLE An example of locale-specific behavior is whether the islower function returns true for
    characters other than the 26 lowercase Latin letters.

    3.4.3
1   undefined behavior
    behavior, upon use of a nonportable or erroneous program construct or of erroneous data,
    for which this International Standard imposes no requirements
2   NOTE Possible undefined behavior ranges from ignoring the situation completely with unpredictable
    results, to behaving during translation or program execution in a documented manner characteristic of the
    environment (with or without the issuance of a diagnostic message), to terminating a translation or
    execution (with the issuance of a diagnostic message).

3   EXAMPLE        An example of undefined behavior is the behavior on integer overflow.

    3.4.4
1   unspecified behavior
    use of an unspecified value, or other behavior where this International Standard provides
    two or more possibilities and imposes no further requirements on which is chosen in any
    instance
2   EXAMPLE        An example of unspecified behavior is the order in which the arguments to a function are
    evaluated.

    3.5
1   bit
    unit of data storage in the execution environment large enough to hold an object that may
    have one of two values
2   NOTE     It need not be possible to express the address of each individual bit of an object.

    3.6
1   byte
    addressable unit of data storage large enough to hold any member of the basic character
    set of the execution environment
2   NOTE 1     It is possible to express the address of each individual byte of an object uniquely.

3   NOTE 2 A byte is composed of a contiguous sequence of bits, the number of which is implementation-
    defined. The least significant bit is called the low-order bit; the most significant bit is called the high-order
    bit.

    3.7
1   character
    <abstract> member of a set of elements used for the organization, control, or
    representation of data
    3.7.1
1   character
    single-byte character
    <C> bit representation that fits in a byte
[page 4]

    3.7.2
1   multibyte character
    sequence of one or more bytes representing a member of the extended character set of
    either the source or the execution environment
2   NOTE    The extended character set is a superset of the basic character set.

    3.7.3
1   wide character
    bit representation that fits in an object of type wchar_t, capable of representing any
    character in the current locale
    3.8
1   constraint
    restriction, either syntactic or semantic, by which the exposition of language elements is
    to be interpreted
    3.9
1   correctly rounded result
    representation in the result format that is nearest in value, subject to the current rounding
    mode, to what the result would be given unlimited range and precision
    3.10
1   diagnostic message
    message belonging to an implementation-defined subset of the implementation's message
    output
    3.11
1   forward reference
    reference to a later subclause of this International Standard that contains additional
    information relevant to this subclause
    3.12
1   implementation
    particular set of software, running in a particular translation environment under particular
    control options, that performs translation of programs for, and supports execution of
    functions in, a particular execution environment
    3.13
1   implementation limit
    restriction imposed upon programs by the implementation
    3.14
1   memory location
    either an object of scalar type, or a maximal sequence of adjacent bit-fields all having
    nonzero width

[page 5]

2   NOTE 1 Two threads of execution can update and access separate memory locations without interfering
    with each other.

3   NOTE 2 A bit-field and an adjacent non-bit-field member are in separate memory locations. The same
    applies to two bit-fields, if one is declared inside a nested structure declaration and the other is not, or if the
    two are separated by a zero-length bit-field declaration, or if they are separated by a non-bit-field member
    declaration. It is not safe to concurrently update two non-atomic bit-fields in the same structure if all
    members declared between them are also (non-zero-length) bit-fields, no matter what the sizes of those
    intervening bit-fields happen to be.

4   EXAMPLE        A structure declared as
             struct {
                   char a;
                   int b:5, c:11, :0, d:8;
                   struct { int ee:8; } e;
             }
    contains four separate memory locations: The member a, and bit-fields d and e.ee are each separate
    memory locations, and can be modified concurrently without interfering with each other. The bit-fields b
    and c together constitute the fourth memory location. The bit-fields b and c cannot be concurrently
    modified, but b and a, for example, can be.

    3.15
1   object
    region of data storage in the execution environment, the contents of which can represent
    values
2   NOTE      When referenced, an object may be interpreted as having a particular type; see 6.3.2.1.

    3.16
1   parameter
    formal parameter
    formal argument (deprecated)
    object declared as part of a function declaration or definition that acquires a value on
    entry to the function, or an identifier from the comma-separated list bounded by the
    parentheses immediately following the macro name in a function-like macro definition
    3.17
1   recommended practice
    specification that is strongly recommended as being in keeping with the intent of the
    standard, but that may be impractical for some implementations
    3.18
1   runtime-constraint
    requirement on a program when calling a library function
2   NOTE 1 Despite the similar terms, a runtime-constraint is not a kind of constraint as defined by 3.8, and
    need not be diagnosed at translation time.

3   NOTE 2 Implementations that support the extensions in annex K are required to verify that the runtime-
    constraints for a library function are not violated by the program; see K.3.1.4.

[page 6]

    3.19
1   value
    precise meaning of the contents of an object when interpreted as having a specific type
    3.19.1
1   implementation-defined value
    unspecified value where each implementation documents how the choice is made
    3.19.2
1   indeterminate value
    either an unspecified value or a trap representation
    3.19.3
1   unspecified value
    valid value of the relevant type where this International Standard imposes no
    requirements on which value is chosen in any instance
2   NOTE     An unspecified value cannot be a trap representation.

    3.19.4
1   trap representation
    an object representation that need not represent a value of the object type
    3.19.5
1   perform a trap
    interrupt execution of the program such that no further operations are performed
2   NOTE In this International Standard, when the word ''trap'' is not immediately followed by
    ''representation'', this is the intended usage.2)

    3.20
1   [^ x^]
    ceiling of x: the least integer greater than or equal to x
2   EXAMPLE       [^2.4^] is 3, [^-2.4^] is -2.

    3.21
1   [_ x_]
    floor of x: the greatest integer less than or equal to x
2   EXAMPLE       [_2.4_] is 2, [_-2.4_] is -3.




    2)   For example, ''Trapping or stopping (if supported) is disabled...'' (F.8.2). Note that fetching a trap
         representation might perform a trap but is not required to (see 6.2.6.1).

[page 7]


    4. Conformance
1   In this International Standard, ''shall'' is to be interpreted as a requirement on an
    implementation or on a program; conversely, ''shall not'' is to be interpreted as a
    prohibition.
2   If a ''shall'' or ''shall not'' requirement that appears outside of a constraint or runtime-
    constraint is violated, the behavior is undefined. Undefined behavior is otherwise
    indicated in this International Standard by the words ''undefined behavior'' or by the
    omission of any explicit definition of behavior. There is no difference in emphasis among
    these three; they all describe ''behavior that is undefined''.
3   A program that is correct in all other aspects, operating on correct data, containing
    unspecified behavior shall be a correct program and act in accordance with 5.1.2.3.
4   The implementation shall not successfully translate a preprocessing translation unit
    containing a #error preprocessing directive unless it is part of a group skipped by
    conditional inclusion.
5   A strictly conforming program shall use only those features of the language and library
    specified in this International Standard.3) It shall not produce output dependent on any
    unspecified, undefined, or implementation-defined behavior, and shall not exceed any
    minimum implementation limit.
6   The two forms of conforming implementation are hosted and freestanding. A conforming
    hosted implementation shall accept any strictly conforming program. A conforming
    freestanding implementation shall accept any strictly conforming program that does not
    use complex types and in which the use of the features specified in the library clause
    (clause 7) is confined to the contents of the standard headers <float.h>,
    <iso646.h>, <limits.h>, <stdalign.h>, <stdarg.h>, <stdbool.h>,
    <stddef.h>, and <stdint.h>. A conforming implementation may have extensions
    (including additional library functions), provided they do not alter the behavior of any
    strictly conforming program.4)



    3)   A strictly conforming program can use conditional features (see 6.10.8.3) provided the use is guarded
         by an appropriate conditional inclusion preprocessing directive using the related macro. For example:
                 #ifdef __STDC_IEC_559__ /* FE_UPWARD defined */
                    /* ... */
                    fesetround(FE_UPWARD);
                    /* ... */
                 #endif

    4)   This implies that a conforming implementation reserves no identifiers other than those explicitly
         reserved in this International Standard.

[page 8]

7   A conforming program is one that is acceptable to a conforming implementation.5)
8   An implementation shall be accompanied by a document that defines all implementation-
    defined and locale-specific characteristics and all extensions.
    Forward references: conditional inclusion (6.10.1), error directive (6.10.5),
    characteristics of floating types <float.h> (7.7), alternative spellings <iso646.h>
    (7.9), sizes of integer types <limits.h> (7.10), alignment <stdalign.h> (7.15),
    variable arguments <stdarg.h> (7.16), boolean type and values <stdbool.h>
    (7.18), common definitions <stddef.h> (7.19), integer types <stdint.h> (7.20).




    5)   Strictly conforming programs are intended to be maximally portable among conforming
         implementations. Conforming programs may depend upon nonportable features of a conforming
         implementation.

[page 9]


    5. Environment
1   An implementation translates C source files and executes C programs in two data-
    processing-system environments, which will be called the translation environment and
    the execution environment in this International Standard. Their characteristics define and
    constrain the results of executing conforming C programs constructed according to the
    syntactic and semantic rules for conforming implementations.
    Forward references: In this clause, only a few of many possible forward references
    have been noted.
    5.1 Conceptual models
    5.1.1 Translation environment
    5.1.1.1 Program structure
1   A C program need not all be translated at the same time. The text of the program is kept
    in units called source files, (or preprocessing files) in this International Standard. A
    source file together with all the headers and source files included via the preprocessing
    directive #include is known as a preprocessing translation unit. After preprocessing, a
    preprocessing translation unit is called a translation unit. Previously translated translation
    units may be preserved individually or in libraries. The separate translation units of a
    program communicate by (for example) calls to functions whose identifiers have external
    linkage, manipulation of objects whose identifiers have external linkage, or manipulation
    of data files. Translation units may be separately translated and then later linked to
    produce an executable program.
    Forward references: linkages of identifiers (6.2.2), external definitions (6.9),
    preprocessing directives (6.10).
    5.1.1.2 Translation phases
1   The precedence among the syntax rules of translation is specified by the following
    phases.6)
         1.   Physical source file multibyte characters are mapped, in an implementation-
              defined manner, to the source character set (introducing new-line characters for
              end-of-line indicators) if necessary. Trigraph sequences are replaced by
              corresponding single-character internal representations.



    6)    Implementations shall behave as if these separate phases occur, even though many are typically folded
          together in practice. Source files, translation units, and translated translation units need not
          necessarily be stored as files, nor need there be any one-to-one correspondence between these entities
          and any external representation. The description is conceptual only, and does not specify any
          particular implementation.

[page 10]

     2.   Each instance of a backslash character (\) immediately followed by a new-line
          character is deleted, splicing physical source lines to form logical source lines.
          Only the last backslash on any physical source line shall be eligible for being part
          of such a splice. A source file that is not empty shall end in a new-line character,
          which shall not be immediately preceded by a backslash character before any such
          splicing takes place.
     3.   The source file is decomposed into preprocessing tokens7) and sequences of
          white-space characters (including comments). A source file shall not end in a
          partial preprocessing token or in a partial comment. Each comment is replaced by
          one space character. New-line characters are retained. Whether each nonempty
          sequence of white-space characters other than new-line is retained or replaced by
          one space character is implementation-defined.
     4. Preprocessing directives are executed, macro invocations are expanded, and
        _Pragma unary operator expressions are executed. If a character sequence that
        matches the syntax of a universal character name is produced by token
        concatenation (6.10.3.3), the behavior is undefined. A #include preprocessing
        directive causes the named header or source file to be processed from phase 1
        through phase 4, recursively. All preprocessing directives are then deleted.
     5. Each source character set member and escape sequence in character constants and
        string literals is converted to the corresponding member of the execution character
        set; if there is no corresponding member, it is converted to an implementation-
        defined member other than the null (wide) character.8)
     6.   Adjacent string literal tokens are concatenated.
     7. White-space characters separating tokens are no longer significant. Each
        preprocessing token is converted into a token. The resulting tokens are
        syntactically and semantically analyzed and translated as a translation unit.
     8.   All external object and function references are resolved. Library components are
          linked to satisfy external references to functions and objects not defined in the
          current translation. All such translator output is collected into a program image
          which contains information needed for execution in its execution environment.
Forward references: universal character names (6.4.3), lexical elements (6.4),
preprocessing directives (6.10), trigraph sequences (5.2.1.1), external definitions (6.9).



7)    As described in 6.4, the process of dividing a source file's characters into preprocessing tokens is
      context-dependent. For example, see the handling of < within a #include preprocessing directive.
8)    An implementation need not convert all non-corresponding source characters to the same execution
      character.

[page 11]

    5.1.1.3 Diagnostics
1   A conforming implementation shall produce at least one diagnostic message (identified in
    an implementation-defined manner) if a preprocessing translation unit or translation unit
    contains a violation of any syntax rule or constraint, even if the behavior is also explicitly
    specified as undefined or implementation-defined. Diagnostic messages need not be
    produced in other circumstances.9)
2   EXAMPLE        An implementation shall issue a diagnostic for the translation unit:
             char i;
             int i;
    because in those cases where wording in this International Standard describes the behavior for a construct
    as being both a constraint error and resulting in undefined behavior, the constraint error shall be diagnosed.

    5.1.2 Execution environments
1   Two execution environments are defined: freestanding and hosted. In both cases,
    program startup occurs when a designated C function is called by the execution
    environment. All objects with static storage duration shall be initialized (set to their
    initial values) before program startup. The manner and timing of such initialization are
    otherwise unspecified. Program termination returns control to the execution
    environment.
    Forward references: storage durations of objects (6.2.4), initialization (6.7.9).
    5.1.2.1 Freestanding environment
1   In a freestanding environment (in which C program execution may take place without any
    benefit of an operating system), the name and type of the function called at program
    startup are implementation-defined. Any library facilities available to a freestanding
    program, other than the minimal set required by clause 4, are implementation-defined.
2   The effect of program termination in a freestanding environment is implementation-
    defined.
    5.1.2.2 Hosted environment
1   A hosted environment need not be provided, but shall conform to the following
    specifications if present.




    9)   The intent is that an implementation should identify the nature of, and where possible localize, each
         violation. Of course, an implementation is free to produce any number of diagnostics as long as a
         valid program is still correctly translated. It may also successfully translate an invalid program.

[page 12]

    5.1.2.2.1 Program startup
1   The function called at program startup is named main. The implementation declares no
    prototype for this function. It shall be defined with a return type of int and with no
    parameters:
            int main(void) { /* ... */ }
    or with two parameters (referred to here as argc and argv, though any names may be
    used, as they are local to the function in which they are declared):
            int main(int argc, char *argv[]) { /* ... */ }
    or equivalent;10) or in some other implementation-defined manner.
2   If they are declared, the parameters to the main function shall obey the following
    constraints:
    -- The value of argc shall be nonnegative.
    -- argv[argc] shall be a null pointer.
    -- If the value of argc is greater than zero, the array members argv[0] through
      argv[argc-1] inclusive shall contain pointers to strings, which are given
      implementation-defined values by the host environment prior to program startup. The
      intent is to supply to the program information determined prior to program startup
      from elsewhere in the hosted environment. If the host environment is not capable of
      supplying strings with letters in both uppercase and lowercase, the implementation
      shall ensure that the strings are received in lowercase.
    -- If the value of argc is greater than zero, the string pointed to by argv[0]
      represents the program name; argv[0][0] shall be the null character if the
      program name is not available from the host environment. If the value of argc is
      greater than one, the strings pointed to by argv[1] through argv[argc-1]
      represent the program parameters.
    -- The parameters argc and argv and the strings pointed to by the argv array shall
      be modifiable by the program, and retain their last-stored values between program
      startup and program termination.
    5.1.2.2.2 Program execution
1   In a hosted environment, a program may use all the functions, macros, type definitions,
    and objects described in the library clause (clause 7).




    10) Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as
        char ** argv, and so on.

[page 13]

    5.1.2.2.3 Program termination
1   If the return type of the main function is a type compatible with int, a return from the
    initial call to the main function is equivalent to calling the exit function with the value
    returned by the main function as its argument;11) reaching the } that terminates the
    main function returns a value of 0. If the return type is not compatible with int, the
    termination status returned to the host environment is unspecified.
    Forward references: definition of terms (7.1.1), the exit function (7.22.4.4).
    5.1.2.3 Program execution
1   The semantic descriptions in this International Standard describe the behavior of an
    abstract machine in which issues of optimization are irrelevant.
2   Accessing a volatile object, modifying an object, modifying a file, or calling a function
    that does any of those operations are all side effects,12) which are changes in the state of
    the execution environment. Evaluation of an expression in general includes both value
    computations and initiation of side effects. Value computation for an lvalue expression
    includes determining the identity of the designated object.
3   Sequenced before is an asymmetric, transitive, pair-wise relation between evaluations
    executed by a single thread, which induces a partial order among those evaluations.
    Given any two evaluations A and B, if A is sequenced before B, then the execution of A
    shall precede the execution of B. (Conversely, if A is sequenced before B, then B is
    sequenced after A.) If A is not sequenced before or after B, then A and B are
    unsequenced. Evaluations A and B are indeterminately sequenced when A is sequenced
    either before or after B, but it is unspecified which.13) The presence of a sequence point
    between the evaluation of expressions A and B implies that every value computation and
    side effect associated with A is sequenced before every value computation and side effect
    associated with B. (A summary of the sequence points is given in annex C.)
4   In the abstract machine, all expressions are evaluated as specified by the semantics. An
    actual implementation need not evaluate part of an expression if it can deduce that its
    value is not used and that no needed side effects are produced (including any caused by

    11) In accordance with 6.2.4, the lifetimes of objects with automatic storage duration declared in main
        will have ended in the former case, even where they would not have in the latter.
    12) The IEC 60559 standard for binary floating-point arithmetic requires certain user-accessible status
        flags and control modes. Floating-point operations implicitly set the status flags; modes affect result
        values of floating-point operations. Implementations that support such floating-point state are
        required to regard changes to it as side effects -- see annex F for details. The floating-point
        environment library <fenv.h> provides a programming facility for indicating when these side
        effects matter, freeing the implementations in other cases.
    13) The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations
        cannot interleave, but can be executed in any order.

[page 14]

     calling a function or accessing a volatile object).
5    When the processing of the abstract machine is interrupted by receipt of a signal, the
     values of objects that are neither lock-free atomic objects nor of type volatile
     sig_atomic_t are unspecified, and the value of any object that is modified by the
     handler that is neither a lock-free atomic object nor of type volatile
     sig_atomic_t becomes undefined.
6    The least requirements on a conforming implementation are:
     -- Accesses to volatile objects are evaluated strictly according to the rules of the abstract
       machine.
     -- At program termination, all data written into files shall be identical to the result that
       execution of the program according to the abstract semantics would have produced.
     -- The input and output dynamics of interactive devices shall take place as specified in
       7.21.3. The intent of these requirements is that unbuffered or line-buffered output
       appear as soon as possible, to ensure that prompting messages actually appear prior to
       a program waiting for input.
     This is the observable behavior of the program.
7    What constitutes an interactive device is implementation-defined.
8    More stringent correspondences between abstract and actual semantics may be defined by
     each implementation.
9    EXAMPLE 1 An implementation might define a one-to-one correspondence between abstract and actual
     semantics: at every sequence point, the values of the actual objects would agree with those specified by the
     abstract semantics. The keyword volatile would then be redundant.
10   Alternatively, an implementation might perform various optimizations within each translation unit, such
     that the actual semantics would agree with the abstract semantics only when making function calls across
     translation unit boundaries. In such an implementation, at the time of each function entry and function
     return where the calling function and the called function are in different translation units, the values of all
     externally linked objects and of all objects accessible via pointers therein would agree with the abstract
     semantics. Furthermore, at the time of each such function entry the values of the parameters of the called
     function and of all objects accessible via pointers therein would agree with the abstract semantics. In this
     type of implementation, objects referred to by interrupt service routines activated by the signal function
     would require explicit specification of volatile storage, as well as other implementation-defined
     restrictions.

11   EXAMPLE 2       In executing the fragment
              char c1, c2;
              /* ... */
              c1 = c1 + c2;
     the ''integer promotions'' require that the abstract machine promote the value of each variable to int size
     and then add the two ints and truncate the sum. Provided the addition of two chars can be done without
     overflow, or with overflow wrapping silently to produce the correct result, the actual execution need only
     produce the same result, possibly omitting the promotions.

[page 15]

12   EXAMPLE 3       Similarly, in the fragment
              float f1, f2;
              double d;
              /* ... */
              f1 = f2 * d;
     the multiplication may be executed using single-precision arithmetic if the implementation can ascertain
     that the result would be the same as if it were executed using double-precision arithmetic (for example, if d
     were replaced by the constant 2.0, which has type double).

13   EXAMPLE 4 Implementations employing wide registers have to take care to honor appropriate
     semantics. Values are independent of whether they are represented in a register or in memory. For
     example, an implicit spilling of a register is not permitted to alter the value. Also, an explicit store and load
     is required to round to the precision of the storage type. In particular, casts and assignments are required to
     perform their specified conversion. For the fragment
              double d1, d2;
              float f;
              d1 = f = expression;
              d2 = (float) expression;
     the values assigned to d1 and d2 are required to have been converted to float.

14   EXAMPLE 5 Rearrangement for floating-point expressions is often restricted because of limitations in
     precision as well as range. The implementation cannot generally apply the mathematical associative rules
     for addition or multiplication, nor the distributive rule, because of roundoff error, even in the absence of
     overflow and underflow. Likewise, implementations cannot generally replace decimal constants in order to
     rearrange expressions. In the following fragment, rearrangements suggested by mathematical rules for real
     numbers are often not valid (see F.9).
              double x, y, z;
              /* ... */
              x = (x * y) * z;            //   not equivalent to x   *= y * z;
              z = (x - y) + y ;           //   not equivalent to z   = x;
              z = x + x * y;              //   not equivalent to z   = x * (1.0 + y);
              y = x / 5.0;                //   not equivalent to y   = x * 0.2;

15   EXAMPLE 6       To illustrate the grouping behavior of expressions, in the following fragment
              int a, b;
              /* ... */
              a = a + 32760 + b + 5;
     the expression statement behaves exactly the same as
              a = (((a + 32760) + b) + 5);
     due to the associativity and precedence of these operators. Thus, the result of the sum (a + 32760) is
     next added to b, and that result is then added to 5 which results in the value assigned to a. On a machine in
     which overflows produce an explicit trap and in which the range of values representable by an int is
     [-32768, +32767], the implementation cannot rewrite this expression as
              a = ((a + b) + 32765);
     since if the values for a and b were, respectively, -32754 and -15, the sum a + b would produce a trap
     while the original expression would not; nor can the expression be rewritten either as


[page 16]

              a = ((a + 32765) + b);
     or
              a = (a + (b + 32765));
     since the values for a and b might have been, respectively, 4 and -8 or -17 and 12. However, on a machine
     in which overflow silently generates some value and where positive and negative overflows cancel, the
     above expression statement can be rewritten by the implementation in any of the above ways because the
     same result will occur.

16   EXAMPLE 7 The grouping of an expression does not completely determine its evaluation. In the
     following fragment
              #include <stdio.h>
              int sum;
              char *p;
              /* ... */
              sum = sum * 10 - '0' + (*p++ = getchar());
     the expression statement is grouped as if it were written as
              sum = (((sum * 10) - '0') + ((*(p++)) = (getchar())));
     but the actual increment of p can occur at any time between the previous sequence point and the next
     sequence point (the ;), and the call to getchar can occur at any point prior to the need of its returned
     value.

     Forward references: expressions (6.5), type qualifiers (6.7.3), statements (6.8), the
     signal function (7.14), files (7.21.3).
     5.1.2.4 Multi-threaded executions and data races
1    Under a hosted implementation, a program can have more than one thread of execution
     (or thread) running concurrently. The execution of each thread proceeds as defined by
     the remainder of this standard. The execution of the entire program consists of an
     execution of all of its threads.14) Under a freestanding implementation, it is
     implementation-defined whether a program can have more than one thread of execution.
2    The value of an object visible to a thread T at a particular point is the initial value of the
     object, a value stored in the object by T , or a value stored in the object by another thread,
     according to the rules below.
3    NOTE 1 In some cases, there may instead be undefined behavior. Much of this section is motivated by
     the desire to support atomic operations with explicit and detailed visibility constraints. However, it also
     implicitly supports a simpler view for more restricted programs.

4    Two expression evaluations conflict if one of them modifies a memory location and the
     other one reads or modifies the same memory location.




     14) The execution can usually be viewed as an interleaving of all of the threads. However, some kinds of
         atomic operations, for example, allow executions inconsistent with a simple interleaving as described
         below.

[page 17]

5    The library defines a number of atomic operations (7.17) and operations on mutexes
     (7.25.4) that are specially identified as synchronization operations. These operations play
     a special role in making assignments in one thread visible to another. A synchronization
     operation on one or more memory locations is either an acquire operation, a release
     operation, both an acquire and release operation, or a consume operation. A
     synchronization operation without an associated memory location is a fence and can be
     either an acquire fence, a release fence, or both an acquire and release fence. In addition,
     there are relaxed atomic operations, which are not synchronization operations, and
     atomic read-modify-write operations, which have special characteristics.
6    NOTE 2 For example, a call that acquires a mutex will perform an acquire operation on the locations
     composing the mutex. Correspondingly, a call that releases the same mutex will perform a release
     operation on those same locations. Informally, performing a release operation on A forces prior side effects
     on other memory locations to become visible to other threads that later perform an acquire or consume
     operation on A. We do not include relaxed atomic operations as synchronization operations although, like
     synchronization operations, they cannot contribute to data races.

7    All modifications to a particular atomic object M occur in some particular total order,
     called the modification order of M. If A and B are modifications of an atomic object M,
     and A happens before B, then A shall precede B in the modification order of M, which is
     defined below.
8    NOTE 3     This states that the modification orders must respect the ''happens before'' relation.

9    NOTE 4 There is a separate order for each atomic object. There is no requirement that these can be
     combined into a single total order for all objects. In general this will be impossible since different threads
     may observe modifications to different variables in inconsistent orders.

10   A release sequence on an atomic object M is a maximal contiguous sub-sequence of side
     effects in the modification order of M, where the first operation is a release and every
     subsequent operation either is performed by the same thread that performed the release or
     is an atomic read-modify-write operation.
11   Certain library calls synchronize with other library calls performed by another thread. In
     particular, an atomic operation A that performs a release operation on an object M
     synchronizes with an atomic operation B that performs an acquire operation on M and
     reads a value written by any side effect in the release sequence headed by A.
12   NOTE 5 Except in the specified cases, reading a later value does not necessarily ensure visibility as
     described below. Such a requirement would sometimes interfere with efficient implementation.

13   NOTE 6 The specifications of the synchronization operations define when one reads the value written by
     another. For atomic variables, the definition is clear. All operations on a given mutex occur in a single total
     order. Each mutex acquisition ''reads the value written'' by the last mutex release.

14   An evaluation A carries a dependency 15) to an evaluation B if:


     15) The ''carries a dependency'' relation is a subset of the ''sequenced before'' relation, and is similarly
         strictly intra-thread.

[page 18]

     -- the value of A is used as an operand of B, unless:
           o B is an invocation of the kill_dependency macro,

           o A is the left operand of a && or || operator,

           o A is the left operand of a ? : operator, or

           o A is the left operand of a , operator;
         or
     -- A writes a scalar object or bit-field M, B reads from M the value written by A, and A
       is sequenced before B, or
     -- for some evaluation X, A carries a dependency to X and X carries a dependency to B.
15   An evaluation A is dependency-ordered before16) an evaluation B if:
     -- A performs a release operation on an atomic object M, and B performs a consume
       operation on M and reads a value written by any side effect in the release sequence
       headed by A, or
     -- for some evaluation X, A is dependency-ordered before X and X carries a
       dependency to B.
16   An evaluation A inter-thread happens before an evaluation B if A synchronizes with B, A
     is dependency-ordered before B, or, for some evaluation X:
     -- A synchronizes with X and X is sequenced before B,
     -- A is sequenced before X and X inter-thread happens before B, or
     -- A inter-thread happens before X and X inter-thread happens before B.
17   NOTE 7 The ''inter-thread happens before'' relation describes arbitrary concatenations of ''sequenced
     before'', ''synchronizes with'', and ''dependency-ordered before'' relationships, with two exceptions. The
     first exception is that a concatenation is not permitted to end with ''dependency-ordered before'' followed
     by ''sequenced before''. The reason for this limitation is that a consume operation participating in a
     ''dependency-ordered before'' relationship provides ordering only with respect to operations to which this
     consume operation actually carries a dependency. The reason that this limitation applies only to the end of
     such a concatenation is that any subsequent release operation will provide the required ordering for a prior
     consume operation. The second exception is that a concatenation is not permitted to consist entirely of
     ''sequenced before''. The reasons for this limitation are (1) to permit ''inter-thread happens before'' to be
     transitively closed and (2) the ''happens before'' relation, defined below, provides for relationships
     consisting entirely of ''sequenced before''.

18   An evaluation A happens before an evaluation B if A is sequenced before B or A inter-
     thread happens before B.



     16) The ''dependency-ordered before'' relation is analogous to the ''synchronizes with'' relation, but uses
         release/consume in place of release/acquire.

[page 19]

19   A visible side effect A on an object M with respect to a value computation B of M
     satisfies the conditions:
     -- A happens before B, and
     -- there is no other side effect X to M such that A happens before X and X happens
         before B.
     The value of a non-atomic scalar object M, as determined by evaluation B, shall be the
     value stored by the visible side effect A.
20   NOTE 8 If there is ambiguity about which side effect to a non-atomic object is visible, then there is a data
     race and the behavior is undefined.

21   NOTE 9 This states that operations on ordinary variables are not visibly reordered. This is not actually
     detectable without data races, but it is necessary to ensure that data races, as defined here, and with suitable
     restrictions on the use of atomics, correspond to data races in a simple interleaved (sequentially consistent)
     execution.

22   The visible sequence of side effects on an atomic object M, with respect to a value
     computation B of M, is a maximal contiguous sub-sequence of side effects in the
     modification order of M, where the first side effect is visible with respect to B, and for
     every subsequent side effect, it is not the case that B happens before it. The value of an
     atomic object M, as determined by evaluation B, shall be the value stored by some
     operation in the visible sequence of M with respect to B. Furthermore, if a value
     computation A of an atomic object M happens before a value computation B of M, and
     the value computed by A corresponds to the value stored by side effect X, then the value
     computed by B shall either equal the value computed by A, or be the value stored by side
     effect Y , where Y follows X in the modification order of M.
23   NOTE 10 This effectively disallows compiler reordering of atomic operations to a single object, even if
     both operations are ''relaxed'' loads. By doing so, we effectively make the ''cache coherence'' guarantee
     provided by most hardware available to C atomic operations.

24   NOTE 11 The visible sequence depends on the ''happens before'' relation, which in turn depends on the
     values observed by loads of atomics, which we are restricting here. The intended reading is that there must
     exist an association of atomic loads with modifications they observe that, together with suitably chosen
     modification orders and the ''happens before'' relation derived as described above, satisfy the resulting
     constraints as imposed here.

25   The execution of a program contains a data race if it contains two conflicting actions in
     different threads, at least one of which is not atomic, and neither happens before the
     other. Any such data race results in undefined behavior.
26   NOTE 12 It can be shown that programs that correctly use simple mutexes and
     memory_order_seq_cst operations to prevent all data races, and use no other synchronization
     operations, behave as though the operations executed by their constituent threads were simply interleaved,
     with each value computation of an object being the last value stored in that interleaving. This is normally
     referred to as ''sequential consistency''. However, this applies only to data-race-free programs, and data-
     race-free programs cannot observe most program transformations that do not change single-threaded
     program semantics. In fact, most single-threaded program transformations continue to be allowed, since
     any program that behaves differently as a result must contain undefined behavior.

[page 20]

27   NOTE 13 Compiler transformations that introduce assignments to a potentially shared memory location
     that would not be modified by the abstract machine are generally precluded by this standard, since such an
     assignment might overwrite another assignment by a different thread in cases in which an abstract machine
     execution would not have encountered a data race. This includes implementations of data member
     assignment that overwrite adjacent members in separate memory locations. We also generally preclude
     reordering of atomic loads in cases in which the atomics in question may alias, since this may violate the
     "visible sequence" rules.

28   NOTE 14 Transformations that introduce a speculative read of a potentially shared memory location may
     not preserve the semantics of the program as defined in this standard, since they potentially introduce a data
     race. However, they are typically valid in the context of an optimizing compiler that targets a specific
     machine with well-defined semantics for data races. They would be invalid for a hypothetical machine that
     is not tolerant of races or provides hardware race detection.




[page 21]

    5.2 Environmental considerations
    5.2.1 Character sets
1   Two sets of characters and their associated collating sequences shall be defined: the set in
    which source files are written (the source character set), and the set interpreted in the
    execution environment (the execution character set). Each set is further divided into a
    basic character set, whose contents are given by this subclause, and a set of zero or more
    locale-specific members (which are not members of the basic character set) called
    extended characters. The combined set is also called the extended character set. The
    values of the members of the execution character set are implementation-defined.
2   In a character constant or string literal, members of the execution character set shall be
    represented by corresponding members of the source character set or by escape
    sequences consisting of the backslash \ followed by one or more characters. A byte with
    all bits set to 0, called the null character, shall exist in the basic execution character set; it
    is used to terminate a character string.
3   Both the basic source and basic execution character sets shall have the following
    members: the 26 uppercase letters of the Latin alphabet
            A    B   C      D   E   F    G    H    I    J    K    L   M
            N    O   P      Q   R   S    T    U    V    W    X    Y   Z
    the 26 lowercase letters of the Latin alphabet
            a    b   c      d   e   f    g    h    i    j    k    l   m
            n    o   p      q   r   s    t    u    v    w    x    y   z
    the 10 decimal digits
            0    1   2      3   4   5    6    7    8    9
    the following 29 graphic characters
            !    "   #      %   &   '    (    )    *    +    ,    -   .    /    :
            ;    <   =      >   ?   [    \    ]    ^    _    {    |   }    ~
    the space character, and control characters representing horizontal tab, vertical tab, and
    form feed. The representation of each member of the source and execution basic
    character sets shall fit in a byte. In both the source and execution basic character sets, the
    value of each character after 0 in the above list of decimal digits shall be one greater than
    the value of the previous. In source files, there shall be some way of indicating the end of
    each line of text; this International Standard treats such an end-of-line indicator as if it
    were a single new-line character. In the basic execution character set, there shall be
    control characters representing alert, backspace, carriage return, and new line. If any
    other characters are encountered in a source file (except in an identifier, a character
    constant, a string literal, a header name, a comment, or a preprocessing token that is never

[page 22]

    converted to a token), the behavior is undefined.
4   A letter is an uppercase letter or a lowercase letter as defined above; in this International
    Standard the term does not include other characters that are letters in other alphabets.
5   The universal character name construct provides a way to name other characters.
    Forward references: universal character names (6.4.3), character constants (6.4.4.4),
    preprocessing directives (6.10), string literals (6.4.5), comments (6.4.9), string (7.1.1).
    5.2.1.1 Trigraph sequences
1   Before any other processing takes place, each occurrence of one of the following
    sequences of three characters (called trigraph sequences17)) is replaced with the
    corresponding single character.
           ??=      #                       ??)      ]                       ??!     |
           ??(      [                       ??'      ^                       ??>     }
           ??/      \                       ??<      {                       ??-     ~
    No other trigraph sequences exist. Each ? that does not begin one of the trigraphs listed
    above is not changed.
2   EXAMPLE 1
              ??=define arraycheck(a, b) a??(b??) ??!??! b??(a??)
    becomes
              #define arraycheck(a, b) a[b] || b[a]

3   EXAMPLE 2      The following source line
              printf("Eh???/n");
    becomes (after replacement of the trigraph sequence ??/)
              printf("Eh?\n");

    5.2.1.2 Multibyte characters
1   The source character set may contain multibyte characters, used to represent members of
    the extended character set. The execution character set may also contain multibyte
    characters, which need not have the same encoding as for the source character set. For
    both character sets, the following shall hold:
    -- The basic character set shall be present and each character shall be encoded as a
      single byte.
    -- The presence, meaning, and representation of any additional members is locale-
      specific.

    17) The trigraph sequences enable the input of characters that are not defined in the Invariant Code Set as
        described in ISO/IEC 646, which is a subset of the seven-bit US ASCII code set.

[page 23]

    -- A multibyte character set may have a state-dependent encoding, wherein each
      sequence of multibyte characters begins in an initial shift state and enters other
      locale-specific shift states when specific multibyte characters are encountered in the
      sequence. While in the initial shift state, all single-byte characters retain their usual
      interpretation and do not alter the shift state. The interpretation for subsequent bytes
      in the sequence is a function of the current shift state.
    -- A byte with all bits zero shall be interpreted as a null character independent of shift
      state. Such a byte shall not occur as part of any other multibyte character.
2   For source files, the following shall hold:
    -- An identifier, comment, string literal, character constant, or header name shall begin
      and end in the initial shift state.
    -- An identifier, comment, string literal, character constant, or header name shall consist
      of a sequence of valid multibyte characters.
    5.2.2 Character display semantics
1   The active position is that location on a display device where the next character output by
    the fputc function would appear. The intent of writing a printing character (as defined
    by the isprint function) to a display device is to display a graphic representation of
    that character at the active position and then advance the active position to the next
    position on the current line. The direction of writing is locale-specific. If the active
    position is at the final position of a line (if there is one), the behavior of the display device
    is unspecified.
2   Alphabetic escape sequences representing nongraphic characters in the execution
    character set are intended to produce actions on display devices as follows:
    \a (alert) Produces an audible or visible alert without changing the active position.
    \b (backspace) Moves the active position to the previous position on the current line. If
       the active position is at the initial position of a line, the behavior of the display
       device is unspecified.
    \f ( form feed) Moves the active position to the initial position at the start of the next
       logical page.
    \n (new line) Moves the active position to the initial position of the next line.
    \r (carriage return) Moves the active position to the initial position of the current line.
    \t (horizontal tab) Moves the active position to the next horizontal tabulation position
       on the current line. If the active position is at or past the last defined horizontal
       tabulation position, the behavior of the display device is unspecified.
    \v (vertical tab) Moves the active position to the initial position of the next vertical
       tabulation position. If the active position is at or past the last defined vertical
[page 24]

         tabulation position, the behavior of the display device is unspecified.
3   Each of these escape sequences shall produce a unique implementation-defined value
    which can be stored in a single char object. The external representations in a text file
    need not be identical to the internal representations, and are outside the scope of this
    International Standard.
    Forward references: the isprint function (7.4.1.8), the fputc function (7.21.7.3).
    5.2.3 Signals and interrupts
1   Functions shall be implemented such that they may be interrupted at any time by a signal,
    or may be called by a signal handler, or both, with no alteration to earlier, but still active,
    invocations' control flow (after the interruption), function return values, or objects with
    automatic storage duration. All such objects shall be maintained outside the function
    image (the instructions that compose the executable representation of a function) on a
    per-invocation basis.
    5.2.4 Environmental limits
1   Both the translation and execution environments constrain the implementation of
    language translators and libraries. The following summarizes the language-related
    environmental limits on a conforming implementation; the library-related limits are
    discussed in clause 7.
    5.2.4.1 Translation limits
1   The implementation shall be able to translate and execute at least one program that
    contains at least one instance of every one of the following limits:18)
    -- 127 nesting levels of blocks
    -- 63 nesting levels of conditional inclusion
    -- 12 pointer, array, and function declarators (in any combinations) modifying an
      arithmetic, structure, union, or void type in a declaration
    -- 63 nesting levels of parenthesized declarators within a full declarator
    -- 63 nesting levels of parenthesized expressions within a full expression
    -- 63 significant initial characters in an internal identifier or a macro name (each
      universal character name or extended source character is considered a single
      character)
    -- 31 significant initial characters in an external identifier (each universal character name
      specifying a short identifier of 0000FFFF or less is considered 6 characters, each


    18) Implementations should avoid imposing fixed translation limits whenever possible.

[page 25]

         universal character name specifying a short identifier of 00010000 or more is
         considered 10 characters, and each extended source character is considered the same
         number of characters as the corresponding universal character name, if any)19)
    -- 4095 external identifiers in one translation unit
    -- 511 identifiers with block scope declared in one block
    -- 4095 macro identifiers simultaneously defined in one preprocessing translation unit
    -- 127 parameters in one function definition
    -- 127 arguments in one function call
    -- 127 parameters in one macro definition
    -- 127 arguments in one macro invocation
    -- 4095 characters in a logical source line
    -- 4095 characters in a string literal (after concatenation)
    -- 65535 bytes in an object (in a hosted environment only)
    -- 15 nesting levels for #included files
    -- 1023 case labels for a switch statement (excluding those for any nested switch
      statements)
    -- 1023 members in a single structure or union
    -- 1023 enumeration constants in a single enumeration
    -- 63 levels of nested structure or union definitions in a single struct-declaration-list
    5.2.4.2 Numerical limits
1   An implementation is required to document all the limits specified in this subclause,
    which are specified in the headers <limits.h> and <float.h>. Additional limits are
    specified in <stdint.h>.
    Forward references: integer types <stdint.h> (7.20).
    5.2.4.2.1 Sizes of integer types <limits.h>
1   The values given below shall be replaced by constant expressions suitable for use in #if
    preprocessing directives. Moreover, except for CHAR_BIT and MB_LEN_MAX, the
    following shall be replaced by expressions that have the same type as would an
    expression that is an object of the corresponding type converted according to the integer
    promotions. Their implementation-defined values shall be equal or greater in magnitude


    19) See ''future language directions'' (6.11.3).

[page 26]

(absolute value) to those shown, with the same sign.
-- number of bits for smallest object that is not a bit-field (byte)
  CHAR_BIT                                            8
-- minimum value for an object of type signed char
  SCHAR_MIN                                -127 // -(27 - 1)
-- maximum value for an object of type signed char
  SCHAR_MAX                                +127 // 27 - 1
-- maximum value for an object of type unsigned char
  UCHAR_MAX                                 255 // 28 - 1
-- minimum value for an object of type char
  CHAR_MIN                               see below
-- maximum value for an object of type char
  CHAR_MAX                              see below
-- maximum number of bytes in a multibyte character, for any supported locale
  MB_LEN_MAX                                    1
-- minimum value for an object of type short int
  SHRT_MIN                               -32767 // -(215 - 1)
-- maximum value for an object of type short int
  SHRT_MAX                               +32767 // 215 - 1
-- maximum value for an object of type unsigned short int
  USHRT_MAX                               65535 // 216 - 1
-- minimum value for an object of type int
  INT_MIN                                 -32767 // -(215 - 1)
-- maximum value for an object of type int
  INT_MAX                                +32767 // 215 - 1
-- maximum value for an object of type unsigned int
  UINT_MAX                                65535 // 216 - 1
-- minimum value for an object of type long int
  LONG_MIN                         -2147483647 // -(231 - 1)
-- maximum value for an object of type long int
  LONG_MAX                         +2147483647 // 231 - 1
-- maximum value for an object of type unsigned long int
  ULONG_MAX                         4294967295 // 232 - 1


[page 27]

    -- minimum value for an object of type long long int
      LLONG_MIN          -9223372036854775807 // -(263 - 1)
    -- maximum value for an object of type long long int
      LLONG_MAX          +9223372036854775807 // 263 - 1
    -- maximum value for an object of type unsigned long long int
      ULLONG_MAX         18446744073709551615 // 264 - 1
2   If the value of an object of type char is treated as a signed integer when used in an
    expression, the value of CHAR_MIN shall be the same as that of SCHAR_MIN and the
    value of CHAR_MAX shall be the same as that of SCHAR_MAX. Otherwise, the value of
    CHAR_MIN shall be 0 and the value of CHAR_MAX shall be the same as that of
    UCHAR_MAX.20) The value UCHAR_MAX shall equal 2CHAR_BIT - 1.
    Forward references: representations of types (6.2.6), conditional inclusion (6.10.1).
    5.2.4.2.2 Characteristics of floating types <float.h>
1   The characteristics of floating types are defined in terms of a model that describes a
    representation of floating-point numbers and values that provide information about an
    implementation's floating-point arithmetic.21) The following parameters are used to
    define the model for each floating-point type:
           s          sign ((+-)1)
           b          base or radix of exponent representation (an integer > 1)
           e          exponent (an integer between a minimum emin and a maximum emax )
           p          precision (the number of base-b digits in the significand)
            fk        nonnegative integers less than b (the significand digits)
2   A floating-point number (x) is defined by the following model:
                       p
           x = sb e   (Sum) f k b-k ,
                      k=1
                                    emin <= e <= emax

3   In addition to normalized floating-point numbers ( f 1 > 0 if x != 0), floating types may be
    able to contain other kinds of floating-point numbers, such as subnormal floating-point
    numbers (x != 0, e = emin , f 1 = 0) and unnormalized floating-point numbers (x != 0,
    e > emin , f 1 = 0), and values that are not floating-point numbers, such as infinities and
    NaNs. A NaN is an encoding signifying Not-a-Number. A quiet NaN propagates
    through almost every arithmetic operation without raising a floating-point exception; a
    signaling NaN generally raises a floating-point exception when occurring as an


    20) See 6.2.5.
    21) The floating-point model is intended to clarify the description of each floating-point characteristic and
        does not require the floating-point arithmetic of the implementation to be identical.

[page 28]

    arithmetic operand.22)
4   An implementation may give zero and values that are not floating-point numbers (such as
    infinities and NaNs) a sign or may leave them unsigned. Wherever such values are
    unsigned, any requirement in this International Standard to retrieve the sign shall produce
    an unspecified sign, and any requirement to set the sign shall be ignored.
5   The minimum range of representable values for a floating type is the most negative finite
    floating-point number representable in that type through the most positive finite floating-
    point number representable in that type. In addition, if negative infinity is representable
    in a type, the range of that type is extended to all negative real numbers; likewise, if
    positive infinity is representable in a type, the range of that type is extended to all positive
    real numbers.
6   The accuracy of the floating-point operations (+, -, *, /) and of the library functions in
    <math.h> and <complex.h> that return floating-point results is implementation-
    defined, as is the accuracy of the conversion between floating-point internal
    representations and string representations performed by the library functions in
    <stdio.h>, <stdlib.h>, and <wchar.h>. The implementation may state that the
    accuracy is unknown.
7   All integer values in the <float.h> header, except FLT_ROUNDS, shall be constant
    expressions suitable for use in #if preprocessing directives; all floating values shall be
    constant expressions. All except DECIMAL_DIG, FLT_EVAL_METHOD, FLT_RADIX,
    and FLT_ROUNDS have separate names for all three floating-point types. The floating-
    point model representation is provided for all values except FLT_EVAL_METHOD and
    FLT_ROUNDS.
8   The rounding mode for floating-point addition is characterized by the implementation-
    defined value of FLT_ROUNDS:23)
          -1      indeterminable
           0      toward zero
           1      to nearest
           2      toward positive infinity
           3      toward negative infinity
    All other values for FLT_ROUNDS characterize implementation-defined rounding
    behavior.


    22) IEC 60559:1989 specifies quiet and signaling NaNs. For implementations that do not support
        IEC 60559:1989, the terms quiet NaN and signaling NaN are intended to apply to encodings with
        similar behavior.
    23) Evaluation of FLT_ROUNDS correctly reflects any execution-time change of rounding mode through
        the function fesetround in <fenv.h>.

[page 29]

9    Except for assignment and cast (which remove all extra range and precision), the values
     yielded by operators with floating operands and values subject to the usual arithmetic
     conversions and of floating constants are evaluated to a format whose range and precision
     may be greater than required by the type. The use of evaluation formats is characterized
     by the implementation-defined value of FLT_EVAL_METHOD:24)
            -1         indeterminable;
              0        evaluate all operations and constants just to the range and precision of the
                       type;
              1        evaluate operations and constants of type float and double to the
                       range and precision of the double type, evaluate long double
                       operations and constants to the range and precision of the long double
                       type;
              2        evaluate all operations and constants to the range and precision of the
                       long double type.
     All other negative values for FLT_EVAL_METHOD characterize implementation-defined
     behavior.
10   The presence or absence of subnormal numbers is characterized by the implementation-
     defined     values     of    FLT_HAS_SUBNORM,          DBL_HAS_SUBNORM,           and
     LDBL_HAS_SUBNORM:
            -1       indeterminable25)
             0       absent26) (type does not support subnormal numbers)
             1       present (type does support subnormal numbers)
11   The values given in the following list shall be replaced by constant expressions with
     implementation-defined values that are greater or equal in magnitude (absolute value) to
     those shown, with the same sign:
     -- radix of exponent representation, b
       FLT_RADIX                                                    2




     24) The evaluation method determines evaluation formats of expressions involving all floating types, not
         just real types. For example, if FLT_EVAL_METHOD is 1, then the product of two float
         _Complex operands is represented in the double _Complex format, and its parts are evaluated to
         double.
     25) Characterization as indeterminable is intended if floating-point operations do not consistently interpret
         subnormal representations as zero, nor as nonzero.
     26) Characterization as absent is intended if no floating-point operations produce subnormal results from
         non-subnormal inputs, even if the type format includes representations of subnormal numbers.

[page 30]

-- number of base-FLT_RADIX digits in the floating-point significand, p
   FLT_MANT_DIG
   DBL_MANT_DIG
   LDBL_MANT_DIG
-- number of decimal digits, n, such that any floating-point number with p radix b digits
  can be rounded to a floating-point number with n decimal digits and back again
  without change to the value,
       { p log10 b        if b is a power of 10
       {
       { [^1 + p log10 b^] otherwise
   FLT_DECIMAL_DIG                                   6
   DBL_DECIMAL_DIG                                  10
   LDBL_DECIMAL_DIG                                 10
-- number of decimal digits, n, such that any floating-point number in the widest
  supported floating type with pmax radix b digits can be rounded to a floating-point
  number with n decimal digits and back again without change to the value,
       { pmax log10 b       if b is a power of 10
       {
       { [^1 + pmax log10 b^] otherwise
   DECIMAL_DIG                                     10
-- number of decimal digits, q, such that any floating-point number with q decimal digits
  can be rounded into a floating-point number with p radix b digits and back again
  without change to the q decimal digits,
       { p log10 b          if b is a power of 10
       {
       { [_( p - 1) log10 b_] otherwise
   FLT_DIG                                          6
   DBL_DIG                                         10
   LDBL_DIG                                        10
-- minimum negative integer such that FLT_RADIX raised to one less than that power is
  a normalized floating-point number, emin
   FLT_MIN_EXP
   DBL_MIN_EXP
   LDBL_MIN_EXP




[page 31]

     -- minimum negative integer such that 10 raised to that power is in the range of
       normalized floating-point numbers, [^log10 b emin -1 ^]
                                         [                  ]
       FLT_MIN_10_EXP                                 -37
       DBL_MIN_10_EXP                                 -37
       LDBL_MIN_10_EXP                                -37
     -- maximum integer such that FLT_RADIX raised to one less than that power is a
       representable finite floating-point number, emax
          FLT_MAX_EXP
          DBL_MAX_EXP
          LDBL_MAX_EXP
     -- maximum integer such that 10 raised to that power is in the range of representable
       finite floating-point numbers, [_log10 ((1 - b- p )b emax )_]
          FLT_MAX_10_EXP                               +37
          DBL_MAX_10_EXP                               +37
          LDBL_MAX_10_EXP                              +37
12   The values given in the following list shall be replaced by constant expressions with
     implementation-defined values that are greater than or equal to those shown:
     -- maximum representable finite floating-point number, (1 - b- p )b emax
          FLT_MAX                                   1E+37
          DBL_MAX                                   1E+37
          LDBL_MAX                                  1E+37
13   The values given in the following list shall be replaced by constant expressions with
     implementation-defined (positive) values that are less than or equal to those shown:
     -- the difference between 1 and the least value greater than 1 that is representable in the
       given floating point type, b1- p
          FLT_EPSILON                                1E-5
          DBL_EPSILON                                1E-9
          LDBL_EPSILON                               1E-9
     -- minimum normalized positive floating-point number, b emin -1
          FLT_MIN                                   1E-37
          DBL_MIN                                   1E-37
          LDBL_MIN                                  1E-37




[page 32]

     -- minimum positive floating-point number27)
         FLT_TRUE_MIN                                       1E-37
         DBL_TRUE_MIN                                       1E-37
         LDBL_TRUE_MIN                                      1E-37
     Recommended practice
14   Conversion from (at least) double to decimal with DECIMAL_DIG digits and back
     should be the identity function.
15   EXAMPLE 1 The following describes an artificial floating-point representation that meets the minimum
     requirements of this International Standard, and the appropriate values in a <float.h> header for type
     float:
                        6
           x = s16e    (Sum) f k 16-k ,
                       k=1
                                       -31 <= e <= +32

             FLT_RADIX                                    16
             FLT_MANT_DIG                                  6
             FLT_EPSILON                     9.53674316E-07F
             FLT_DECIMAL_DIG                               9
             FLT_DIG                                       6
             FLT_MIN_EXP                                 -31
             FLT_MIN                         2.93873588E-39F
             FLT_MIN_10_EXP                              -38
             FLT_MAX_EXP                                 +32
             FLT_MAX                         3.40282347E+38F
             FLT_MAX_10_EXP                              +38

16   EXAMPLE 2 The following describes floating-point representations that also meet the requirements for
     single-precision and double-precision numbers in IEC 60559,28) and the appropriate values in a
     <float.h> header for types float and double:
                       24
           x f = s2e   (Sum) f k 2-k ,
                       k=1
                                      -125 <= e <= +128

                       53
           x d = s2e   (Sum) f k 2-k ,
                       k=1
                                      -1021 <= e <= +1024

             FLT_RADIX                                     2
             DECIMAL_DIG                                  17
             FLT_MANT_DIG                                 24
             FLT_EPSILON                     1.19209290E-07F // decimal constant
             FLT_EPSILON                            0X1P-23F // hex constant
             FLT_DECIMAL_DIG                               9


     27) If the presence or absence of subnormal numbers is indeterminable, then the value is intended to be a
         positive number no greater than the minimum normalized positive number for the type.
     28) The floating-point model in that standard sums powers of b from zero, so the values of the exponent
         limits are one less than shown here.

[page 33]

        FLT_DIG                             6
        FLT_MIN_EXP                      -125
        FLT_MIN               1.17549435E-38F               //   decimal constant
        FLT_MIN                     0X1P-126F               //   hex constant
        FLT_TRUE_MIN          1.40129846E-45F               //   decimal constant
        FLT_TRUE_MIN                0X1P-149F               //   hex constant
        FLT_HAS_SUBNORM                     1
        FLT_MIN_10_EXP                    -37
        FLT_MAX_EXP                      +128
        FLT_MAX               3.40282347E+38F               // decimal constant
        FLT_MAX               0X1.fffffeP127F               // hex constant
        FLT_MAX_10_EXP                    +38
        DBL_MANT_DIG                       53
        DBL_EPSILON    2.2204460492503131E-16               // decimal constant
        DBL_EPSILON                   0X1P-52               // hex constant
        DBL_DECIMAL_DIG                    17
        DBL_DIG                            15
        DBL_MIN_EXP                     -1021
        DBL_MIN      2.2250738585072014E-308                //   decimal constant
        DBL_MIN                     0X1P-1022               //   hex constant
        DBL_TRUE_MIN 4.9406564584124654E-324                //   decimal constant
        DBL_TRUE_MIN                0X1P-1074               //   hex constant
        DBL_HAS_SUBNORM                     1
        DBL_MIN_10_EXP                   -307
        DBL_MAX_EXP                     +1024
        DBL_MAX      1.7976931348623157E+308                // decimal constant
        DBL_MAX        0X1.fffffffffffffP1023               // hex constant
        DBL_MAX_10_EXP                   +308
If a type wider than double were supported, then DECIMAL_DIG would be greater than 17. For
example, if the widest type were to use the minimal-width IEC 60559 double-extended format (64 bits of
precision), then DECIMAL_DIG would be 21.

Forward references:        conditional inclusion (6.10.1), complex arithmetic
<complex.h> (7.3), extended multibyte and wide character utilities <wchar.h>
(7.28), floating-point environment <fenv.h> (7.6), general utilities <stdlib.h>
(7.22), input/output <stdio.h> (7.21), mathematics <math.h> (7.12).




[page 34]


    6. Language
    6.1 Notation
1   In the syntax notation used in this clause, syntactic categories (nonterminals) are
    indicated by italic type, and literal words and character set members (terminals) by bold
    type. A colon (:) following a nonterminal introduces its definition. Alternative
    definitions are listed on separate lines, except when prefaced by the words ''one of''. An
    optional symbol is indicated by the subscript ''opt'', so that
             { expressionopt }
    indicates an optional expression enclosed in braces.
2   When syntactic categories are referred to in the main text, they are not italicized and
    words are separated by spaces instead of hyphens.
3   A summary of the language syntax is given in annex A.
    6.2 Concepts
    6.2.1 Scopes of identifiers
1   An identifier can denote an object; a function; a tag or a member of a structure, union, or
    enumeration; a typedef name; a label name; a macro name; or a macro parameter. The
    same identifier can denote different entities at different points in the program. A member
    of an enumeration is called an enumeration constant. Macro names and macro
    parameters are not considered further here, because prior to the semantic phase of
    program translation any occurrences of macro names in the source file are replaced by the
    preprocessing token sequences that constitute their macro definitions.
2   For each different entity that an identifier designates, the identifier is visible (i.e., can be
    used) only within a region of program text called its scope. Different entities designated
    by the same identifier either have different scopes, or are in different name spaces. There
    are four kinds of scopes: function, file, block, and function prototype. (A function
    prototype is a declaration of a function that declares the types of its parameters.)
3   A label name is the only kind of identifier that has function scope. It can be used (in a
    goto statement) anywhere in the function in which it appears, and is declared implicitly
    by its syntactic appearance (followed by a : and a statement).
4   Every other identifier has scope determined by the placement of its declaration (in a
    declarator or type specifier). If the declarator or type specifier that declares the identifier
    appears outside of any block or list of parameters, the identifier has file scope, which
    terminates at the end of the translation unit. If the declarator or type specifier that
    declares the identifier appears inside a block or within the list of parameter declarations in
    a function definition, the identifier has block scope, which terminates at the end of the
    associated block. If the declarator or type specifier that declares the identifier appears

[page 35]

    within the list of parameter declarations in a function prototype (not part of a function
    definition), the identifier has function prototype scope, which terminates at the end of the
    function declarator. If an identifier designates two different entities in the same name
    space, the scopes might overlap. If so, the scope of one entity (the inner scope) will end
    strictly before the scope of the other entity (the outer scope). Within the inner scope, the
    identifier designates the entity declared in the inner scope; the entity declared in the outer
    scope is hidden (and not visible) within the inner scope.
5   Unless explicitly stated otherwise, where this International Standard uses the term
    ''identifier'' to refer to some entity (as opposed to the syntactic construct), it refers to the
    entity in the relevant name space whose declaration is visible at the point the identifier
    occurs.
6   Two identifiers have the same scope if and only if their scopes terminate at the same
    point.
7   Structure, union, and enumeration tags have scope that begins just after the appearance of
    the tag in a type specifier that declares the tag. Each enumeration constant has scope that
    begins just after the appearance of its defining enumerator in an enumerator list. Any
    other identifier has scope that begins just after the completion of its declarator.
8   As a special case, a type name (which is not a declaration of an identifier) is considered to
    have a scope that begins just after the place within the type name where the omitted
    identifier would appear were it not omitted.
    Forward references: declarations (6.7), function calls (6.5.2.2), function definitions
    (6.9.1), identifiers (6.4.2), macro replacement (6.10.3), name spaces of identifiers (6.2.3),
    source file inclusion (6.10.2), statements (6.8).
    6.2.2 Linkages of identifiers
1   An identifier declared in different scopes or in the same scope more than once can be
    made to refer to the same object or function by a process called linkage.29) There are
    three kinds of linkage: external, internal, and none.
2   In the set of translation units and libraries that constitutes an entire program, each
    declaration of a particular identifier with external linkage denotes the same object or
    function. Within one translation unit, each declaration of an identifier with internal
    linkage denotes the same object or function. Each declaration of an identifier with no
    linkage denotes a unique entity.
3   If the declaration of a file scope identifier for an object or a function contains the storage-
    class specifier static, the identifier has internal linkage.30)



    29) There is no linkage between different identifiers.

[page 36]

4   For an identifier declared with the storage-class specifier extern in a scope in which a
    prior declaration of that identifier is visible,31) if the prior declaration specifies internal or
    external linkage, the linkage of the identifier at the later declaration is the same as the
    linkage specified at the prior declaration. If no prior declaration is visible, or if the prior
    declaration specifies no linkage, then the identifier has external linkage.
5   If the declaration of an identifier for a function has no storage-class specifier, its linkage
    is determined exactly as if it were declared with the storage-class specifier extern. If
    the declaration of an identifier for an object has file scope and no storage-class specifier,
    its linkage is external.
6   The following identifiers have no linkage: an identifier declared to be anything other than
    an object or a function; an identifier declared to be a function parameter; a block scope
    identifier for an object declared without the storage-class specifier extern.
7   If, within a translation unit, the same identifier appears with both internal and external
    linkage, the behavior is undefined.
    Forward references: declarations (6.7), expressions (6.5), external definitions (6.9),
    statements (6.8).
    6.2.3 Name spaces of identifiers
1   If more than one declaration of a particular identifier is visible at any point in a
    translation unit, the syntactic context disambiguates uses that refer to different entities.
    Thus, there are separate name spaces for various categories of identifiers, as follows:
    -- label names (disambiguated by the syntax of the label declaration and use);
    -- the tags of structures, unions, and enumerations (disambiguated by following any32)
      of the keywords struct, union, or enum);
    -- the members of structures or unions; each structure or union has a separate name
      space for its members (disambiguated by the type of the expression used to access the
      member via the . or -> operator);
    -- all other identifiers, called ordinary identifiers (declared in ordinary declarators or as
      enumeration constants).
    Forward references: enumeration specifiers (6.7.2.2), labeled statements (6.8.1),
    structure and union specifiers (6.7.2.1), structure and union members (6.5.2.3), tags
    (6.7.2.3), the goto statement (6.8.6.1).

    30) A function declaration can contain the storage-class specifier static only if it is at file scope; see
        6.7.1.
    31) As specified in 6.2.1, the later declaration might hide the prior declaration.
    32) There is only one name space for tags even though three are possible.

[page 37]

    6.2.4 Storage durations of objects
1   An object has a storage duration that determines its lifetime. There are four storage
    durations: static, thread, automatic, and allocated. Allocated storage is described in
    7.22.3.
2   The lifetime of an object is the portion of program execution during which storage is
    guaranteed to be reserved for it. An object exists, has a constant address,33) and retains
    its last-stored value throughout its lifetime.34) If an object is referred to outside of its
    lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when
    the object it points to (or just past) reaches the end of its lifetime.
3   An object whose identifier is declared without the storage-class specifier
    _Thread_local, and either with external or internal linkage or with the storage-class
    specifier static, has static storage duration. Its lifetime is the entire execution of the
    program and its stored value is initialized only once, prior to program startup.
4   An object whose identifier is declared with the storage-class specifier _Thread_local
    has thread storage duration. Its lifetime is the entire execution of the thread for which it
    is created, and its stored value is initialized when the thread is started. There is a distinct
    object per thread, and use of the declared name in an expression refers to the object
    associated with the thread evaluating the expression. The result of attempting to
    indirectly access an object with thread storage duration from a thread other than the one
    with which the object is associated is implementation-defined.
5   An object whose identifier is declared with no linkage and without the storage-class
    specifier static has automatic storage duration, as do some compound literals. The
    result of attempting to indirectly access an object with automatic storage duration from a
    thread other than the one with which the object is associated is implementation-defined.
6   For such an object that does not have a variable length array type, its lifetime extends
    from entry into the block with which it is associated until execution of that block ends in
    any way. (Entering an enclosed block or calling a function suspends, but does not end,
    execution of the current block.) If the block is entered recursively, a new instance of the
    object is created each time. The initial value of the object is indeterminate. If an
    initialization is specified for the object, it is performed each time the declaration or
    compound literal is reached in the execution of the block; otherwise, the value becomes
    indeterminate each time the declaration is reached.



    33) The term ''constant address'' means that two pointers to the object constructed at possibly different
        times will compare equal. The address may be different during two different executions of the same
        program.
    34) In the case of a volatile object, the last store need not be explicit in the program.

[page 38]

7   For such an object that does have a variable length array type, its lifetime extends from
    the declaration of the object until execution of the program leaves the scope of the
    declaration.35) If the scope is entered recursively, a new instance of the object is created
    each time. The initial value of the object is indeterminate.
8   A non-lvalue expression with structure or union type, where the structure or union
    contains a member with array type (including, recursively, members of all contained
    structures and unions) refers to an object with automatic storage duration and temporary
    lifetime.36) Its lifetime begins when the expression is evaluated and its initial value is the
    value of the expression. Its lifetime ends when the evaluation of the containing full
    expression or full declarator ends. Any attempt to modify an object with temporary
    lifetime results in undefined behavior.
    Forward references: array declarators (6.7.6.2), compound literals (6.5.2.5), declarators
    (6.7.6), function calls (6.5.2.2), initialization (6.7.9), statements (6.8).
    6.2.5 Types
1   The meaning of a value stored in an object or returned by a function is determined by the
    type of the expression used to access it. (An identifier declared to be an object is the
    simplest such expression; the type is specified in the declaration of the identifier.) Types
    are partitioned into object types (types that describe objects) and function types (types
    that describe functions). At various points within a translation unit an object type may be
    incomplete (lacking sufficient information to determine the size of objects of that type) or
    complete (having sufficient information).37)
2   An object declared as type _Bool is large enough to store the values 0 and 1.
3   An object declared as type char is large enough to store any member of the basic
    execution character set. If a member of the basic execution character set is stored in a
    char object, its value is guaranteed to be nonnegative. If any other character is stored in
    a char object, the resulting value is implementation-defined but shall be within the range
    of values that can be represented in that type.
4   There are five standard signed integer types, designated as signed char, short
    int, int, long int, and long long int. (These and other types may be
    designated in several additional ways, as described in 6.7.2.) There may also be
    implementation-defined extended signed integer types.38) The standard and extended
    signed integer types are collectively called signed integer types.39)

    35) Leaving the innermost block containing the declaration, or jumping to a point in that block or an
        embedded block prior to the declaration, leaves the scope of the declaration.
    36) The address of such an object is taken implicitly when an array member is accessed.
    37) A type may be incomplete or complete throughout an entire translation unit, or it may change states at
        different points within a translation unit.

[page 39]

5    An object declared as type signed char occupies the same amount of storage as a
     ''plain'' char object. A ''plain'' int object has the natural size suggested by the
     architecture of the execution environment (large enough to contain any value in the range
     INT_MIN to INT_MAX as defined in the header <limits.h>).
6    For each of the signed integer types, there is a corresponding (but different) unsigned
     integer type (designated with the keyword unsigned) that uses the same amount of
     storage (including sign information) and has the same alignment requirements. The type
     _Bool and the unsigned integer types that correspond to the standard signed integer
     types are the standard unsigned integer types. The unsigned integer types that
     correspond to the extended signed integer types are the extended unsigned integer types.
     The standard and extended unsigned integer types are collectively called unsigned integer
     types.40)
7    The standard signed integer types and standard unsigned integer types are collectively
     called the standard integer types, the extended signed integer types and extended
     unsigned integer types are collectively called the extended integer types.
8    For any two integer types with the same signedness and different integer conversion rank
     (see 6.3.1.1), the range of values of the type with smaller integer conversion rank is a
     subrange of the values of the other type.
9    The range of nonnegative values of a signed integer type is a subrange of the
     corresponding unsigned integer type, and the representation of the same value in each
     type is the same.41) A computation involving unsigned operands can never overflow,
     because a result that cannot be represented by the resulting unsigned integer type is
     reduced modulo the number that is one greater than the largest value that can be
     represented by the resulting type.
10   There are three real floating types, designated as float, double, and long
     double.42) The set of values of the type float is a subset of the set of values of the
     type double; the set of values of the type double is a subset of the set of values of the
     type long double.


     38) Implementation-defined keywords shall have the form of an identifier reserved for any use as
         described in 7.1.3.
     39) Therefore, any statement in this Standard about signed integer types also applies to the extended
         signed integer types.
     40) Therefore, any statement in this Standard about unsigned integer types also applies to the extended
         unsigned integer types.
     41) The same representation and alignment requirements are meant to imply interchangeability as
         arguments to functions, return values from functions, and members of unions.
     42) See ''future language directions'' (6.11.1).

[page 40]

11   There are three complex types, designated as float _Complex, double
     _Complex, and long double _Complex.43) (Complex types are a conditional
     feature that implementations need not support; see 6.10.8.3.) The real floating and
     complex types are collectively called the floating types.
12   For each floating type there is a corresponding real type, which is always a real floating
     type. For real floating types, it is the same type. For complex types, it is the type given
     by deleting the keyword _Complex from the type name.
13   Each complex type has the same representation and alignment requirements as an array
     type containing exactly two elements of the corresponding real type; the first element is
     equal to the real part, and the second element to the imaginary part, of the complex
     number.
14   The type char, the signed and unsigned integer types, and the floating types are
     collectively called the basic types. The basic types are complete object types. Even if the
     implementation defines two or more basic types to have the same representation, they are
     nevertheless different types.44)
15   The three types char, signed char, and unsigned char are collectively called
     the character types. The implementation shall define char to have the same range,
     representation, and behavior as either signed char or unsigned char.45)
16   An enumeration comprises a set of named integer constant values. Each distinct
     enumeration constitutes a different enumerated type.
17   The type char, the signed and unsigned integer types, and the enumerated types are
     collectively called integer types. The integer and real floating types are collectively called
     real types.
18   Integer and floating types are collectively called arithmetic types. Each arithmetic type
     belongs to one type domain: the real type domain comprises the real types, the complex
     type domain comprises the complex types.
19   The void type comprises an empty set of values; it is an incomplete object type that
     cannot be completed.



     43) A specification for imaginary types is in annex G.
     44) An implementation may define new keywords that provide alternative ways to designate a basic (or
         any other) type; this does not violate the requirement that all basic types be different.
         Implementation-defined keywords shall have the form of an identifier reserved for any use as
         described in 7.1.3.
     45) CHAR_MIN, defined in <limits.h>, will have one of the values 0 or SCHAR_MIN, and this can be
         used to distinguish the two options. Irrespective of the choice made, char is a separate type from the
         other two and is not compatible with either.

[page 41]

20   Any number of derived types can be constructed from the object and function types, as
     follows:
     -- An array type describes a contiguously allocated nonempty set of objects with a
       particular member object type, called the element type. The element type shall be
       complete whenever the array type is specified. Array types are characterized by their
       element type and by the number of elements in the array. An array type is said to be
       derived from its element type, and if its element type is T , the array type is sometimes
       called ''array of T ''. The construction of an array type from an element type is called
       ''array type derivation''.
     -- A structure type describes a sequentially allocated nonempty set of member objects
       (and, in certain circumstances, an incomplete array), each of which has an optionally
       specified name and possibly distinct type.
     -- A union type describes an overlapping nonempty set of member objects, each of
       which has an optionally specified name and possibly distinct type.
     -- A function type describes a function with specified return type. A function type is
       characterized by its return type and the number and types of its parameters. A
       function type is said to be derived from its return type, and if its return type is T , the
       function type is sometimes called ''function returning T ''. The construction of a
       function type from a return type is called ''function type derivation''.
     -- A pointer type may be derived from a function type or an object type, called the
       referenced type. A pointer type describes an object whose value provides a reference
       to an entity of the referenced type. A pointer type derived from the referenced type T
       is sometimes called ''pointer to T ''. The construction of a pointer type from a
       referenced type is called ''pointer type derivation''. A pointer type is a complete
       object type.
     -- An atomic type describes the type designated by the construct _Atomic ( type-
       name ). (Atomic types are a conditional feature that implementations need not
       support; see 6.10.8.3.)
     These methods of constructing derived types can be applied recursively.
21   Arithmetic types and pointer types are collectively called scalar types. Array and
     structure types are collectively called aggregate types.46)
22   An array type of unknown size is an incomplete type. It is completed, for an identifier of
     that type, by specifying the size in a later declaration (with internal or external linkage).
     A structure or union type of unknown content (as described in 6.7.2.3) is an incomplete


     46) Note that aggregate type does not include union type because an object with union type can only
         contain one member at a time.

[page 42]

     type. It is completed, for all declarations of that type, by declaring the same structure or
     union tag with its defining content later in the same scope.
23   A type has known constant size if the type is not incomplete and is not a variable length
     array type.
24   Array, function, and pointer types are collectively called derived declarator types. A
     declarator type derivation from a type T is the construction of a derived declarator type
     from T by the application of an array-type, a function-type, or a pointer-type derivation to
     T.
25   A type is characterized by its type category, which is either the outermost derivation of a
     derived type (as noted above in the construction of derived types), or the type itself if the
     type consists of no derived types.
26   Any type so far mentioned is an unqualified type. Each unqualified type has several
     qualified versions of its type,47) corresponding to the combinations of one, two, or all
     three of the const, volatile, and restrict qualifiers. The qualified or unqualified
     versions of a type are distinct types that belong to the same type category and have the
     same representation and alignment requirements.48) A derived type is not qualified by the
     qualifiers (if any) of the type from which it is derived.
27   Further, there is the _Atomic qualifier. The presence of the _Atomic qualifier
     designates an atomic type. The size, representation, and alignment of an atomic type
     need not be the same as those of the corresponding unqualified type. Therefore, this
     Standard explicitly uses the phrase ''atomic, qualified or unqualified type'' whenever the
     atomic version of a type is permitted along with the other qualified versions of a type.
     The phrase ''qualified or unqualified type'', without specific mention of atomic, does not
     include the atomic types.
28   A pointer to void shall have the same representation and alignment requirements as a
     pointer to a character type.48) Similarly, pointers to qualified or unqualified versions of
     compatible types shall have the same representation and alignment requirements. All
     pointers to structure types shall have the same representation and alignment requirements
     as each other. All pointers to union types shall have the same representation and
     alignment requirements as each other. Pointers to other types need not have the same
     representation or alignment requirements.
29   EXAMPLE 1 The type designated as ''float *'' has type ''pointer to float''. Its type category is
     pointer, not a floating type. The const-qualified version of this type is designated as ''float * const''
     whereas the type designated as ''const float *'' is not a qualified type -- its type is ''pointer to const-


     47) See 6.7.3 regarding qualified array and function types.
     48) The same representation and alignment requirements are meant to imply interchangeability as
         arguments to functions, return values from functions, and members of unions.

[page 43]

     qualified float'' and is a pointer to a qualified type.

30   EXAMPLE 2 The type designated as ''struct tag (*[5])(float)'' has type ''array of pointer to
     function returning struct tag''. The array has length five and the function has a single parameter of type
     float. Its type category is array.

     Forward references: compatible type and composite type (6.2.7), declarations (6.7).
     6.2.6 Representations of types
     6.2.6.1 General
1    The representations of all types are unspecified except as stated in this subclause.
2    Except for bit-fields, objects are composed of contiguous sequences of one or more bytes,
     the number, order, and encoding of which are either explicitly specified or
     implementation-defined.
3    Values stored in unsigned bit-fields and objects of type unsigned char shall be
     represented using a pure binary notation.49)
4    Values stored in non-bit-field objects of any other object type consist of n x CHAR_BIT
     bits, where n is the size of an object of that type, in bytes. The value may be copied into
     an object of type unsigned char [n] (e.g., by memcpy); the resulting set of bytes is
     called the object representation of the value. Values stored in bit-fields consist of m bits,
     where m is the size specified for the bit-field. The object representation is the set of m
     bits the bit-field comprises in the addressable storage unit holding it. Two values (other
     than NaNs) with the same object representation compare equal, but values that compare
     equal may have different object representations.
5    Certain object representations need not represent a value of the object type. If the stored
     value of an object has such a representation and is read by an lvalue expression that does
     not have character type, the behavior is undefined. If such a representation is produced
     by a side effect that modifies all or any part of the object by an lvalue expression that
     does not have character type, the behavior is undefined.50) Such a representation is called
     a trap representation.
6    When a value is stored in an object of structure or union type, including in a member
     object, the bytes of the object representation that correspond to any padding bytes take
     unspecified values.51) The value of a structure or union object is never a trap


     49) A positional representation for integers that uses the binary digits 0 and 1, in which the values
         represented by successive bits are additive, begin with 1, and are multiplied by successive integral
         powers of 2, except perhaps the bit with the highest position. (Adapted from the American National
         Dictionary for Information Processing Systems.) A byte contains CHAR_BIT bits, and the values of
         type unsigned char range from 0 to 2
                                                   CHAR_BIT
                                                             - 1.
     50) Thus, an automatic variable can be initialized to a trap representation without causing undefined
         behavior, but the value of the variable cannot be used until a proper value is stored in it.

[page 44]

    representation, even though the value of a member of the structure or union object may be
    a trap representation.
7   When a value is stored in a member of an object of union type, the bytes of the object
    representation that do not correspond to that member but do correspond to other members
    take unspecified values.
8   Where an operator is applied to a value that has more than one object representation,
    which object representation is used shall not affect the value of the result.52) Where a
    value is stored in an object using a type that has more than one object representation for
    that value, it is unspecified which representation is used, but a trap representation shall
    not be generated.
9   Loads and stores of objects with                            atomic       types     are     done      with
    memory_order_seq_cst semantics.
    Forward references: declarations (6.7), expressions (6.5), lvalues, arrays, and function
    designators (6.3.2.1), order and consistency (7.17.3).
    6.2.6.2 Integer types
1   For unsigned integer types other than unsigned char, the bits of the object
    representation shall be divided into two groups: value bits and padding bits (there need
    not be any of the latter). If there are N value bits, each bit shall represent a different
    power of 2 between 1 and 2 N -1 , so that objects of that type shall be capable of
    representing values from 0 to 2 N - 1 using a pure binary representation; this shall be
    known as the value representation. The values of any padding bits are unspecified.53)
2   For signed integer types, the bits of the object representation shall be divided into three
    groups: value bits, padding bits, and the sign bit. There need not be any padding bits;
    signed char shall not have any padding bits. There shall be exactly one sign bit.
    Each bit that is a value bit shall have the same value as the same bit in the object
    representation of the corresponding unsigned type (if there are M value bits in the signed
    type and N in the unsigned type, then M <= N ). If the sign bit is zero, it shall not affect

    51) Thus, for example, structure assignment need not copy any padding bits.
    52) It is possible for objects x and y with the same effective type T to have the same value when they are
        accessed as objects of type T, but to have different values in other contexts. In particular, if == is
        defined for type T, then x == y does not imply that memcmp(&x, &y, sizeof (T)) == 0.
        Furthermore, x == y does not necessarily imply that x and y have the same value; other operations
        on values of type T may distinguish between them.
    53) Some combinations of padding bits might generate trap representations, for example, if one padding
        bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
        representation other than as part of an exceptional condition such as an overflow, and this cannot occur
        with unsigned types. All other combinations of padding bits are alternative object representations of
        the value specified by the value bits.

[page 45]

    the resulting value. If the sign bit is one, the value shall be modified in one of the
    following ways:
    -- the corresponding value with sign bit 0 is negated (sign and magnitude);
    -- the sign bit has the value -(2 M ) (two's complement);
    -- the sign bit has the value -(2 M - 1) (ones' complement).
    Which of these applies is implementation-defined, as is whether the value with sign bit 1
    and all value bits zero (for the first two), or with sign bit and all value bits 1 (for ones'
    complement), is a trap representation or a normal value. In the case of sign and
    magnitude and ones' complement, if this representation is a normal value it is called a
    negative zero.
3   If the implementation supports negative zeros, they shall be generated only by:
    -- the &, |, ^, ~, <<, and >> operators with operands that produce such a value;
    -- the +, -, *, /, and % operators where one operand is a negative zero and the result is
      zero;
    -- compound assignment operators based on the above cases.
    It is unspecified whether these cases actually generate a negative zero or a normal zero,
    and whether a negative zero becomes a normal zero when stored in an object.
4   If the implementation does not support negative zeros, the behavior of the &, |, ^, ~, <<,
    and >> operators with operands that would produce such a value is undefined.
5   The values of any padding bits are unspecified.54) A valid (non-trap) object representation
    of a signed integer type where the sign bit is zero is a valid object representation of the
    corresponding unsigned type, and shall represent the same value. For any integer type,
    the object representation where all the bits are zero shall be a representation of the value
    zero in that type.
6   The precision of an integer type is the number of bits it uses to represent values,
    excluding any sign and padding bits. The width of an integer type is the same but
    including any sign bit; thus for unsigned integer types the two values are the same, while
    for signed integer types the width is one greater than the precision.




    54) Some combinations of padding bits might generate trap representations, for example, if one padding
        bit is a parity bit. Regardless, no arithmetic operation on valid values can generate a trap
        representation other than as part of an exceptional condition such as an overflow. All other
        combinations of padding bits are alternative object representations of the value specified by the value
        bits.

[page 46]

    6.2.7 Compatible type and composite type
1   Two types have compatible type if their types are the same. Additional rules for
    determining whether two types are compatible are described in 6.7.2 for type specifiers,
    in 6.7.3 for type qualifiers, and in 6.7.6 for declarators.55) Moreover, two structure,
    union, or enumerated types declared in separate translation units are compatible if their
    tags and members satisfy the following requirements: If one is declared with a tag, the
    other shall be declared with the same tag. If both are completed anywhere within their
    respective translation units, then the following additional requirements apply: there shall
    be a one-to-one correspondence between their members such that each pair of
    corresponding members are declared with compatible types; if one member of the pair is
    declared with an alignment specifier, the other is declared with an equivalent alignment
    specifier; and if one member of the pair is declared with a name, the other is declared
    with the same name. For two structures, corresponding members shall be declared in the
    same order. For two structures or unions, corresponding bit-fields shall have the same
    widths. For two enumerations, corresponding members shall have the same values.
2   All declarations that refer to the same object or function shall have compatible type;
    otherwise, the behavior is undefined.
3   A composite type can be constructed from two types that are compatible; it is a type that
    is compatible with both of the two types and satisfies the following conditions:
    -- If both types are array types, the following rules are applied:
          o If one type is an array of known constant size, the composite type is an array of
             that size.
          o Otherwise, if one type is a variable length array whose size is specified by an
             expression that is not evaluated, the behavior is undefined.
          o Otherwise, if one type is a variable length array whose size is specified, the
             composite type is a variable length array of that size.
          o Otherwise, if one type is a variable length array of unspecified size, the composite
             type is a variable length array of unspecified size.
          o Otherwise, both types are arrays of unknown size and the composite type is an
             array of unknown size.
        The element type of the composite type is the composite type of the two element
        types.
    -- If only one type is a function type with a parameter type list (a function prototype),
      the composite type is a function prototype with the parameter type list.


    55) Two types need not be identical to be compatible.

[page 47]

    -- If both types are function types with parameter type lists, the type of each parameter
      in the composite parameter type list is the composite type of the corresponding
      parameters.
    These rules apply recursively to the types from which the two types are derived.
4   For an identifier with internal or external linkage declared in a scope in which a prior
    declaration of that identifier is visible,56) if the prior declaration specifies internal or
    external linkage, the type of the identifier at the later declaration becomes the composite
    type.
    Forward references: array declarators (6.7.6.2).
5   EXAMPLE        Given the following two file scope declarations:
             int f(int (*)(), double (*)[3]);
             int f(int (*)(char *), double (*)[]);
    The resulting composite type for the function is:
             int f(int (*)(char *), double (*)[3]);

    6.2.8 Alignment of objects
1   Complete object types have alignment requirements which place restrictions on the
    addresses at which objects of that type may be allocated. An alignment is an
    implementation-defined integer value representing the number of bytes between
    successive addresses at which a given object can be allocated. An object type imposes an
    alignment requirement on every object of that type: stricter alignment can be requested
    using the _Alignas keyword.
2   A fundamental alignment is represented by an alignment less than or equal to the greatest
    alignment supported by the implementation in all contexts, which is equal to
    alignof(max_align_t).
3   An extended alignment is represented by an alignment greater than
    alignof(max_align_t). It is implementation-defined whether any extended
    alignments are supported and the contexts in which they are supported. A type having an
    extended alignment requirement is an over-aligned type.57)
4   Alignments are represented as values of the type size_t. Valid alignments include only
    those values returned by an alignof expression for fundamental types, plus an
    additional implementation-defined set of values, which may be empty. Every valid
    alignment value shall be a nonnegative integral power of two.


    56) As specified in 6.2.1, the later declaration might hide the prior declaration.
    57) Every over-aligned type is, or contains, a structure or union type with a member to which an extended
        alignment has been applied.

[page 48]

5   Alignments have an order from weaker to stronger or stricter alignments. Stricter
    alignments have larger alignment values. An address that satisfies an alignment
    requirement also satisfies any weaker valid alignment requirement.
6   The alignment requirement of a complete type can be queried using an alignof
    expression. The types char, signed char, and unsigned char shall have the
    weakest alignment requirement.
7   Comparing alignments is meaningful and provides the obvious results:
    -- Two alignments are equal when their numeric values are equal.
    -- Two alignments are different when their numeric values are not equal.
    -- When an alignment is larger than another it represents a stricter alignment.




[page 49]

    6.3 Conversions
1   Several operators convert operand values from one type to another automatically. This
    subclause specifies the result required from such an implicit conversion, as well as those
    that result from a cast operation (an explicit conversion). The list in 6.3.1.8 summarizes
    the conversions performed by most ordinary operators; it is supplemented as required by
    the discussion of each operator in 6.5.
2   Conversion of an operand value to a compatible type causes no change to the value or the
    representation.
    Forward references: cast operators (6.5.4).
    6.3.1 Arithmetic operands
    6.3.1.1 Boolean, characters, and integers
1   Every integer type has an integer conversion rank defined as follows:
    -- No two signed integer types shall have the same rank, even if they have the same
      representation.
    -- The rank of a signed integer type shall be greater than the rank of any signed integer
      type with less precision.
    -- The rank of long long int shall be greater than the rank of long int, which
      shall be greater than the rank of int, which shall be greater than the rank of short
      int, which shall be greater than the rank of signed char.
    -- The rank of any unsigned integer type shall equal the rank of the corresponding
      signed integer type, if any.
    -- The rank of any standard integer type shall be greater than the rank of any extended
      integer type with the same width.
    -- The rank of char shall equal the rank of signed char and unsigned char.
    -- The rank of _Bool shall be less than the rank of all other standard integer types.
    -- The rank of any enumerated type shall equal the rank of the compatible integer type
      (see 6.7.2.2).
    -- The rank of any extended signed integer type relative to another extended signed
      integer type with the same precision is implementation-defined, but still subject to the
      other rules for determining the integer conversion rank.
    -- For all integer types T1, T2, and T3, if T1 has greater rank than T2 and T2 has
      greater rank than T3, then T1 has greater rank than T3.
2   The following may be used in an expression wherever an int or unsigned int may
    be used:

[page 50]

    -- An object or expression with an integer type (other than int or unsigned int)
      whose integer conversion rank is less than or equal to the rank of int and
      unsigned int.
    -- A bit-field of type _Bool, int, signed int, or unsigned int.
    If an int can represent all values of the original type (as restricted by the width, for a
    bit-field), the value is converted to an int; otherwise, it is converted to an unsigned
    int. These are called the integer promotions.58) All other types are unchanged by the
    integer promotions.
3   The integer promotions preserve value including sign. As discussed earlier, whether a
    ''plain'' char is treated as signed is implementation-defined.
    Forward references: enumeration specifiers (6.7.2.2), structure and union specifiers
    (6.7.2.1).
    6.3.1.2 Boolean type
1   When any scalar value is converted to _Bool, the result is 0 if the value compares equal
    to 0; otherwise, the result is 1.59)
    6.3.1.3 Signed and unsigned integers
1   When a value with integer type is converted to another integer type other than _Bool, if
    the value can be represented by the new type, it is unchanged.
2   Otherwise, if the new type is unsigned, the value is converted by repeatedly adding or
    subtracting one more than the maximum value that can be represented in the new type
    until the value is in the range of the new type.60)
3   Otherwise, the new type is signed and the value cannot be represented in it; either the
    result is implementation-defined or an implementation-defined signal is raised.
    6.3.1.4 Real floating and integer
1   When a finite value of real floating type is converted to an integer type other than _Bool,
    the fractional part is discarded (i.e., the value is truncated toward zero). If the value of
    the integral part cannot be represented by the integer type, the behavior is undefined.61)


    58) The integer promotions are applied only: as part of the usual arithmetic conversions, to certain
        argument expressions, to the operands of the unary +, -, and ~ operators, and to both operands of the
        shift operators, as specified by their respective subclauses.
    59) NaNs do not compare equal to 0 and thus convert to 1.
    60) The rules describe arithmetic on the mathematical value, not the value of a given type of expression.
    61) The remaindering operation performed when a value of integer type is converted to unsigned type
        need not be performed when a value of real floating type is converted to unsigned type. Thus, the
        range of portable real floating values is (-1, Utype_MAX+1).

[page 51]

2   When a value of integer type is converted to a real floating type, if the value being
    converted can be represented exactly in the new type, it is unchanged. If the value being
    converted is in the range of values that can be represented but cannot be represented
    exactly, the result is either the nearest higher or nearest lower representable value, chosen
    in an implementation-defined manner. If the value being converted is outside the range of
    values that can be represented, the behavior is undefined. Results of some implicit
    conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that
    required by the new type.
    6.3.1.5 Real floating types
1   When a value of real floating type is converted to a real floating type, if the value being
    converted can be represented exactly in the new type, it is unchanged. If the value being
    converted is in the range of values that can be represented but cannot be represented
    exactly, the result is either the nearest higher or nearest lower representable value, chosen
    in an implementation-defined manner. If the value being converted is outside the range of
    values that can be represented, the behavior is undefined. Results of some implicit
    conversions (6.3.1.8, 6.8.6.4) may be represented in greater precision and range than that
    required by the new type.
    6.3.1.6 Complex types
1   When a value of complex type is converted to another complex type, both the real and
    imaginary parts follow the conversion rules for the corresponding real types.
    6.3.1.7 Real and complex
1   When a value of real type is converted to a complex type, the real part of the complex
    result value is determined by the rules of conversion to the corresponding real type and
    the imaginary part of the complex result value is a positive zero or an unsigned zero.
2   When a value of complex type is converted to a real type, the imaginary part of the
    complex value is discarded and the value of the real part is converted according to the
    conversion rules for the corresponding real type.
    6.3.1.8 Usual arithmetic conversions
1   Many operators that expect operands of arithmetic type cause conversions and yield result
    types in a similar way. The purpose is to determine a common real type for the operands
    and result. For the specified operands, each operand is converted, without change of type
    domain, to a type whose corresponding real type is the common real type. Unless
    explicitly stated otherwise, the common real type is also the corresponding real type of
    the result, whose type domain is the type domain of the operands if they are the same,
    and complex otherwise. This pattern is called the usual arithmetic conversions:
          First, if the corresponding real type of either operand is long double, the other
          operand is converted, without change of type domain, to a type whose

[page 52]

           corresponding real type is long double.
           Otherwise, if the corresponding real type of either operand is double, the other
           operand is converted, without change of type domain, to a type whose
           corresponding real type is double.
           Otherwise, if the corresponding real type of either operand is float, the other
           operand is converted, without change of type domain, to a type whose
           corresponding real type is float.62)
           Otherwise, the integer promotions are performed on both operands. Then the
           following rules are applied to the promoted operands:
                  If both operands have the same type, then no further conversion is needed.
                  Otherwise, if both operands have signed integer types or both have unsigned
                  integer types, the operand with the type of lesser integer conversion rank is
                  converted to the type of the operand with greater rank.
                  Otherwise, if the operand that has unsigned integer type has rank greater or
                  equal to the rank of the type of the other operand, then the operand with
                  signed integer type is converted to the type of the operand with unsigned
                  integer type.
                  Otherwise, if the type of the operand with signed integer type can represent
                  all of the values of the type of the operand with unsigned integer type, then
                  the operand with unsigned integer type is converted to the type of the
                  operand with signed integer type.
                  Otherwise, both operands are converted to the unsigned integer type
                  corresponding to the type of the operand with signed integer type.
2   The values of floating operands and of the results of floating expressions may be
    represented in greater precision and range than that required by the type; the types are not
    changed thereby.63)




    62) For example, addition of a double _Complex and a float entails just the conversion of the
        float operand to double (and yields a double _Complex result).
    63) The cast and assignment operators are still required to remove extra range and precision.

[page 53]

    6.3.2 Other operands
    6.3.2.1 Lvalues, arrays, and function designators
1   An lvalue is an expression (with an object type other than void) that potentially
    designates an object;64) if an lvalue does not designate an object when it is evaluated, the
    behavior is undefined. When an object is said to have a particular type, the type is
    specified by the lvalue used to designate the object. A modifiable lvalue is an lvalue that
    does not have array type, does not have an incomplete type, does not have a const-
    qualified type, and if it is a structure or union, does not have any member (including,
    recursively, any member or element of all contained aggregates or unions) with a const-
    qualified type.
2   Except when it is the operand of the sizeof operator, the unary & operator, the ++
    operator, the -- operator, or the left operand of the . operator or an assignment operator,
    an lvalue that does not have array type is converted to the value stored in the designated
    object (and is no longer an lvalue); this is called lvalue conversion. If the lvalue has
    qualified type, the value has the unqualified version of the type of the lvalue; additionally,
    if the lvalue has atomic type, the value has the non-atomic version of the type of the
    lvalue; otherwise, the value has the type of the lvalue. If the lvalue has an incomplete
    type and does not have array type, the behavior is undefined. If the lvalue designates an
    object of automatic storage duration that could have been declared with the register
    storage class (never had its address taken), and that object is uninitialized (not declared
    with an initializer and no assignment to it has been performed prior to use), the behavior
    is undefined.
3   Except when it is the operand of the sizeof operator or the unary & operator, or is a
    string literal used to initialize an array, an expression that has type ''array of type'' is
    converted to an expression with type ''pointer to type'' that points to the initial element of
    the array object and is not an lvalue. If the array object has register storage class, the
    behavior is undefined.
4   A function designator is an expression that has function type. Except when it is the
    operand of the sizeof operator65) or the unary & operator, a function designator with
    type ''function returning type'' is converted to an expression that has type ''pointer to


    64) The name ''lvalue'' comes originally from the assignment expression E1 = E2, in which the left
        operand E1 is required to be a (modifiable) lvalue. It is perhaps better considered as representing an
        object ''locator value''. What is sometimes called ''rvalue'' is in this International Standard described
        as the ''value of an expression''.
         An obvious example of an lvalue is an identifier of an object. As a further example, if E is a unary
         expression that is a pointer to an object, *E is an lvalue that designates the object to which E points.
    65) Because this conversion does not occur, the operand of the sizeof operator remains a function
        designator and violates the constraint in 6.5.3.4.

[page 54]

    function returning type''.
    Forward references: address and indirection operators (6.5.3.2), assignment operators
    (6.5.16), common definitions <stddef.h> (7.19), initialization (6.7.9), postfix
    increment and decrement operators (6.5.2.4), prefix increment and decrement operators
    (6.5.3.1), the sizeof operator (6.5.3.4), structure and union members (6.5.2.3).
    6.3.2.2 void
1   The (nonexistent) value of a void expression (an expression that has type void) shall not
    be used in any way, and implicit or explicit conversions (except to void) shall not be
    applied to such an expression. If an expression of any other type is evaluated as a void
    expression, its value or designator is discarded. (A void expression is evaluated for its
    side effects.)
    6.3.2.3 Pointers
1   A pointer to void may be converted to or from a pointer to any object type. A pointer to
    any object type may be converted to a pointer to void and back again; the result shall
    compare equal to the original pointer.
2   For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to
    the q-qualified version of the type; the values stored in the original and converted pointers
    shall compare equal.
3   An integer constant expression with the value 0, or such an expression cast to type
    void *, is called a null pointer constant.66) If a null pointer constant is converted to a
    pointer type, the resulting pointer, called a null pointer, is guaranteed to compare unequal
    to a pointer to any object or function.
4   Conversion of a null pointer to another pointer type yields a null pointer of that type.
    Any two null pointers shall compare equal.
5   An integer may be converted to any pointer type. Except as previously specified, the
    result is implementation-defined, might not be correctly aligned, might not point to an
    entity of the referenced type, and might be a trap representation.67)
6   Any pointer type may be converted to an integer type. Except as previously specified, the
    result is implementation-defined. If the result cannot be represented in the integer type,
    the behavior is undefined. The result need not be in the range of values of any integer
    type.




    66) The macro NULL is defined in <stddef.h> (and other headers) as a null pointer constant; see 7.19.
    67) The mapping functions for converting a pointer to an integer or an integer to a pointer are intended to
        be consistent with the addressing structure of the execution environment.

[page 55]

7   A pointer to an object type may be converted to a pointer to a different object type. If the
    resulting pointer is not correctly aligned68) for the referenced type, the behavior is
    undefined. Otherwise, when converted back again, the result shall compare equal to the
    original pointer. When a pointer to an object is converted to a pointer to a character type,
    the result points to the lowest addressed byte of the object. Successive increments of the
    result, up to the size of the object, yield pointers to the remaining bytes of the object.
8   A pointer to a function of one type may be converted to a pointer to a function of another
    type and back again; the result shall compare equal to the original pointer. If a converted
    pointer is used to call a function whose type is not compatible with the referenced type,
    the behavior is undefined.
    Forward references: cast operators (6.5.4), equality operators (6.5.9), integer types
    capable of holding object pointers (7.20.1.4), simple assignment (6.5.16.1).




    68) In general, the concept ''correctly aligned'' is transitive: if a pointer to type A is correctly aligned for a
        pointer to type B, which in turn is correctly aligned for a pointer to type C, then a pointer to type A is
        correctly aligned for a pointer to type C.

[page 56]

    6.4 Lexical elements
    Syntax
1            token:
                      keyword
                      identifier
                      constant
                      string-literal
                      punctuator
             preprocessing-token:
                    header-name
                    identifier
                    pp-number
                    character-constant
                    string-literal
                    punctuator
                    each non-white-space character that cannot be one of the above
    Constraints
2   Each preprocessing token that is converted to a token shall have the lexical form of a
    keyword, an identifier, a constant, a string literal, or a punctuator.
    Semantics
3   A token is the minimal lexical element of the language in translation phases 7 and 8. The
    categories of tokens are: keywords, identifiers, constants, string literals, and punctuators.
    A preprocessing token is the minimal lexical element of the language in translation
    phases 3 through 6. The categories of preprocessing tokens are: header names,
    identifiers, preprocessing numbers, character constants, string literals, punctuators, and
    single non-white-space characters that do not lexically match the other preprocessing
    token categories.69) If a ' or a " character matches the last category, the behavior is
    undefined. Preprocessing tokens can be separated by white space; this consists of
    comments (described later), or white-space characters (space, horizontal tab, new-line,
    vertical tab, and form-feed), or both. As described in 6.10, in certain circumstances
    during translation phase 4, white space (or the absence thereof) serves as more than
    preprocessing token separation. White space may appear within a preprocessing token
    only as part of a header name or between the quotation characters in a character constant
    or string literal.



    69) An additional category, placemarkers, is used internally in translation phase 4 (see 6.10.3.3); it cannot
        occur in source files.

[page 57]

4   If the input stream has been parsed into preprocessing tokens up to a given character, the
    next preprocessing token is the longest sequence of characters that could constitute a
    preprocessing token. There is one exception to this rule: header name preprocessing
    tokens are recognized only within #include preprocessing directives and in
    implementation-defined locations within #pragma directives. In such contexts, a
    sequence of characters that could be either a header name or a string literal is recognized
    as the former.
5   EXAMPLE 1 The program fragment 1Ex is parsed as a preprocessing number token (one that is not a
    valid floating or integer constant token), even though a parse as the pair of preprocessing tokens 1 and Ex
    might produce a valid expression (for example, if Ex were a macro defined as +1). Similarly, the program
    fragment 1E1 is parsed as a preprocessing number (one that is a valid floating constant token), whether or
    not E is a macro name.

6   EXAMPLE 2 The program fragment x+++++y is parsed as x ++ ++ + y, which violates a constraint on
    increment operators, even though the parse x ++ + ++ y might yield a correct expression.

    Forward references: character constants (6.4.4.4), comments (6.4.9), expressions (6.5),
    floating constants (6.4.4.2), header names (6.4.7), macro replacement (6.10.3), postfix
    increment and decrement operators (6.5.2.4), prefix increment and decrement operators
    (6.5.3.1), preprocessing directives (6.10), preprocessing numbers (6.4.8), string literals
    (6.4.5).
    6.4.1 Keywords
    Syntax
1            keyword: one of
                   alignof                         goto                         union
                   auto                            if                           unsigned
                   break                           inline                       void
                   case                            int                          volatile
                   char                            long                         while
                   const                           register                     _Alignas
                   continue                        restrict                     _Atomic
                   default                         return                       _Bool
                   do                              short                        _Complex
                   double                          signed                       _Generic
                   else                            sizeof                       _Imaginary
                   enum                            static                       _Noreturn
                   extern                          struct                       _Static_assert
                   float                           switch                       _Thread_local
                   for                             typedef
    Semantics
2   The above tokens (case sensitive) are reserved (in translation phases 7 and 8) for use as
    keywords, and shall not be used otherwise. The keyword _Imaginary is reserved for
[page 58]

    specifying imaginary types.70)
    6.4.2 Identifiers
    6.4.2.1 General
    Syntax
1            identifier:
                    identifier-nondigit
                    identifier identifier-nondigit
                    identifier digit
             identifier-nondigit:
                    nondigit
                    universal-character-name
                    other implementation-defined characters
             nondigit: one of
                    _ a b            c    d    e    f     g    h    i    j     k    l    m
                        n o          p    q    r    s     t    u    v    w     x    y    z
                        A B          C    D    E    F     G    H    I    J     K    L    M
                        N O          P    Q    R    S     T    U    V    W     X    Y    Z
             digit: one of
                    0 1        2     3    4    5    6     7    8    9
    Semantics
2   An identifier is a sequence of nondigit characters (including the underscore _, the
    lowercase and uppercase Latin letters, and other characters) and digits, which designates
    one or more entities as described in 6.2.1. Lowercase and uppercase letters are distinct.
    There is no specific limit on the maximum length of an identifier.
3   Each universal character name in an identifier shall designate a character whose encoding
    in ISO/IEC 10646 falls into one of the ranges specified in D.1.71) The initial character
    shall not be a universal character name designating a character whose encoding falls into
    one of the ranges specified in D.2. An implementation may allow multibyte characters
    that are not part of the basic source character set to appear in identifiers; which characters
    and their correspondence to universal character names is implementation-defined.



    70) One possible specification for imaginary types appears in annex G.
    71) On systems in which linkers cannot accept extended characters, an encoding of the universal character
        name may be used in forming valid external identifiers. For example, some otherwise unused
        character or sequence of characters may be used to encode the \u in a universal character name.
        Extended characters may produce a long external identifier.

[page 59]

4   When preprocessing tokens are converted to tokens during translation phase 7, if a
    preprocessing token could be converted to either a keyword or an identifier, it is converted
    to a keyword.
    Implementation limits
5   As discussed in 5.2.4.1, an implementation may limit the number of significant initial
    characters in an identifier; the limit for an external name (an identifier that has external
    linkage) may be more restrictive than that for an internal name (a macro name or an
    identifier that does not have external linkage). The number of significant characters in an
    identifier is implementation-defined.
6   Any identifiers that differ in a significant character are different identifiers. If two
    identifiers differ only in nonsignificant characters, the behavior is undefined.
    Forward references: universal character names (6.4.3), macro replacement (6.10.3).
    6.4.2.2 Predefined identifiers
    Semantics
1   The identifier __func__ shall be implicitly declared by the translator as if,
    immediately following the opening brace of each function definition, the declaration
             static const char __func__[] = "function-name";
    appeared, where function-name is the name of the lexically-enclosing function.72)
2   This name is encoded as if the implicit declaration had been written in the source
    character set and then translated into the execution character set as indicated in translation
    phase 5.
3   EXAMPLE        Consider the code fragment:
             #include <stdio.h>
             void myfunc(void)
             {
                   printf("%s\n", __func__);
                   /* ... */
             }
    Each time the function is called, it will print to the standard output stream:
             myfunc

    Forward references: function definitions (6.9.1).




    72) Since the name __func__ is reserved for any use by the implementation (7.1.3), if any other
        identifier is explicitly declared using the name __func__, the behavior is undefined.

[page 60]

    6.4.3 Universal character names
    Syntax
1            universal-character-name:
                    \u hex-quad
                    \U hex-quad hex-quad
             hex-quad:
                    hexadecimal-digit hexadecimal-digit
                                 hexadecimal-digit hexadecimal-digit
    Constraints
2   A universal character name shall not specify a character whose short identifier is less than
    00A0 other than 0024 ($), 0040 (@), or 0060 ('), nor one in the range D800 through
    DFFF inclusive.73)
    Description
3   Universal character names may be used in identifiers, character constants, and string
    literals to designate characters that are not in the basic character set.
    Semantics
4   The universal character name \Unnnnnnnn designates the character whose eight-digit
    short identifier (as specified by ISO/IEC 10646) is nnnnnnnn.74) Similarly, the universal
    character name \unnnn designates the character whose four-digit short identifier is nnnn
    (and whose eight-digit short identifier is 0000nnnn).




    73) The disallowed characters are the characters in the basic character set and the code positions reserved
        by ISO/IEC 10646 for control characters, the character DELETE, and the S-zone (reserved for use by
        UTF-16).

    74) Short identifiers for characters were first specified in ISO/IEC 10646-1/AMD9:1997.

[page 61]

    6.4.4 Constants
    Syntax
1            constant:
                    integer-constant
                    floating-constant
                    enumeration-constant
                    character-constant
    Constraints
2   Each constant shall have a type and the value of a constant shall be in the range of
    representable values for its type.
    Semantics
3   Each constant has a type, determined by its form and value, as detailed later.
    6.4.4.1 Integer constants
    Syntax
1            integer-constant:
                     decimal-constant integer-suffixopt
                     octal-constant integer-suffixopt
                     hexadecimal-constant integer-suffixopt
             decimal-constant:
                   nonzero-digit
                   decimal-constant digit
             octal-constant:
                    0
                    octal-constant octal-digit
             hexadecimal-constant:
                   hexadecimal-prefix hexadecimal-digit
                   hexadecimal-constant hexadecimal-digit
             hexadecimal-prefix: one of
                   0x 0X
             nonzero-digit: one of
                    1 2 3 4          5     6     7   8    9
             octal-digit: one of
                     0 1 2 3         4     5     6   7




[page 62]

            hexadecimal-digit:   one of
                  0 1 2           3 4     5    6   7     8   9
                  a b c           d e     f
                  A B C           D E     F
            integer-suffix:
                    unsigned-suffix long-suffixopt
                    unsigned-suffix long-long-suffix
                    long-suffix unsigned-suffixopt
                    long-long-suffix unsigned-suffixopt
            unsigned-suffix: one of
                   u U
            long-suffix: one of
                   l L
            long-long-suffix: one of
                   ll LL
    Description
2   An integer constant begins with a digit, but has no period or exponent part. It may have a
    prefix that specifies its base and a suffix that specifies its type.
3   A decimal constant begins with a nonzero digit and consists of a sequence of decimal
    digits. An octal constant consists of the prefix 0 optionally followed by a sequence of the
    digits 0 through 7 only. A hexadecimal constant consists of the prefix 0x or 0X followed
    by a sequence of the decimal digits and the letters a (or A) through f (or F) with values
    10 through 15 respectively.
    Semantics
4   The value of a decimal constant is computed base 10; that of an octal constant, base 8;
    that of a hexadecimal constant, base 16. The lexically first digit is the most significant.
5   The type of an integer constant is the first of the corresponding list in which its value can
    be represented.




[page 63]

                                                                     Octal or Hexadecimal
    Suffix                       Decimal Constant                           Constant

    none                int                                    int
                        long int                               unsigned int
                        long long int                          long int
                                                               unsigned long int
                                                               long long int
                                                               unsigned long long int

    u or U              unsigned int                           unsigned int
                        unsigned long int                      unsigned long int
                        unsigned long long int                 unsigned long long int

    l or L              long int                               long int
                        long long int                          unsigned long int
                                                               long long int
                                                               unsigned long long int

    Both u or U         unsigned long int                      unsigned long int
    and l or L          unsigned long long int                 unsigned long long int

    ll or LL            long long int                          long long int
                                                               unsigned long long int

    Both u or U         unsigned long long int                 unsigned long long int
    and ll or LL
6   If an integer constant cannot be represented by any type in its list, it may have an
    extended integer type, if the extended integer type can represent its value. If all of the
    types in the list for the constant are signed, the extended integer type shall be signed. If
    all of the types in the list for the constant are unsigned, the extended integer type shall be
    unsigned. If the list contains both signed and unsigned types, the extended integer type
    may be signed or unsigned. If an integer constant cannot be represented by any type in
    its list and has no extended integer type, then the integer constant has no type.




[page 64]

    6.4.4.2 Floating constants
    Syntax
1            floating-constant:
                    decimal-floating-constant
                    hexadecimal-floating-constant
             decimal-floating-constant:
                   fractional-constant exponent-partopt floating-suffixopt
                   digit-sequence exponent-part floating-suffixopt
             hexadecimal-floating-constant:
                   hexadecimal-prefix hexadecimal-fractional-constant
                                  binary-exponent-part floating-suffixopt
                   hexadecimal-prefix hexadecimal-digit-sequence
                                  binary-exponent-part floating-suffixopt
             fractional-constant:
                     digit-sequenceopt . digit-sequence
                     digit-sequence .
             exponent-part:
                   e signopt digit-sequence
                   E signopt digit-sequence
             sign: one of
                    + -
             digit-sequence:
                     digit
                     digit-sequence digit
             hexadecimal-fractional-constant:
                   hexadecimal-digit-sequenceopt .
                                  hexadecimal-digit-sequence
                   hexadecimal-digit-sequence .
             binary-exponent-part:
                    p signopt digit-sequence
                    P signopt digit-sequence
             hexadecimal-digit-sequence:
                   hexadecimal-digit
                   hexadecimal-digit-sequence hexadecimal-digit
             floating-suffix: one of
                    f l F L

[page 65]

    Description
2   A floating constant has a significand part that may be followed by an exponent part and a
    suffix that specifies its type. The components of the significand part may include a digit
    sequence representing the whole-number part, followed by a period (.), followed by a
    digit sequence representing the fraction part. The components of the exponent part are an
    e, E, p, or P followed by an exponent consisting of an optionally signed digit sequence.
    Either the whole-number part or the fraction part has to be present; for decimal floating
    constants, either the period or the exponent part has to be present.
    Semantics
3   The significand part is interpreted as a (decimal or hexadecimal) rational number; the
    digit sequence in the exponent part is interpreted as a decimal integer. For decimal
    floating constants, the exponent indicates the power of 10 by which the significand part is
    to be scaled. For hexadecimal floating constants, the exponent indicates the power of 2
    by which the significand part is to be scaled. For decimal floating constants, and also for
    hexadecimal floating constants when FLT_RADIX is not a power of 2, the result is either
    the nearest representable value, or the larger or smaller representable value immediately
    adjacent to the nearest representable value, chosen in an implementation-defined manner.
    For hexadecimal floating constants when FLT_RADIX is a power of 2, the result is
    correctly rounded.
4   An unsuffixed floating constant has type double. If suffixed by the letter f or F, it has
    type float. If suffixed by the letter l or L, it has type long double.
5   Floating constants are converted to internal format as if at translation-time. The
    conversion of a floating constant shall not raise an exceptional condition or a floating-
    point exception at execution time. All floating constants of the same source form75) shall
    convert to the same internal format with the same value.
    Recommended practice
6   The implementation should produce a diagnostic message if a hexadecimal constant
    cannot be represented exactly in its evaluation format; the implementation should then
    proceed with the translation of the program.
7   The translation-time conversion of floating constants should match the execution-time
    conversion of character strings by library functions, such as strtod, given matching
    inputs suitable for both conversions, the same result format, and default execution-time
    rounding.76)

    75) 1.23, 1.230, 123e-2, 123e-02, and 1.23L are all different source forms and thus need not
        convert to the same internal format and value.
    76) The specification for the library functions recommends more accurate conversion than required for
        floating constants (see 7.22.1.3).

[page 66]

    6.4.4.3 Enumeration constants
    Syntax
1            enumeration-constant:
                   identifier
    Semantics
2   An identifier declared as an enumeration constant has type int.
    Forward references: enumeration specifiers (6.7.2.2).
    6.4.4.4 Character constants
    Syntax
1            character-constant:
                    ' c-char-sequence '
                    L' c-char-sequence '
                    u' c-char-sequence '
                    U' c-char-sequence '
             c-char-sequence:
                    c-char
                    c-char-sequence c-char
             c-char:
                       any member of the source character set except
                                    the single-quote ', backslash \, or new-line character
                       escape-sequence
             escape-sequence:
                    simple-escape-sequence
                    octal-escape-sequence
                    hexadecimal-escape-sequence
                    universal-character-name
             simple-escape-sequence: one of
                    \' \" \? \\
                    \a \b \f \n \r                  \t    \v
             octal-escape-sequence:
                     \ octal-digit
                     \ octal-digit octal-digit
                     \ octal-digit octal-digit octal-digit




[page 67]

           hexadecimal-escape-sequence:
                 \x hexadecimal-digit
                 hexadecimal-escape-sequence hexadecimal-digit
    Description
2   An integer character constant is a sequence of one or more multibyte characters enclosed
    in single-quotes, as in 'x'. A wide character constant is the same, except prefixed by the
    letter L, u, or U. With a few exceptions detailed later, the elements of the sequence are
    any members of the source character set; they are mapped in an implementation-defined
    manner to members of the execution character set.
3   The single-quote ', the double-quote ", the question-mark ?, the backslash \, and
    arbitrary integer values are representable according to the following table of escape
    sequences:
          single quote '            \'
          double quote "            \"
          question mark ?           \?
          backslash \               \\
          octal character           \octal digits
          hexadecimal character     \x hexadecimal digits
4   The double-quote " and question-mark ? are representable either by themselves or by the
    escape sequences \" and \?, respectively, but the single-quote ' and the backslash \
    shall be represented, respectively, by the escape sequences \' and \\.
5   The octal digits that follow the backslash in an octal escape sequence are taken to be part
    of the construction of a single character for an integer character constant or of a single
    wide character for a wide character constant. The numerical value of the octal integer so
    formed specifies the value of the desired character or wide character.
6   The hexadecimal digits that follow the backslash and the letter x in a hexadecimal escape
    sequence are taken to be part of the construction of a single character for an integer
    character constant or of a single wide character for a wide character constant. The
    numerical value of the hexadecimal integer so formed specifies the value of the desired
    character or wide character.
7   Each octal or hexadecimal escape sequence is the longest sequence of characters that can
    constitute the escape sequence.
8   In addition, characters not in the basic character set are representable by universal
    character names and certain nongraphic characters are representable by escape sequences
    consisting of the backslash \ followed by a lowercase letter: \a, \b, \f, \n, \r, \t,
    and \v.77)



[page 68]

     Constraints
9    The value of an octal or hexadecimal escape sequence shall be in the range of
     representable values for the corresponding type:
            Prefix      Corresponding Type
            none       unsigned char
            L          the unsigned type corresponding to wchar_t
            u          char16_t
            U          char32_t
     Semantics
10   An integer character constant has type int. The value of an integer character constant
     containing a single character that maps to a single-byte execution character is the
     numerical value of the representation of the mapped character interpreted as an integer.
     The value of an integer character constant containing more than one character (e.g.,
     'ab'), or containing a character or escape sequence that does not map to a single-byte
     execution character, is implementation-defined. If an integer character constant contains
     a single character or escape sequence, its value is the one that results when an object with
     type char whose value is that of the single character or escape sequence is converted to
     type int.
11   A wide character constant prefixed by the letter L has type wchar_t, an integer type
     defined in the <stddef.h> header; a wide character constant prefixed by the letter u or
     U has type char16_t or char32_t, respectively, unsigned integer types defined in the
     <uchar.h> header. The value of a wide character constant containing a single
     multibyte character that maps to a single member of the extended execution character set
     is the wide character corresponding to that multibyte character, as defined by the
     mbtowc, mbrtoc16, or mbrtoc32 function as appropriate for its type, with an
     implementation-defined current locale. The value of a wide character constant containing
     more than one multibyte character or a single multibyte character that maps to multiple
     members of the extended execution character set, or containing a multibyte character or
     escape sequence not represented in the extended execution character set, is
     implementation-defined.
12   EXAMPLE 1      The construction '\0' is commonly used to represent the null character.

13   EXAMPLE 2 Consider implementations that use two's complement representation for integers and eight
     bits for objects that have type char. In an implementation in which type char has the same range of
     values as signed char, the integer character constant '\xFF' has the value -1; if type char has the
     same range of values as unsigned char, the character constant '\xFF' has the value +255.




     77) The semantics of these characters were discussed in 5.2.2. If any other character follows a backslash,
         the result is not a token and a diagnostic is required. See ''future language directions'' (6.11.4).

[page 69]

14   EXAMPLE 3 Even if eight bits are used for objects that have type char, the construction '\x123'
     specifies an integer character constant containing only one character, since a hexadecimal escape sequence
     is terminated only by a non-hexadecimal character. To specify an integer character constant containing the
     two characters whose values are '\x12' and '3', the construction '\0223' may be used, since an octal
     escape sequence is terminated after three octal digits. (The value of this two-character integer character
     constant is implementation-defined.)

15   EXAMPLE 4 Even if 12 or more bits are used for objects that have type wchar_t, the construction
     L'\1234' specifies the implementation-defined value that results from the combination of the values
     0123 and '4'.

     Forward references: common definitions <stddef.h> (7.19), the mbtowc function
     (7.22.7.2), Unicode utilities <uchar.h> (7.27).
     6.4.5 String literals
     Syntax
1             string-literal:
                      encoding-prefixopt " s-char-sequenceopt "
              encoding-prefix:
                     u8
                     u
                     U
                     L
              s-char-sequence:
                     s-char
                     s-char-sequence s-char
              s-char:
                        any member of the source character set except
                                     the double-quote ", backslash \, or new-line character
                        escape-sequence
     Constraints
2    A sequence of adjacent string literal tokens shall not include both a wide string literal and
     a UTF-8 string literal.
     Description
3    A character string literal is a sequence of zero or more multibyte characters enclosed in
     double-quotes, as in "xyz". A UTF-8 string literal is the same, except prefixed by u8.
     A wide string literal is the same, except prefixed by the letter L, u, or U.
4    The same considerations apply to each element of the sequence in a string literal as if it
     were in an integer character constant (for a character or UTF-8 string literal) or a wide
     character constant (for a wide string literal), except that the single-quote ' is
     representable either by itself or by the escape sequence \', but the double-quote " shall
[page 70]

    be represented by the escape sequence \".
    Semantics
5   In translation phase 6, the multibyte character sequences specified by any sequence of
    adjacent character and identically-prefixed string literal tokens are concatenated into a
    single multibyte character sequence. If any of the tokens has an encoding prefix, the
    resulting multibyte character sequence is treated as having the same prefix; otherwise, it
    is treated as a character string literal. Whether differently-prefixed wide string literal
    tokens can be concatenated and, if so, the treatment of the resulting multibyte character
    sequence are implementation-defined.
6   In translation phase 7, a byte or code of value zero is appended to each multibyte
    character sequence that results from a string literal or literals.78) The multibyte character
    sequence is then used to initialize an array of static storage duration and length just
    sufficient to contain the sequence. For character string literals, the array elements have
    type char, and are initialized with the individual bytes of the multibyte character
    sequence. For UTF-8 string literals, the array elements have type char, and are
    initialized with the characters of the multibyte character sequence, as encoded in UTF-8.
    For wide string literals prefixed by the letter L, the array elements have type wchar_t
    and are initialized with the sequence of wide characters corresponding to the multibyte
    character sequence, as defined by the mbstowcs function with an implementation-
    defined current locale. For wide string literals prefixed by the letter u or U, the array
    elements have type char16_t or char32_t, respectively, and are initialized with the
    sequence of wide characters corresponding to the multibyte character sequence, as
    defined by successive calls to the mbrtoc16, or mbrtoc32 function as appropriate for
    its type, with an implementation-defined current locale. The value of a string literal
    containing a multibyte character or escape sequence not represented in the execution
    character set is implementation-defined.
7   It is unspecified whether these arrays are distinct provided their elements have the
    appropriate values. If the program attempts to modify such an array, the behavior is
    undefined.
8   EXAMPLE 1      This pair of adjacent character string literals
             "\x12" "3"
    produces a single character string literal containing the two characters whose values are '\x12' and '3',
    because escape sequences are converted into single members of the execution character set just prior to
    adjacent string literal concatenation.

9   EXAMPLE 2      Each of the sequences of adjacent string literal tokens



    78) A string literal need not be a string (see 7.1.1), because a null character may be embedded in it by a
        \0 escape sequence.

[page 71]

             "a" "b" L"c"
             "a" L"b" "c"
             L"a" "b" L"c"
             L"a" L"b" L"c"
    is equivalent to the string literal
             L"abc"
    Likewise, each of the sequences
             "a" "b" u"c"
             "a" u"b" "c"
             u"a" "b" u"c"
             u"a" u"b" u"c"
    is equivalent to
             u"abc"

    Forward references: common definitions <stddef.h> (7.19), the mbstowcs
    function (7.22.8.1), Unicode utilities <uchar.h> (7.27).
    6.4.6 Punctuators
    Syntax
1            punctuator: one of
                    [ ] ( ) { } . ->
                    ++ -- & * + - ~ !
                    / % << >> < > <= >=                         ==    !=    ^    |   &&   ||
                    ? : ; ...
                    = *= /= %= += -= <<=                        >>=    &=       ^=   |=
                    , # ##
                    <: :> <% %> %: %:%:
    Semantics
2   A punctuator is a symbol that has independent syntactic and semantic significance.
    Depending on context, it may specify an operation to be performed (which in turn may
    yield a value or a function designator, produce a side effect, or some combination thereof)
    in which case it is known as an operator (other forms of operator also exist in some
    contexts). An operand is an entity on which an operator acts.




[page 72]

3   In all aspects of the language, the six tokens79)
             <:    :>      <%    %>     %:     %:%:
    behave, respectively, the same as the six tokens
             [     ]       {     }      #      ##
    except for their spelling.80)
    Forward references: expressions (6.5), declarations (6.7), preprocessing directives
    (6.10), statements (6.8).
    6.4.7 Header names
    Syntax
1            header-name:
                    < h-char-sequence >
                    " q-char-sequence "
             h-char-sequence:
                    h-char
                    h-char-sequence h-char
             h-char:
                       any member of the source character set except
                                    the new-line character and >
             q-char-sequence:
                    q-char
                    q-char-sequence q-char
             q-char:
                       any member of the source character set except
                                    the new-line character and "
    Semantics
2   The sequences in both forms of header names are mapped in an implementation-defined
    manner to headers or external source file names as specified in 6.10.2.
3   If the characters ', \, ", //, or /* occur in the sequence between the < and > delimiters,
    the behavior is undefined. Similarly, if the characters ', \, //, or /* occur in the




    79) These tokens are sometimes called ''digraphs''.
    80) Thus [ and <: behave differently when ''stringized'' (see 6.10.3.2), but can otherwise be freely
        interchanged.

[page 73]

    sequence between the " delimiters, the behavior is undefined.81) Header name
    preprocessing tokens are recognized only within #include preprocessing directives and
    in implementation-defined locations within #pragma directives.82)
4   EXAMPLE       The following sequence of characters:
             0x3<1/a.h>1e2
             #include <1/a.h>
             #define const.member@$
    forms the following sequence of preprocessing tokens (with each individual preprocessing token delimited
    by a { on the left and a } on the right).
             {0x3}{<}{1}{/}{a}{.}{h}{>}{1e2}
             {#}{include} {<1/a.h>}
             {#}{define} {const}{.}{member}{@}{$}

    Forward references: source file inclusion (6.10.2).
    6.4.8 Preprocessing numbers
    Syntax
1            pp-number:
                   digit
                   . digit
                   pp-number       digit
                   pp-number       identifier-nondigit
                   pp-number       e sign
                   pp-number       E sign
                   pp-number       p sign
                   pp-number       P sign
                   pp-number       .
    Description
2   A preprocessing number begins with a digit optionally preceded by a period (.) and may
    be followed by valid identifier characters and the character sequences e+, e-, E+, E-,
    p+, p-, P+, or P-.
3   Preprocessing number tokens lexically include all floating and integer constant tokens.
    Semantics
4   A preprocessing number does not have type or a value; it acquires both after a successful
    conversion (as part of translation phase 7) to a floating constant token or an integer
    constant token.


    81) Thus, sequences of characters that resemble escape sequences cause undefined behavior.
    82) For an example of a header name preprocessing token used in a #pragma directive, see 6.10.9.

[page 74]

    6.4.9 Comments
1   Except within a character constant, a string literal, or a comment, the characters /*
    introduce a comment. The contents of such a comment are examined only to identify
    multibyte characters and to find the characters */ that terminate it.83)
2   Except within a character constant, a string literal, or a comment, the characters //
    introduce a comment that includes all multibyte characters up to, but not including, the
    next new-line character. The contents of such a comment are examined only to identify
    multibyte characters and to find the terminating new-line character.
3   EXAMPLE
             "a//b"                             //   four-character string literal
             #include "//e"                     //   undefined behavior
             // */                              //   comment, not syntax error
             f = g/**//h;                       //   equivalent to f = g / h;
             //\
             i();                               // part of a two-line comment
             /\
             / j();                             // part of a two-line comment
             #define glue(x,y) x##y
             glue(/,/) k();                     // syntax error, not comment
             /*//*/ l();                        // equivalent to l();
             m = n//**/o
                + p;                            // equivalent to m = n + p;




    83) Thus, /* ... */ comments do not nest.

[page 75]

    6.5 Expressions
1   An expression is a sequence of operators and operands that specifies computation of a
    value, or that designates an object or a function, or that generates side effects, or that
    performs a combination thereof. The value computations of the operands of an operator
    are sequenced before the value computation of the result of the operator.
2   If a side effect on a scalar object is unsequenced relative to either a different side effect
    on the same scalar object or a value computation using the value of the same scalar
    object, the behavior is undefined. If there are multiple allowable orderings of the
    subexpressions of an expression, the behavior is undefined if such an unsequenced side
    effect occurs in any of the orderings.84)
3   The grouping of operators and operands is indicated by the syntax.85) Except as specified
    later, side effects and value computations of subexpressions are unsequenced.86)         *
4   Some operators (the unary operator ~, and the binary operators <<, >>, &, ^, and |,
    collectively described as bitwise operators) are required to have operands that have
    integer type. These operators yield values that depend on the internal representations of
    integers, and have implementation-defined and undefined aspects for signed types.
5   If an exceptional condition occurs during the evaluation of an expression (that is, if the
    result is not mathematically defined or not in the range of representable values for its
    type), the behavior is undefined.



    84) This paragraph renders undefined statement expressions such as
                  i = ++i + 1;
                  a[i++] = i;
         while allowing
                  i = i + 1;
                  a[i] = i;

    85) The syntax specifies the precedence of operators in the evaluation of an expression, which is the same
        as the order of the major subclauses of this subclause, highest precedence first. Thus, for example, the
        expressions allowed as the operands of the binary + operator (6.5.6) are those expressions defined in
        6.5.1 through 6.5.6. The exceptions are cast expressions (6.5.4) as operands of unary operators
        (6.5.3), and an operand contained between any of the following pairs of operators: grouping
        parentheses () (6.5.1), subscripting brackets [] (6.5.2.1), function-call parentheses () (6.5.2.2), and
        the conditional operator ? : (6.5.15).
         Within each major subclause, the operators have the same precedence. Left- or right-associativity is
         indicated in each subclause by the syntax for the expressions discussed therein.
    86) In an expression that is evaluated more than once during the execution of a program, unsequenced and
        indeterminately sequenced evaluations of its subexpressions need not be performed consistently in
        different evaluations.

[page 76]

6   The effective type of an object for an access to its stored value is the declared type of the
    object, if any.87) If a value is stored into an object having no declared type through an
    lvalue having a type that is not a character type, then the type of the lvalue becomes the
    effective type of the object for that access and for subsequent accesses that do not modify
    the stored value. If a value is copied into an object having no declared type using
    memcpy or memmove, or is copied as an array of character type, then the effective type
    of the modified object for that access and for subsequent accesses that do not modify the
    value is the effective type of the object from which the value is copied, if it has one. For
    all other accesses to an object having no declared type, the effective type of the object is
    simply the type of the lvalue used for the access.
7   An object shall have its stored value accessed only by an lvalue expression that has one of
    the following types:88)
    -- a type compatible with the effective type of the object,
    -- a qualified version of a type compatible with the effective type of the object,
    -- a type that is the signed or unsigned type corresponding to the effective type of the
      object,
    -- a type that is the signed or unsigned type corresponding to a qualified version of the
      effective type of the object,
    -- an aggregate or union type that includes one of the aforementioned types among its
      members (including, recursively, a member of a subaggregate or contained union), or
    -- a character type.
8   A floating expression may be contracted, that is, evaluated as though it were a single
    operation, thereby omitting rounding errors implied by the source code and the
    expression evaluation method.89) The FP_CONTRACT pragma in <math.h> provides a
    way to disallow contracted expressions. Otherwise, whether and how expressions are
    contracted is implementation-defined.90)
    Forward references: the FP_CONTRACT pragma (7.12.2), copying functions (7.23.2).


    87) Allocated objects have no declared type.
    88) The intent of this list is to specify those circumstances in which an object may or may not be aliased.
    89) The intermediate operations in the contracted expression are evaluated as if to infinite precision and
        range, while the final operation is rounded to the format determined by the expression evaluation
        method. A contracted expression might also omit the raising of floating-point exceptions.
    90) This license is specifically intended to allow implementations to exploit fast machine instructions that
        combine multiple C operators. As contractions potentially undermine predictability, and can even
        decrease accuracy for containing expressions, their use needs to be well-defined and clearly
        documented.

[page 77]

    6.5.1 Primary expressions
    Syntax
1            primary-expression:
                    identifier
                    constant
                    string-literal
                    ( expression )
                    generic-selection
    Semantics
2   An identifier is a primary expression, provided it has been declared as designating an
    object (in which case it is an lvalue) or a function (in which case it is a function
    designator).91)
3   A constant is a primary expression. Its type depends on its form and value, as detailed in
    6.4.4.
4   A string literal is a primary expression. It is an lvalue with type as detailed in 6.4.5.
5   A parenthesized expression is a primary expression. Its type and value are identical to
    those of the unparenthesized expression. It is an lvalue, a function designator, or a void
    expression if the unparenthesized expression is, respectively, an lvalue, a function
    designator, or a void expression.
    Forward references: declarations (6.7).
    6.5.1.1 Generic selection
    Syntax
1            generic-selection:
                    _Generic ( assignment-expression , generic-assoc-list )
             generic-assoc-list:
                    generic-association
                    generic-assoc-list , generic-association
             generic-association:
                    type-name : assignment-expression
                    default : assignment-expression
    Constraints
2   A generic selection shall have no more than one default generic association. The type
    name in a generic association shall specify a complete object type other than a variably

    91) Thus, an undeclared identifier is a violation of the syntax.

[page 78]

    modified type. No two generic associations in the same generic selection shall specify
    compatible types. The controlling expression of a generic selection shall have type
    compatible with at most one of the types named in its generic association list. If a
    generic selection has no default generic association, its controlling expression shall
    have type compatible with exactly one of the types named in its generic association list.
    Semantics
3   The controlling expression of a generic selection is not evaluated. If a generic selection
    has a generic association with a type name that is compatible with the type of the
    controlling expression, then the result expression of the generic selection is the
    expression in that generic association. Otherwise, the result expression of the generic
    selection is the expression in the default generic association. None of the expressions
    from any other generic association of the generic selection is evaluated.
4   The type and value of a generic selection are identical to those of its result expression. It
    is an lvalue, a function designator, or a void expression if its result expression is,
    respectively, an lvalue, a function designator, or a void expression.
5   EXAMPLE      The cbrt type-generic macro could be implemented as follows:
             #define cbrt(X) _Generic((X),                                      \
                                     long double: cbrtl,                        \
                                     default: cbrt,                             \
                                     float: cbrtf                               \
                                     )(X)

    6.5.2 Postfix operators
    Syntax
1            postfix-expression:
                    primary-expression
                    postfix-expression [ expression ]
                    postfix-expression ( argument-expression-listopt )
                    postfix-expression . identifier
                    postfix-expression -> identifier
                    postfix-expression ++
                    postfix-expression --
                    ( type-name ) { initializer-list }
                    ( type-name ) { initializer-list , }
             argument-expression-list:
                   assignment-expression
                   argument-expression-list , assignment-expression




[page 79]

    6.5.2.1 Array subscripting
    Constraints
1   One of the expressions shall have type ''pointer to complete object type'', the other
    expression shall have integer type, and the result has type ''type''.
    Semantics
2   A postfix expression followed by an expression in square brackets [] is a subscripted
    designation of an element of an array object. The definition of the subscript operator []
    is that E1[E2] is identical to (*((E1)+(E2))). Because of the conversion rules that
    apply to the binary + operator, if E1 is an array object (equivalently, a pointer to the
    initial element of an array object) and E2 is an integer, E1[E2] designates the E2-th
    element of E1 (counting from zero).
3   Successive subscript operators designate an element of a multidimensional array object.
    If E is an n-dimensional array (n >= 2) with dimensions i x j x . . . x k, then E (used as
    other than an lvalue) is converted to a pointer to an (n - 1)-dimensional array with
    dimensions j x . . . x k. If the unary * operator is applied to this pointer explicitly, or
    implicitly as a result of subscripting, the result is the referenced (n - 1)-dimensional
    array, which itself is converted into a pointer if used as other than an lvalue. It follows
    from this that arrays are stored in row-major order (last subscript varies fastest).
4   EXAMPLE        Consider the array object defined by the declaration
             int x[3][5];
    Here x is a 3 x 5 array of ints; more precisely, x is an array of three element objects, each of which is an
    array of five ints. In the expression x[i], which is equivalent to (*((x)+(i))), x is first converted to
    a pointer to the initial array of five ints. Then i is adjusted according to the type of x, which conceptually
    entails multiplying i by the size of the object to which the pointer points, namely an array of five int
    objects. The results are added and indirection is applied to yield an array of five ints. When used in the
    expression x[i][j], that array is in turn converted to a pointer to the first of the ints, so x[i][j]
    yields an int.

    Forward references: additive operators (6.5.6), address and indirection operators
    (6.5.3.2), array declarators (6.7.6.2).
    6.5.2.2 Function calls
    Constraints
1   The expression that denotes the called function92) shall have type pointer to function
    returning void or returning a complete object type other than an array type.
2   If the expression that denotes the called function has a type that includes a prototype, the
    number of arguments shall agree with the number of parameters. Each argument shall


    92) Most often, this is the result of converting an identifier that is a function designator.

[page 80]

    have a type such that its value may be assigned to an object with the unqualified version
    of the type of its corresponding parameter.
    Semantics
3   A postfix expression followed by parentheses () containing a possibly empty, comma-
    separated list of expressions is a function call. The postfix expression denotes the called
    function. The list of expressions specifies the arguments to the function.
4   An argument may be an expression of any complete object type. In preparing for the call
    to a function, the arguments are evaluated, and each parameter is assigned the value of the
    corresponding argument.93)
5   If the expression that denotes the called function has type pointer to function returning an
    object type, the function call expression has the same type as that object type, and has the
    value determined as specified in 6.8.6.4. Otherwise, the function call has type void.         *
6   If the expression that denotes the called function has a type that does not include a
    prototype, the integer promotions are performed on each argument, and arguments that
    have type float are promoted to double. These are called the default argument
    promotions. If the number of arguments does not equal the number of parameters, the
    behavior is undefined. If the function is defined with a type that includes a prototype, and
    either the prototype ends with an ellipsis (, ...) or the types of the arguments after
    promotion are not compatible with the types of the parameters, the behavior is undefined.
    If the function is defined with a type that does not include a prototype, and the types of
    the arguments after promotion are not compatible with those of the parameters after
    promotion, the behavior is undefined, except for the following cases:
    -- one promoted type is a signed integer type, the other promoted type is the
      corresponding unsigned integer type, and the value is representable in both types;
    -- both types are pointers to qualified or unqualified versions of a character type or
      void.
7   If the expression that denotes the called function has a type that does include a prototype,
    the arguments are implicitly converted, as if by assignment, to the types of the
    corresponding parameters, taking the type of each parameter to be the unqualified version
    of its declared type. The ellipsis notation in a function prototype declarator causes
    argument type conversion to stop after the last declared parameter. The default argument
    promotions are performed on trailing arguments.



    93) A function may change the values of its parameters, but these changes cannot affect the values of the
        arguments. On the other hand, it is possible to pass a pointer to an object, and the function may
        change the value of the object pointed to. A parameter declared to have array or function type is
        adjusted to have a pointer type as described in 6.9.1.

[page 81]

8    No other conversions are performed implicitly; in particular, the number and types of
     arguments are not compared with those of the parameters in a function definition that
     does not include a function prototype declarator.
9    If the function is defined with a type that is not compatible with the type (of the
     expression) pointed to by the expression that denotes the called function, the behavior is
     undefined.
10   There is a sequence point after the evaluations of the function designator and the actual
     arguments but before the actual call. Every evaluation in the calling function (including
     other function calls) that is not otherwise specifically sequenced before or after the
     execution of the body of the called function is indeterminately sequenced with respect to
     the execution of the called function.94)
11   Recursive function calls shall be permitted, both directly and indirectly through any chain
     of other functions.
12   EXAMPLE        In the function call
              (*pf[f1()]) (f2(), f3() + f4())
     the functions f1, f2, f3, and f4 may be called in any order. All side effects have to be completed before
     the function pointed to by pf[f1()] is called.

     Forward references: function declarators (including prototypes) (6.7.6.3), function
     definitions (6.9.1), the return statement (6.8.6.4), simple assignment (6.5.16.1).
     6.5.2.3 Structure and union members
     Constraints
1    The first operand of the . operator shall have an atomic, qualified, or unqualified
     structure or union type, and the second operand shall name a member of that type.
2    The first operand of the -> operator shall have type ''pointer to atomic, qualified, or
     unqualified structure'' or ''pointer to atomic, qualified, or unqualified union'', and the
     second operand shall name a member of the type pointed to.
     Semantics
3    A postfix expression followed by the . operator and an identifier designates a member of
     a structure or union object. The value is that of the named member,95) and is an lvalue if
     the first expression is an lvalue. If the first expression has qualified type, the result has
     the so-qualified version of the type of the designated member.

     94) In other words, function executions do not ''interleave'' with each other.
     95) If the member used to read the contents of a union object is not the same as the member last used to
         store a value in the object, the appropriate part of the object representation of the value is reinterpreted
         as an object representation in the new type as described in 6.2.6 (a process sometimes called ''type
         punning''). This might be a trap representation.

[page 82]

4   A postfix expression followed by the -> operator and an identifier designates a member
    of a structure or union object. The value is that of the named member of the object to
    which the first expression points, and is an lvalue.96) If the first expression is a pointer to
    a qualified type, the result has the so-qualified version of the type of the designated
    member.
5   Accessing a member of an atomic structure or union object results in undefined
    behavior.97)
6   One special guarantee is made in order to simplify the use of unions: if a union contains
    several structures that share a common initial sequence (see below), and if the union
    object currently contains one of these structures, it is permitted to inspect the common
    initial part of any of them anywhere that a declaration of the completed type of the union
    is visible. Two structures share a common initial sequence if corresponding members
    have compatible types (and, for bit-fields, the same widths) for a sequence of one or more
    initial members.
7   EXAMPLE 1 If f is a function returning a structure or union, and x is a member of that structure or
    union, f().x is a valid postfix expression but is not an lvalue.

8   EXAMPLE 2       In:
             struct s { int i; const int ci; };
             struct s s;
             const struct s cs;
             volatile struct s vs;
    the various members have the types:
             s.i          int
             s.ci         const int
             cs.i         const int
             cs.ci        const int
             vs.i         volatile int
             vs.ci        volatile const int




    96) If &E is a valid pointer expression (where & is the ''address-of '' operator, which generates a pointer to
        its operand), the expression (&E)->MOS is the same as E.MOS.
    97) For example, a data race would occur if access to the entire structure or union in one thread conflicts
        with access to a member from another thread, where at least one access is a modification. Members
        can be safely accessed using a non-atomic object which is assigned to or from the atomic object.

[page 83]

9   EXAMPLE 3       The following is a valid fragment:
             union {
                     struct {
                           int      alltypes;
                     } n;
                     struct {
                           int      type;
                           int      intnode;
                     } ni;
                     struct {
                           int      type;
                           double doublenode;
                     } nf;
             } u;
             u.nf.type = 1;
             u.nf.doublenode = 3.14;
             /* ... */
             if (u.n.alltypes == 1)
                     if (sin(u.nf.doublenode) == 0.0)
                           /* ... */
    The following is not a valid fragment (because the union type is not visible within function f):
             struct t1 { int m; };
             struct t2 { int m; };
             int f(struct t1 *p1, struct t2 *p2)
             {
                   if (p1->m < 0)
                           p2->m = -p2->m;
                   return p1->m;
             }
             int g()
             {
                   union {
                           struct t1 s1;
                           struct t2 s2;
                   } u;
                   /* ... */
                   return f(&u.s1, &u.s2);
             }

    Forward references: address and indirection operators (6.5.3.2), structure and union
    specifiers (6.7.2.1).




[page 84]

    6.5.2.4 Postfix increment and decrement operators
    Constraints
1   The operand of the postfix increment or decrement operator shall have atomic, qualified,
    or unqualified real or pointer type, and shall be a modifiable lvalue.
    Semantics
2   The result of the postfix ++ operator is the value of the operand. As a side effect, the
    value of the operand object is incremented (that is, the value 1 of the appropriate type is
    added to it). See the discussions of additive operators and compound assignment for
    information on constraints, types, and conversions and the effects of operations on
    pointers. The value computation of the result is sequenced before the side effect of
    updating the stored value of the operand. With respect to an indeterminately-sequenced
    function call, the operation of postfix ++ is a single evaluation. Postfix ++ on an object
    with atomic type is a read-modify-write operation with memory_order_seq_cst
    memory order semantics.98)
3   The postfix -- operator is analogous to the postfix ++ operator, except that the value of
    the operand is decremented (that is, the value 1 of the appropriate type is subtracted from
    it).
    Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
    6.5.2.5 Compound literals
    Constraints
1   The type name shall specify a complete object type or an array of unknown size, but not a
    variable length array type.
2   All the constraints for initializer lists in 6.7.9 also apply to compound literals.
    Semantics
3   A postfix expression that consists of a parenthesized type name followed by a brace-
    enclosed list of initializers is a compound literal. It provides an unnamed object whose
    value is given by the initializer list.99)


    98) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
        where T is the type of E:
                 T tmp;
                 T result = E;
                 do {
                        tmp = result + 1;
                 } while (!atomic_compare_exchange_strong(&E, &result, tmp));
         with result being the result of the operation.

[page 85]

4    If the type name specifies an array of unknown size, the size is determined by the
     initializer list as specified in 6.7.9, and the type of the compound literal is that of the
     completed array type. Otherwise (when the type name specifies an object type), the type
     of the compound literal is that specified by the type name. In either case, the result is an
     lvalue.
5    The value of the compound literal is that of an unnamed object initialized by the
     initializer list. If the compound literal occurs outside the body of a function, the object
     has static storage duration; otherwise, it has automatic storage duration associated with
     the enclosing block.
6    All the semantic rules for initializer lists in 6.7.9 also apply to compound literals.100)
7    String literals, and compound literals with const-qualified types, need not designate
     distinct objects.101)
8    EXAMPLE 1       The file scope definition
              int *p = (int []){2, 4};
     initializes p to point to the first element of an array of two ints, the first having the value two and the
     second, four. The expressions in this compound literal are required to be constant. The unnamed object
     has static storage duration.

9    EXAMPLE 2       In contrast, in
              void f(void)
              {
                    int *p;
                    /*...*/
                    p = (int [2]){*p};
                    /*...*/
              }
     p is assigned the address of the first element of an array of two ints, the first having the value previously
     pointed to by p and the second, zero. The expressions in this compound literal need not be constant. The
     unnamed object has automatic storage duration.

10   EXAMPLE 3 Initializers with designations can be combined with compound literals. Structure objects
     created using compound literals can be passed to functions without depending on member order:
              drawline((struct point){.x=1, .y=1},
                    (struct point){.x=3, .y=4});
     Or, if drawline instead expected pointers to struct point:



     99) Note that this differs from a cast expression. For example, a cast specifies a conversion to scalar types
         or void only, and the result of a cast expression is not an lvalue.
     100) For example, subobjects without explicit initializers are initialized to zero.
     101) This allows implementations to share storage for string literals and constant compound literals with
          the same or overlapping representations.

[page 86]

              drawline(&(struct point){.x=1, .y=1},
                    &(struct point){.x=3, .y=4});

11   EXAMPLE 4        A read-only compound literal can be specified through constructions like:
              (const float []){1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6}

12   EXAMPLE 5        The following three expressions have different meanings:
              "/tmp/fileXXXXXX"
              (char []){"/tmp/fileXXXXXX"}
              (const char []){"/tmp/fileXXXXXX"}
     The first always has static storage duration and has type array of char, but need not be modifiable; the last
     two have automatic storage duration when they occur within the body of a function, and the first of these
     two is modifiable.

13   EXAMPLE 6 Like string literals, const-qualified compound literals can be placed into read-only memory
     and can even be shared. For example,
              (const char []){"abc"} == "abc"
     might yield 1 if the literals' storage is shared.

14   EXAMPLE 7 Since compound literals are unnamed, a single compound literal cannot specify a circularly
     linked object. For example, there is no way to write a self-referential compound literal that could be used
     as the function argument in place of the named object endless_zeros below:
              struct int_list { int car; struct int_list *cdr; };
              struct int_list endless_zeros = {0, &endless_zeros};
              eval(endless_zeros);

15   EXAMPLE 8        Each compound literal creates only a single object in a given scope:
              struct s { int i; };
              int f (void)
              {
                    struct s *p = 0, *q;
                    int j = 0;
              again:
                        q = p, p = &((struct s){ j++ });
                        if (j < 2) goto again;
                        return p == q && q->i == 1;
              }
     The function f() always returns the value 1.
16   Note that if an iteration statement were used instead of an explicit goto and a labeled statement, the
     lifetime of the unnamed object would be the body of the loop only, and on entry next time around p would
     have an indeterminate value, which would result in undefined behavior.

     Forward references: type names (6.7.7), initialization (6.7.9).




[page 87]

    6.5.3 Unary operators
    Syntax
1            unary-expression:
                    postfix-expression
                    ++ unary-expression
                    -- unary-expression
                    unary-operator cast-expression
                    sizeof unary-expression
                    sizeof ( type-name )
                    alignof ( type-name )
             unary-operator: one of
                    & * + - ~             !
    6.5.3.1 Prefix increment and decrement operators
    Constraints
1   The operand of the prefix increment or decrement operator shall have atomic, qualified,
    or unqualified real or pointer type, and shall be a modifiable lvalue.
    Semantics
2   The value of the operand of the prefix ++ operator is incremented. The result is the new
    value of the operand after incrementation. The expression ++E is equivalent to (E+=1).
    See the discussions of additive operators and compound assignment for information on
    constraints, types, side effects, and conversions and the effects of operations on pointers.
3   The prefix -- operator is analogous to the prefix ++ operator, except that the value of the
    operand is decremented.
    Forward references: additive operators (6.5.6), compound assignment (6.5.16.2).
    6.5.3.2 Address and indirection operators
    Constraints
1   The operand of the unary & operator shall be either a function designator, the result of a
    [] or unary * operator, or an lvalue that designates an object that is not a bit-field and is
    not declared with the register storage-class specifier.
2   The operand of the unary * operator shall have pointer type.
    Semantics
3   The unary & operator yields the address of its operand. If the operand has type ''type'',
    the result has type ''pointer to type''. If the operand is the result of a unary * operator,
    neither that operator nor the & operator is evaluated and the result is as if both were
    omitted, except that the constraints on the operators still apply and the result is not an

[page 88]

    lvalue. Similarly, if the operand is the result of a [] operator, neither the & operator nor
    the unary * that is implied by the [] is evaluated and the result is as if the & operator
    were removed and the [] operator were changed to a + operator. Otherwise, the result is
    a pointer to the object or function designated by its operand.
4   The unary * operator denotes indirection. If the operand points to a function, the result is
    a function designator; if it points to an object, the result is an lvalue designating the
    object. If the operand has type ''pointer to type'', the result has type ''type''. If an
    invalid value has been assigned to the pointer, the behavior of the unary * operator is
    undefined.102)
    Forward references: storage-class specifiers (6.7.1), structure and union specifiers
    (6.7.2.1).
    6.5.3.3 Unary arithmetic operators
    Constraints
1   The operand of the unary + or - operator shall have arithmetic type; of the ~ operator,
    integer type; of the ! operator, scalar type.
    Semantics
2   The result of the unary + operator is the value of its (promoted) operand. The integer
    promotions are performed on the operand, and the result has the promoted type.
3   The result of the unary - operator is the negative of its (promoted) operand. The integer
    promotions are performed on the operand, and the result has the promoted type.
4   The result of the ~ operator is the bitwise complement of its (promoted) operand (that is,
    each bit in the result is set if and only if the corresponding bit in the converted operand is
    not set). The integer promotions are performed on the operand, and the result has the
    promoted type. If the promoted type is an unsigned type, the expression ~E is equivalent
    to the maximum value representable in that type minus E.
5   The result of the logical negation operator ! is 0 if the value of its operand compares
    unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int.
    The expression !E is equivalent to (0==E).



    102) Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). It is
         always true that if E is a function designator or an lvalue that is a valid operand of the unary &
         operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of
         an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points.
         Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an
         address inappropriately aligned for the type of object pointed to, and the address of an object after the
         end of its lifetime.

[page 89]

    6.5.3.4 The sizeof and alignof operators
    Constraints
1   The sizeof operator shall not be applied to an expression that has function type or an
    incomplete type, to the parenthesized name of such a type, or to an expression that
    designates a bit-field member. The alignof operator shall not be applied to a function
    type or an incomplete type.
    Semantics
2   The sizeof operator yields the size (in bytes) of its operand, which may be an
    expression or the parenthesized name of a type. The size is determined from the type of
    the operand. The result is an integer. If the type of the operand is a variable length array
    type, the operand is evaluated; otherwise, the operand is not evaluated and the result is an
    integer constant.
3   The alignof operator yields the alignment requirement of its operand type. The result
    is an integer constant. When applied to an array type, the result is the alignment
    requirement of the element type.
4   When sizeof is applied to an operand that has type char, unsigned char, or
    signed char, (or a qualified version thereof) the result is 1. When applied to an
    operand that has array type, the result is the total number of bytes in the array.103) When
    applied to an operand that has structure or union type, the result is the total number of
    bytes in such an object, including internal and trailing padding.
5   The value of the result of both operators is implementation-defined, and its type (an
    unsigned integer type) is size_t, defined in <stddef.h> (and other headers).
6   EXAMPLE 1 A principal use of the sizeof operator is in communication with routines such as storage
    allocators and I/O systems. A storage-allocation function might accept a size (in bytes) of an object to
    allocate and return a pointer to void. For example:
            extern void *alloc(size_t);
            double *dp = alloc(sizeof *dp);
    The implementation of the alloc function should ensure that its return value is aligned suitably for
    conversion to a pointer to double.

7   EXAMPLE 2      Another use of the sizeof operator is to compute the number of elements in an array:
            sizeof array / sizeof array[0]

8   EXAMPLE 3      In this example, the size of a variable length array is computed and returned from a
    function:
            #include <stddef.h>



    103) When applied to a parameter declared to have array or function type, the sizeof operator yields the
         size of the adjusted (pointer) type (see 6.9.1).

[page 90]

             size_t fsize3(int n)
             {
                   char b[n+3];                  // variable length array
                   return sizeof b;              // execution time sizeof
             }
             int main()
             {
                   size_t size;
                   size = fsize3(10); // fsize3 returns 13
                   return 0;
             }

    Forward references: common definitions <stddef.h> (7.19), declarations (6.7),
    structure and union specifiers (6.7.2.1), type names (6.7.7), array declarators (6.7.6.2).
    6.5.4 Cast operators
    Syntax
1            cast-expression:
                    unary-expression
                    ( type-name ) cast-expression
    Constraints
2   Unless the type name specifies a void type, the type name shall specify atomic, qualified,
    or unqualified scalar type, and the operand shall have scalar type.
3   Conversions that involve pointers, other than where permitted by the constraints of
    6.5.16.1, shall be specified by means of an explicit cast.
4   A pointer type shall not be converted to any floating type. A floating type shall not be
    converted to any pointer type.
    Semantics
5   Preceding an expression by a parenthesized type name converts the value of the
    expression to the named type. This construction is called a cast.104) A cast that specifies
    no conversion has no effect on the type or value of an expression.
6   If the value of the expression is represented with greater precision or range than required
    by the type named by the cast (6.3.1.8), then the cast specifies a conversion even if the
    type of the expression is the same as the named type and removes any extra range and
    precision.
    Forward references: equality operators (6.5.9), function declarators (including
    prototypes) (6.7.6.3), simple assignment (6.5.16.1), type names (6.7.7).

    104) A cast does not yield an lvalue. Thus, a cast to a qualified type has the same effect as a cast to the
         unqualified version of the type.

[page 91]

    6.5.5 Multiplicative operators
    Syntax
1            multiplicative-expression:
                     cast-expression
                     multiplicative-expression * cast-expression
                     multiplicative-expression / cast-expression
                     multiplicative-expression % cast-expression
    Constraints
2   Each of the operands shall have arithmetic type. The operands of the % operator shall
    have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the binary * operator is the product of the operands.
5   The result of the / operator is the quotient from the division of the first operand by the
    second; the result of the % operator is the remainder. In both operations, if the value of
    the second operand is zero, the behavior is undefined.
6   When integers are divided, the result of the / operator is the algebraic quotient with any
    fractional part discarded.105) If the quotient a/b is representable, the expression
    (a/b)*b + a%b shall equal a; otherwise, the behavior of both a/b and a%b is
    undefined.
    6.5.6 Additive operators
    Syntax
1            additive-expression:
                    multiplicative-expression
                    additive-expression + multiplicative-expression
                    additive-expression - multiplicative-expression
    Constraints
2   For addition, either both operands shall have arithmetic type, or one operand shall be a
    pointer to a complete object type and the other shall have integer type. (Incrementing is
    equivalent to adding 1.)
3   For subtraction, one of the following shall hold:




    105) This is often called ''truncation toward zero''.

[page 92]

    -- both operands have arithmetic type;
    -- both operands are pointers to qualified or unqualified versions of compatible complete
      object types; or
    -- the left operand is a pointer to a complete object type and the right operand has
      integer type.
    (Decrementing is equivalent to subtracting 1.)
    Semantics
4   If both operands have arithmetic type, the usual arithmetic conversions are performed on
    them.
5   The result of the binary + operator is the sum of the operands.
6   The result of the binary - operator is the difference resulting from the subtraction of the
    second operand from the first.
7   For the purposes of these operators, a pointer to an object that is not an element of an
    array behaves the same as a pointer to the first element of an array of length one with the
    type of the object as its element type.
8   When an expression that has integer type is added to or subtracted from a pointer, the
    result has the type of the pointer operand. If the pointer operand points to an element of
    an array object, and the array is large enough, the result points to an element offset from
    the original element such that the difference of the subscripts of the resulting and original
    array elements equals the integer expression. In other words, if the expression P points to
    the i-th element of an array object, the expressions (P)+N (equivalently, N+(P)) and
    (P)-N (where N has the value n) point to, respectively, the i+n-th and i-n-th elements of
    the array object, provided they exist. Moreover, if the expression P points to the last
    element of an array object, the expression (P)+1 points one past the last element of the
    array object, and if the expression Q points one past the last element of an array object,
    the expression (Q)-1 points to the last element of the array object. If both the pointer
    operand and the result point to elements of the same array object, or one past the last
    element of the array object, the evaluation shall not produce an overflow; otherwise, the
    behavior is undefined. If the result points one past the last element of the array object, it
    shall not be used as the operand of a unary * operator that is evaluated.
9   When two pointers are subtracted, both shall point to elements of the same array object,
    or one past the last element of the array object; the result is the difference of the
    subscripts of the two array elements. The size of the result is implementation-defined,
    and its type (a signed integer type) is ptrdiff_t defined in the <stddef.h> header.
    If the result is not representable in an object of that type, the behavior is undefined. In
    other words, if the expressions P and Q point to, respectively, the i-th and j-th elements of
    an array object, the expression (P)-(Q) has the value i-j provided the value fits in an

[page 93]

     object of type ptrdiff_t. Moreover, if the expression P points either to an element of
     an array object or one past the last element of an array object, and the expression Q points
     to the last element of the same array object, the expression ((Q)+1)-(P) has the same
     value as ((Q)-(P))+1 and as -((P)-((Q)+1)), and has the value zero if the
     expression P points one past the last element of the array object, even though the
     expression (Q)+1 does not point to an element of the array object.106)
10   EXAMPLE        Pointer arithmetic is well defined with pointers to variable length array types.
              {
                       int n = 4, m = 3;
                       int a[n][m];
                       int (*p)[m] = a;            //   p == &a[0]
                       p += 1;                     //   p == &a[1]
                       (*p)[2] = 99;               //   a[1][2] == 99
                       n = p - a;                  //   n == 1
              }
11   If array a in the above example were declared to be an array of known constant size, and pointer p were
     declared to be a pointer to an array of the same known constant size (pointing to a), the results would be
     the same.

     Forward references: array declarators (6.7.6.2), common definitions <stddef.h>
     (7.19).
     6.5.7 Bitwise shift operators
     Syntax
1             shift-expression:
                      additive-expression
                      shift-expression << additive-expression
                      shift-expression >> additive-expression
     Constraints
2    Each of the operands shall have integer type.
     Semantics
3    The integer promotions are performed on each of the operands. The type of the result is
     that of the promoted left operand. If the value of the right operand is negative or is

     106) Another way to approach pointer arithmetic is first to convert the pointer(s) to character pointer(s): In
          this scheme the integer expression added to or subtracted from the converted pointer is first multiplied
          by the size of the object originally pointed to, and the resulting pointer is converted back to the
          original type. For pointer subtraction, the result of the difference between the character pointers is
          similarly divided by the size of the object originally pointed to.
          When viewed in this way, an implementation need only provide one extra byte (which may overlap
          another object in the program) just after the end of the object in order to satisfy the ''one past the last
          element'' requirements.

[page 94]

    greater than or equal to the width of the promoted left operand, the behavior is undefined.
4   The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are filled with
    zeros. If E1 has an unsigned type, the value of the result is E1 x 2E2 , reduced modulo
    one more than the maximum value representable in the result type. If E1 has a signed
    type and nonnegative value, and E1 x 2E2 is representable in the result type, then that is
    the resulting value; otherwise, the behavior is undefined.
5   The result of E1 >> E2 is E1 right-shifted E2 bit positions. If E1 has an unsigned type
    or if E1 has a signed type and a nonnegative value, the value of the result is the integral
    part of the quotient of E1 / 2E2 . If E1 has a signed type and a negative value, the
    resulting value is implementation-defined.
    6.5.8 Relational operators
    Syntax
1            relational-expression:
                     shift-expression
                     relational-expression   <    shift-expression
                     relational-expression   >    shift-expression
                     relational-expression   <=   shift-expression
                     relational-expression   >=   shift-expression
    Constraints
2   One of the following shall hold:
    -- both operands have real type; or                                                            *
    -- both operands are pointers to qualified or unqualified versions of compatible object
      types.
    Semantics
3   If both of the operands have arithmetic type, the usual arithmetic conversions are
    performed.
4   For the purposes of these operators, a pointer to an object that is not an element of an
    array behaves the same as a pointer to the first element of an array of length one with the
    type of the object as its element type.
5   When two pointers are compared, the result depends on the relative locations in the
    address space of the objects pointed to. If two pointers to object types both point to the
    same object, or both point one past the last element of the same array object, they
    compare equal. If the objects pointed to are members of the same aggregate object,
    pointers to structure members declared later compare greater than pointers to members
    declared earlier in the structure, and pointers to array elements with larger subscript
    values compare greater than pointers to elements of the same array with lower subscript

[page 95]

    values. All pointers to members of the same union object compare equal. If the
    expression P points to an element of an array object and the expression Q points to the
    last element of the same array object, the pointer expression Q+1 compares greater than
    P. In all other cases, the behavior is undefined.
6   Each of the operators < (less than), > (greater than), <= (less than or equal to), and >=
    (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is
    false.107) The result has type int.
    6.5.9 Equality operators
    Syntax
1            equality-expression:
                    relational-expression
                    equality-expression == relational-expression
                    equality-expression != relational-expression
    Constraints
2   One of the following shall hold:
    -- both operands have arithmetic type;
    -- both operands are pointers to qualified or unqualified versions of compatible types;
    -- one operand is a pointer to an object type and the other is a pointer to a qualified or
      unqualified version of void; or
    -- one operand is a pointer and the other is a null pointer constant.
    Semantics
3   The == (equal to) and != (not equal to) operators are analogous to the relational
    operators except for their lower precedence.108) Each of the operators yields 1 if the
    specified relation is true and 0 if it is false. The result has type int. For any pair of
    operands, exactly one of the relations is true.
4   If both of the operands have arithmetic type, the usual arithmetic conversions are
    performed. Values of complex types are equal if and only if both their real parts are equal
    and also their imaginary parts are equal. Any two values of arithmetic types from
    different type domains are equal if and only if the results of their conversions to the
    (complex) result type determined by the usual arithmetic conversions are equal.



    107) The expression a<b<c is not interpreted as in ordinary mathematics. As the syntax indicates, it
         means (a<b)<c; in other words, ''if a is less than b, compare 1 to c; otherwise, compare 0 to c''.
    108) Because of the precedences, a<b == c<d is 1 whenever a<b and c<d have the same truth-value.

[page 96]

5   Otherwise, at least one operand is a pointer. If one operand is a pointer and the other is a
    null pointer constant, the null pointer constant is converted to the type of the pointer. If
    one operand is a pointer to an object type and the other is a pointer to a qualified or
    unqualified version of void, the former is converted to the type of the latter.
6   Two pointers compare equal if and only if both are null pointers, both are pointers to the
    same object (including a pointer to an object and a subobject at its beginning) or function,
    both are pointers to one past the last element of the same array object, or one is a pointer
    to one past the end of one array object and the other is a pointer to the start of a different
    array object that happens to immediately follow the first array object in the address
    space.109)
7   For the purposes of these operators, a pointer to an object that is not an element of an
    array behaves the same as a pointer to the first element of an array of length one with the
    type of the object as its element type.
    6.5.10 Bitwise AND operator
    Syntax
1            AND-expression:
                   equality-expression
                   AND-expression & equality-expression
    Constraints
2   Each of the operands shall have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the binary & operator is the bitwise AND of the operands (that is, each bit in
    the result is set if and only if each of the corresponding bits in the converted operands is
    set).




    109) Two objects may be adjacent in memory because they are adjacent elements of a larger array or
         adjacent members of a structure with no padding between them, or because the implementation chose
         to place them so, even though they are unrelated. If prior invalid pointer operations (such as accesses
         outside array bounds) produced undefined behavior, subsequent comparisons also produce undefined
         behavior.

[page 97]

    6.5.11 Bitwise exclusive OR operator
    Syntax
1            exclusive-OR-expression:
                     AND-expression
                     exclusive-OR-expression ^ AND-expression
    Constraints
2   Each of the operands shall have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the ^ operator is the bitwise exclusive OR of the operands (that is, each bit
    in the result is set if and only if exactly one of the corresponding bits in the converted
    operands is set).
    6.5.12 Bitwise inclusive OR operator
    Syntax
1            inclusive-OR-expression:
                     exclusive-OR-expression
                     inclusive-OR-expression | exclusive-OR-expression
    Constraints
2   Each of the operands shall have integer type.
    Semantics
3   The usual arithmetic conversions are performed on the operands.
4   The result of the | operator is the bitwise inclusive OR of the operands (that is, each bit in
    the result is set if and only if at least one of the corresponding bits in the converted
    operands is set).




[page 98]

    6.5.13 Logical AND operator
    Syntax
1            logical-AND-expression:
                     inclusive-OR-expression
                     logical-AND-expression && inclusive-OR-expression
    Constraints
2   Each of the operands shall have scalar type.
    Semantics
3   The && operator shall yield 1 if both of its operands compare unequal to 0; otherwise, it
    yields 0. The result has type int.
4   Unlike the bitwise binary & operator, the && operator guarantees left-to-right evaluation;
    if the second operand is evaluated, there is a sequence point between the evaluations of
    the first and second operands. If the first operand compares equal to 0, the second
    operand is not evaluated.
    6.5.14 Logical OR operator
    Syntax
1            logical-OR-expression:
                     logical-AND-expression
                     logical-OR-expression || logical-AND-expression
    Constraints
2   Each of the operands shall have scalar type.
    Semantics
3   The || operator shall yield 1 if either of its operands compare unequal to 0; otherwise, it
    yields 0. The result has type int.
4   Unlike the bitwise | operator, the || operator guarantees left-to-right evaluation; if the
    second operand is evaluated, there is a sequence point between the evaluations of the first
    and second operands. If the first operand compares unequal to 0, the second operand is
    not evaluated.




[page 99]

    6.5.15 Conditional operator
    Syntax
1            conditional-expression:
                    logical-OR-expression
                    logical-OR-expression ? expression : conditional-expression
    Constraints
2   The first operand shall have scalar type.
3   One of the following shall hold for the second and third operands:
    -- both operands have arithmetic type;
    -- both operands have the same structure or union type;
    -- both operands have void type;
    -- both operands are pointers to qualified or unqualified versions of compatible types;
    -- one operand is a pointer and the other is a null pointer constant; or
    -- one operand is a pointer to an object type and the other is a pointer to a qualified or
      unqualified version of void.
    Semantics
4   The first operand is evaluated; there is a sequence point between its evaluation and the
    evaluation of the second or third operand (whichever is evaluated). The second operand
    is evaluated only if the first compares unequal to 0; the third operand is evaluated only if
    the first compares equal to 0; the result is the value of the second or third operand
    (whichever is evaluated), converted to the type described below.110)                        *
5   If both the second and third operands have arithmetic type, the result type that would be
    determined by the usual arithmetic conversions, were they applied to those two operands,
    is the type of the result. If both the operands have structure or union type, the result has
    that type. If both operands have void type, the result has void type.
6   If both the second and third operands are pointers or one is a null pointer constant and the
    other is a pointer, the result type is a pointer to a type qualified with all the type qualifiers
    of the types referenced by both operands. Furthermore, if both operands are pointers to
    compatible types or to differently qualified versions of compatible types, the result type is
    a pointer to an appropriately qualified version of the composite type; if one operand is a
    null pointer constant, the result has the type of the other operand; otherwise, one operand
    is a pointer to void or a qualified version of void, in which case the result type is a
    pointer to an appropriately qualified version of void.

    110) A conditional expression does not yield an lvalue.

[page 100]

7   EXAMPLE The common type that results when the second and third operands are pointers is determined
    in two independent stages. The appropriate qualifiers, for example, do not depend on whether the two
    pointers have compatible types.
8   Given the declarations
              const void *c_vp;
              void *vp;
              const int *c_ip;
              volatile int *v_ip;
              int *ip;
              const char *c_cp;
    the third column in the following table is the common type that is the result of a conditional expression in
    which the first two columns are the second and third operands (in either order):
              c_vp    c_ip      const void *
              v_ip    0         volatile int *
              c_ip    v_ip      const volatile int *
              vp      c_cp      const void *
              ip      c_ip      const int *
              vp      ip        void *

    6.5.16 Assignment operators
    Syntax
1            assignment-expression:
                    conditional-expression
                    unary-expression assignment-operator assignment-expression
             assignment-operator: one of
                    = *= /= %= +=                       -=     <<=      >>=      &=     ^=     |=
    Constraints
2   An assignment operator shall have a modifiable lvalue as its left operand.
    Semantics
3   An assignment operator stores a value in the object designated by the left operand. An
    assignment expression has the value of the left operand after the assignment,111) but is not
    an lvalue. The type of an assignment expression is the type the left operand would have
    after lvalue conversion. The side effect of updating the stored value of the left operand is
    sequenced after the value computations of the left and right operands. The evaluations of
    the operands are unsequenced.




    111) The implementation is permitted to read the object to determine the value but is not required to, even
         when the object has volatile-qualified type.

[page 101]

    6.5.16.1 Simple assignment
    Constraints
1   One of the following shall hold:112)
    -- the left operand has atomic, qualified, or unqualified arithmetic type, and the right has
      arithmetic type;
    -- the left operand has an atomic, qualified, or unqualified version of a structure or union
      type compatible with the type of the right;
    -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
      the type the left operand would have after lvalue conversion) both operands are
      pointers to qualified or unqualified versions of compatible types, and the type pointed
      to by the left has all the qualifiers of the type pointed to by the right;
    -- the left operand has atomic, qualified, or unqualified pointer type, and (considering
      the type the left operand would have after lvalue conversion) one operand is a pointer
      to an object type, and the other is a pointer to a qualified or unqualified version of
      void, and the type pointed to by the left has all the qualifiers of the type pointed to
      by the right;
    -- the left operand is an atomic, qualified, or unqualified pointer, and the right is a null
      pointer constant; or
    -- the left operand has type atomic, qualified, or unqualified _Bool, and the right is a
      pointer.
    Semantics
2   In simple assignment (=), the value of the right operand is converted to the type of the
    assignment expression and replaces the value stored in the object designated by the left
    operand.
3   If the value being stored in an object is read from another object that overlaps in any way
    the storage of the first object, then the overlap shall be exact and the two objects shall
    have qualified or unqualified versions of a compatible type; otherwise, the behavior is
    undefined.
4   EXAMPLE 1       In the program fragment




    112) The asymmetric appearance of these constraints with respect to type qualifiers is due to the conversion
         (specified in 6.3.2.1) that changes lvalues to ''the value of the expression'' and thus removes any type
         qualifiers that were applied to the type category of the expression (for example, it removes const but
         not volatile from the type int volatile * const).

[page 102]

            int f(void);
            char c;
            /* ... */
            if ((c = f()) == -1)
                    /* ... */
    the int value returned by the function may be truncated when stored in the char, and then converted back
    to int width prior to the comparison. In an implementation in which ''plain'' char has the same range of
    values as unsigned char (and char is narrower than int), the result of the conversion cannot be
    negative, so the operands of the comparison can never compare equal. Therefore, for full portability, the
    variable c should be declared as int.

5   EXAMPLE 2       In the fragment:
            char c;
            int i;
            long l;
            l = (c = i);
    the value of i is converted to the type of the assignment expression c = i, that is, char type. The value
    of the expression enclosed in parentheses is then converted to the type of the outer assignment expression,
    that is, long int type.

6   EXAMPLE 3       Consider the fragment:
            const char **cpp;
            char *p;
            const char c = 'A';
            cpp = &p;                  // constraint violation
            *cpp = &c;                 // valid
            *p = 0;                    // valid
    The first assignment is unsafe because it would allow the following valid code to attempt to change the
    value of the const object c.

    6.5.16.2 Compound assignment
    Constraints
1   For the operators += and -= only, either the left operand shall be an atomic, qualified, or
    unqualified pointer to a complete object type, and the right shall have integer type; or the
    left operand shall have atomic, qualified, or unqualified arithmetic type, and the right
    shall have arithmetic type.
2   For the other operators, the left operand shall have atomic, qualified, or unqualified
    arithmetic type, and (considering the type the left operand would have after lvalue
    conversion) each operand shall have arithmetic type consistent with those allowed by the
    corresponding binary operator.
    Semantics
3   A compound assignment of the form E1 op = E2 is equivalent to the simple assignment
    expression E1 = E1 op (E2), except that the lvalue E1 is evaluated only once, and with
    respect to an indeterminately-sequenced function call, the operation of a compound
[page 103]

    assignment is a single evaluation. If E1 has an atomic type, compound assignment is a
    read-modify-write operation with memory_order_seq_cst memory order
    semantics.113)
    6.5.17 Comma operator
    Syntax
1            expression:
                    assignment-expression
                    expression , assignment-expression
    Semantics
2   The left operand of a comma operator is evaluated as a void expression; there is a
    sequence point between its evaluation and that of the right operand. Then the right
    operand is evaluated; the result has its type and value.114)                        *
3   EXAMPLE As indicated by the syntax, the comma operator (as described in this subclause) cannot
    appear in contexts where a comma is used to separate items in a list (such as arguments to functions or lists
    of initializers). On the other hand, it can be used within a parenthesized expression or within the second
    expression of a conditional operator in such contexts. In the function call
             f(a, (t=3, t+2), c)
    the function has three arguments, the second of which has the value 5.

    Forward references: initialization (6.7.9).




    113) Where a pointer to an atomic object can be formed, this is equivalent to the following code sequence
         where T is the type of E1:
                  T tmp = E1;
                  T result;
                  do {
                        result = tmp op (E2);
                  } while (!atomic_compare_exchange_strong(&E1, &tmp, result));
          with result being the result of the operation.
    114) A comma operator does not yield an lvalue.

[page 104]

    6.6 Constant expressions
    Syntax
1            constant-expression:
                    conditional-expression
    Description
2   A constant expression can be evaluated during translation rather than runtime, and
    accordingly may be used in any place that a constant may be.
    Constraints
3   Constant expressions shall not contain assignment, increment, decrement, function-call,
    or comma operators, except when they are contained within a subexpression that is not
    evaluated.115)
4   Each constant expression shall evaluate to a constant that is in the range of representable
    values for its type.
    Semantics
5   An expression that evaluates to a constant is required in several contexts. If a floating
    expression is evaluated in the translation environment, the arithmetic precision and range
    shall be at least as great as if the expression were being evaluated in the execution
    environment.116)
6   An integer constant expression117) shall have integer type and shall only have operands
    that are integer constants, enumeration constants, character constants, sizeof
    expressions whose results are integer constants, and floating constants that are the
    immediate operands of casts. Cast operators in an integer constant expression shall only
    convert arithmetic types to integer types, except as part of an operand to the sizeof
    operator.
7   More latitude is permitted for constant expressions in initializers. Such a constant
    expression shall be, or evaluate to, one of the following:
    -- an arithmetic constant expression,



    115) The operand of a sizeof operator is usually not evaluated (6.5.3.4).
    116) The use of evaluation formats as characterized by FLT_EVAL_METHOD also applies to evaluation in
         the translation environment.
    117) An integer constant expression is required in a number of contexts such as the size of a bit-field
         member of a structure, the value of an enumeration constant, and the size of a non-variable length
         array. Further constraints that apply to the integer constant expressions used in conditional-inclusion
         preprocessing directives are discussed in 6.10.1.

[page 105]

     -- a null pointer constant,
     -- an address constant, or
     -- an address constant for a complete object type plus or minus an integer constant
       expression.
8    An arithmetic constant expression shall have arithmetic type and shall only have
     operands that are integer constants, floating constants, enumeration constants, character
     constants, and sizeof expressions. Cast operators in an arithmetic constant expression
     shall only convert arithmetic types to arithmetic types, except as part of an operand to a
     sizeof operator whose result is an integer constant.
9    An address constant is a null pointer, a pointer to an lvalue designating an object of static
     storage duration, or a pointer to a function designator; it shall be created explicitly using
     the unary & operator or an integer constant cast to pointer type, or implicitly by the use of
     an expression of array or function type. The array-subscript [] and member-access .
     and -> operators, the address & and indirection * unary operators, and pointer casts may
     be used in the creation of an address constant, but the value of an object shall not be
     accessed by use of these operators.
10   An implementation may accept other forms of constant expressions.
11   The semantic rules for the evaluation of a constant expression are the same as for
     nonconstant expressions.118)
     Forward references: array declarators (6.7.6.2), initialization (6.7.9).




     118) Thus, in the following initialization,
                    static int i = 2 || 1 / 0;
           the expression is a valid integer constant expression with value one.

[page 106]

    6.7 Declarations
    Syntax
1            declaration:
                    declaration-specifiers init-declarator-listopt ;
                    static_assert-declaration
             declaration-specifiers:
                    storage-class-specifier declaration-specifiersopt
                    type-specifier declaration-specifiersopt
                    type-qualifier declaration-specifiersopt
                    function-specifier declaration-specifiersopt
                    alignment-specifier declaration-specifiersopt
             init-declarator-list:
                     init-declarator
                     init-declarator-list , init-declarator
             init-declarator:
                     declarator
                     declarator = initializer
    Constraints
2   A declaration other than a static_assert declaration shall declare at least a declarator
    (other than the parameters of a function or the members of a structure or union), a tag, or
    the members of an enumeration.
3   If an identifier has no linkage, there shall be no more than one declaration of the identifier
    (in a declarator or type specifier) with the same scope and in the same name space, except
    that a typedef name can be redefined to denote the same type as it currently does and tags
    may be redeclared as specified in 6.7.2.3.
4   All declarations in the same scope that refer to the same object or function shall specify
    compatible types.
    Semantics
5   A declaration specifies the interpretation and attributes of a set of identifiers. A definition
    of an identifier is a declaration for that identifier that:
    -- for an object, causes storage to be reserved for that object;
    -- for a function, includes the function body;119)



    119) Function definitions have a different syntax, described in 6.9.1.

[page 107]

    -- for an enumeration constant or typedef name, is the (only) declaration of the
      identifier.
6   The declaration specifiers consist of a sequence of specifiers that indicate the linkage,
    storage duration, and part of the type of the entities that the declarators denote. The init-
    declarator-list is a comma-separated sequence of declarators, each of which may have
    additional type information, or an initializer, or both. The declarators contain the
    identifiers (if any) being declared.
7   If an identifier for an object is declared with no linkage, the type for the object shall be
    complete by the end of its declarator, or by the end of its init-declarator if it has an
    initializer; in the case of function parameters (including in prototypes), it is the adjusted
    type (see 6.7.6.3) that is required to be complete.
    Forward references: declarators (6.7.6), enumeration specifiers (6.7.2.2), initialization
    (6.7.9), type names (6.7.7), type qualifiers (6.7.3).
    6.7.1 Storage-class specifiers
    Syntax
1            storage-class-specifier:
                    typedef
                    extern
                    static
                    _Thread_local
                    auto
                    register
    Constraints
2   At most, one storage-class specifier may be given in the declaration specifiers in a
    declaration, except that _Thread_local may appear with static or extern.120)
3   In the declaration of an object with block scope, if the declaration specifiers include
    _Thread_local, they shall also include either static or extern. If
    _Thread_local appears in any declaration of an object, it shall be present in every
    declaration of that object.
    Semantics
4   The typedef specifier is called a ''storage-class specifier'' for syntactic convenience
    only; it is discussed in 6.7.8. The meanings of the various linkages and storage durations
    were discussed in 6.2.2 and 6.2.4.



    120) See ''future language directions'' (6.11.5).

[page 108]

5   A declaration of an identifier for an object with storage-class specifier register
    suggests that access to the object be as fast as possible. The extent to which such
    suggestions are effective is implementation-defined.121)
6   The declaration of an identifier for a function that has block scope shall have no explicit
    storage-class specifier other than extern.
7   If an aggregate or union object is declared with a storage-class specifier other than
    typedef, the properties resulting from the storage-class specifier, except with respect to
    linkage, also apply to the members of the object, and so on recursively for any aggregate
    or union member objects.
    Forward references: type definitions (6.7.8).
    6.7.2 Type specifiers
    Syntax
1            type-specifier:
                    void
                    char
                    short
                    int
                    long
                    float
                    double
                    signed
                    unsigned
                    _Bool
                    _Complex
                    atomic-type-specifier
                    struct-or-union-specifier
                    enum-specifier
                    typedef-name
    Constraints
2   At least one type specifier shall be given in the declaration specifiers in each declaration,
    and in the specifier-qualifier list in each struct declaration and type name. Each list of


    121) The implementation may treat any register declaration simply as an auto declaration. However,
         whether or not addressable storage is actually used, the address of any part of an object declared with
         storage-class specifier register cannot be computed, either explicitly (by use of the unary &
         operator as discussed in 6.5.3.2) or implicitly (by converting an array name to a pointer as discussed in
         6.3.2.1). Thus, the only operator that can be applied to an array declared with storage-class specifier
         register is sizeof.

[page 109]

    type specifiers shall be one of the following multisets (delimited by commas, when there
    is more than one multiset per item); the type specifiers may occur in any order, possibly
    intermixed with the other declaration specifiers.
    -- void
    -- char
    -- signed char
    -- unsigned char
    -- short, signed short, short int, or signed short int
    -- unsigned short, or unsigned short int
    -- int, signed, or signed int
    -- unsigned, or unsigned int
    -- long, signed long, long int, or signed long int
    -- unsigned long, or unsigned long int
    -- long long, signed long long, long long int, or
      signed long long int
    -- unsigned long long, or unsigned long long int
    -- float
    -- double
    -- long double
    -- _Bool
    -- float _Complex
    -- double _Complex
    -- long double _Complex
    -- atomic type specifier
    -- struct or union specifier
    -- enum specifier
    -- typedef name
3   The type specifier _Complex shall not be used if the implementation does not support
    complex types (see 6.10.8.3).




[page 110]

    Semantics
4   Specifiers for structures, unions, enumerations, and atomic types are discussed in 6.7.2.1
    through 6.7.2.4. Declarations of typedef names are discussed in 6.7.8. The
    characteristics of the other types are discussed in 6.2.5.
5   Each of the comma-separated multisets designates the same type, except that for bit-
    fields, it is implementation-defined whether the specifier int designates the same type as
    signed int or the same type as unsigned int.
    Forward references: atomic type specifiers (6.7.2.4), enumeration specifiers (6.7.2.2),
    structure and union specifiers (6.7.2.1), tags (6.7.2.3), type definitions (6.7.8).
    6.7.2.1 Structure and union specifiers
    Syntax
1            struct-or-union-specifier:
                     struct-or-union identifieropt { struct-declaration-list }
                     struct-or-union identifier
             struct-or-union:
                     struct
                     union
             struct-declaration-list:
                     struct-declaration
                     struct-declaration-list struct-declaration
             struct-declaration:
                     specifier-qualifier-list struct-declarator-listopt ;
                     static_assert-declaration
             specifier-qualifier-list:
                    type-specifier specifier-qualifier-listopt
                    type-qualifier specifier-qualifier-listopt
             struct-declarator-list:
                     struct-declarator
                     struct-declarator-list , struct-declarator
             struct-declarator:
                     declarator
                     declaratoropt : constant-expression
    Constraints
2   A struct-declaration that does not declare an anonymous structure or anonymous union
    shall contain a struct-declarator-list.


[page 111]

3    A structure or union shall not contain a member with incomplete or function type (hence,
     a structure shall not contain an instance of itself, but may contain a pointer to an instance
     of itself), except that the last member of a structure with more than one named member
     may have incomplete array type; such a structure (and any union containing, possibly
     recursively, a member that is such a structure) shall not be a member of a structure or an
     element of an array.
4    The expression that specifies the width of a bit-field shall be an integer constant
     expression with a nonnegative value that does not exceed the width of an object of the
     type that would be specified were the colon and expression omitted.122) If the value is
     zero, the declaration shall have no declarator.
5    A bit-field shall have a type that is a qualified or unqualified version of _Bool, signed
     int, unsigned int, or some other implementation-defined type. It is
     implementation-defined whether atomic types are permitted.
     Semantics
6    As discussed in 6.2.5, a structure is a type consisting of a sequence of members, whose
     storage is allocated in an ordered sequence, and a union is a type consisting of a sequence
     of members whose storage overlap.
7    Structure and union specifiers have the same form. The keywords struct and union
     indicate that the type being specified is, respectively, a structure type or a union type.
8    The presence of a struct-declaration-list in a struct-or-union-specifier declares a new type,
     within a translation unit. The struct-declaration-list is a sequence of declarations for the
     members of the structure or union. If the struct-declaration-list contains no named
     members, no anonymous structures, and no anonymous unions, the behavior is undefined.
     The type is incomplete until immediately after the } that terminates the list, and complete
     thereafter.
9    A member of a structure or union may have any complete object type other than a
     variably modified type.123) In addition, a member may be declared to consist of a
     specified number of bits (including a sign bit, if any). Such a member is called a
     bit-field;124) its width is preceded by a colon.
10   A bit-field is interpreted as having a signed or unsigned integer type consisting of the
     specified number of bits.125) If the value 0 or 1 is stored into a nonzero-width bit-field of

     122) While the number of bits in a _Bool object is at least CHAR_BIT, the width (number of sign and
          value bits) of a _Bool may be just 1 bit.
     123) A structure or union cannot contain a member with a variably modified type because member names
          are not ordinary identifiers as defined in 6.2.3.
     124) The unary & (address-of) operator cannot be applied to a bit-field object; thus, there are no pointers to
          or arrays of bit-field objects.

[page 112]

     type _Bool, the value of the bit-field shall compare equal to the value stored; a _Bool
     bit-field has the semantics of a _Bool.
11   An implementation may allocate any addressable storage unit large enough to hold a bit-
     field. If enough space remains, a bit-field that immediately follows another bit-field in a
     structure shall be packed into adjacent bits of the same unit. If insufficient space remains,
     whether a bit-field that does not fit is put into the next unit or overlaps adjacent units is
     implementation-defined. The order of allocation of bit-fields within a unit (high-order to
     low-order or low-order to high-order) is implementation-defined. The alignment of the
     addressable storage unit is unspecified.
12   A bit-field declaration with no declarator, but only a colon and a width, indicates an
     unnamed bit-field.126) As a special case, a bit-field structure member with a width of 0
     indicates that no further bit-field is to be packed into the unit in which the previous bit-
     field, if any, was placed.
13   An unnamed member of structure type with no tag is called an anonymous structure; an
     unnamed member of union type with no tag is called an anonymous union. The members
     of an anonymous structure or union are considered to be members of the containing
     structure or union. This applies recursively if the containing structure or union is also
     anonymous.
14   Each non-bit-field member of a structure or union object is aligned in an implementation-
     defined manner appropriate to its type.
15   Within a structure object, the non-bit-field members and the units in which bit-fields
     reside have addresses that increase in the order in which they are declared. A pointer to a
     structure object, suitably converted, points to its initial member (or if that member is a
     bit-field, then to the unit in which it resides), and vice versa. There may be unnamed
     padding within a structure object, but not at its beginning.
16   The size of a union is sufficient to contain the largest of its members. The value of at
     most one of the members can be stored in a union object at any time. A pointer to a
     union object, suitably converted, points to each of its members (or if a member is a bit-
     field, then to the unit in which it resides), and vice versa.
17   There may be unnamed padding at the end of a structure or union.
18   As a special case, the last element of a structure with more than one named member may
     have an incomplete array type; this is called a flexible array member. In most situations,


     125) As specified in 6.7.2 above, if the actual type specifier used is int or a typedef-name defined as int,
          then it is implementation-defined whether the bit-field is signed or unsigned.
     126) An unnamed bit-field structure member is useful for padding to conform to externally imposed
          layouts.

[page 113]

     the flexible array member is ignored. In particular, the size of the structure is as if the
     flexible array member were omitted except that it may have more trailing padding than
     the omission would imply. However, when a . (or ->) operator has a left operand that is
     (a pointer to) a structure with a flexible array member and the right operand names that
     member, it behaves as if that member were replaced with the longest array (with the same
     element type) that would not make the structure larger than the object being accessed; the
     offset of the array shall remain that of the flexible array member, even if this would differ
     from that of the replacement array. If this array would have no elements, it behaves as if
     it had one element but the behavior is undefined if any attempt is made to access that
     element or to generate a pointer one past it.
19   EXAMPLE 1       The following illustrates anonymous structures and unions:
              struct v {
                    union {      // anonymous union
                           struct { int i, j; };    // anonymous structure
                           struct { long k, l; } w;
                    };
                    int m;
              } v1;
              v1.i = 2;   // valid
              v1.k = 3;   // invalid: inner structure is not anonymous
              v1.w.k = 5; // valid

20   EXAMPLE 2       After the declaration:
              struct s { int n; double d[]; };
     the structure struct s has a flexible array member d. A typical way to use this is:
              int m = /* some value */;
              struct s *p = malloc(sizeof (struct s) + sizeof (double [m]));
     and assuming that the call to malloc succeeds, the object pointed to by p behaves, for most purposes, as if
     p had been declared as:
              struct { int n; double d[m]; } *p;
     (there are circumstances in which this equivalence is broken; in particular, the offsets of member d might
     not be the same).
21   Following the above declaration:
              struct s t1 = { 0 };                         //   valid
              struct s t2 = { 1, { 4.2 }};                 //   invalid
              t1.n = 4;                                    //   valid
              t1.d[0] = 4.2;                               //   might be undefined behavior
     The initialization of t2 is invalid (and violates a constraint) because struct s is treated as if it did not
     contain member d. The assignment to t1.d[0] is probably undefined behavior, but it is possible that
              sizeof (struct s) >= offsetof(struct s, d) + sizeof (double)
     in which case the assignment would be legitimate. Nevertheless, it cannot appear in strictly conforming
     code.

[page 114]

22   After the further declaration:
              struct ss { int n; };
     the expressions:
              sizeof (struct s) >= sizeof (struct ss)
              sizeof (struct s) >= offsetof(struct s, d)
     are always equal to 1.
23   If sizeof (double) is 8, then after the following code is executed:
              struct s *s1;
              struct s *s2;
              s1 = malloc(sizeof (struct s) + 64);
              s2 = malloc(sizeof (struct s) + 46);
     and assuming that the calls to malloc succeed, the objects pointed to by s1 and s2 behave, for most
     purposes, as if the identifiers had been declared as:
              struct { int n; double d[8]; } *s1;
              struct { int n; double d[5]; } *s2;
24   Following the further successful assignments:
              s1 = malloc(sizeof (struct s) + 10);
              s2 = malloc(sizeof (struct s) + 6);
     they then behave as if the declarations were:
              struct { int n; double d[1]; } *s1, *s2;
     and:
              double *dp;
              dp = &(s1->d[0]);          //   valid
              *dp = 42;                  //   valid
              dp = &(s2->d[0]);          //   valid
              *dp = 42;                  //   undefined behavior
25   The assignment:
              *s1 = *s2;
     only copies the member n; if any of the array elements are within the first sizeof (struct s) bytes
     of the structure, they might be copied or simply overwritten with indeterminate values.

     Forward references: declarators (6.7.6), tags (6.7.2.3).




[page 115]

    6.7.2.2 Enumeration specifiers
    Syntax
1            enum-specifier:
                   enum identifieropt { enumerator-list }
                   enum identifieropt { enumerator-list , }
                   enum identifier
             enumerator-list:
                   enumerator
                   enumerator-list , enumerator
             enumerator:
                   enumeration-constant
                   enumeration-constant = constant-expression
    Constraints
2   The expression that defines the value of an enumeration constant shall be an integer
    constant expression that has a value representable as an int.
    Semantics
3   The identifiers in an enumerator list are declared as constants that have type int and
    may appear wherever such are permitted.127) An enumerator with = defines its
    enumeration constant as the value of the constant expression. If the first enumerator has
    no =, the value of its enumeration constant is 0. Each subsequent enumerator with no =
    defines its enumeration constant as the value of the constant expression obtained by
    adding 1 to the value of the previous enumeration constant. (The use of enumerators with
    = may produce enumeration constants with values that duplicate other values in the same
    enumeration.) The enumerators of an enumeration are also known as its members.
4   Each enumerated type shall be compatible with char, a signed integer type, or an
    unsigned integer type. The choice of type is implementation-defined,128) but shall be
    capable of representing the values of all the members of the enumeration. The
    enumerated type is incomplete until immediately after the } that terminates the list of
    enumerator declarations, and complete thereafter.




    127) Thus, the identifiers of enumeration constants declared in the same scope shall all be distinct from
         each other and from other identifiers declared in ordinary declarators.
    128) An implementation may delay the choice of which integer type until all enumeration constants have
         been seen.

[page 116]

5   EXAMPLE       The following fragment:
             enum hue { chartreuse, burgundy, claret=20, winedark };
             enum hue col, *cp;
             col = claret;
             cp = &col;
             if (*cp != burgundy)
                   /* ... */
    makes hue the tag of an enumeration, and then declares col as an object that has that type and cp as a
    pointer to an object that has that type. The enumerated values are in the set { 0, 1, 20, 21 }.

    Forward references: tags (6.7.2.3).
    6.7.2.3 Tags
    Constraints
1   A specific type shall have its content defined at most once.
2   Where two declarations that use the same tag declare the same type, they shall both use
    the same choice of struct, union, or enum.
3   A type specifier of the form
            enum identifier
    without an enumerator list shall only appear after the type it specifies is complete.
    Semantics
4   All declarations of structure, union, or enumerated types that have the same scope and
    use the same tag declare the same type. Irrespective of whether there is a tag or what
    other declarations of the type are in the same translation unit, the type is incomplete129)
    until immediately after the closing brace of the list defining the content, and complete
    thereafter.
5   Two declarations of structure, union, or enumerated types which are in different scopes or
    use different tags declare distinct types. Each declaration of a structure, union, or
    enumerated type which does not include a tag declares a distinct type.
6   A type specifier of the form




    129) An incomplete type may only by used when the size of an object of that type is not needed. It is not
         needed, for example, when a typedef name is declared to be a specifier for a structure or union, or
         when a pointer to or a function returning a structure or union is being declared. (See incomplete types
         in 6.2.5.) The specification has to be complete before such a function is called or defined.

[page 117]

              struct-or-union identifieropt { struct-declaration-list }
     or
              enum identifieropt { enumerator-list }
     or
              enum identifieropt { enumerator-list , }
     declares a structure, union, or enumerated type. The list defines the structure content,
     union content, or enumeration content. If an identifier is provided,130) the type specifier
     also declares the identifier to be the tag of that type.
7    A declaration of the form
              struct-or-union identifier ;
     specifies a structure or union type and declares the identifier as a tag of that type.131)
8    If a type specifier of the form
              struct-or-union identifier
     occurs other than as part of one of the above forms, and no other declaration of the
     identifier as a tag is visible, then it declares an incomplete structure or union type, and
     declares the identifier as the tag of that type.131)
9    If a type specifier of the form
              struct-or-union identifier
     or
              enum identifier
     occurs other than as part of one of the above forms, and a declaration of the identifier as a
     tag is visible, then it specifies the same type as that other declaration, and does not
     redeclare the tag.
10   EXAMPLE 1       This mechanism allows declaration of a self-referential structure.
              struct tnode {
                    int count;
                    struct tnode *left, *right;
              };
     specifies a structure that contains an integer and two pointers to objects of the same type. Once this
     declaration has been given, the declaration




     130) If there is no identifier, the type can, within the translation unit, only be referred to by the declaration
          of which it is a part. Of course, when the declaration is of a typedef name, subsequent declarations
          can make use of that typedef name to declare objects having the specified structure, union, or
          enumerated type.
     131) A similar construction with enum does not exist.

[page 118]

              struct tnode s, *sp;
     declares s to be an object of the given type and sp to be a pointer to an object of the given type. With
     these declarations, the expression sp->left refers to the left struct tnode pointer of the object to
     which sp points; the expression s.right->count designates the count member of the right struct
     tnode pointed to from s.
11   The following alternative formulation uses the typedef mechanism:
              typedef struct tnode TNODE;
              struct tnode {
                    int count;
                    TNODE *left, *right;
              };
              TNODE s, *sp;

12   EXAMPLE 2 To illustrate the use of prior declaration of a tag to specify a pair of mutually referential
     structures, the declarations
              struct s1 { struct s2 *s2p; /* ... */ }; // D1
              struct s2 { struct s1 *s1p; /* ... */ }; // D2
     specify a pair of structures that contain pointers to each other. Note, however, that if s2 were already
     declared as a tag in an enclosing scope, the declaration D1 would refer to it, not to the tag s2 declared in
     D2. To eliminate this context sensitivity, the declaration
              struct s2;
     may be inserted ahead of D1. This declares a new tag s2 in the inner scope; the declaration D2 then
     completes the specification of the new type.

     Forward references: declarators (6.7.6), type definitions (6.7.8).
     6.7.2.4 Atomic type specifiers
     Syntax
1             atomic-type-specifier:
                     _Atomic ( type-name )
     Constraints
2    Atomic type specifiers shall not be used if the implementation does not support atomic
     types (see 6.10.8.3).
3    The type name in an atomic type specifier shall not refer to an array type, a function type,
     an atomic type, or a qualified type.
     Semantics
4    The properties associated with atomic types are meaningful only for expressions that are
     lvalues. If the _Atomic keyword is immediately followed by a left parenthesis, it is
     interpreted as a type specifier (with a type name), not as a type qualifier.




[page 119]

    6.7.3 Type qualifiers
    Syntax
1            type-qualifier:
                    const
                    restrict
                    volatile
                    _Atomic
    Constraints
2   Types other than pointer types whose referenced type is an object type shall not be
    restrict-qualified.
3   The type modified by the _Atomic qualifier shall not be an array type or a function
    type.
    Semantics
4   The properties associated with qualified types are meaningful only for expressions that
    are lvalues.132)
5   If the same qualifier appears more than once in the same specifier-qualifier-list, either
    directly or via one or more typedefs, the behavior is the same as if it appeared only
    once. If other qualifiers appear along with the _Atomic qualifier in a specifier-qualifier-
    list, the resulting type is the so-qualified atomic type.
6   If an attempt is made to modify an object defined with a const-qualified type through use
    of an lvalue with non-const-qualified type, the behavior is undefined. If an attempt is
    made to refer to an object defined with a volatile-qualified type through use of an lvalue
    with non-volatile-qualified type, the behavior is undefined.133)
7   An object that has volatile-qualified type may be modified in ways unknown to the
    implementation or have other unknown side effects. Therefore any expression referring
    to such an object shall be evaluated strictly according to the rules of the abstract machine,
    as described in 5.1.2.3. Furthermore, at every sequence point the value last stored in the
    object shall agree with that prescribed by the abstract machine, except as modified by the




    132) The implementation may place a const object that is not volatile in a read-only region of
         storage. Moreover, the implementation need not allocate storage for such an object if its address is
         never used.
    133) This applies to those objects that behave as if they were defined with qualified types, even if they are
         never actually defined as objects in the program (such as an object at a memory-mapped input/output
         address).

[page 120]

     unknown factors mentioned previously.134) What constitutes an access to an object that
     has volatile-qualified type is implementation-defined.
8    An object that is accessed through a restrict-qualified pointer has a special association
     with that pointer. This association, defined in 6.7.3.1 below, requires that all accesses to
     that object use, directly or indirectly, the value of that particular pointer.135) The intended
     use of the restrict qualifier (like the register storage class) is to promote
     optimization, and deleting all instances of the qualifier from all preprocessing translation
     units composing a conforming program does not change its meaning (i.e., observable
     behavior).
9    If the specification of an array type includes any type qualifiers, the element type is so-
     qualified, not the array type. If the specification of a function type includes any type
     qualifiers, the behavior is undefined.136)
10   For two qualified types to be compatible, both shall have the identically qualified version
     of a compatible type; the order of type qualifiers within a list of specifiers or qualifiers
     does not affect the specified type.
11   EXAMPLE 1      An object declared
              extern const volatile int real_time_clock;
     may be modifiable by hardware, but cannot be assigned to, incremented, or decremented.

12   EXAMPLE 2 The following declarations and expressions illustrate the behavior when type qualifiers
     modify an aggregate type:
              const struct s { int mem; } cs = { 1 };
              struct s ncs; // the object ncs is modifiable
              typedef int A[2][3];
              const A a = {{4, 5, 6}, {7, 8, 9}}; // array of array of const int
              int *pi;
              const int *pci;
              ncs = cs;            //    valid
              cs = ncs;            //    violates modifiable lvalue constraint for =
              pi = &ncs.mem;       //    valid
              pi = &cs.mem;        //    violates type constraints for =
              pci = &cs.mem;       //    valid
              pi = a[0];           //    invalid: a[0] has type ''const int *''



     134) A volatile declaration may be used to describe an object corresponding to a memory-mapped
          input/output port or an object accessed by an asynchronously interrupting function. Actions on
          objects so declared shall not be ''optimized out'' by an implementation or reordered except as
          permitted by the rules for evaluating expressions.
     135) For example, a statement that assigns a value returned by malloc to a single pointer establishes this
          association between the allocated object and the pointer.
     136) Both of these can occur through the use of typedefs.

[page 121]

13   EXAMPLE 3       The declaration
              _Atomic volatile int *p;
     specifies that p has the type ''pointer to volatile atomic int'', a pointer to a volatile-qualified atomic type.

     6.7.3.1 Formal definition of restrict
1    Let D be a declaration of an ordinary identifier that provides a means of designating an
     object P as a restrict-qualified pointer to type T.
2    If D appears inside a block and does not have storage class extern, let B denote the
     block. If D appears in the list of parameter declarations of a function definition, let B
     denote the associated block. Otherwise, let B denote the block of main (or the block of
     whatever function is called at program startup in a freestanding environment).
3    In what follows, a pointer expression E is said to be based on object P if (at some
     sequence point in the execution of B prior to the evaluation of E) modifying P to point to
     a copy of the array object into which it formerly pointed would change the value of E.137)
     Note that ''based'' is defined only for expressions with pointer types.
4    During each execution of B, let L be any lvalue that has &L based on P. If L is used to
     access the value of the object X that it designates, and X is also modified (by any means),
     then the following requirements apply: T shall not be const-qualified. Every other lvalue
     used to access the value of X shall also have its address based on P. Every access that
     modifies X shall be considered also to modify P, for the purposes of this subclause. If P
     is assigned the value of a pointer expression E that is based on another restricted pointer
     object P2, associated with block B2, then either the execution of B2 shall begin before
     the execution of B, or the execution of B2 shall end prior to the assignment. If these
     requirements are not met, then the behavior is undefined.
5    Here an execution of B means that portion of the execution of the program that would
     correspond to the lifetime of an object with scalar type and automatic storage duration
     associated with B.
6    A translator is free to ignore any or all aliasing implications of uses of restrict.
7    EXAMPLE 1       The file scope declarations
              int * restrict a;
              int * restrict b;
              extern int c[];
     assert that if an object is accessed using one of a, b, or c, and that object is modified anywhere in the
     program, then it is never accessed using either of the other two.


     137) In other words, E depends on the value of P itself rather than on the value of an object referenced
          indirectly through P. For example, if identifier p has type (int **restrict), then the pointer
          expressions p and p+1 are based on the restricted pointer object designated by p, but the pointer
          expressions *p and p[1] are not.

[page 122]

8    EXAMPLE 2       The function parameter declarations in the following example
             void f(int n, int * restrict p, int * restrict q)
             {
                   while (n-- > 0)
                         *p++ = *q++;
             }
     assert that, during each execution of the function, if an object is accessed through one of the pointer
     parameters, then it is not also accessed through the other.
9    The benefit of the restrict qualifiers is that they enable a translator to make an effective dependence
     analysis of function f without examining any of the calls of f in the program. The cost is that the
     programmer has to examine all of those calls to ensure that none give undefined behavior. For example, the
     second call of f in g has undefined behavior because each of d[1] through d[49] is accessed through
     both p and q.
              void g(void)
              {
                    extern int d[100];
                    f(50, d + 50, d); // valid
                    f(50, d + 1, d); // undefined behavior
              }

10   EXAMPLE 3       The function parameter declarations
             void h(int n, int * restrict p, int * restrict q, int * restrict r)
             {
                   int i;
                   for (i = 0; i < n; i++)
                          p[i] = q[i] + r[i];
             }
     illustrate how an unmodified object can be aliased through two restricted pointers. In particular, if a and b
     are disjoint arrays, a call of the form h(100, a, b, b) has defined behavior, because array b is not
     modified within function h.

11   EXAMPLE 4 The rule limiting assignments between restricted pointers does not distinguish between a
     function call and an equivalent nested block. With one exception, only ''outer-to-inner'' assignments
     between restricted pointers declared in nested blocks have defined behavior.
             {
                      int * restrict p1;
                      int * restrict q1;
                      p1 = q1; // undefined behavior
                      {
                            int * restrict p2 = p1; // valid
                            int * restrict q2 = q1; // valid
                            p1 = q2;                // undefined behavior
                            p2 = q2;                // undefined behavior
                      }
             }




[page 123]

12   The one exception allows the value of a restricted pointer to be carried out of the block in which it (or, more
     precisely, the ordinary identifier used to designate it) is declared when that block finishes execution. For
     example, this permits new_vector to return a vector.
              typedef struct { int n; float * restrict v; } vector;
              vector new_vector(int n)
              {
                    vector t;
                    t.n = n;
                    t.v = malloc(n * sizeof (float));
                    return t;
              }

     6.7.4 Function specifiers
     Syntax
1             function-specifier:
                     inline
                     _Noreturn
     Constraints
2    Function specifiers shall be used only in the declaration of an identifier for a function.
3    An inline definition of a function with external linkage shall not contain a definition of a
     modifiable object with static or thread storage duration, and shall not contain a reference
     to an identifier with internal linkage.
4    In a hosted environment, no function specifier(s) shall appear in a declaration of main.
     Semantics
5    A function specifier may appear more than once; the behavior is the same as if it
     appeared only once.
6    A function declared with an inline function specifier is an inline function. Making a *
     function an inline function suggests that calls to the function be as fast as possible.138)
     The extent to which such suggestions are effective is implementation-defined.139)




     138) By using, for example, an alternative to the usual function call mechanism, such as ''inline
          substitution''. Inline substitution is not textual substitution, nor does it create a new function.
          Therefore, for example, the expansion of a macro used within the body of the function uses the
          definition it had at the point the function body appears, and not where the function is called; and
          identifiers refer to the declarations in scope where the body occurs. Likewise, the function has a
          single address, regardless of the number of inline definitions that occur in addition to the external
          definition.
     139) For example, an implementation might never perform inline substitution, or might only perform inline
          substitutions to calls in the scope of an inline declaration.

[page 124]

7    Any function with internal linkage can be an inline function. For a function with external
     linkage, the following restrictions apply: If a function is declared with an inline
     function specifier, then it shall also be defined in the same translation unit. If all of the
     file scope declarations for a function in a translation unit include the inline function
     specifier without extern, then the definition in that translation unit is an inline
     definition. An inline definition does not provide an external definition for the function,
     and does not forbid an external definition in another translation unit. An inline definition
     provides an alternative to an external definition, which a translator may use to implement
     any call to the function in the same translation unit. It is unspecified whether a call to the
     function uses the inline definition or the external definition.140)
8    A function declared with a _Noreturn function specifier shall not return to its caller.
     Recommended practice
9    The implementation should produce a diagnostic message for a function declared with a
     _Noreturn function specifier that appears to be capable of returning to its caller.
10   EXAMPLE 1 The declaration of an inline function with external linkage can result in either an external
     definition, or a definition available for use only within the translation unit. A file scope declaration with
     extern creates an external definition. The following example shows an entire translation unit.
              inline double fahr(double t)
              {
                    return (9.0 * t) / 5.0 + 32.0;
              }
              inline double cels(double t)
              {
                    return (5.0 * (t - 32.0)) / 9.0;
              }
              extern double fahr(double);                  // creates an external definition
              double convert(int is_fahr, double temp)
              {
                    /* A translator may perform inline substitutions */
                    return is_fahr ? cels(temp) : fahr(temp);
              }
11   Note that the definition of fahr is an external definition because fahr is also declared with extern, but
     the definition of cels is an inline definition. Because cels has external linkage and is referenced, an
     external definition has to appear in another translation unit (see 6.9); the inline definition and the external
     definition are distinct and either may be used for the call.

12   EXAMPLE 2




     140) Since an inline definition is distinct from the corresponding external definition and from any other
          corresponding inline definitions in other translation units, all corresponding objects with static storage
          duration are also distinct in each of the definitions.

[page 125]

             _Noreturn void f () {
                   abort(); // ok
             }
             _Noreturn void g (int i) { // causes undefined behavior if i <= 0
                   if (i > 0) abort();
             }

    Forward references: function definitions (6.9.1).
    6.7.5 Alignment specifier
    Syntax
1            alignment-specifier:
                   _Alignas ( type-name )
                   _Alignas ( constant-expression )
    Constraints
2   An alignment attribute shall not be specified in a declaration of a typedef, or a bit-field, or
    a function, or a parameter, or an object declared with the register storage-class
    specifier.
3   The constant expression shall be an integer constant expression. It shall evaluate to a
    valid fundamental alignment, or to a valid extended alignment supported by the
    implementation in the context in which it appears, or to zero.
4   The combined effect of all alignment attributes in a declaration shall not specify an
    alignment that is less strict than the alignment that would otherwise be required for the
    type of the object or member being declared.
    Semantics
5   The first form is equivalent to _Alignas(alignof(type-name)).
6   The alignment requirement of the declared object or member is taken to be the specified
    alignment. An alignment specification of zero has no effect.141) When multiple
    alignment specifiers occur in a declaration, the effective alignment requirement is the
    strictest specified alignment.
7   If the definition of an object has an alignment specifier, any other declaration of that
    object shall either specify equivalent alignment or have no alignment specifier. If the
    definition of an object does not have an alignment specifier, any other declaration of that
    object shall also have no alignment specifier. If declarations of an object in different
    translation units have different alignment specifiers, the behavior is undefined.



    141) An alignment specification of zero also does not affect other alignment specifications in the same
         declaration.

[page 126]

    6.7.6 Declarators
    Syntax
1            declarator:
                    pointeropt direct-declarator
             direct-declarator:
                     identifier
                     ( declarator )
                     direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
                     direct-declarator [ static type-qualifier-listopt assignment-expression ]
                     direct-declarator [ type-qualifier-list static assignment-expression ]
                     direct-declarator [ type-qualifier-listopt * ]
                     direct-declarator ( parameter-type-list )
                     direct-declarator ( identifier-listopt )
             pointer:
                    * type-qualifier-listopt
                    * type-qualifier-listopt pointer
             type-qualifier-list:
                    type-qualifier
                    type-qualifier-list type-qualifier
             parameter-type-list:
                   parameter-list
                   parameter-list , ...
             parameter-list:
                   parameter-declaration
                   parameter-list , parameter-declaration
             parameter-declaration:
                   declaration-specifiers declarator
                   declaration-specifiers abstract-declaratoropt
             identifier-list:
                    identifier
                    identifier-list , identifier
    Semantics
2   Each declarator declares one identifier, and asserts that when an operand of the same
    form as the declarator appears in an expression, it designates a function or object with the
    scope, storage duration, and type indicated by the declaration specifiers.
3   A full declarator is a declarator that is not part of another declarator. The end of a full
    declarator is a sequence point. If, in the nested sequence of declarators in a full
[page 127]

    declarator, there is a declarator specifying a variable length array type, the type specified
    by the full declarator is said to be variably modified. Furthermore, any type derived by
    declarator type derivation from a variably modified type is itself variably modified.
4   In the following subclauses, consider a declaration
            T D1
    where T contains the declaration specifiers that specify a type T (such as int) and D1 is
    a declarator that contains an identifier ident. The type specified for the identifier ident in
    the various forms of declarator is described inductively using this notation.
5   If, in the declaration ''T D1'', D1 has the form
            identifier
    then the type specified for ident is T .
6   If, in the declaration ''T D1'', D1 has the form
            ( D )
    then ident has the type specified by the declaration ''T D''. Thus, a declarator in
    parentheses is identical to the unparenthesized declarator, but the binding of complicated
    declarators may be altered by parentheses.
    Implementation limits
7   As discussed in 5.2.4.1, an implementation may limit the number of pointer, array, and
    function declarators that modify an arithmetic, structure, union, or void type, either
    directly or via one or more typedefs.
    Forward references: array declarators (6.7.6.2), type definitions (6.7.8).
    6.7.6.1 Pointer declarators
    Semantics
1   If, in the declaration ''T D1'', D1 has the form
            * type-qualifier-listopt D
    and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
    T '', then the type specified for ident is ''derived-declarator-type-list type-qualifier-list
    pointer to T ''. For each type qualifier in the list, ident is a so-qualified pointer.
2   For two pointer types to be compatible, both shall be identically qualified and both shall
    be pointers to compatible types.
3   EXAMPLE The following pair of declarations demonstrates the difference between a ''variable pointer
    to a constant value'' and a ''constant pointer to a variable value''.




[page 128]

             const int *ptr_to_constant;
             int *const constant_ptr;
    The contents of any object pointed to by ptr_to_constant shall not be modified through that pointer,
    but ptr_to_constant itself may be changed to point to another object. Similarly, the contents of the
    int pointed to by constant_ptr may be modified, but constant_ptr itself shall always point to the
    same location.
4   The declaration of the constant pointer constant_ptr may be clarified by including a definition for the
    type ''pointer to int''.
             typedef int *int_ptr;
             const int_ptr constant_ptr;
    declares constant_ptr as an object that has type ''const-qualified pointer to int''.

    6.7.6.2 Array declarators
    Constraints
1   In addition to optional type qualifiers and the keyword static, the [ and ] may delimit
    an expression or *. If they delimit an expression (which specifies the size of an array), the
    expression shall have an integer type. If the expression is a constant expression, it shall
    have a value greater than zero. The element type shall not be an incomplete or function
    type. The optional type qualifiers and the keyword static shall appear only in a
    declaration of a function parameter with an array type, and then only in the outermost
    array type derivation.
2   If an identifier is declared as having a variably modified type, it shall be an ordinary
    identifier (as defined in 6.2.3), have no linkage, and have either block scope or function
    prototype scope. If an identifier is declared to be an object with static or thread storage
    duration, it shall not have a variable length array type.
    Semantics
3   If, in the declaration ''T D1'', D1 has one of the forms:
             D[ type-qualifier-listopt assignment-expressionopt ]
             D[ static type-qualifier-listopt assignment-expression ]
             D[ type-qualifier-list static assignment-expression ]
             D[ type-qualifier-listopt * ]
    and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
    T '', then the type specified for ident is ''derived-declarator-type-list array of T ''.142)
    (See 6.7.6.3 for the meaning of the optional type qualifiers and the keyword static.)
4   If the size is not present, the array type is an incomplete type. If the size is * instead of
    being an expression, the array type is a variable length array type of unspecified size,
    which can only be used in declarations or type names with function prototype scope;143)

    142) When several ''array of'' specifications are adjacent, a multidimensional array is declared.

[page 129]

    such arrays are nonetheless complete types. If the size is an integer constant expression
    and the element type has a known constant size, the array type is not a variable length
    array type; otherwise, the array type is a variable length array type. (Variable length
    arrays are a conditional feature that implementations need not support; see 6.10.8.3.)
5   If the size is an expression that is not an integer constant expression: if it occurs in a
    declaration at function prototype scope, it is treated as if it were replaced by *; otherwise,
    each time it is evaluated it shall have a value greater than zero. The size of each instance
    of a variable length array type does not change during its lifetime. Where a size
    expression is part of the operand of a sizeof operator and changing the value of the
    size expression would not affect the result of the operator, it is unspecified whether or not
    the size expression is evaluated.
6   For two array types to be compatible, both shall have compatible element types, and if
    both size specifiers are present, and are integer constant expressions, then both size
    specifiers shall have the same constant value. If the two array types are used in a context
    which requires them to be compatible, it is undefined behavior if the two size specifiers
    evaluate to unequal values.
7   EXAMPLE 1
             float fa[11], *afp[17];
    declares an array of float numbers and an array of pointers to float numbers.

8   EXAMPLE 2       Note the distinction between the declarations
             extern int *x;
             extern int y[];
    The first declares x to be a pointer to int; the second declares y to be an array of int of unspecified size
    (an incomplete type), the storage for which is defined elsewhere.

9   EXAMPLE 3       The following declarations demonstrate the compatibility rules for variably modified types.
             extern int n;
             extern int m;
             void fcompat(void)
             {
                   int a[n][6][m];
                   int (*p)[4][n+1];
                   int c[n][n][6][m];
                   int (*r)[n][n][n+1];
                   p = a;       // invalid: not compatible because 4 != 6
                   r = c;       // compatible, but defined behavior only if
                                // n == 6 and m == n+1
             }




    143) Thus, * can be used only in function declarations that are not definitions (see 6.7.6.3).

[page 130]

10   EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
     function prototype scope. Array objects declared with the _Thread_local, static, or extern
     storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
     the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
     identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
     structures or unions.
             extern int n;
             int A[n];                                           // invalid: file scope VLA
             extern int (*p2)[n];                                // invalid: file scope VM
             int B[100];                                         // valid: file scope but not VM
             void fvla(int m, int C[m][m]);                      // valid: VLA with prototype scope
             void fvla(int m, int C[m][m])                       // valid: adjusted to auto pointer to VLA
             {
                   typedef int VLA[m][m];                        // valid: block scope typedef VLA
                      struct tag {
                            int (*y)[n];                         // invalid: y not ordinary identifier
                            int z[n];                            // invalid: z not ordinary identifier
                      };
                      int D[m];                                  //   valid: auto VLA
                      static int E[m];                           //   invalid: static block scope VLA
                      extern int F[m];                           //   invalid: F has linkage and is VLA
                      int (*s)[m];                               //   valid: auto pointer to VLA
                      extern int (*r)[m];                        //   invalid: r has linkage and points to VLA
                      static int (*q)[m] = &B;                   //   valid: q is a static block pointer to VLA
             }

     Forward references:          function declarators (6.7.6.3), function definitions (6.9.1),
     initialization (6.7.9).
     6.7.6.3 Function declarators (including prototypes)
     Constraints
1    A function declarator shall not specify a return type that is a function type or an array
     type.
2    The only storage-class specifier that shall occur in a parameter declaration is register.
3    An identifier list in a function declarator that is not part of a definition of that function
     shall be empty.
4    After adjustment, the parameters in a parameter type list in a function declarator that is
     part of a definition of that function shall not have incomplete type.
     Semantics
5    If, in the declaration ''T D1'', D1 has the form




[page 131]

            D( parameter-type-list )
     or
            D( identifier-listopt )
     and the type specified for ident in the declaration ''T D'' is ''derived-declarator-type-list
     T '', then the type specified for ident is ''derived-declarator-type-list function returning
     T ''.
6    A parameter type list specifies the types of, and may declare identifiers for, the
     parameters of the function.
7    A declaration of a parameter as ''array of type'' shall be adjusted to ''qualified pointer to
     type'', where the type qualifiers (if any) are those specified within the [ and ] of the
     array type derivation. If the keyword static also appears within the [ and ] of the
     array type derivation, then for each call to the function, the value of the corresponding
     actual argument shall provide access to the first element of an array with at least as many
     elements as specified by the size expression.
8    A declaration of a parameter as ''function returning type'' shall be adjusted to ''pointer to
     function returning type'', as in 6.3.2.1.
9    If the list terminates with an ellipsis (, ...), no information about the number or types
     of the parameters after the comma is supplied.144)
10   The special case of an unnamed parameter of type void as the only item in the list
     specifies that the function has no parameters.
11   If, in a parameter declaration, an identifier can be treated either as a typedef name or as a
     parameter name, it shall be taken as a typedef name.
12   If the function declarator is not part of a definition of that function, parameters may have
     incomplete type and may use the [*] notation in their sequences of declarator specifiers
     to specify variable length array types.
13   The storage-class specifier in the declaration specifiers for a parameter declaration, if
     present, is ignored unless the declared parameter is one of the members of the parameter
     type list for a function definition.
14   An identifier list declares only the identifiers of the parameters of the function. An empty
     list in a function declarator that is part of a definition of that function specifies that the
     function has no parameters. The empty list in a function declarator that is not part of a
     definition of that function specifies that no information about the number or types of the
     parameters is supplied.145)



     144) The macros defined in the <stdarg.h> header (7.16) may be used to access arguments that
          correspond to the ellipsis.

[page 132]

15   For two function types to be compatible, both shall specify compatible return types.146)
     Moreover, the parameter type lists, if both are present, shall agree in the number of
     parameters and in use of the ellipsis terminator; corresponding parameters shall have
     compatible types. If one type has a parameter type list and the other type is specified by a
     function declarator that is not part of a function definition and that contains an empty
     identifier list, the parameter list shall not have an ellipsis terminator and the type of each
     parameter shall be compatible with the type that results from the application of the
     default argument promotions. If one type has a parameter type list and the other type is
     specified by a function definition that contains a (possibly empty) identifier list, both shall
     agree in the number of parameters, and the type of each prototype parameter shall be
     compatible with the type that results from the application of the default argument
     promotions to the type of the corresponding identifier. (In the determination of type
     compatibility and of a composite type, each parameter declared with function or array
     type is taken as having the adjusted type and each parameter declared with qualified type
     is taken as having the unqualified version of its declared type.)
16   EXAMPLE 1       The declaration
              int f(void), *fip(), (*pfi)();
     declares a function f with no parameters returning an int, a function fip with no parameter specification
     returning a pointer to an int, and a pointer pfi to a function with no parameter specification returning an
     int. It is especially useful to compare the last two. The binding of *fip() is *(fip()), so that the
     declaration suggests, and the same construction in an expression requires, the calling of a function fip,
     and then using indirection through the pointer result to yield an int. In the declarator (*pfi)(), the
     extra parentheses are necessary to indicate that indirection through a pointer to a function yields a function
     designator, which is then used to call the function; it returns an int.
17   If the declaration occurs outside of any function, the identifiers have file scope and external linkage. If the
     declaration occurs inside a function, the identifiers of the functions f and fip have block scope and either
     internal or external linkage (depending on what file scope declarations for these identifiers are visible), and
     the identifier of the pointer pfi has block scope and no linkage.

18   EXAMPLE 2       The declaration
              int (*apfi[3])(int *x, int *y);
     declares an array apfi of three pointers to functions returning int. Each of these functions has two
     parameters that are pointers to int. The identifiers x and y are declared for descriptive purposes only and
     go out of scope at the end of the declaration of apfi.

19   EXAMPLE 3       The declaration
              int (*fpfi(int (*)(long), int))(int, ...);
     declares a function fpfi that returns a pointer to a function returning an int. The function fpfi has two
     parameters: a pointer to a function returning an int (with one parameter of type long int), and an int.
     The pointer returned by fpfi points to a function that has one int parameter and accepts zero or more


     145) See ''future language directions'' (6.11.6).
     146) If both function types are ''old style'', parameter types are not compared.

[page 133]

     additional arguments of any type.

20   EXAMPLE 4        The following prototype has a variably modified parameter.
               void addscalar(int n, int m,
                     double a[n][n*m+300], double x);
               int main()
               {
                     double b[4][308];
                     addscalar(4, 2, b, 2.17);
                     return 0;
               }
               void addscalar(int n, int m,
                     double a[n][n*m+300], double x)
               {
                     for (int i = 0; i < n; i++)
                           for (int j = 0, k = n*m+300; j < k; j++)
                                 // a is a pointer to a VLA with n*m+300 elements
                                 a[i][j] += x;
               }

21   EXAMPLE 5        The following are all compatible function prototype declarators.
               double    maximum(int       n,   int   m,   double   a[n][m]);
               double    maximum(int       n,   int   m,   double   a[*][*]);
               double    maximum(int       n,   int   m,   double   a[ ][*]);
               double    maximum(int       n,   int   m,   double   a[ ][m]);
     as are:
               void   f(double     (* restrict a)[5]);
               void   f(double     a[restrict][5]);
               void   f(double     a[restrict 3][5]);
               void   f(double     a[restrict static 3][5]);
     (Note that the last declaration also specifies that the argument corresponding to a in any call to f must be a
     non-null pointer to the first of at least three arrays of 5 doubles, which the others do not.)

     Forward references: function definitions (6.9.1), type names (6.7.7).




[page 134]

    6.7.7 Type names
    Syntax
1            type-name:
                    specifier-qualifier-list abstract-declaratoropt
             abstract-declarator:
                    pointer
                    pointeropt direct-abstract-declarator
             direct-abstract-declarator:
                     ( abstract-declarator )
                     direct-abstract-declaratoropt [ type-qualifier-listopt
                                    assignment-expressionopt ]
                     direct-abstract-declaratoropt [ static type-qualifier-listopt
                                    assignment-expression ]
                     direct-abstract-declaratoropt [ type-qualifier-list static
                                    assignment-expression ]
                     direct-abstract-declaratoropt [ * ]
                     direct-abstract-declaratoropt ( parameter-type-listopt )
    Semantics
2   In several contexts, it is necessary to specify a type. This is accomplished using a type
    name, which is syntactically a declaration for a function or an object of that type that
    omits the identifier.147)
3   EXAMPLE        The constructions
             (a)      int
             (b)      int   *
             (c)      int   *[3]
             (d)      int   (*)[3]
             (e)      int   (*)[*]
             (f)      int   *()
             (g)      int   (*)(void)
             (h)      int   (*const [])(unsigned int, ...)
    name respectively the types (a) int, (b) pointer to int, (c) array of three pointers to int, (d) pointer to an
    array of three ints, (e) pointer to a variable length array of an unspecified number of ints, (f) function
    with no parameter specification returning a pointer to int, (g) pointer to function with no parameters
    returning an int, and (h) array of an unspecified number of constant pointers to functions, each with one
    parameter that has type unsigned int and an unspecified number of other parameters, returning an
    int.




    147) As indicated by the syntax, empty parentheses in a type name are interpreted as ''function with no
         parameter specification'', rather than redundant parentheses around the omitted identifier.

[page 135]

    6.7.8 Type definitions
    Syntax
1            typedef-name:
                    identifier
    Constraints
2   If a typedef name specifies a variably modified type then it shall have block scope.
    Semantics
3   In a declaration whose storage-class specifier is typedef, each declarator defines an
    identifier to be a typedef name that denotes the type specified for the identifier in the way
    described in 6.7.6. Any array size expressions associated with variable length array
    declarators are evaluated each time the declaration of the typedef name is reached in the
    order of execution. A typedef declaration does not introduce a new type, only a
    synonym for the type so specified. That is, in the following declarations:
             typedef T type_ident;
             type_ident D;
    type_ident is defined as a typedef name with the type specified by the declaration
    specifiers in T (known as T ), and the identifier in D has the type ''derived-declarator-
    type-list T '' where the derived-declarator-type-list is specified by the declarators of D. A
    typedef name shares the same name space as other identifiers declared in ordinary
    declarators.
4   EXAMPLE 1       After
             typedef int MILES, KLICKSP();
             typedef struct { double hi, lo; } range;
    the constructions
             MILES distance;
             extern KLICKSP *metricp;
             range x;
             range z, *zp;
    are all valid declarations. The type of distance is int, that of metricp is ''pointer to function with no
    parameter specification returning int'', and that of x and z is the specified structure; zp is a pointer to
    such a structure. The object distance has a type compatible with any other int object.

5   EXAMPLE 2       After the declarations
             typedef struct s1 { int x; } t1, *tp1;
             typedef struct s2 { int x; } t2, *tp2;
    type t1 and the type pointed to by tp1 are compatible. Type t1 is also compatible with type struct
    s1, but not compatible with the types struct s2, t2, the type pointed to by tp2, or int.




[page 136]

6   EXAMPLE 3       The following obscure constructions
             typedef signed int t;
             typedef int plain;
             struct tag {
                   unsigned t:4;
                   const t:5;
                   plain r:5;
             };
    declare a typedef name t with type signed int, a typedef name plain with type int, and a structure
    with three bit-field members, one named t that contains values in the range [0, 15], an unnamed const-
    qualified bit-field which (if it could be accessed) would contain values in either the range [-15, +15] or
    [-16, +15], and one named r that contains values in one of the ranges [0, 31], [-15, +15], or [-16, +15].
    (The choice of range is implementation-defined.) The first two bit-field declarations differ in that
    unsigned is a type specifier (which forces t to be the name of a structure member), while const is a
    type qualifier (which modifies t which is still visible as a typedef name). If these declarations are followed
    in an inner scope by
             t f(t (t));
             long t;
    then a function f is declared with type ''function returning signed int with one unnamed parameter
    with type pointer to function returning signed int with one unnamed parameter with type signed
    int'', and an identifier t with type long int.

7   EXAMPLE 4 On the other hand, typedef names can be used to improve code readability. All three of the
    following declarations of the signal function specify exactly the same type, the first without making use
    of any typedef names.
             typedef void fv(int), (*pfv)(int);
             void (*signal(int, void (*)(int)))(int);
             fv *signal(int, fv *);
             pfv signal(int, pfv);

8   EXAMPLE 5 If a typedef name denotes a variable length array type, the length of the array is fixed at the
    time the typedef name is defined, not each time it is used:
             void copyt(int n)
             {
                   typedef int B[n];   //               B is n ints, n evaluated now
                   n += 1;
                   B a;                //               a is n ints, n without += 1
                   int b[n];           //               a and b are different sizes
                   for (int i = 1; i < n;               i++)
                         a[i-1] = b[i];
             }




[page 137]

    6.7.9 Initialization
    Syntax
1            initializer:
                      assignment-expression
                      { initializer-list }
                      { initializer-list , }
             initializer-list:
                      designationopt initializer
                      initializer-list , designationopt initializer
             designation:
                    designator-list =
             designator-list:
                    designator
                    designator-list designator
             designator:
                    [ constant-expression ]
                    . identifier
    Constraints
2   No initializer shall attempt to provide a value for an object not contained within the entity
    being initialized.
3   The type of the entity to be initialized shall be an array of unknown size or a complete
    object type that is not a variable length array type.
4   All the expressions in an initializer for an object that has static or thread storage duration
    shall be constant expressions or string literals.
5   If the declaration of an identifier has block scope, and the identifier has external or
    internal linkage, the declaration shall have no initializer for the identifier.
6   If a designator has the form
             [ constant-expression ]
    then the current object (defined below) shall have array type and the expression shall be
    an integer constant expression. If the array is of unknown size, any nonnegative value is
    valid.
7   If a designator has the form
             . identifier
    then the current object (defined below) shall have structure or union type and the
    identifier shall be the name of a member of that type.
[page 138]

     Semantics
8    An initializer specifies the initial value stored in an object.
9    Except where explicitly stated otherwise, for the purposes of this subclause unnamed
     members of objects of structure and union type do not participate in initialization.
     Unnamed members of structure objects have indeterminate value even after initialization.
10   If an object that has automatic storage duration is not initialized explicitly, its value is
     indeterminate. If an object that has static or thread storage duration is not initialized
     explicitly, then:
     -- if it has pointer type, it is initialized to a null pointer;
     -- if it has arithmetic type, it is initialized to (positive or unsigned) zero;
     -- if it is an aggregate, every member is initialized (recursively) according to these rules,
       and any padding is initialized to zero bits;
     -- if it is a union, the first named member is initialized (recursively) according to these
       rules, and any padding is initialized to zero bits;
11   The initializer for a scalar shall be a single expression, optionally enclosed in braces. The
     initial value of the object is that of the expression (after conversion); the same type
     constraints and conversions as for simple assignment apply, taking the type of the scalar
     to be the unqualified version of its declared type.
12   The rest of this subclause deals with initializers for objects that have aggregate or union
     type.
13   The initializer for a structure or union object that has automatic storage duration shall be
     either an initializer list as described below, or a single expression that has compatible
     structure or union type. In the latter case, the initial value of the object, including
     unnamed members, is that of the expression.
14   An array of character type may be initialized by a character string literal or UTF-8 string
     literal, optionally enclosed in braces. Successive bytes of the string literal (including the
     terminating null character if there is room or if the array is of unknown size) initialize the
     elements of the array.
15   An array with element type compatible with a qualified or unqualified version of
     wchar_t may be initialized by a wide string literal, optionally enclosed in braces.
     Successive wide characters of the wide string literal (including the terminating null wide
     character if there is room or if the array is of unknown size) initialize the elements of the
     array.
16   Otherwise, the initializer for an object that has aggregate or union type shall be a brace-
     enclosed list of initializers for the elements or named members.


[page 139]

17   Each brace-enclosed initializer list has an associated current object. When no
     designations are present, subobjects of the current object are initialized in order according
     to the type of the current object: array elements in increasing subscript order, structure
     members in declaration order, and the first named member of a union.148) In contrast, a
     designation causes the following initializer to begin initialization of the subobject
     described by the designator. Initialization then continues forward in order, beginning
     with the next subobject after that described by the designator.149)
18   Each designator list begins its description with the current object associated with the
     closest surrounding brace pair. Each item in the designator list (in order) specifies a
     particular member of its current object and changes the current object for the next
     designator (if any) to be that member.150) The current object that results at the end of the
     designator list is the subobject to be initialized by the following initializer.
19   The initialization shall occur in initializer list order, each initializer provided for a
     particular subobject overriding any previously listed initializer for the same subobject;151)
     all subobjects that are not initialized explicitly shall be initialized implicitly the same as
     objects that have static storage duration.
20   If the aggregate or union contains elements or members that are aggregates or unions,
     these rules apply recursively to the subaggregates or contained unions. If the initializer of
     a subaggregate or contained union begins with a left brace, the initializers enclosed by
     that brace and its matching right brace initialize the elements or members of the
     subaggregate or the contained union. Otherwise, only enough initializers from the list are
     taken to account for the elements or members of the subaggregate or the first member of
     the contained union; any remaining initializers are left to initialize the next element or
     member of the aggregate of which the current subaggregate or contained union is a part.
21   If there are fewer initializers in a brace-enclosed list than there are elements or members
     of an aggregate, or fewer characters in a string literal used to initialize an array of known
     size than there are elements in the array, the remainder of the aggregate shall be
     initialized implicitly the same as objects that have static storage duration.



     148) If the initializer list for a subaggregate or contained union does not begin with a left brace, its
          subobjects are initialized as usual, but the subaggregate or contained union does not become the
          current object: current objects are associated only with brace-enclosed initializer lists.
     149) After a union member is initialized, the next object is not the next member of the union; instead, it is
          the next subobject of an object containing the union.
     150) Thus, a designator can only specify a strict subobject of the aggregate or union that is associated with
          the surrounding brace pair. Note, too, that each separate designator list is independent.
     151) Any initializer for the subobject which is overridden and so not used to initialize that subobject might
          not be evaluated at all.

[page 140]

22   If an array of unknown size is initialized, its size is determined by the largest indexed
     element with an explicit initializer. The array type is completed at the end of its
     initializer list.
23   The evaluations of the initialization list expressions are indeterminately sequenced with
     respect to one another and thus the order in which any side effects occur is
     unspecified.152)
24   EXAMPLE 1       Provided that <complex.h> has been #included, the declarations
              int i = 3.5;
              double complex c = 5 + 3 * I;
     define and initialize i with the value 3 and c with the value 5.0 + i3.0.

25   EXAMPLE 2       The declaration
              int x[] = { 1, 3, 5 };
     defines and initializes x as a one-dimensional array object that has three elements, as no size was specified
     and there are three initializers.

26   EXAMPLE 3       The declaration
              int y[4][3] =         {
                    { 1, 3,         5 },
                    { 2, 4,         6 },
                    { 3, 5,         7 },
              };
     is a definition with a fully bracketed initialization: 1, 3, and 5 initialize the first row of y (the array object
     y[0]), namely y[0][0], y[0][1], and y[0][2]. Likewise the next two lines initialize y[1] and
     y[2]. The initializer ends early, so y[3] is initialized with zeros. Precisely the same effect could have
     been achieved by
              int y[4][3] = {
                    1, 3, 5, 2, 4, 6, 3, 5, 7
              };
     The initializer for y[0] does not begin with a left brace, so three items from the list are used. Likewise the
     next three are taken successively for y[1] and y[2].

27   EXAMPLE 4       The declaration
              int z[4][3] = {
                    { 1 }, { 2 }, { 3 }, { 4 }
              };
     initializes the first column of z as specified and initializes the rest with zeros.

28   EXAMPLE 5       The declaration
              struct { int a[3], b; } w[] = { { 1 }, 2 };
     is a definition with an inconsistently bracketed initialization. It defines an array with two element



     152) In particular, the evaluation order need not be the same as the order of subobject initialization.

[page 141]

     structures: w[0].a[0] is 1 and w[1].a[0] is 2; all the other elements are zero.

29   EXAMPLE 6         The declaration
               short q[4][3][2] = {
                     { 1 },
                     { 2, 3 },
                     { 4, 5, 6 }
               };
     contains an incompletely but consistently bracketed initialization. It defines a three-dimensional array
     object: q[0][0][0] is 1, q[1][0][0] is 2, q[1][0][1] is 3, and 4, 5, and 6 initialize
     q[2][0][0], q[2][0][1], and q[2][1][0], respectively; all the rest are zero. The initializer for
     q[0][0] does not begin with a left brace, so up to six items from the current list may be used. There is
     only one, so the values for the remaining five elements are initialized with zero. Likewise, the initializers
     for q[1][0] and q[2][0] do not begin with a left brace, so each uses up to six items, initializing their
     respective two-dimensional subaggregates. If there had been more than six items in any of the lists, a
     diagnostic message would have been issued. The same initialization result could have been achieved by:
               short q[4][3][2] = {
                     1, 0, 0, 0, 0, 0,
                     2, 3, 0, 0, 0, 0,
                     4, 5, 6
               };
     or by:
               short q[4][3][2] = {
                     {
                           { 1 },
                     },
                     {
                           { 2, 3 },
                     },
                     {
                           { 4, 5 },
                           { 6 },
                     }
               };
     in a fully bracketed form.
30   Note that the fully bracketed and minimally bracketed forms of initialization are, in general, less likely to
     cause confusion.

31   EXAMPLE 7         One form of initialization that completes array types involves typedef names. Given the
     declaration
               typedef int A[];          // OK - declared with block scope
     the declaration
               A a = { 1, 2 }, b = { 3, 4, 5 };
     is identical to
               int a[] = { 1, 2 }, b[] = { 3, 4, 5 };
     due to the rules for incomplete types.

[page 142]

32   EXAMPLE 8       The declaration
              char s[] = "abc", t[3] = "abc";
     defines ''plain'' char array objects s and t whose elements are initialized with character string literals.
     This declaration is identical to
              char s[] = { 'a', 'b', 'c', '\0' },
                   t[] = { 'a', 'b', 'c' };
     The contents of the arrays are modifiable. On the other hand, the declaration
              char *p = "abc";
     defines p with type ''pointer to char'' and initializes it to point to an object with type ''array of char''
     with length 4 whose elements are initialized with a character string literal. If an attempt is made to use p to
     modify the contents of the array, the behavior is undefined.

33   EXAMPLE 9       Arrays can be initialized to correspond to the elements of an enumeration by using
     designators:
              enum { member_one,           member_two };
              const char *nm[] =           {
                    [member_two]           = "member two",
                    [member_one]           = "member one",
              };

34   EXAMPLE 10       Structure members can be initialized to nonzero values without depending on their order:
              div_t answer = { .quot = 2, .rem = -1 };

35   EXAMPLE 11 Designators can be used to provide explicit initialization when unadorned initializer lists
     might be misunderstood:
              struct { int a[3], b; } w[] =
                    { [0].a = {1}, [1].a[0] = 2 };

36   EXAMPLE 12       Space can be ''allocated'' from both ends of an array by using a single designator:
              int a[MAX] = {
                    1, 3, 5, 7, 9, [MAX-5] = 8, 6, 4, 2, 0
              };
37   In the above, if MAX is greater than ten, there will be some zero-valued elements in the middle; if it is less
     than ten, some of the values provided by the first five initializers will be overridden by the second five.

38   EXAMPLE 13       Any member of a union can be initialized:
              union { /* ... */ } u = { .any_member = 42 };

     Forward references: common definitions <stddef.h> (7.19).




[page 143]

    6.7.10 Static assertions
    Syntax
1            static_assert-declaration:
                     _Static_assert ( constant-expression , string-literal ) ;
    Constraints
2   The constant expression shall compare unequal to 0.
    Semantics
3   The constant expression shall be an integer constant expression. If the value of the
    constant expression compares unequal to 0, the declaration has no effect. Otherwise, the
    constraint is violated and the implementation shall produce a diagnostic message that
    includes the text of the string literal, except that characters not in the basic source
    character set are not required to appear in the message.
    Forward references: diagnostics (7.2).




[page 144]

    6.8 Statements and blocks
    Syntax
1            statement:
                    labeled-statement
                    compound-statement
                    expression-statement
                    selection-statement
                    iteration-statement
                    jump-statement
    Semantics
2   A statement specifies an action to be performed. Except as indicated, statements are
    executed in sequence.
3   A block allows a set of declarations and statements to be grouped into one syntactic unit.
    The initializers of objects that have automatic storage duration, and the variable length
    array declarators of ordinary identifiers with block scope, are evaluated and the values are
    stored in the objects (including storing an indeterminate value in objects without an
    initializer) each time the declaration is reached in the order of execution, as if it were a
    statement, and within each declaration in the order that declarators appear.
4   A full expression is an expression that is not part of another expression or of a declarator.
    Each of the following is a full expression: an initializer that is not part of a compound
    literal; the expression in an expression statement; the controlling expression of a selection
    statement (if or switch); the controlling expression of a while or do statement; each
    of the (optional) expressions of a for statement; the (optional) expression in a return
    statement. There is a sequence point between the evaluation of a full expression and the
    evaluation of the next full expression to be evaluated.
    Forward references: expression and null statements (6.8.3), selection statements
    (6.8.4), iteration statements (6.8.5), the return statement (6.8.6.4).
    6.8.1 Labeled statements
    Syntax
1            labeled-statement:
                    identifier : statement
                    case constant-expression : statement
                    default : statement
    Constraints
2   A case or default label shall appear only in a switch statement. Further
    constraints on such labels are discussed under the switch statement.

[page 145]

3   Label names shall be unique within a function.
    Semantics
4   Any statement may be preceded by a prefix that declares an identifier as a label name.
    Labels in themselves do not alter the flow of control, which continues unimpeded across
    them.
    Forward references: the goto statement (6.8.6.1), the switch statement (6.8.4.2).
    6.8.2 Compound statement
    Syntax
1            compound-statement:
                   { block-item-listopt }
             block-item-list:
                     block-item
                     block-item-list block-item
             block-item:
                     declaration
                     statement
    Semantics
2   A compound statement is a block.
    6.8.3 Expression and null statements
    Syntax
1            expression-statement:
                    expressionopt ;
    Semantics
2   The expression in an expression statement is evaluated as a void expression for its side
    effects.153)
3   A null statement (consisting of just a semicolon) performs no operations.
4   EXAMPLE 1 If a function call is evaluated as an expression statement for its side effects only, the
    discarding of its value may be made explicit by converting the expression to a void expression by means of
    a cast:
             int p(int);
             /* ... */
             (void)p(0);



    153) Such as assignments, and function calls which have side effects.

[page 146]

5   EXAMPLE 2       In the program fragment
             char *s;
             /* ... */
             while (*s++ != '\0')
                     ;
    a null statement is used to supply an empty loop body to the iteration statement.

6   EXAMPLE 3       A null statement may also be used to carry a label just before the closing } of a compound
    statement.
             while (loop1) {
                   /* ... */
                   while (loop2) {
                           /* ... */
                           if (want_out)
                                   goto end_loop1;
                           /* ... */
                   }
                   /* ... */
             end_loop1: ;
             }

    Forward references: iteration statements (6.8.5).
    6.8.4 Selection statements
    Syntax
1            selection-statement:
                     if ( expression ) statement
                     if ( expression ) statement else statement
                     switch ( expression ) statement
    Semantics
2   A selection statement selects among a set of statements depending on the value of a
    controlling expression.
3   A selection statement is a block whose scope is a strict subset of the scope of its
    enclosing block. Each associated substatement is also a block whose scope is a strict
    subset of the scope of the selection statement.
    6.8.4.1 The if statement
    Constraints
1   The controlling expression of an if statement shall have scalar type.
    Semantics
2   In both forms, the first substatement is executed if the expression compares unequal to 0.
    In the else form, the second substatement is executed if the expression compares equal


[page 147]

    to 0. If the first substatement is reached via a label, the second substatement is not
    executed.
3   An else is associated with the lexically nearest preceding if that is allowed by the
    syntax.
    6.8.4.2 The switch statement
    Constraints
1   The controlling expression of a switch statement shall have integer type.
2   If a switch statement has an associated case or default label within the scope of an
    identifier with a variably modified type, the entire switch statement shall be within the
    scope of that identifier.154)
3   The expression of each case label shall be an integer constant expression and no two of
    the case constant expressions in the same switch statement shall have the same value
    after conversion. There may be at most one default label in a switch statement.
    (Any enclosed switch statement may have a default label or case constant
    expressions with values that duplicate case constant expressions in the enclosing
    switch statement.)
    Semantics
4   A switch statement causes control to jump to, into, or past the statement that is the
    switch body, depending on the value of a controlling expression, and on the presence of a
    default label and the values of any case labels on or in the switch body. A case or
    default label is accessible only within the closest enclosing switch statement.
5   The integer promotions are performed on the controlling expression. The constant
    expression in each case label is converted to the promoted type of the controlling
    expression. If a converted value matches that of the promoted controlling expression,
    control jumps to the statement following the matched case label. Otherwise, if there is
    a default label, control jumps to the labeled statement. If no converted case constant
    expression matches and there is no default label, no part of the switch body is
    executed.
    Implementation limits
6   As discussed in 5.2.4.1, the implementation may limit the number of case values in a
    switch statement.




    154) That is, the declaration either precedes the switch statement, or it follows the last case or
         default label associated with the switch that is in the block containing the declaration.

[page 148]

7   EXAMPLE        In the artificial program fragment
             switch (expr)
             {
                   int i = 4;
                   f(i);
             case 0:
                   i = 17;
                   /* falls through into default code */
             default:
                   printf("%d\n", i);
             }
    the object whose identifier is i exists with automatic storage duration (within the block) but is never
    initialized, and thus if the controlling expression has a nonzero value, the call to the printf function will
    access an indeterminate value. Similarly, the call to the function f cannot be reached.

    6.8.5 Iteration statements
    Syntax
1            iteration-statement:
                     while ( expression ) statement
                     do statement while ( expression ) ;
                     for ( expressionopt ; expressionopt ; expressionopt ) statement
                     for ( declaration expressionopt ; expressionopt ) statement
    Constraints
2   The controlling expression of an iteration statement shall have scalar type.
3   The declaration part of a for statement shall only declare identifiers for objects having
    storage class auto or register.
    Semantics
4   An iteration statement causes a statement called the loop body to be executed repeatedly
    until the controlling expression compares equal to 0. The repetition occurs regardless of
    whether the loop body is entered from the iteration statement or by a jump.155)
5   An iteration statement is a block whose scope is a strict subset of the scope of its
    enclosing block. The loop body is also a block whose scope is a strict subset of the scope
    of the iteration statement.
6   An iteration statement whose controlling expression is not a constant expression,156) that
    performs no input/output operations, does not access volatile objects, and performs no
    synchronization or atomic operations in its body, controlling expression, or (in the case of

    155) Code jumped over is not executed. In particular, the controlling expression of a for or while
         statement is not evaluated before entering the loop body, nor is clause-1 of a for statement.
    156) An omitted controlling expression is replaced by a nonzero constant, which is a constant expression.

[page 149]

    a for statement) its expression-3, may be assumed by the implementation to
    terminate.157)
    6.8.5.1 The while statement
1   The evaluation of the controlling expression takes place before each execution of the loop
    body.
    6.8.5.2 The do statement
1   The evaluation of the controlling expression takes place after each execution of the loop
    body.
    6.8.5.3 The for statement
1   The statement
             for ( clause-1 ; expression-2 ; expression-3 ) statement
    behaves as follows: The expression expression-2 is the controlling expression that is
    evaluated before each execution of the loop body. The expression expression-3 is
    evaluated as a void expression after each execution of the loop body. If clause-1 is a
    declaration, the scope of any identifiers it declares is the remainder of the declaration and
    the entire loop, including the other two expressions; it is reached in the order of execution
    before the first evaluation of the controlling expression. If clause-1 is an expression, it is
    evaluated as a void expression before the first evaluation of the controlling expression.158)
2   Both clause-1 and expression-3 can be omitted. An omitted expression-2 is replaced by a
    nonzero constant.
    6.8.6 Jump statements
    Syntax
1            jump-statement:
                    goto identifier ;
                    continue ;
                    break ;
                    return expressionopt ;




    157) This is intended to allow compiler transformations such as removal of empty loops even when
         termination cannot be proven.
    158) Thus, clause-1 specifies initialization for the loop, possibly declaring one or more variables for use in
         the loop; the controlling expression, expression-2, specifies an evaluation made before each iteration,
         such that execution of the loop continues until the expression compares equal to 0; and expression-3
         specifies an operation (such as incrementing) that is performed after each iteration.

[page 150]

    Semantics
2   A jump statement causes an unconditional jump to another place.
    6.8.6.1 The goto statement
    Constraints
1   The identifier in a goto statement shall name a label located somewhere in the enclosing
    function. A goto statement shall not jump from outside the scope of an identifier having
    a variably modified type to inside the scope of that identifier.
    Semantics
2   A goto statement causes an unconditional jump to the statement prefixed by the named
    label in the enclosing function.
3   EXAMPLE 1 It is sometimes convenient to jump into the middle of a complicated set of statements. The
    following outline presents one possible approach to a problem based on these three assumptions:
      1.   The general initialization code accesses objects only visible to the current function.
      2.   The general initialization code is too large to warrant duplication.
      3. The code to determine the next operation is at the head of the loop. (To allow it to be reached by
         continue statements, for example.)
            /* ... */
            goto first_time;
            for (;;) {
                    // determine next operation
                    /* ... */
                    if (need to reinitialize) {
                            // reinitialize-only code
                            /* ... */
                    first_time:
                            // general initialization code
                            /* ... */
                            continue;
                    }
                    // handle other operations
                    /* ... */
            }




[page 151]

4   EXAMPLE 2 A goto statement is not allowed to jump past any declarations of objects with variably
    modified types. A jump within the scope, however, is permitted.
            goto lab3;                         // invalid: going INTO scope of VLA.
            {
                  double a[n];
                  a[j] = 4.4;
            lab3:
                  a[j] = 3.3;
                  goto lab4;                   // valid: going WITHIN scope of VLA.
                  a[j] = 5.5;
            lab4:
                  a[j] = 6.6;
            }
            goto lab4;                         // invalid: going INTO scope of VLA.

    6.8.6.2 The continue statement
    Constraints
1   A continue statement shall appear only in or as a loop body.
    Semantics
2   A continue statement causes a jump to the loop-continuation portion of the smallest
    enclosing iteration statement; that is, to the end of the loop body. More precisely, in each
    of the statements
    while (/* ... */) {                  do {                                 for (/* ... */) {
       /* ... */                            /* ... */                            /* ... */
       continue;                            continue;                            continue;
       /* ... */                            /* ... */                            /* ... */
    contin: ;                            contin: ;                            contin: ;
    }                                    } while (/* ... */);                 }
    unless the continue statement shown is in an enclosed iteration statement (in which
    case it is interpreted within that statement), it is equivalent to goto contin;.159)
    6.8.6.3 The break statement
    Constraints
1   A break statement shall appear only in or as a switch body or loop body.
    Semantics
2   A break statement terminates execution of the smallest enclosing switch or iteration
    statement.



    159) Following the contin: label is a null statement.

[page 152]

    6.8.6.4 The return statement
    Constraints
1   A return statement with an expression shall not appear in a function whose return type
    is void. A return statement without an expression shall only appear in a function
    whose return type is void.
    Semantics
2   A return statement terminates execution of the current function and returns control to
    its caller. A function may have any number of return statements.
3   If a return statement with an expression is executed, the value of the expression is
    returned to the caller as the value of the function call expression. If the expression has a
    type different from the return type of the function in which it appears, the value is
    converted as if by assignment to an object having the return type of the function.160)
4   EXAMPLE       In:
            struct s { double i; } f(void);
            union {
                  struct {
                        int f1;
                        struct s f2;
                  } u1;
                  struct {
                        struct s f3;
                        int f4;
                  } u2;
            } g;
            struct s f(void)
            {
                  return g.u1.f2;
            }
            /* ... */
            g.u2.f3 = f();
    there is no undefined behavior, although there would be if the assignment were done directly (without using
    a function call to fetch the value).




    160) The return statement is not an assignment. The overlap restriction of subclause 6.5.16.1 does not
         apply to the case of function return. The representation of floating-point values may have wider range
         or precision than implied by the type; a cast may be used to remove this extra range and precision.

[page 153]

    6.9 External definitions
    Syntax
1            translation-unit:
                     external-declaration
                     translation-unit external-declaration
             external-declaration:
                    function-definition
                    declaration
    Constraints
2   The storage-class specifiers auto and register shall not appear in the declaration
    specifiers in an external declaration.
3   There shall be no more than one external definition for each identifier declared with
    internal linkage in a translation unit. Moreover, if an identifier declared with internal
    linkage is used in an expression (other than as a part of the operand of a sizeof
    operator whose result is an integer constant), there shall be exactly one external definition
    for the identifier in the translation unit.
    Semantics
4   As discussed in 5.1.1.1, the unit of program text after preprocessing is a translation unit,
    which consists of a sequence of external declarations. These are described as ''external''
    because they appear outside any function (and hence have file scope). As discussed in
    6.7, a declaration that also causes storage to be reserved for an object or a function named
    by the identifier is a definition.
5   An external definition is an external declaration that is also a definition of a function
    (other than an inline definition) or an object. If an identifier declared with external
    linkage is used in an expression (other than as part of the operand of a sizeof operator
    whose result is an integer constant), somewhere in the entire program there shall be
    exactly one external definition for the identifier; otherwise, there shall be no more than
    one.161)




    161) Thus, if an identifier declared with external linkage is not used in an expression, there need be no
         external definition for it.

[page 154]

    6.9.1 Function definitions
    Syntax
1            function-definition:
                    declaration-specifiers declarator declaration-listopt compound-statement
             declaration-list:
                    declaration
                    declaration-list declaration
    Constraints
2   The identifier declared in a function definition (which is the name of the function) shall
    have a function type, as specified by the declarator portion of the function definition.162)
3   The return type of a function shall be void or a complete object type other than array
    type.
4   The storage-class specifier, if any, in the declaration specifiers shall be either extern or
    static.
5   If the declarator includes a parameter type list, the declaration of each parameter shall
    include an identifier, except for the special case of a parameter list consisting of a single
    parameter of type void, in which case there shall not be an identifier. No declaration list
    shall follow.
6   If the declarator includes an identifier list, each declaration in the declaration list shall
    have at least one declarator, those declarators shall declare only identifiers from the
    identifier list, and every identifier in the identifier list shall be declared. An identifier
    declared as a typedef name shall not be redeclared as a parameter. The declarations in the
    declaration list shall contain no storage-class specifier other than register and no
    initializations.



    162) The intent is that the type category in a function definition cannot be inherited from a typedef:
                  typedef int F(void);                          //   type F is ''function with no parameters
                                                                //                  returning int''
                  F f, g;                                       //   f and g both have type compatible with F
                  F f { /* ... */ }                             //   WRONG: syntax/constraint error
                  F g() { /* ... */ }                           //   WRONG: declares that g returns a function
                  int f(void) { /* ... */ }                     //   RIGHT: f has type compatible with F
                  int g() { /* ... */ }                         //   RIGHT: g has type compatible with F
                  F *e(void) { /* ... */ }                      //   e returns a pointer to a function
                  F *((e))(void) { /* ... */ }                  //   same: parentheses irrelevant
                  int (*fp)(void);                              //   fp points to a function that has type F
                  F *Fp;                                        //   Fp points to a function that has type F


[page 155]

     Semantics
7    The declarator in a function definition specifies the name of the function being defined
     and the identifiers of its parameters. If the declarator includes a parameter type list, the
     list also specifies the types of all the parameters; such a declarator also serves as a
     function prototype for later calls to the same function in the same translation unit. If the
     declarator includes an identifier list,163) the types of the parameters shall be declared in a
     following declaration list. In either case, the type of each parameter is adjusted as
     described in 6.7.6.3 for a parameter type list; the resulting type shall be a complete object
     type.
8    If a function that accepts a variable number of arguments is defined without a parameter
     type list that ends with the ellipsis notation, the behavior is undefined.
9    Each parameter has automatic storage duration; its identifier is an lvalue.164) The layout
     of the storage for parameters is unspecified.
10   On entry to the function, the size expressions of each variably modified parameter are
     evaluated and the value of each argument expression is converted to the type of the
     corresponding parameter as if by assignment. (Array expressions and function
     designators as arguments were converted to pointers before the call.)
11   After all parameters have been assigned, the compound statement that constitutes the
     body of the function definition is executed.
12   If the } that terminates a function is reached, and the value of the function call is used by
     the caller, the behavior is undefined.
13   EXAMPLE 1       In the following:
              extern int max(int a, int b)
              {
                    return a > b ? a : b;
              }
     extern is the storage-class specifier and int is the type specifier; max(int a, int b) is the
     function declarator; and
              { return a > b ? a : b; }
     is the function body. The following similar definition uses the identifier-list form for the parameter
     declarations:




     163) See ''future language directions'' (6.11.7).
     164) A parameter identifier cannot be redeclared in the function body except in an enclosed block.

[page 156]

              extern int max(a, b)
              int a, b;
              {
                    return a > b ? a : b;
              }
     Here int a, b; is the declaration list for the parameters. The difference between these two definitions is
     that the first form acts as a prototype declaration that forces conversion of the arguments of subsequent calls
     to the function, whereas the second form does not.

14   EXAMPLE 2           To pass one function to another, one might say
                          int f(void);
                          /* ... */
                          g(f);
     Then the definition of g might read
              void g(int (*funcp)(void))
              {
                    /* ... */
                    (*funcp)(); /* or funcp(); ...                    */
              }
     or, equivalently,
              void g(int func(void))
              {
                    /* ... */
                    func(); /* or (*func)(); ...                   */
              }

     6.9.2 External object definitions
     Semantics
1    If the declaration of an identifier for an object has file scope and an initializer, the
     declaration is an external definition for the identifier.
2    A declaration of an identifier for an object that has file scope without an initializer, and
     without a storage-class specifier or with the storage-class specifier static, constitutes a
     tentative definition. If a translation unit contains one or more tentative definitions for an
     identifier, and the translation unit contains no external definition for that identifier, then
     the behavior is exactly as if the translation unit contains a file scope declaration of that
     identifier, with the composite type as of the end of the translation unit, with an initializer
     equal to 0.
3    If the declaration of an identifier for an object is a tentative definition and has internal
     linkage, the declared type shall not be an incomplete type.




[page 157]

4   EXAMPLE 1
             int i1 = 1;                    // definition, external linkage
             static int i2 = 2;             // definition, internal linkage
             extern int i3 = 3;             // definition, external linkage
             int i4;                        // tentative definition, external linkage
             static int i5;                 // tentative definition, internal linkage
             int   i1;                      // valid tentative definition, refers to previous
             int   i2;                      // 6.2.2 renders undefined, linkage disagreement
             int   i3;                      // valid tentative definition, refers to previous
             int   i4;                      // valid tentative definition, refers to previous
             int   i5;                      // 6.2.2 renders undefined, linkage disagreement
             extern    int   i1;            // refers to previous, whose linkage is external
             extern    int   i2;            // refers to previous, whose linkage is internal
             extern    int   i3;            // refers to previous, whose linkage is external
             extern    int   i4;            // refers to previous, whose linkage is external
             extern    int   i5;            // refers to previous, whose linkage is internal

5   EXAMPLE 2       If at the end of the translation unit containing
             int i[];
    the array i still has incomplete type, the implicit initializer causes it to have one element, which is set to
    zero on program startup.




[page 158]

    6.10 Preprocessing directives
    Syntax
1            preprocessing-file:
                    groupopt
             group:
                      group-part
                      group group-part
             group-part:
                    if-section
                    control-line
                    text-line
                    # non-directive
             if-section:
                      if-group elif-groupsopt else-groupopt endif-line
             if-group:
                     # if     constant-expression new-line groupopt
                     # ifdef identifier new-line groupopt
                     # ifndef identifier new-line groupopt
             elif-groups:
                     elif-group
                     elif-groups elif-group
             elif-group:
                     # elif       constant-expression new-line groupopt
             else-group:
                     # else       new-line groupopt
             endif-line:
                     # endif      new-line




[page 159]

             control-line:
                    # include pp-tokens new-line
                    # define identifier replacement-list new-line
                    # define identifier lparen identifier-listopt )
                                                    replacement-list new-line
                    # define identifier lparen ... ) replacement-list new-line
                    # define identifier lparen identifier-list , ... )
                                                    replacement-list new-line
                    # undef   identifier new-line
                    # line    pp-tokens new-line
                    # error   pp-tokensopt new-line
                    # pragma pp-tokensopt new-line
                    #         new-line
             text-line:
                     pp-tokensopt new-line
             non-directive:
                    pp-tokens new-line
             lparen:
                       a ( character not immediately preceded by white-space
             replacement-list:
                    pp-tokensopt
             pp-tokens:
                    preprocessing-token
                    pp-tokens preprocessing-token
             new-line:
                    the new-line character
    Description
2   A preprocessing directive consists of a sequence of preprocessing tokens that satisfies the
    following constraints: The first token in the sequence is a # preprocessing token that (at
    the start of translation phase 4) is either the first character in the source file (optionally
    after white space containing no new-line characters) or that follows white space
    containing at least one new-line character. The last token in the sequence is the first new-
    line character that follows the first token in the sequence.165) A new-line character ends
    the preprocessing directive even if it occurs within what would otherwise be an

    165) Thus, preprocessing directives are commonly called ''lines''. These ''lines'' have no other syntactic
         significance, as all white space is equivalent except in certain situations during preprocessing (see the
         # character string literal creation operator in 6.10.3.2, for example).

[page 160]

    invocation of a function-like macro.
3   A text line shall not begin with a # preprocessing token. A non-directive shall not begin
    with any of the directive names appearing in the syntax.
4   When in a group that is skipped (6.10.1), the directive syntax is relaxed to allow any
    sequence of preprocessing tokens to occur between the directive name and the following
    new-line character.
    Constraints
5   The only white-space characters that shall appear between preprocessing tokens within a
    preprocessing directive (from just after the introducing # preprocessing token through
    just before the terminating new-line character) are space and horizontal-tab (including
    spaces that have replaced comments or possibly other white-space characters in
    translation phase 3).
    Semantics
6   The implementation can process and skip sections of source files conditionally, include
    other source files, and replace macros. These capabilities are called preprocessing,
    because conceptually they occur before translation of the resulting translation unit.
7   The preprocessing tokens within a preprocessing directive are not subject to macro
    expansion unless otherwise stated.
8   EXAMPLE        In:
              #define EMPTY
              EMPTY # include <file.h>
    the sequence of preprocessing tokens on the second line is not a preprocessing directive, because it does not
    begin with a # at the start of translation phase 4, even though it will do so after the macro EMPTY has been
    replaced.

    6.10.1 Conditional inclusion
    Constraints
1   The expression that controls conditional inclusion shall be an integer constant expression
    except that: identifiers (including those lexically identical to keywords) are interpreted as *
    described below;166) and it may contain unary operator expressions of the form
         defined identifier
    or
         defined ( identifier )
    which evaluate to 1 if the identifier is currently defined as a macro name (that is, if it is


    166) Because the controlling constant expression is evaluated during translation phase 4, all identifiers
         either are or are not macro names -- there simply are no keywords, enumeration constants, etc.

[page 161]

    predefined or if it has been the subject of a #define preprocessing directive without an
    intervening #undef directive with the same subject identifier), 0 if it is not.
2   Each preprocessing token that remains (in the list of preprocessing tokens that will
    become the controlling expression) after all macro replacements have occurred shall be in
    the lexical form of a token (6.4).
    Semantics
3   Preprocessing directives of the forms
       # if   constant-expression new-line groupopt
       # elif constant-expression new-line groupopt
    check whether the controlling constant expression evaluates to nonzero.
4   Prior to evaluation, macro invocations in the list of preprocessing tokens that will become
    the controlling constant expression are replaced (except for those macro names modified
    by the defined unary operator), just as in normal text. If the token defined is
    generated as a result of this replacement process or use of the defined unary operator
    does not match one of the two specified forms prior to macro replacement, the behavior is
    undefined. After all replacements due to macro expansion and the defined unary
    operator have been performed, all remaining identifiers (including those lexically
    identical to keywords) are replaced with the pp-number 0, and then each preprocessing
    token is converted into a token. The resulting tokens compose the controlling constant
    expression which is evaluated according to the rules of 6.6. For the purposes of this
    token conversion and evaluation, all signed integer types and all unsigned integer types
    act as if they have the same representation as, respectively, the types intmax_t and
    uintmax_t defined in the header <stdint.h>.167) This includes interpreting
    character constants, which may involve converting escape sequences into execution
    character set members. Whether the numeric value for these character constants matches
    the value obtained when an identical character constant occurs in an expression (other
    than within a #if or #elif directive) is implementation-defined.168) Also, whether a
    single-character character constant may have a negative value is implementation-defined.




    167) Thus, on an implementation where INT_MAX is 0x7FFF and UINT_MAX is 0xFFFF, the constant
         0x8000 is signed and positive within a #if expression even though it would be unsigned in
         translation phase 7.
    168) Thus, the constant expression in the following #if directive and if statement is not guaranteed to
         evaluate to the same value in these two contexts.
           #if 'z' - 'a' == 25
           if ('z' - 'a' == 25)


[page 162]

5   Preprocessing directives of the forms
       # ifdef identifier new-line groupopt
       # ifndef identifier new-line groupopt
    check whether the identifier is or is not currently defined as a macro name. Their
    conditions are equivalent to #if defined identifier and #if !defined identifier
    respectively.
6   Each directive's condition is checked in order. If it evaluates to false (zero), the group
    that it controls is skipped: directives are processed only through the name that determines
    the directive in order to keep track of the level of nested conditionals; the rest of the
    directives' preprocessing tokens are ignored, as are the other preprocessing tokens in the
    group. Only the first group whose control condition evaluates to true (nonzero) is
    processed. If none of the conditions evaluates to true, and there is a #else directive, the
    group controlled by the #else is processed; lacking a #else directive, all the groups
    until the #endif are skipped.169)
    Forward references: macro replacement (6.10.3), source file inclusion (6.10.2), largest
    integer types (7.20.1.5).
    6.10.2 Source file inclusion
    Constraints
1   A #include directive shall identify a header or source file that can be processed by the
    implementation.
    Semantics
2   A preprocessing directive of the form
       # include <h-char-sequence> new-line
    searches a sequence of implementation-defined places for a header identified uniquely by
    the specified sequence between the < and > delimiters, and causes the replacement of that
    directive by the entire contents of the header. How the places are specified or the header
    identified is implementation-defined.
3   A preprocessing directive of the form
       # include "q-char-sequence" new-line
    causes the replacement of that directive by the entire contents of the source file identified
    by the specified sequence between the " delimiters. The named source file is searched


    169) As indicated by the syntax, a preprocessing token shall not follow a #else or #endif directive
         before the terminating new-line character. However, comments may appear anywhere in a source file,
         including within a preprocessing directive.

[page 163]

    for in an implementation-defined manner. If this search is not supported, or if the search
    fails, the directive is reprocessed as if it read
       # include <h-char-sequence> new-line
    with the identical contained sequence (including > characters, if any) from the original
    directive.
4   A preprocessing directive of the form
       # include pp-tokens new-line
    (that does not match one of the two previous forms) is permitted. The preprocessing
    tokens after include in the directive are processed just as in normal text. (Each
    identifier currently defined as a macro name is replaced by its replacement list of
    preprocessing tokens.) The directive resulting after all replacements shall match one of
    the two previous forms.170) The method by which a sequence of preprocessing tokens
    between a < and a > preprocessing token pair or a pair of " characters is combined into a
    single header name preprocessing token is implementation-defined.
5   The implementation shall provide unique mappings for sequences consisting of one or
    more nondigits or digits (6.4.2.1) followed by a period (.) and a single nondigit. The
    first character shall not be a digit. The implementation may ignore distinctions of
    alphabetical case and restrict the mapping to eight significant characters before the
    period.
6   A #include preprocessing directive may appear in a source file that has been read
    because of a #include directive in another file, up to an implementation-defined
    nesting limit (see 5.2.4.1).
7   EXAMPLE 1       The most common uses of #include preprocessing directives are as in the following:
             #include <stdio.h>
             #include "myprog.h"




    170) Note that adjacent string literals are not concatenated into a single string literal (see the translation
         phases in 5.1.1.2); thus, an expansion that results in two string literals is an invalid directive.

[page 164]

8   EXAMPLE 2      This illustrates macro-replaced #include directives:
              #if VERSION == 1
                    #define INCFILE          "vers1.h"
              #elif VERSION == 2
                    #define INCFILE          "vers2.h"        // and so on
              #else
                     #define INCFILE         "versN.h"
              #endif
              #include INCFILE

    Forward references: macro replacement (6.10.3).
    6.10.3 Macro replacement
    Constraints
1   Two replacement lists are identical if and only if the preprocessing tokens in both have
    the same number, ordering, spelling, and white-space separation, where all white-space
    separations are considered identical.
2   An identifier currently defined as an object-like macro shall not be redefined by another
    #define preprocessing directive unless the second definition is an object-like macro
    definition and the two replacement lists are identical. Likewise, an identifier currently
    defined as a function-like macro shall not be redefined by another #define
    preprocessing directive unless the second definition is a function-like macro definition
    that has the same number and spelling of parameters, and the two replacement lists are
    identical.
3   There shall be white-space between the identifier and the replacement list in the definition
    of an object-like macro.
4   If the identifier-list in the macro definition does not end with an ellipsis, the number of
    arguments (including those arguments consisting of no preprocessing tokens) in an
    invocation of a function-like macro shall equal the number of parameters in the macro
    definition. Otherwise, there shall be more arguments in the invocation than there are
    parameters in the macro definition (excluding the ...). There shall exist a )
    preprocessing token that terminates the invocation.
5   The identifier __VA_ARGS__ shall occur only in the replacement-list of a function-like
    macro that uses the ellipsis notation in the parameters.
6   A parameter identifier in a function-like macro shall be uniquely declared within its
    scope.
    Semantics
7   The identifier immediately following the define is called the macro name. There is one
    name space for macro names. Any white-space characters preceding or following the
    replacement list of preprocessing tokens are not considered part of the replacement list

[page 165]

     for either form of macro.
8    If a # preprocessing token, followed by an identifier, occurs lexically at the point at which
     a preprocessing directive could begin, the identifier is not subject to macro replacement.
9    A preprocessing directive of the form
        # define identifier replacement-list new-line
     defines an object-like macro that causes each subsequent instance of the macro name171)
     to be replaced by the replacement list of preprocessing tokens that constitute the
     remainder of the directive. The replacement list is then rescanned for more macro names
     as specified below.
10   A preprocessing directive of the form
        # define identifier lparen identifier-listopt ) replacement-list new-line
        # define identifier lparen ... ) replacement-list new-line
        # define identifier lparen identifier-list , ... ) replacement-list new-line
     defines a function-like macro with parameters, whose use is similar syntactically to a
     function call. The parameters are specified by the optional list of identifiers, whose scope
     extends from their declaration in the identifier list until the new-line character that
     terminates the #define preprocessing directive. Each subsequent instance of the
     function-like macro name followed by a ( as the next preprocessing token introduces the
     sequence of preprocessing tokens that is replaced by the replacement list in the definition
     (an invocation of the macro). The replaced sequence of preprocessing tokens is
     terminated by the matching ) preprocessing token, skipping intervening matched pairs of
     left and right parenthesis preprocessing tokens. Within the sequence of preprocessing
     tokens making up an invocation of a function-like macro, new-line is considered a normal
     white-space character.
11   The sequence of preprocessing tokens bounded by the outside-most matching parentheses
     forms the list of arguments for the function-like macro. The individual arguments within
     the list are separated by comma preprocessing tokens, but comma preprocessing tokens
     between matching inner parentheses do not separate arguments. If there are sequences of
     preprocessing tokens within the list of arguments that would otherwise act as
     preprocessing directives,172) the behavior is undefined.
12   If there is a ... in the identifier-list in the macro definition, then the trailing arguments,
     including any separating comma preprocessing tokens, are merged to form a single item:


     171) Since, by macro-replacement time, all character constants and string literals are preprocessing tokens,
          not sequences possibly containing identifier-like subsequences (see 5.1.1.2, translation phases), they
          are never scanned for macro names or parameters.
     172) Despite the name, a non-directive is a preprocessing directive.

[page 166]

    the variable arguments. The number of arguments so combined is such that, following
    merger, the number of arguments is one more than the number of parameters in the macro
    definition (excluding the ...).
    6.10.3.1 Argument substitution
1   After the arguments for the invocation of a function-like macro have been identified,
    argument substitution takes place. A parameter in the replacement list, unless preceded
    by a # or ## preprocessing token or followed by a ## preprocessing token (see below), is
    replaced by the corresponding argument after all macros contained therein have been
    expanded. Before being substituted, each argument's preprocessing tokens are
    completely macro replaced as if they formed the rest of the preprocessing file; no other
    preprocessing tokens are available.
2   An identifier __VA_ARGS__ that occurs in the replacement list shall be treated as if it
    were a parameter, and the variable arguments shall form the preprocessing tokens used to
    replace it.
    6.10.3.2 The # operator
    Constraints
1   Each # preprocessing token in the replacement list for a function-like macro shall be
    followed by a parameter as the next preprocessing token in the replacement list.
    Semantics
2   If, in the replacement list, a parameter is immediately preceded by a # preprocessing
    token, both are replaced by a single character string literal preprocessing token that
    contains the spelling of the preprocessing token sequence for the corresponding
    argument. Each occurrence of white space between the argument's preprocessing tokens
    becomes a single space character in the character string literal. White space before the
    first preprocessing token and after the last preprocessing token composing the argument
    is deleted. Otherwise, the original spelling of each preprocessing token in the argument
    is retained in the character string literal, except for special handling for producing the
    spelling of string literals and character constants: a \ character is inserted before each "
    and \ character of a character constant or string literal (including the delimiting "
    characters), except that it is implementation-defined whether a \ character is inserted
    before the \ character beginning a universal character name. If the replacement that
    results is not a valid character string literal, the behavior is undefined. The character
    string literal corresponding to an empty argument is "". The order of evaluation of # and
    ## operators is unspecified.




[page 167]

    6.10.3.3 The ## operator
    Constraints
1   A ## preprocessing token shall not occur at the beginning or at the end of a replacement
    list for either form of macro definition.
    Semantics
2   If, in the replacement list of a function-like macro, a parameter is immediately preceded
    or followed by a ## preprocessing token, the parameter is replaced by the corresponding
    argument's preprocessing token sequence; however, if an argument consists of no
    preprocessing tokens, the parameter is replaced by a placemarker preprocessing token
    instead.173)
3   For both object-like and function-like macro invocations, before the replacement list is
    reexamined for more macro names to replace, each instance of a ## preprocessing token
    in the replacement list (not from an argument) is deleted and the preceding preprocessing
    token is concatenated with the following preprocessing token. Placemarker
    preprocessing tokens are handled specially: concatenation of two placemarkers results in
    a single placemarker preprocessing token, and concatenation of a placemarker with a
    non-placemarker preprocessing token results in the non-placemarker preprocessing token.
    If the result is not a valid preprocessing token, the behavior is undefined. The resulting
    token is available for further macro replacement. The order of evaluation of ## operators
    is unspecified.
4   EXAMPLE       In the following fragment:
            #define     hash_hash # ## #
            #define     mkstr(a) # a
            #define     in_between(a) mkstr(a)
            #define     join(c, d) in_between(c hash_hash d)
            char p[] = join(x, y); // equivalent to
                                   // char p[] = "x ## y";
    The expansion produces, at various stages:
            join(x, y)
            in_between(x hash_hash y)
            in_between(x ## y)
            mkstr(x ## y)
            "x ## y"
    In other words, expanding hash_hash produces a new token, consisting of two adjacent sharp signs, but
    this new token is not the ## operator.


    173) Placemarker preprocessing tokens do not appear in the syntax because they are temporary entities that
         exist only within translation phase 4.

[page 168]

    6.10.3.4 Rescanning and further replacement
1   After all parameters in the replacement list have been substituted and # and ##
    processing has taken place, all placemarker preprocessing tokens are removed. The
    resulting preprocessing token sequence is then rescanned, along with all subsequent
    preprocessing tokens of the source file, for more macro names to replace.
2   If the name of the macro being replaced is found during this scan of the replacement list
    (not including the rest of the source file's preprocessing tokens), it is not replaced.
    Furthermore, if any nested replacements encounter the name of the macro being replaced,
    it is not replaced. These nonreplaced macro name preprocessing tokens are no longer
    available for further replacement even if they are later (re)examined in contexts in which
    that macro name preprocessing token would otherwise have been replaced.
3   The resulting completely macro-replaced preprocessing token sequence is not processed
    as a preprocessing directive even if it resembles one, but all pragma unary operator
    expressions within it are then processed as specified in 6.10.9 below.
    6.10.3.5 Scope of macro definitions
1   A macro definition lasts (independent of block structure) until a corresponding #undef
    directive is encountered or (if none is encountered) until the end of the preprocessing
    translation unit. Macro definitions have no significance after translation phase 4.
2   A preprocessing directive of the form
       # undef identifier new-line
    causes the specified identifier no longer to be defined as a macro name. It is ignored if
    the specified identifier is not currently defined as a macro name.
3   EXAMPLE 1      The simplest use of this facility is to define a ''manifest constant'', as in
            #define TABSIZE 100
            int table[TABSIZE];

4   EXAMPLE 2 The following defines a function-like macro whose value is the maximum of its arguments.
    It has the advantages of working for any compatible types of the arguments and of generating in-line code
    without the overhead of function calling. It has the disadvantages of evaluating one or the other of its
    arguments a second time (including side effects) and generating more code than a function if invoked
    several times. It also cannot have its address taken, as it has none.
            #define max(a, b) ((a) > (b) ? (a) : (b))
    The parentheses ensure that the arguments and the resulting expression are bound properly.




[page 169]

5   EXAMPLE 3     To illustrate the rules for redefinition and reexamination, the sequence
             #define   x         3
             #define   f(a)      f(x * (a))
             #undef    x
             #define   x         2
             #define   g         f
             #define   z         z[0]
             #define   h         g(~
             #define   m(a)      a(w)
             #define   w         0,1
             #define   t(a)      a
             #define   p()       int
             #define   q(x)      x
             #define   r(x,y)    x ## y
             #define   str(x)    # x
             f(y+1) + f(f(z)) % t(t(g)(0) + t)(1);
             g(x+(3,4)-w) | h 5) & m
                   (f)^m(m);
             p() i[q()] = { q(1), r(2,3), r(4,), r(,5), r(,) };
             char c[2][6] = { str(hello), str() };
    results in
             f(2 * (y+1)) + f(2 * (f(2 * (z[0])))) % f(2 * (0)) + t(1);
             f(2 * (2+(3,4)-0,1)) | f(2 * (~ 5)) & f(2 * (0,1))^m(0,1);
             int i[] = { 1, 23, 4, 5, };
             char c[2][6] = { "hello", "" };

6   EXAMPLE 4     To illustrate the rules for creating character string literals and concatenating tokens, the
    sequence
             #define str(s)      # s
             #define xstr(s)     str(s)
             #define debug(s, t) printf("x" # s "= %d, x" # t "= %s", \
                                     x ## s, x ## t)
             #define INCFILE(n) vers ## n
             #define glue(a, b) a ## b
             #define xglue(a, b) glue(a, b)
             #define HIGHLOW     "hello"
             #define LOW         LOW ", world"
             debug(1, 2);
             fputs(str(strncmp("abc\0d", "abc", '\4') // this goes away
                   == 0) str(: @\n), s);
             #include xstr(INCFILE(2).h)
             glue(HIGH, LOW);
             xglue(HIGH, LOW)
    results in




[page 170]

             printf("x" "1" "= %d, x" "2" "= %s", x1, x2);
             fputs(
               "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0" ": @\n",
               s);
             #include "vers2.h"    (after macro replacement, before file access)
             "hello";
             "hello" ", world"
    or, after concatenation of the character string literals,
             printf("x1= %d, x2= %s", x1, x2);
             fputs(
               "strncmp(\"abc\\0d\", \"abc\", '\\4') == 0: @\n",
               s);
             #include "vers2.h"    (after macro replacement, before file access)
             "hello";
             "hello, world"
    Space around the # and ## tokens in the macro definition is optional.

7   EXAMPLE 5        To illustrate the rules for placemarker preprocessing tokens, the sequence
             #define t(x,y,z) x ## y ## z
             int j[] = { t(1,2,3), t(,4,5), t(6,,7), t(8,9,),
                        t(10,,), t(,11,), t(,,12), t(,,) };
    results in
             int j[] = { 123, 45, 67, 89,
                         10, 11, 12, };

8   EXAMPLE 6        To demonstrate the redefinition rules, the following sequence is valid.
             #define      OBJ_LIKE      (1-1)
             #define      OBJ_LIKE      /* white space */ (1-1) /* other */
             #define      FUNC_LIKE(a)   ( a )
             #define      FUNC_LIKE( a )( /* note the white space */ \
                                          a /* other stuff on this line
                                              */ )
    But the following redefinitions are invalid:
             #define      OBJ_LIKE    (0)     // different token sequence
             #define      OBJ_LIKE    (1 - 1) // different white space
             #define      FUNC_LIKE(b) ( a ) // different parameter usage
             #define      FUNC_LIKE(b) ( b ) // different parameter spelling

9   EXAMPLE 7        Finally, to show the variable argument list macro facilities:
             #define debug(...)       fprintf(stderr, __VA_ARGS__)
             #define showlist(...)    puts(#__VA_ARGS__)
             #define report(test, ...) ((test)?puts(#test):\
                         printf(__VA_ARGS__))
             debug("Flag");
             debug("X = %d\n", x);
             showlist(The first, second, and third items.);
             report(x>y, "x is %d but y is %d", x, y);


[page 171]

    results in
             fprintf(stderr, "Flag" );
             fprintf(stderr, "X = %d\n", x );
             puts( "The first, second, and third items." );
             ((x>y)?puts("x>y"):
                         printf("x is %d but y is %d", x, y));

    6.10.4 Line control
    Constraints
1   The string literal of a #line directive, if present, shall be a character string literal.
    Semantics
2   The line number of the current source line is one greater than the number of new-line
    characters read or introduced in translation phase 1 (5.1.1.2) while processing the source
    file to the current token.
3   A preprocessing directive of the form
       # line digit-sequence new-line
    causes the implementation to behave as if the following sequence of source lines begins
    with a source line that has a line number as specified by the digit sequence (interpreted as
    a decimal integer). The digit sequence shall not specify zero, nor a number greater than
    2147483647.
4   A preprocessing directive of the form
       # line digit-sequence "s-char-sequenceopt" new-line
    sets the presumed line number similarly and changes the presumed name of the source
    file to be the contents of the character string literal.
5   A preprocessing directive of the form
       # line pp-tokens new-line
    (that does not match one of the two previous forms) is permitted. The preprocessing
    tokens after line on the directive are processed just as in normal text (each identifier
    currently defined as a macro name is replaced by its replacement list of preprocessing
    tokens). The directive resulting after all replacements shall match one of the two
    previous forms and is then processed as appropriate.




[page 172]

    6.10.5 Error directive
    Semantics
1   A preprocessing directive of the form
       # error pp-tokensopt new-line
    causes the implementation to produce a diagnostic message that includes the specified
    sequence of preprocessing tokens.
    6.10.6 Pragma directive
    Semantics
1   A preprocessing directive of the form
       # pragma pp-tokensopt new-line
    where the preprocessing token STDC does not immediately follow pragma in the
    directive (prior to any macro replacement)174) causes the implementation to behave in an
    implementation-defined manner. The behavior might cause translation to fail or cause the
    translator or the resulting program to behave in a non-conforming manner. Any such
    pragma that is not recognized by the implementation is ignored.
2   If the preprocessing token STDC does immediately follow pragma in the directive (prior
    to any macro replacement), then no macro replacement is performed on the directive, and
    the directive shall have one of the following forms175) whose meanings are described
    elsewhere:
       #pragma STDC FP_CONTRACT on-off-switch
       #pragma STDC FENV_ACCESS on-off-switch
       #pragma STDC CX_LIMITED_RANGE on-off-switch
       on-off-switch: one of
                   ON     OFF           DEFAULT
    Forward references: the FP_CONTRACT pragma (7.12.2), the FENV_ACCESS pragma
    (7.6.1), the CX_LIMITED_RANGE pragma (7.3.4).




    174) An implementation is not required to perform macro replacement in pragmas, but it is permitted
         except for in standard pragmas (where STDC immediately follows pragma). If the result of macro
         replacement in a non-standard pragma has the same form as a standard pragma, the behavior is still
         implementation-defined; an implementation is permitted to behave as if it were the standard pragma,
         but is not required to.
    175) See ''future language directions'' (6.11.8).

[page 173]

    6.10.7 Null directive
    Semantics
1   A preprocessing directive of the form
       # new-line
    has no effect.
    6.10.8 Predefined macro names
1   The values of the predefined macros listed in the following subclauses176) (except for
    __FILE__ and __LINE__) remain constant throughout the translation unit.
2   None of these macro names, nor the identifier defined, shall be the subject of a
    #define or a #undef preprocessing directive. Any other predefined macro names
    shall begin with a leading underscore followed by an uppercase letter or a second
    underscore.
3   The implementation shall not predefine the macro __cplusplus, nor shall it define it
    in any standard header.
    Forward references: standard headers (7.1.2).
    6.10.8.1 Mandatory macros
1   The following macro names shall be defined by the implementation:
    __DATE__ The date of translation of the preprocessing translation unit: a character
               string literal of the form "Mmm dd yyyy", where the names of the
               months are the same as those generated by the asctime function, and the
               first character of dd is a space character if the value is less than 10. If the
               date of translation is not available, an implementation-defined valid date
               shall be supplied.
    __FILE__ The presumed name of the current source file (a character string literal).177)
    __LINE__ The presumed line number (within the current source file) of the current
               source line (an integer constant).177)
    __STDC__ The integer constant 1, intended to indicate a conforming implementation.
    __STDC_HOSTED__ The integer constant 1 if the implementation is a hosted
              implementation or the integer constant 0 if it is not.




    176) See ''future language directions'' (6.11.9).
    177) The presumed source file name and line number can be changed by the #line directive.

[page 174]

    __STDC_VERSION__ The integer constant 201ymmL.178)
    __TIME__ The time of translation of the preprocessing translation unit: a character
               string literal of the form "hh:mm:ss" as in the time generated by the
               asctime function. If the time of translation is not available, an
               implementation-defined valid time shall be supplied.
    Forward references: the asctime function (7.26.3.1).
    6.10.8.2 Environment macros
1   The following macro names are conditionally defined by the implementation:
    __STDC_ISO_10646__ An integer constant of the form yyyymmL (for example,
              199712L). If this symbol is defined, then every character in the Unicode
              required set, when stored in an object of type wchar_t, has the same
              value as the short identifier of that character. The Unicode required set
              consists of all the characters that are defined by ISO/IEC 10646, along with
              all amendments and technical corrigenda, as of the specified year and
              month. If some other encoding is used, the macro shall not be defined and
              the actual encoding used is implementation-defined.
    __STDC_MB_MIGHT_NEQ_WC__ The integer constant 1, intended to indicate that, in
              the encoding for wchar_t, a member of the basic character set need not
              have a code value equal to its value when used as the lone character in an
              integer character constant.
    __STDC_UTF_16__ The integer constant 1, intended to indicate that values of type
              char16_t are UTF-16 encoded. If some other encoding is used, the
              macro shall not be defined and the actual encoding used is implementation-
              defined.
    __STDC_UTF_32__ The integer constant 1, intended to indicate that values of type
              char32_t are UTF-32 encoded. If some other encoding is used, the
              macro shall not be defined and the actual encoding used is implementation-
              defined.
    Forward references: common definitions (7.19), unicode utilities (7.27).




    178) This macro was not specified in ISO/IEC 9899:1990 and was specified as 199409L in
         ISO/IEC 9899/AMD1:1995 and as 199901L in ISO/IEC 9899:1999. The intention is that this will
         remain an integer constant of type long int that is increased with each revision of this International
         Standard.

[page 175]

    6.10.8.3 Conditional feature macros
1   The following macro names are conditionally defined by the implementation:
    __STDC_ANALYZABLE__ The integer constant 1, intended to indicate conformance to
              the specifications in annex L (Analyzability).
    __STDC_IEC_559__ The integer constant 1, intended to indicate conformance to the
              specifications in annex F (IEC 60559 floating-point arithmetic).
    __STDC_IEC_559_COMPLEX__ The integer constant 1, intended to indicate
              adherence to the specifications in annex G (IEC 60559 compatible complex
              arithmetic).
    __STDC_LIB_EXT1__ The integer constant 201ymmL, intended to indicate support
              for the extensions defined in annex K (Bounds-checking interfaces).179)
    __STDC_NO_COMPLEX__ The integer constant 1, intended to indicate that the
              implementation does not support complex types or the <complex.h>
              header.
    __STDC_NO_THREADS__ The integer constant 1, intended to indicate that the
              implementation does not support atomic types (including the _Atomic
              type qualifier and the <stdatomic.h> header) or the <threads.h>
              header.
    __STDC_NO_VLA__ The integer constant 1, intended to indicate that the
              implementation does not support variable length arrays or variably
              modified types.
2   An implementation that defines __STDC_NO_COMPLEX__ shall not define
    __STDC_IEC_559_COMPLEX__.
    6.10.9 Pragma operator
    Semantics
1   A unary operator expression of the form:
       _Pragma ( string-literal )
    is processed as follows: The string literal is destringized by deleting the L prefix, if
    present, deleting the leading and trailing double-quotes, replacing each escape sequence
    \" by a double-quote, and replacing each escape sequence \\ by a single backslash. The
    resulting sequence of characters is processed through translation phase 3 to produce
    preprocessing tokens that are executed as if they were the pp-tokens in a pragma


    179) The intention is that this will remain an integer constant of type long int that is increased with
         each revision of this International Standard.

[page 176]

    directive. The original four preprocessing tokens in the unary operator expression are
    removed.
2   EXAMPLE       A directive of the form:
              #pragma listing on "..\listing.dir"
    can also be expressed as:
              _Pragma ( "listing on \"..\\listing.dir\"" )
    The latter form is processed in the same way whether it appears literally as shown, or results from macro
    replacement, as in:
              #define LISTING(x) PRAGMA(listing on #x)
              #define PRAGMA(x) _Pragma(#x)
              LISTING ( ..\listing.dir )




[page 177]

    6.11 Future language directions
    6.11.1 Floating types
1   Future standardization may include additional floating-point types, including those with
    greater range, precision, or both than long double.
    6.11.2 Linkages of identifiers
1   Declaring an identifier with internal linkage at file scope without the static storage-
    class specifier is an obsolescent feature.
    6.11.3 External names
1   Restriction of the significance of an external name to fewer than 255 characters
    (considering each universal character name or extended source character as a single
    character) is an obsolescent feature that is a concession to existing implementations.
    6.11.4 Character escape sequences
1   Lowercase letters as escape sequences are reserved for future standardization. Other
    characters may be used in extensions.
    6.11.5 Storage-class specifiers
1   The placement of a storage-class specifier other than at the beginning of the declaration
    specifiers in a declaration is an obsolescent feature.
    6.11.6 Function declarators
1   The use of function declarators with empty parentheses (not prototype-format parameter
    type declarators) is an obsolescent feature.
    6.11.7 Function definitions
1   The use of function definitions with separate parameter identifier and declaration lists
    (not prototype-format parameter type and identifier declarators) is an obsolescent feature.
    6.11.8 Pragma directives
1   Pragmas whose first preprocessing token is STDC are reserved for future standardization.
    6.11.9 Predefined macro names
1   Macro names beginning with __STDC_ are reserved for future standardization.




[page 178]


    7. Library
    7.1 Introduction
    7.1.1 Definitions of terms
1   A string is a contiguous sequence of characters terminated by and including the first null
    character. The term multibyte string is sometimes used instead to emphasize special
    processing given to multibyte characters contained in the string or to avoid confusion
    with a wide string. A pointer to a string is a pointer to its initial (lowest addressed)
    character. The length of a string is the number of bytes preceding the null character and
    the value of a string is the sequence of the values of the contained characters, in order.
2   The decimal-point character is the character used by functions that convert floating-point
    numbers to or from character sequences to denote the beginning of the fractional part of
    such character sequences.180) It is represented in the text and examples by a period, but
    may be changed by the setlocale function.
3   A null wide character is a wide character with code value zero.
4   A wide string is a contiguous sequence of wide characters terminated by and including
    the first null wide character. A pointer to a wide string is a pointer to its initial (lowest
    addressed) wide character. The length of a wide string is the number of wide characters
    preceding the null wide character and the value of a wide string is the sequence of code
    values of the contained wide characters, in order.
5   A shift sequence is a contiguous sequence of bytes within a multibyte string that
    (potentially) causes a change in shift state (see 5.2.1.2). A shift sequence shall not have a
    corresponding wide character; it is instead taken to be an adjunct to an adjacent multibyte
    character.181)
    Forward references: character handling (7.4), the setlocale function (7.11.1.1).




    180) The functions that make use of the decimal-point character are the numeric conversion functions
         (7.22.1, 7.28.4.1) and the formatted input/output functions (7.21.6, 7.28.2).
    181) For state-dependent encodings, the values for MB_CUR_MAX and MB_LEN_MAX shall thus be large
         enough to count all the bytes in any complete multibyte character plus at least one adjacent shift
         sequence of maximum length. Whether these counts provide for more than one shift sequence is the
         implementation's choice.

[page 179]

    7.1.2 Standard headers
1   Each library function is declared, with a type that includes a prototype, in a header,182)
    whose contents are made available by the #include preprocessing directive. The
    header declares a set of related functions, plus any necessary types and additional macros
    needed to facilitate their use. Declarations of types described in this clause shall not
    include type qualifiers, unless explicitly stated otherwise.
2   The standard headers are183)
           <assert.h>             <iso646.h>              <stdarg.h>              <string.h>
           <complex.h>            <limits.h>              <stdatomic.h>           <tgmath.h>
           <ctype.h>              <locale.h>              <stdbool.h>             <threads.h>
           <errno.h>              <math.h>                <stddef.h>              <time.h>
           <fenv.h>               <setjmp.h>              <stdint.h>              <uchar.h>
           <float.h>              <signal.h>              <stdio.h>               <wchar.h>
           <inttypes.h>           <stdalign.h>            <stdlib.h>              <wctype.h>
3   If a file with the same name as one of the above < and > delimited sequences, not
    provided as part of the implementation, is placed in any of the standard places that are
    searched for included source files, the behavior is undefined.
4   Standard headers may be included in any order; each may be included more than once in
    a given scope, with no effect different from being included only once, except that the
    effect of including <assert.h> depends on the definition of NDEBUG (see 7.2). If
    used, a header shall be included outside of any external declaration or definition, and it
    shall first be included before the first reference to any of the functions or objects it
    declares, or to any of the types or macros it defines. However, if an identifier is declared
    or defined in more than one header, the second and subsequent associated headers may be
    included after the initial reference to the identifier. The program shall not have any
    macros with names lexically identical to keywords currently defined prior to the
    inclusion.
5   Any definition of an object-like macro described in this clause shall expand to code that is
    fully protected by parentheses where necessary, so that it groups in an arbitrary
    expression as if it were a single identifier.
6   Any declaration of a library function shall have external linkage.




    182) A header is not necessarily a source file, nor are the < and > delimited sequences in header names
         necessarily valid source file names.
    183) The headers <complex.h>, <stdatomic.h>, and <threads.h> are conditional features that
         implementations need not support; see 6.10.8.3.

[page 180]

7   A summary of the contents of the standard headers is given in annex B.
    Forward references: diagnostics (7.2).
    7.1.3 Reserved identifiers
1   Each header declares or defines all identifiers listed in its associated subclause, and
    optionally declares or defines identifiers listed in its associated future library directions
    subclause and identifiers which are always reserved either for any use or for use as file
    scope identifiers.
    -- All identifiers that begin with an underscore and either an uppercase letter or another
      underscore are always reserved for any use.
    -- All identifiers that begin with an underscore are always reserved for use as identifiers
      with file scope in both the ordinary and tag name spaces.
    -- Each macro name in any of the following subclauses (including the future library
      directions) is reserved for use as specified if any of its associated headers is included;
      unless explicitly stated otherwise (see 7.1.4).
    -- All identifiers with external linkage in any of the following subclauses (including the
      future library directions) and errno are always reserved for use as identifiers with
      external linkage.184)
    -- Each identifier with file scope listed in any of the following subclauses (including the
      future library directions) is reserved for use as a macro name and as an identifier with
      file scope in the same name space if any of its associated headers is included.
2   No other identifiers are reserved. If the program declares or defines an identifier in a
    context in which it is reserved (other than as allowed by 7.1.4), or defines a reserved
    identifier as a macro name, the behavior is undefined.
3   If the program removes (with #undef) any macro definition of an identifier in the first
    group listed above, the behavior is undefined.




    184) The list of reserved identifiers with external linkage includes math_errhandling, setjmp,
         va_copy, and va_end.

[page 181]

    7.1.4 Use of library functions
1   Each of the following statements applies unless explicitly stated otherwise in the detailed
    descriptions that follow: If an argument to a function has an invalid value (such as a value
    outside the domain of the function, or a pointer outside the address space of the program,
    or a null pointer, or a pointer to non-modifiable storage when the corresponding
    parameter is not const-qualified) or a type (after promotion) not expected by a function
    with variable number of arguments, the behavior is undefined. If a function argument is
    described as being an array, the pointer actually passed to the function shall have a value
    such that all address computations and accesses to objects (that would be valid if the
    pointer did point to the first element of such an array) are in fact valid. Any function
    declared in a header may be additionally implemented as a function-like macro defined in
    the header, so if a library function is declared explicitly when its header is included, one
    of the techniques shown below can be used to ensure the declaration is not affected by
    such a macro. Any macro definition of a function can be suppressed locally by enclosing
    the name of the function in parentheses, because the name is then not followed by the left
    parenthesis that indicates expansion of a macro function name. For the same syntactic
    reason, it is permitted to take the address of a library function even if it is also defined as
    a macro.185) The use of #undef to remove any macro definition will also ensure that an
    actual function is referred to. Any invocation of a library function that is implemented as
    a macro shall expand to code that evaluates each of its arguments exactly once, fully
    protected by parentheses where necessary, so it is generally safe to use arbitrary
    expressions as arguments.186) Likewise, those function-like macros described in the
    following subclauses may be invoked in an expression anywhere a function with a
    compatible return type could be called.187) All object-like macros listed as expanding to


    185) This means that an implementation shall provide an actual function for each library function, even if it
         also provides a macro for that function.
    186) Such macros might not contain the sequence points that the corresponding function calls do.
    187) Because external identifiers and some macro names beginning with an underscore are reserved,
         implementations may provide special semantics for such names. For example, the identifier
         _BUILTIN_abs could be used to indicate generation of in-line code for the abs function. Thus, the
         appropriate header could specify
                   #define abs(x) _BUILTIN_abs(x)
          for a compiler whose code generator will accept it.
          In this manner, a user desiring to guarantee that a given library function such as abs will be a genuine
          function may write
                   #undef abs
          whether the implementation's header provides a macro implementation of abs or a built-in
          implementation. The prototype for the function, which precedes and is hidden by any macro
          definition, is thereby revealed also.

[page 182]

    integer constant expressions shall additionally be suitable for use in #if preprocessing
    directives.
2   Provided that a library function can be declared without reference to any type defined in a
    header, it is also permissible to declare the function and use it without including its
    associated header.
3   There is a sequence point immediately before a library function returns.
4   The functions in the standard library are not guaranteed to be reentrant and may modify
    objects with static or thread storage duration.188)
5   Unless explicitly stated otherwise in the detailed descriptions that follow, library
    functions shall prevent data races as follows: A library function shall not directly or
    indirectly access objects accessible by threads other than the current thread unless the
    objects are accessed directly or indirectly via the function's arguments. A library
    function shall not directly or indirectly modify objects accessible by threads other than
    the current thread unless the objects are accessed directly or indirectly via the function's
    non-const arguments.189) Implementations may share their own internal objects between
    threads if the objects are not visible to users and are protected against data races.
6   Unless otherwise specified, library functions shall perform all operations solely within the
    current thread if those operations have effects that are visible to users.190)
7   EXAMPLE        The function atoi may be used in any of several ways:
    -- by use of its associated header (possibly generating a macro expansion)
                 #include <stdlib.h>
                 const char *str;
                 /* ... */
                 i = atoi(str);
    -- by use of its associated header (assuredly generating a true function reference)




    188) Thus, a signal handler cannot, in general, call standard library functions.
    189) This means, for example, that an implementation is not permitted to use a static object for internal
         purposes without synchronization because it could cause a data race even in programs that do not
         explicitly share objects between threads.
    190) This allows implementations to parallelize operations if there are no visible side effects.

[page 183]

            #include <stdlib.h>
            #undef atoi
            const char *str;
            /* ... */
            i = atoi(str);
   or
            #include <stdlib.h>
            const char *str;
            /* ... */
            i = (atoi)(str);
-- by explicit declaration
            extern int atoi(const char *);
            const char *str;
            /* ... */
            i = atoi(str);




[page 184]

    7.2 Diagnostics <assert.h>
1   The header <assert.h> defines the assert and static_assert macros and
    refers to another macro,
            NDEBUG
    which is not defined by <assert.h>. If NDEBUG is defined as a macro name at the
    point in the source file where <assert.h> is included, the assert macro is defined
    simply as
            #define assert(ignore) ((void)0)
    The assert macro is redefined according to the current state of NDEBUG each time that
    <assert.h> is included.
2   The assert macro shall be implemented as a macro, not as an actual function. If the
    macro definition is suppressed in order to access an actual function, the behavior is
    undefined.
3   The macro
            static_assert
    expands to _Static_assert.
    7.2.1 Program diagnostics
    7.2.1.1 The assert macro
    Synopsis
1           #include <assert.h>
            void assert(scalar expression);
    Description
2   The assert macro puts diagnostic tests into programs; it expands to a void expression.
    When it is executed, if expression (which shall have a scalar type) is false (that is,
    compares equal to 0), the assert macro writes information about the particular call that
    failed (including the text of the argument, the name of the source file, the source line
    number, and the name of the enclosing function -- the latter are respectively the values of
    the preprocessing macros __FILE__ and __LINE__ and of the identifier
    __func__) on the standard error stream in an implementation-defined format.191) It
    then calls the abort function.



    191) The message written might be of the form:
         Assertion failed: expression, function abc, file xyz, line nnn.


[page 185]

    Returns
3   The assert macro returns no value.
    Forward references: the abort function (7.22.4.1).




[page 186]

    7.3 Complex arithmetic <complex.h>
    7.3.1 Introduction
1   The header <complex.h> defines macros and declares functions that support complex
    arithmetic.192)
2   Implementations that define the macro __STDC_NO_COMPLEX__ need not provide
    this header nor support any of its facilities.
3   Each synopsis specifies a family of functions consisting of a principal function with one
    or more double complex parameters and a double complex or double return
    value; and other functions with the same name but with f and l suffixes which are
    corresponding functions with float and long double parameters and return values.
4   The macro
             complex
    expands to _Complex; the macro
             _Complex_I
    expands to a constant expression of type const float _Complex, with the value of
    the imaginary unit.193)
5   The macros
             imaginary
    and
             _Imaginary_I
    are defined if and only if the implementation supports imaginary types;194) if defined,
    they expand to _Imaginary and a constant expression of type const float
    _Imaginary with the value of the imaginary unit.
6   The macro
             I
    expands to either _Imaginary_I or _Complex_I. If _Imaginary_I is not
    defined, I shall expand to _Complex_I.
7   Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
    redefine the macros complex, imaginary, and I.

    192) See ''future library directions'' (7.30.1).
    193) The imaginary unit is a number i such that i 2 = -1.
    194) A specification for imaginary types is in informative annex G.

[page 187]

    Forward references: IEC 60559-compatible complex arithmetic (annex G).
    7.3.2 Conventions
1   Values are interpreted as radians, not degrees. An implementation may set errno but is
    not required to.
    7.3.3 Branch cuts
1   Some of the functions below have branch cuts, across which the function is
    discontinuous. For implementations with a signed zero (including all IEC 60559
    implementations) that follow the specifications of annex G, the sign of zero distinguishes
    one side of a cut from another so the function is continuous (except for format
    limitations) as the cut is approached from either side. For example, for the square root
    function, which has a branch cut along the negative real axis, the top of the cut, with
    imaginary part +0, maps to the positive imaginary axis, and the bottom of the cut, with
    imaginary part -0, maps to the negative imaginary axis.
2   Implementations that do not support a signed zero (see annex F) cannot distinguish the
    sides of branch cuts. These implementations shall map a cut so the function is continuous
    as the cut is approached coming around the finite endpoint of the cut in a counter
    clockwise direction. (Branch cuts for the functions specified here have just one finite
    endpoint.) For example, for the square root function, coming counter clockwise around
    the finite endpoint of the cut along the negative real axis approaches the cut from above,
    so the cut maps to the positive imaginary axis.
    7.3.4 The CX_LIMITED_RANGE pragma
    Synopsis
1          #include <complex.h>
           #pragma STDC CX_LIMITED_RANGE on-off-switch
    Description
2   The usual mathematical formulas for complex multiply, divide, and absolute value are
    problematic because of their treatment of infinities and because of undue overflow and
    underflow. The CX_LIMITED_RANGE pragma can be used to inform the
    implementation that (where the state is ''on'') the usual mathematical formulas are
    acceptable.195) The pragma can occur either outside external declarations or preceding all
    explicit declarations and statements inside a compound statement. When outside external
    declarations, the pragma takes effect from its occurrence until another
    CX_LIMITED_RANGE pragma is encountered, or until the end of the translation unit.
    When inside a compound statement, the pragma takes effect from its occurrence until
    another CX_LIMITED_RANGE pragma is encountered (including within a nested
    compound statement), or until the end of the compound statement; at the end of a
    compound statement the state for the pragma is restored to its condition just before the

[page 188]

    compound statement. If this pragma is used in any other context, the behavior is
    undefined. The default state for the pragma is ''off''.
    7.3.5 Trigonometric functions
    7.3.5.1 The cacos functions
    Synopsis
1           #include <complex.h>
            double complex cacos(double complex z);
            float complex cacosf(float complex z);
            long double complex cacosl(long double complex z);
    Description
2   The cacos functions compute the complex arc cosine of z, with branch cuts outside the
    interval [-1, +1] along the real axis.
    Returns
3   The cacos functions return the complex arc cosine value, in the range of a strip
    mathematically unbounded along the imaginary axis and in the interval [0, pi ] along the
    real axis.
    7.3.5.2 The casin functions
    Synopsis
1           #include <complex.h>
            double complex casin(double complex z);
            float complex casinf(float complex z);
            long double complex casinl(long double complex z);
    Description
2   The casin functions compute the complex arc sine of z, with branch cuts outside the
    interval [-1, +1] along the real axis.
    Returns
3   The casin functions return the complex arc sine value, in the range of a strip
    mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]

    195) The purpose of the pragma is to allow the implementation to use the formulas:
            (x + iy) x (u + iv) = (xu - yv) + i(yu + xv)
            (x + iy) / (u + iv) = [(xu + yv) + i(yu - xv)]/(u2 + v 2 )
            | x + iy | = sqrt: x 2 + y 2
                         -----
         where the programmer can determine they are safe.

[page 189]

    along the real axis.
    7.3.5.3 The catan functions
    Synopsis
1          #include <complex.h>
           double complex catan(double complex z);
           float complex catanf(float complex z);
           long double complex catanl(long double complex z);
    Description
2   The catan functions compute the complex arc tangent of z, with branch cuts outside the
    interval [-i, +i] along the imaginary axis.
    Returns
3   The catan functions return the complex arc tangent value, in the range of a strip
    mathematically unbounded along the imaginary axis and in the interval [-pi /2, +pi /2]
    along the real axis.
    7.3.5.4 The ccos functions
    Synopsis
1          #include <complex.h>
           double complex ccos(double complex z);
           float complex ccosf(float complex z);
           long double complex ccosl(long double complex z);
    Description
2   The ccos functions compute the complex cosine of z.
    Returns
3   The ccos functions return the complex cosine value.
    7.3.5.5 The csin functions
    Synopsis
1          #include <complex.h>
           double complex csin(double complex z);
           float complex csinf(float complex z);
           long double complex csinl(long double complex z);
    Description
2   The csin functions compute the complex sine of z.



[page 190]

    Returns
3   The csin functions return the complex sine value.
    7.3.5.6 The ctan functions
    Synopsis
1           #include <complex.h>
            double complex ctan(double complex z);
            float complex ctanf(float complex z);
            long double complex ctanl(long double complex z);
    Description
2   The ctan functions compute the complex tangent of z.
    Returns
3   The ctan functions return the complex tangent value.
    7.3.6 Hyperbolic functions
    7.3.6.1 The cacosh functions
    Synopsis
1           #include <complex.h>
            double complex cacosh(double complex z);
            float complex cacoshf(float complex z);
            long double complex cacoshl(long double complex z);
    Description
2   The cacosh functions compute the complex arc hyperbolic cosine of z, with a branch
    cut at values less than 1 along the real axis.
    Returns
3   The cacosh functions return the complex arc hyperbolic cosine value, in the range of a
    half-strip of nonnegative values along the real axis and in the interval [-ipi , +ipi ] along the
    imaginary axis.
    7.3.6.2 The casinh functions
    Synopsis
1           #include <complex.h>
            double complex casinh(double complex z);
            float complex casinhf(float complex z);
            long double complex casinhl(long double complex z);



[page 191]

    Description
2   The casinh functions compute the complex arc hyperbolic sine of z, with branch cuts
    outside the interval [-i, +i] along the imaginary axis.
    Returns
3   The casinh functions return the complex arc hyperbolic sine value, in the range of a
    strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
    along the imaginary axis.
    7.3.6.3 The catanh functions
    Synopsis
1          #include <complex.h>
           double complex catanh(double complex z);
           float complex catanhf(float complex z);
           long double complex catanhl(long double complex z);
    Description
2   The catanh functions compute the complex arc hyperbolic tangent of z, with branch
    cuts outside the interval [-1, +1] along the real axis.
    Returns
3   The catanh functions return the complex arc hyperbolic tangent value, in the range of a
    strip mathematically unbounded along the real axis and in the interval [-ipi /2, +ipi /2]
    along the imaginary axis.
    7.3.6.4 The ccosh functions
    Synopsis
1          #include <complex.h>
           double complex ccosh(double complex z);
           float complex ccoshf(float complex z);
           long double complex ccoshl(long double complex z);
    Description
2   The ccosh functions compute the complex hyperbolic cosine of z.
    Returns
3   The ccosh functions return the complex hyperbolic cosine value.




[page 192]

    7.3.6.5 The csinh functions
    Synopsis
1           #include <complex.h>
            double complex csinh(double complex z);
            float complex csinhf(float complex z);
            long double complex csinhl(long double complex z);
    Description
2   The csinh functions compute the complex hyperbolic sine of z.
    Returns
3   The csinh functions return the complex hyperbolic sine value.
    7.3.6.6 The ctanh functions
    Synopsis
1           #include <complex.h>
            double complex ctanh(double complex z);
            float complex ctanhf(float complex z);
            long double complex ctanhl(long double complex z);
    Description
2   The ctanh functions compute the complex hyperbolic tangent of z.
    Returns
3   The ctanh functions return the complex hyperbolic tangent value.
    7.3.7 Exponential and logarithmic functions
    7.3.7.1 The cexp functions
    Synopsis
1           #include <complex.h>
            double complex cexp(double complex z);
            float complex cexpf(float complex z);
            long double complex cexpl(long double complex z);
    Description
2   The cexp functions compute the complex base-e exponential of z.
    Returns
3   The cexp functions return the complex base-e exponential value.



[page 193]

    7.3.7.2 The clog functions
    Synopsis
1          #include <complex.h>
           double complex clog(double complex z);
           float complex clogf(float complex z);
           long double complex clogl(long double complex z);
    Description
2   The clog functions compute the complex natural (base-e) logarithm of z, with a branch
    cut along the negative real axis.
    Returns
3   The clog functions return the complex natural logarithm value, in the range of a strip
    mathematically unbounded along the real axis and in the interval [-ipi , +ipi ] along the
    imaginary axis.
    7.3.8 Power and absolute-value functions
    7.3.8.1 The cabs functions
    Synopsis
1          #include <complex.h>
           double cabs(double complex z);
           float cabsf(float complex z);
           long double cabsl(long double complex z);
    Description
2   The cabs functions compute the complex absolute value (also called norm, modulus, or
    magnitude) of z.
    Returns
3   The cabs functions return the complex absolute value.
    7.3.8.2 The cpow functions
    Synopsis
1          #include <complex.h>
           double complex cpow(double complex x, double complex y);
           float complex cpowf(float complex x, float complex y);
           long double complex cpowl(long double complex x,
                long double complex y);




[page 194]

    Description
2   The cpow functions compute the complex power function xy , with a branch cut for the
    first parameter along the negative real axis.
    Returns
3   The cpow functions return the complex power function value.
    7.3.8.3 The csqrt functions
    Synopsis
1           #include <complex.h>
            double complex csqrt(double complex z);
            float complex csqrtf(float complex z);
            long double complex csqrtl(long double complex z);
    Description
2   The csqrt functions compute the complex square root of z, with a branch cut along the
    negative real axis.
    Returns
3   The csqrt functions return the complex square root value, in the range of the right half-
    plane (including the imaginary axis).
    7.3.9 Manipulation functions
    7.3.9.1 The carg functions
    Synopsis
1           #include <complex.h>
            double carg(double complex z);
            float cargf(float complex z);
            long double cargl(long double complex z);
    Description
2   The carg functions compute the argument (also called phase angle) of z, with a branch
    cut along the negative real axis.
    Returns
3   The carg functions return the value of the argument in the interval [-pi , +pi ].




[page 195]

    7.3.9.2 The cimag functions
    Synopsis
1          #include <complex.h>
           double cimag(double complex z);
           float cimagf(float complex z);
           long double cimagl(long double complex z);
    Description
2   The cimag functions compute the imaginary part of z.196)
    Returns
3   The cimag functions return the imaginary part value (as a real).
    7.3.9.3 The CMPLX macros
    Synopsis
1          #include <complex.h>
           double complex CMPLX(double x, double y);
           float complex CMPLXF(float x, float y);
           long double complex CMPLXL(long double x, long double y);
    Description
2   The CMPLX macros expand to an expression of the specified complex type, with the real
    part having the (converted) value of x and the imaginary part having the (converted)
    value of y.
    Recommended practice
3   The resulting expression should be suitable for use as an initializer for an object with
    static or thread storage duration, provided both arguments are likewise suitable.
    Returns
4   The CMPLX macros return the complex value x + i y.
5   NOTE    These macros act as if the implementation supported imaginary types and the definitions were:
          #define CMPLX(x, y)  ((double complex)((double)(x) + \
                                        _Imaginary_I * (double)(y)))
          #define CMPLXF(x, y) ((float complex)((float)(x) + \
                                        _Imaginary_I * (float)(y)))
          #define CMPLXL(x, y) ((long double complex)((long double)(x) + \
                                        _Imaginary_I * (long double)(y)))




    196) For a variable z of complex type, z == creal(z) + cimag(z)*I.

[page 196]

    7.3.9.4 The conj functions
    Synopsis
1           #include <complex.h>
            double complex conj(double complex z);
            float complex conjf(float complex z);
            long double complex conjl(long double complex z);
    Description
2   The conj functions compute the complex conjugate of z, by reversing the sign of its
    imaginary part.
    Returns
3   The conj functions return the complex conjugate value.
    7.3.9.5 The cproj functions
    Synopsis
1           #include <complex.h>
            double complex cproj(double complex z);
            float complex cprojf(float complex z);
            long double complex cprojl(long double complex z);
    Description
2   The cproj functions compute a projection of z onto the Riemann sphere: z projects to
    z except that all complex infinities (even those with one infinite part and one NaN part)
    project to positive infinity on the real axis. If z has an infinite part, then cproj(z) is
    equivalent to
            INFINITY + I * copysign(0.0, cimag(z))
    Returns
3   The cproj functions return the value of the projection onto the Riemann sphere.
    7.3.9.6 The creal functions
    Synopsis
1           #include <complex.h>
            double creal(double complex z);
            float crealf(float complex z);
            long double creall(long double complex z);
    Description
2   The creal functions compute the real part of z.197)


[page 197]

    Returns
3   The creal functions return the real part value.




    197) For a variable z of complex type, z == creal(z) + cimag(z)*I.

[page 198]

    7.4 Character handling <ctype.h>
1   The header <ctype.h> declares several functions useful for classifying and mapping
    characters.198) In all cases the argument is an int, the value of which shall be
    representable as an unsigned char or shall equal the value of the macro EOF. If the
    argument has any other value, the behavior is undefined.
2   The behavior of these functions is affected by the current locale. Those functions that
    have locale-specific aspects only when not in the "C" locale are noted below.
3   The term printing character refers to a member of a locale-specific set of characters, each
    of which occupies one printing position on a display device; the term control character
    refers to a member of a locale-specific set of characters that are not printing
    characters.199) All letters and digits are printing characters.
    Forward references: EOF (7.21.1), localization (7.11).
    7.4.1 Character classification functions
1   The functions in this subclause return nonzero (true) if and only if the value of the
    argument c conforms to that in the description of the function.
    7.4.1.1 The isalnum function
    Synopsis
1            #include <ctype.h>
             int isalnum(int c);
    Description
2   The isalnum function tests for any character for which isalpha or isdigit is true.
    7.4.1.2 The isalpha function
    Synopsis
1            #include <ctype.h>
             int isalpha(int c);
    Description
2   The isalpha function tests for any character for which isupper or islower is true,
    or any character that is one of a locale-specific set of alphabetic characters for which



    198) See ''future library directions'' (7.30.2).
    199) In an implementation that uses the seven-bit US ASCII character set, the printing characters are those
         whose values lie from 0x20 (space) through 0x7E (tilde); the control characters are those whose
         values lie from 0 (NUL) through 0x1F (US), and the character 0x7F (DEL).

[page 199]

    none of iscntrl, isdigit, ispunct, or isspace is true.200) In the "C" locale,
    isalpha returns true only for the characters for which isupper or islower is true.
    7.4.1.3 The isblank function
    Synopsis
1           #include <ctype.h>
            int isblank(int c);
    Description
2   The isblank function tests for any character that is a standard blank character or is one
    of a locale-specific set of characters for which isspace is true and that is used to
    separate words within a line of text. The standard blank characters are the following:
    space (' '), and horizontal tab ('\t'). In the "C" locale, isblank returns true only
    for the standard blank characters.
    7.4.1.4 The iscntrl function
    Synopsis
1           #include <ctype.h>
            int iscntrl(int c);
    Description
2   The iscntrl function tests for any control character.
    7.4.1.5 The isdigit function
    Synopsis
1           #include <ctype.h>
            int isdigit(int c);
    Description
2   The isdigit function tests for any decimal-digit character (as defined in 5.2.1).
    7.4.1.6 The isgraph function
    Synopsis
1           #include <ctype.h>
            int isgraph(int c);




    200) The functions islower and isupper test true or false separately for each of these additional
         characters; all four combinations are possible.

[page 200]

    Description
2   The isgraph function tests for any printing character except space (' ').
    7.4.1.7 The islower function
    Synopsis
1           #include <ctype.h>
            int islower(int c);
    Description
2   The islower function tests for any character that is a lowercase letter or is one of a
    locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
    isspace is true. In the "C" locale, islower returns true only for the lowercase
    letters (as defined in 5.2.1).
    7.4.1.8 The isprint function
    Synopsis
1           #include <ctype.h>
            int isprint(int c);
    Description
2   The isprint function tests for any printing character including space (' ').
    7.4.1.9 The ispunct function
    Synopsis
1           #include <ctype.h>
            int ispunct(int c);
    Description
2   The ispunct function tests for any printing character that is one of a locale-specific set
    of punctuation characters for which neither isspace nor isalnum is true. In the "C"
    locale, ispunct returns true for every printing character for which neither isspace
    nor isalnum is true.
    7.4.1.10 The isspace function
    Synopsis
1           #include <ctype.h>
            int isspace(int c);
    Description
2   The isspace function tests for any character that is a standard white-space character or
    is one of a locale-specific set of characters for which isalnum is false. The standard

[page 201]

    white-space characters are the following: space (' '), form feed ('\f'), new-line
    ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the
    "C" locale, isspace returns true only for the standard white-space characters.
    7.4.1.11 The isupper function
    Synopsis
1          #include <ctype.h>
           int isupper(int c);
    Description
2   The isupper function tests for any character that is an uppercase letter or is one of a
    locale-specific set of characters for which none of iscntrl, isdigit, ispunct, or
    isspace is true. In the "C" locale, isupper returns true only for the uppercase
    letters (as defined in 5.2.1).
    7.4.1.12 The isxdigit function
    Synopsis
1          #include <ctype.h>
           int isxdigit(int c);
    Description
2   The isxdigit function tests for any hexadecimal-digit character (as defined in 6.4.4.1).
    7.4.2 Character case mapping functions
    7.4.2.1 The tolower function
    Synopsis
1          #include <ctype.h>
           int tolower(int c);
    Description
2   The tolower function converts an uppercase letter to a corresponding lowercase letter.
    Returns
3   If the argument is a character for which isupper is true and there are one or more
    corresponding characters, as specified by the current locale, for which islower is true,
    the tolower function returns one of the corresponding characters (always the same one
    for any given locale); otherwise, the argument is returned unchanged.




[page 202]

    7.4.2.2 The toupper function
    Synopsis
1           #include <ctype.h>
            int toupper(int c);
    Description
2   The toupper function converts a lowercase letter to a corresponding uppercase letter.
    Returns
3   If the argument is a character for which islower is true and there are one or more
    corresponding characters, as specified by the current locale, for which isupper is true,
    the toupper function returns one of the corresponding characters (always the same one
    for any given locale); otherwise, the argument is returned unchanged.




[page 203]

    7.5 Errors <errno.h>
1   The header <errno.h> defines several macros, all relating to the reporting of error
    conditions.
2   The macros are
             EDOM
             EILSEQ
             ERANGE
    which expand to integer constant expressions with type int, distinct positive values, and
    which are suitable for use in #if preprocessing directives; and
             errno
    which expands to a modifiable lvalue201) that has type int and thread local storage
    duration, the value of which is set to a positive error number by several library functions.
    If a macro definition is suppressed in order to access an actual object, or a program
    defines an identifier with the name errno, the behavior is undefined.
3   The value of errno in the initial thread is zero at program startup (the initial value of
    errno in other threads is an indeterminate value), but is never set to zero by any library
    function.202) The value of errno may be set to nonzero by a library function call
    whether or not there is an error, provided the use of errno is not documented in the
    description of the function in this International Standard.
4   Additional macro definitions, beginning with E and a digit or E and an uppercase
    letter,203) may also be specified by the implementation.




    201) The macro errno need not be the identifier of an object. It might expand to a modifiable lvalue
         resulting from a function call (for example, *errno()).
    202) Thus, a program that uses errno for error checking should set it to zero before a library function call,
         then inspect it before a subsequent library function call. Of course, a library function can save the
         value of errno on entry and then set it to zero, as long as the original value is restored if errno's
         value is still zero just before the return.
    203) See ''future library directions'' (7.30.3).

[page 204]

    7.6 Floating-point environment <fenv.h>
1   The header <fenv.h> defines several macros, and declares types and functions that
    provide access to the floating-point environment. The floating-point environment refers
    collectively to any floating-point status flags and control modes supported by the
    implementation.204) A floating-point status flag is a system variable whose value is set
    (but never cleared) when a floating-point exception is raised, which occurs as a side effect
    of exceptional floating-point arithmetic to provide auxiliary information.205) A floating-
    point control mode is a system variable whose value may be set by the user to affect the
    subsequent behavior of floating-point arithmetic.
2   The floating-point environment has thread storage duration. The initial state for a
    thread's floating-point environment is the current state of the floating-point environment
    of the thread that creates it at the time of creation.
3   Certain programming conventions support the intended model of use for the floating-
    point environment:206)
    -- a function call does not alter its caller's floating-point control modes, clear its caller's
      floating-point status flags, nor depend on the state of its caller's floating-point status
      flags unless the function is so documented;
    -- a function call is assumed to require default floating-point control modes, unless its
      documentation promises otherwise;
    -- a function call is assumed to have the potential for raising floating-point exceptions,
      unless its documentation promises otherwise.
4   The type
            fenv_t
    represents the entire floating-point environment.
5   The type
            fexcept_t
    represents the floating-point status flags collectively, including any status the
    implementation associates with the flags.


    204) This header is designed to support the floating-point exception status flags and directed-rounding
         control modes required by IEC 60559, and other similar floating-point state information. It is also
         designed to facilitate code portability among all systems.
    205) A floating-point status flag is not an object and can be set more than once within an expression.
    206) With these conventions, a programmer can safely assume default floating-point control modes (or be
         unaware of them). The responsibilities associated with accessing the floating-point environment fall
         on the programmer or program that does so explicitly.

[page 205]

6   Each of the macros
             FE_DIVBYZERO
             FE_INEXACT
             FE_INVALID
             FE_OVERFLOW
             FE_UNDERFLOW
    is defined if and only if the implementation supports the floating-point exception by
    means of the functions in 7.6.2.207) Additional implementation-defined floating-point
    exceptions, with macro definitions beginning with FE_ and an uppercase letter, may also
    be specified by the implementation. The defined macros expand to integer constant
    expressions with values such that bitwise ORs of all combinations of the macros result in
    distinct values, and furthermore, bitwise ANDs of all combinations of the macros result in
    zero.208)
7   The macro
             FE_ALL_EXCEPT
    is simply the bitwise OR of all floating-point exception macros defined by the
    implementation. If no such macros are defined, FE_ALL_EXCEPT shall be defined as 0.
8   Each of the macros
             FE_DOWNWARD
             FE_TONEAREST
             FE_TOWARDZERO
             FE_UPWARD
    is defined if and only if the implementation supports getting and setting the represented
    rounding direction by means of the fegetround and fesetround functions.
    Additional implementation-defined rounding directions, with macro definitions beginning
    with FE_ and an uppercase letter, may also be specified by the implementation. The
    defined macros expand to integer constant expressions whose values are distinct
    nonnegative values.209)
9   The macro



    207) The implementation supports a floating-point exception if there are circumstances where a call to at
         least one of the functions in 7.6.2, using the macro as the appropriate argument, will succeed. It is not
         necessary for all the functions to succeed all the time.
    208) The macros should be distinct powers of two.
    209) Even though the rounding direction macros may expand to constants corresponding to the values of
         FLT_ROUNDS, they are not required to do so.

[page 206]

              FE_DFL_ENV
     represents the default floating-point environment -- the one installed at program startup
     -- and has type ''pointer to const-qualified fenv_t''. It can be used as an argument to
     <fenv.h> functions that manage the floating-point environment.
10   Additional implementation-defined environments, with macro definitions beginning with
     FE_ and an uppercase letter, and having type ''pointer to const-qualified fenv_t'', may
     also be specified by the implementation.
     7.6.1 The FENV_ACCESS pragma
     Synopsis
1             #include <fenv.h>
              #pragma STDC FENV_ACCESS on-off-switch
     Description
2    The FENV_ACCESS pragma provides a means to inform the implementation when a
     program might access the floating-point environment to test floating-point status flags or
     run under non-default floating-point control modes.210) The pragma shall occur either
     outside external declarations or preceding all explicit declarations and statements inside a
     compound statement. When outside external declarations, the pragma takes effect from
     its occurrence until another FENV_ACCESS pragma is encountered, or until the end of
     the translation unit. When inside a compound statement, the pragma takes effect from its
     occurrence until another FENV_ACCESS pragma is encountered (including within a
     nested compound statement), or until the end of the compound statement; at the end of a
     compound statement the state for the pragma is restored to its condition just before the
     compound statement. If this pragma is used in any other context, the behavior is
     undefined. If part of a program tests floating-point status flags, sets floating-point control
     modes, or runs under non-default mode settings, but was translated with the state for the
     FENV_ACCESS pragma ''off'', the behavior is undefined. The default state (''on'' or
     ''off'') for the pragma is implementation-defined. (When execution passes from a part of
     the program translated with FENV_ACCESS ''off'' to a part translated with
     FENV_ACCESS ''on'', the state of the floating-point status flags is unspecified and the
     floating-point control modes have their default settings.)




     210) The purpose of the FENV_ACCESS pragma is to allow certain optimizations that could subvert flag
          tests and mode changes (e.g., global common subexpression elimination, code motion, and constant
          folding). In general, if the state of FENV_ACCESS is ''off'', the translator can assume that default
          modes are in effect and the flags are not tested.

[page 207]

3   EXAMPLE
            #include <fenv.h>
            void f(double x)
            {
                  #pragma STDC FENV_ACCESS ON
                  void g(double);
                  void h(double);
                  /* ... */
                  g(x + 1);
                  h(x + 1);
                  /* ... */
            }
4   If the function g might depend on status flags set as a side effect of the first x + 1, or if the second
    x + 1 might depend on control modes set as a side effect of the call to function g, then the program shall
    contain an appropriately placed invocation of #pragma STDC FENV_ACCESS ON.211)

    7.6.2 Floating-point exceptions
1   The following functions provide access to the floating-point status flags.212) The int
    input argument for the functions represents a subset of floating-point exceptions, and can
    be zero or the bitwise OR of one or more floating-point exception macros, for example
    FE_OVERFLOW | FE_INEXACT. For other argument values the behavior of these
    functions is undefined.
    7.6.2.1 The feclearexcept function
    Synopsis
1           #include <fenv.h>
            int feclearexcept(int excepts);
    Description
2   The feclearexcept function attempts to clear the supported floating-point exceptions
    represented by its argument.
    Returns
3   The feclearexcept function returns zero if the excepts argument is zero or if all
    the specified exceptions were successfully cleared. Otherwise, it returns a nonzero value.


    211) The side effects impose a temporal ordering that requires two evaluations of x + 1. On the other
         hand, without the #pragma STDC FENV_ACCESS ON pragma, and assuming the default state is
         ''off'', just one evaluation of x + 1 would suffice.
    212) The functions fetestexcept, feraiseexcept, and feclearexcept support the basic
         abstraction of flags that are either set or clear. An implementation may endow floating-point status
         flags with more information -- for example, the address of the code which first raised the floating-
         point exception; the functions fegetexceptflag and fesetexceptflag deal with the full
         content of flags.

[page 208]

    7.6.2.2 The fegetexceptflag function
    Synopsis
1            #include <fenv.h>
             int fegetexceptflag(fexcept_t *flagp,
                  int excepts);
    Description
2   The fegetexceptflag function attempts to store an implementation-defined
    representation of the states of the floating-point status flags indicated by the argument
    excepts in the object pointed to by the argument flagp.
    Returns
3   The fegetexceptflag function returns zero if the representation was successfully
    stored. Otherwise, it returns a nonzero value.
    7.6.2.3 The feraiseexcept function
    Synopsis
1            #include <fenv.h>
             int feraiseexcept(int excepts);
    Description
2   The feraiseexcept function attempts to raise the supported floating-point exceptions
    represented by its argument.213) The order in which these floating-point exceptions are
    raised is unspecified, except as stated in F.8.6. Whether the feraiseexcept function
    additionally raises the ''inexact'' floating-point exception whenever it raises the
    ''overflow'' or ''underflow'' floating-point exception is implementation-defined.
    Returns
3   The feraiseexcept function returns zero if the excepts argument is zero or if all
    the specified exceptions were successfully raised. Otherwise, it returns a nonzero value.




    213) The effect is intended to be similar to that of floating-point exceptions raised by arithmetic operations.
         Hence, enabled traps for floating-point exceptions raised by this function are taken. The specification
         in F.8.6 is in the same spirit.

[page 209]

    7.6.2.4 The fesetexceptflag function
    Synopsis
1           #include <fenv.h>
            int fesetexceptflag(const fexcept_t *flagp,
                 int excepts);
    Description
2   The fesetexceptflag function attempts to set the floating-point status flags
    indicated by the argument excepts to the states stored in the object pointed to by
    flagp. The value of *flagp shall have been set by a previous call to
    fegetexceptflag whose second argument represented at least those floating-point
    exceptions represented by the argument excepts. This function does not raise floating-
    point exceptions, but only sets the state of the flags.
    Returns
3   The fesetexceptflag function returns zero if the excepts argument is zero or if
    all the specified flags were successfully set to the appropriate state. Otherwise, it returns
    a nonzero value.
    7.6.2.5 The fetestexcept function
    Synopsis
1           #include <fenv.h>
            int fetestexcept(int excepts);
    Description
2   The fetestexcept function determines which of a specified subset of the floating-
    point exception flags are currently set. The excepts argument specifies the floating-
    point status flags to be queried.214)
    Returns
3   The fetestexcept function returns the value of the bitwise OR of the floating-point
    exception macros corresponding to the currently set floating-point exceptions included in
    excepts.
4   EXAMPLE       Call f if ''invalid'' is set, then g if ''overflow'' is set:




    214) This mechanism allows testing several floating-point exceptions with just one function call.

[page 210]

            #include <fenv.h>
            /* ... */
            {
                    #pragma STDC FENV_ACCESS ON
                    int set_excepts;
                    feclearexcept(FE_INVALID | FE_OVERFLOW);
                    // maybe raise exceptions
                    set_excepts = fetestexcept(FE_INVALID | FE_OVERFLOW);
                    if (set_excepts & FE_INVALID) f();
                    if (set_excepts & FE_OVERFLOW) g();
                    /* ... */
            }

    7.6.3 Rounding
1   The fegetround and fesetround functions provide control of rounding direction
    modes.
    7.6.3.1 The fegetround function
    Synopsis
1           #include <fenv.h>
            int fegetround(void);
    Description
2   The fegetround function gets the current rounding direction.
    Returns
3   The fegetround function returns the value of the rounding direction macro
    representing the current rounding direction or a negative value if there is no such
    rounding direction macro or the current rounding direction is not determinable.
    7.6.3.2 The fesetround function
    Synopsis
1           #include <fenv.h>
            int fesetround(int round);
    Description
2   The fesetround function establishes the rounding direction represented by its
    argument round. If the argument is not equal to the value of a rounding direction macro,
    the rounding direction is not changed.
    Returns
3   The fesetround function returns zero if and only if the requested rounding direction
    was established.


[page 211]

4   EXAMPLE Save, set, and restore the rounding direction. Report an error and abort if setting the
    rounding direction fails.
           #include <fenv.h>
           #include <assert.h>
           void f(int round_dir)
           {
                 #pragma STDC FENV_ACCESS ON
                 int save_round;
                 int setround_ok;
                 save_round = fegetround();
                 setround_ok = fesetround(round_dir);
                 assert(setround_ok == 0);
                 /* ... */
                 fesetround(save_round);
                 /* ... */
           }

    7.6.4 Environment
1   The functions in this section manage the floating-point environment -- status flags and
    control modes -- as one entity.
    7.6.4.1 The fegetenv function
    Synopsis
1          #include <fenv.h>
           int fegetenv(fenv_t *envp);
    Description
2   The fegetenv function attempts to store the current floating-point environment in the
    object pointed to by envp.
    Returns
3   The fegetenv function returns zero if the environment was successfully stored.
    Otherwise, it returns a nonzero value.
    7.6.4.2 The feholdexcept function
    Synopsis
1          #include <fenv.h>
           int feholdexcept(fenv_t *envp);
    Description
2   The feholdexcept function saves the current floating-point environment in the object
    pointed to by envp, clears the floating-point status flags, and then installs a non-stop
    (continue on floating-point exceptions) mode, if available, for all floating-point
    exceptions.215)

[page 212]

    Returns
3   The feholdexcept function returns zero if and only if non-stop floating-point
    exception handling was successfully installed.
    7.6.4.3 The fesetenv function
    Synopsis
1           #include <fenv.h>
            int fesetenv(const fenv_t *envp);
    Description
2   The fesetenv function attempts to establish the floating-point environment represented
    by the object pointed to by envp. The argument envp shall point to an object set by a
    call to fegetenv or feholdexcept, or equal a floating-point environment macro.
    Note that fesetenv merely installs the state of the floating-point status flags
    represented through its argument, and does not raise these floating-point exceptions.
    Returns
3   The fesetenv function returns zero if the environment was successfully established.
    Otherwise, it returns a nonzero value.
    7.6.4.4 The feupdateenv function
    Synopsis
1           #include <fenv.h>
            int feupdateenv(const fenv_t *envp);
    Description
2   The feupdateenv function attempts to save the currently raised floating-point
    exceptions in its automatic storage, install the floating-point environment represented by
    the object pointed to by envp, and then raise the saved floating-point exceptions. The
    argument envp shall point to an object set by a call to feholdexcept or fegetenv,
    or equal a floating-point environment macro.
    Returns
3   The feupdateenv function returns zero if all the actions were successfully carried out.
    Otherwise, it returns a nonzero value.




    215) IEC 60559 systems have a default non-stop mode, and typically at least one other mode for trap
         handling or aborting; if the system provides only the non-stop mode then installing it is trivial. For
         such systems, the feholdexcept function can be used in conjunction with the feupdateenv
         function to write routines that hide spurious floating-point exceptions from their callers.

[page 213]

4   EXAMPLE   Hide spurious underflow floating-point exceptions:
          #include <fenv.h>
          double f(double x)
          {
                #pragma STDC FENV_ACCESS ON
                double result;
                fenv_t save_env;
                if (feholdexcept(&save_env))
                      return /* indication of an environmental problem */;
                // compute result
                if (/* test spurious underflow */)
                      if (feclearexcept(FE_UNDERFLOW))
                               return /* indication of an environmental problem */;
                if (feupdateenv(&save_env))
                      return /* indication of an environmental problem */;
                return result;
          }




[page 214]

    7.7 Characteristics of floating types <float.h>
1   The header <float.h> defines several macros that expand to various limits and
    parameters of the standard floating-point types.
2   The macros, their meanings, and the constraints (or restrictions) on their values are listed
    in 5.2.4.2.2.




[page 215]

    7.8 Format conversion of integer types <inttypes.h>
1   The header <inttypes.h> includes the header <stdint.h> and extends it with
    additional facilities provided by hosted implementations.
2   It declares functions for manipulating greatest-width integers and converting numeric
    character strings to greatest-width integers, and it declares the type
             imaxdiv_t
    which is a structure type that is the type of the value returned by the imaxdiv function.
    For each type declared in <stdint.h>, it defines corresponding macros for conversion
    specifiers for use with the formatted input/output functions.216)
    Forward references: integer types <stdint.h> (7.20), formatted input/output
    functions (7.21.6), formatted wide character input/output functions (7.28.2).
    7.8.1 Macros for format specifiers
1   Each of the following object-like macros expands to a character string literal containing a *
    conversion specifier, possibly modified by a length modifier, suitable for use within the
    format argument of a formatted input/output function when converting the corresponding
    integer type. These macro names have the general form of PRI (character string literals
    for the fprintf and fwprintf family) or SCN (character string literals for the
    fscanf and fwscanf family),217) followed by the conversion specifier, followed by a
    name corresponding to a similar type name in 7.20.1. In these names, N represents the
    width of the type as described in 7.20.1. For example, PRIdFAST32 can be used in a
    format string to print the value of an integer of type int_fast32_t.
2   The fprintf macros for signed integers are:
           PRIdN             PRIdLEASTN                PRIdFASTN          PRIdMAX             PRIdPTR
           PRIiN             PRIiLEASTN                PRIiFASTN          PRIiMAX             PRIiPTR
3   The fprintf macros for unsigned integers are:
           PRIoN             PRIoLEASTN                PRIoFASTN          PRIoMAX             PRIoPTR
           PRIuN             PRIuLEASTN                PRIuFASTN          PRIuMAX             PRIuPTR
           PRIxN             PRIxLEASTN                PRIxFASTN          PRIxMAX             PRIxPTR
           PRIXN             PRIXLEASTN                PRIXFASTN          PRIXMAX             PRIXPTR
4   The fscanf macros for signed integers are:



    216) See ''future library directions'' (7.30.4).
    217) Separate macros are given for use with fprintf and fscanf functions because, in the general case,
         different format specifiers may be required for fprintf and fscanf, even when the type is the
         same.

[page 216]

           SCNdN           SCNdLEASTN               SCNdFASTN              SCNdMAX             SCNdPTR
           SCNiN           SCNiLEASTN               SCNiFASTN              SCNiMAX             SCNiPTR
5   The fscanf macros for unsigned integers are:
           SCNoN           SCNoLEASTN               SCNoFASTN              SCNoMAX             SCNoPTR
           SCNuN           SCNuLEASTN               SCNuFASTN              SCNuMAX             SCNuPTR
           SCNxN           SCNxLEASTN               SCNxFASTN              SCNxMAX             SCNxPTR
6   For each type that the implementation provides in <stdint.h>, the corresponding
    fprintf macros shall be defined and the corresponding fscanf macros shall be
    defined unless the implementation does not have a suitable fscanf length modifier for
    the type.
7   EXAMPLE
            #include <inttypes.h>
            #include <wchar.h>
            int main(void)
            {
                  uintmax_t i = UINTMAX_MAX;    // this type always exists
                  wprintf(L"The largest integer value is %020"
                        PRIxMAX "\n", i);
                  return 0;
            }

    7.8.2 Functions for greatest-width integer types
    7.8.2.1 The imaxabs function
    Synopsis
1           #include <inttypes.h>
            intmax_t imaxabs(intmax_t j);
    Description
2   The imaxabs function computes the absolute value of an integer j. If the result cannot
    be represented, the behavior is undefined.218)
    Returns
3   The imaxabs function returns the absolute value.




    218) The absolute value of the most negative number cannot be represented in two's complement.

[page 217]

    7.8.2.2 The imaxdiv function
    Synopsis
1          #include <inttypes.h>
           imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
    Description
2   The imaxdiv function computes numer / denom and numer % denom in a single
    operation.
    Returns
3   The imaxdiv function returns a structure of type imaxdiv_t comprising both the
    quotient and the remainder. The structure shall contain (in either order) the members
    quot (the quotient) and rem (the remainder), each of which has type intmax_t. If
    either part of the result cannot be represented, the behavior is undefined.
    7.8.2.3 The strtoimax and strtoumax functions
    Synopsis
1          #include <inttypes.h>
           intmax_t strtoimax(const char * restrict nptr,
                char ** restrict endptr, int base);
           uintmax_t strtoumax(const char * restrict nptr,
                char ** restrict endptr, int base);
    Description
2   The strtoimax and strtoumax functions are equivalent to the strtol, strtoll,
    strtoul, and strtoull functions, except that the initial portion of the string is
    converted to intmax_t and uintmax_t representation, respectively.
    Returns
3   The strtoimax and strtoumax functions return the converted value, if any. If no
    conversion could be performed, zero is returned. If the correct value is outside the range
    of representable values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned
    (according to the return type and sign of the value, if any), and the value of the macro
    ERANGE is stored in errno.
    Forward references: the strtol, strtoll, strtoul, and strtoull functions
    (7.22.1.4).




[page 218]

    7.8.2.4 The wcstoimax and wcstoumax functions
    Synopsis
1           #include <stddef.h>           // for wchar_t
            #include <inttypes.h>
            intmax_t wcstoimax(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr, int base);
            uintmax_t wcstoumax(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr, int base);
    Description
2   The wcstoimax and wcstoumax functions are equivalent to the wcstol, wcstoll,
    wcstoul, and wcstoull functions except that the initial portion of the wide string is
    converted to intmax_t and uintmax_t representation, respectively.
    Returns
3   The wcstoimax function returns the converted value, if any. If no conversion could be
    performed, zero is returned. If the correct value is outside the range of representable
    values, INTMAX_MAX, INTMAX_MIN, or UINTMAX_MAX is returned (according to the
    return type and sign of the value, if any), and the value of the macro ERANGE is stored in
    errno.
    Forward references: the wcstol, wcstoll, wcstoul, and wcstoull functions
    (7.28.4.1.2).




[page 219]

    7.9 Alternative spellings <iso646.h>
1   The header <iso646.h> defines the following eleven macros (on the left) that expand
    to the corresponding tokens (on the right):
          and           &&
          and_eq        &=
          bitand        &
          bitor         |
          compl         ~
          not           !
          not_eq        !=
          or            ||
          or_eq         |=
          xor           ^
          xor_eq        ^=




[page 220]

    7.10 Sizes of integer types <limits.h>
1   The header <limits.h> defines several macros that expand to various limits and
    parameters of the standard integer types.
2   The macros, their meanings, and the constraints (or restrictions) on their values are listed
    in 5.2.4.2.1.




[page 221]

    7.11 Localization <locale.h>
1   The header <locale.h> declares two functions, one type, and defines several macros.
2   The type is
           struct lconv
    which contains members related to the formatting of numeric values. The structure shall
    contain at least the following members, in any order. The semantics of the members and
    their normal ranges are explained in 7.11.2.1. In the "C" locale, the members shall have
    the values specified in the comments.
           char   *decimal_point;                 //   "."
           char   *thousands_sep;                 //   ""
           char   *grouping;                      //   ""
           char   *mon_decimal_point;             //   ""
           char   *mon_thousands_sep;             //   ""
           char   *mon_grouping;                  //   ""
           char   *positive_sign;                 //   ""
           char   *negative_sign;                 //   ""
           char   *currency_symbol;               //   ""
           char   frac_digits;                    //   CHAR_MAX
           char   p_cs_precedes;                  //   CHAR_MAX
           char   n_cs_precedes;                  //   CHAR_MAX
           char   p_sep_by_space;                 //   CHAR_MAX
           char   n_sep_by_space;                 //   CHAR_MAX
           char   p_sign_posn;                    //   CHAR_MAX
           char   n_sign_posn;                    //   CHAR_MAX
           char   *int_curr_symbol;               //   ""
           char   int_frac_digits;                //   CHAR_MAX
           char   int_p_cs_precedes;              //   CHAR_MAX
           char   int_n_cs_precedes;              //   CHAR_MAX
           char   int_p_sep_by_space;             //   CHAR_MAX
           char   int_n_sep_by_space;             //   CHAR_MAX
           char   int_p_sign_posn;                //   CHAR_MAX
           char   int_n_sign_posn;                //   CHAR_MAX




[page 222]

3   The macros defined are NULL (described in 7.19); and
             LC_ALL
             LC_COLLATE
             LC_CTYPE
             LC_MONETARY
             LC_NUMERIC
             LC_TIME
    which expand to integer constant expressions with distinct values, suitable for use as the
    first argument to the setlocale function.219) Additional macro definitions, beginning
    with the characters LC_ and an uppercase letter,220) may also be specified by the
    implementation.
    7.11.1 Locale control
    7.11.1.1 The setlocale function
    Synopsis
1            #include <locale.h>
             char *setlocale(int category, const char *locale);
    Description
2   The setlocale function selects the appropriate portion of the program's locale as
    specified by the category and locale arguments. The setlocale function may be
    used to change or query the program's entire current locale or portions thereof. The value
    LC_ALL for category names the program's entire locale; the other values for
    category name only a portion of the program's locale. LC_COLLATE affects the
    behavior of the strcoll and strxfrm functions. LC_CTYPE affects the behavior of
    the character handling functions221) and the multibyte and wide character functions.
    LC_MONETARY affects the monetary formatting information returned by the
    localeconv function. LC_NUMERIC affects the decimal-point character for the
    formatted input/output functions and the string conversion functions, as well as the
    nonmonetary formatting information returned by the localeconv function. LC_TIME
    affects the behavior of the strftime and wcsftime functions.
3   A value of "C" for locale specifies the minimal environment for C translation; a value
    of "" for locale specifies the locale-specific native environment. Other
    implementation-defined strings may be passed as the second argument to setlocale.

    219) ISO/IEC 9945-2 specifies locale and charmap formats that may be used to specify locales for C.
    220) See ''future library directions'' (7.30.5).
    221) The only functions in 7.4 whose behavior is not affected by the current locale are isdigit and
         isxdigit.

[page 223]

4   At program startup, the equivalent of
            setlocale(LC_ALL, "C");
    is executed.
5   A call to the setlocale function may introduce a data race with other calls to the
    setlocale function or with calls to functions that are affected by the current locale.
    The implementation shall behave as if no library function calls the setlocale function.
    Returns
6   If a pointer to a string is given for locale and the selection can be honored, the
    setlocale function returns a pointer to the string associated with the specified
    category for the new locale. If the selection cannot be honored, the setlocale
    function returns a null pointer and the program's locale is not changed.
7   A null pointer for locale causes the setlocale function to return a pointer to the
    string associated with the category for the program's current locale; the program's
    locale is not changed.222)
8   The pointer to string returned by the setlocale function is such that a subsequent call
    with that string value and its associated category will restore that part of the program's
    locale. The string pointed to shall not be modified by the program, but may be
    overwritten by a subsequent call to the setlocale function.
    Forward references: formatted input/output functions (7.21.6), multibyte/wide
    character conversion functions (7.22.7), multibyte/wide string conversion functions
    (7.22.8), numeric conversion functions (7.22.1), the strcoll function (7.23.4.3), the
    strftime function (7.26.3.5), the strxfrm function (7.23.4.5).
    7.11.2 Numeric formatting convention inquiry
    7.11.2.1 The localeconv function
    Synopsis
1           #include <locale.h>
            struct lconv *localeconv(void);
    Description
2   The localeconv function sets the components of an object with type struct lconv
    with values appropriate for the formatting of numeric quantities (monetary and otherwise)
    according to the rules of the current locale.



    222) The implementation shall arrange to encode in a string the various categories due to a heterogeneous
         locale when category has the value LC_ALL.

[page 224]

3   The members of the structure with type char * are pointers to strings, any of which
    (except decimal_point) can point to "", to indicate that the value is not available in
    the current locale or is of zero length. Apart from grouping and mon_grouping, the
    strings shall start and end in the initial shift state. The members with type char are
    nonnegative numbers, any of which can be CHAR_MAX to indicate that the value is not
    available in the current locale. The members include the following:
    char *decimal_point
              The decimal-point character used to format nonmonetary quantities.
    char *thousands_sep
              The character used to separate groups of digits before the decimal-point
              character in formatted nonmonetary quantities.
    char *grouping
              A string whose elements indicate the size of each group of digits in
              formatted nonmonetary quantities.
    char *mon_decimal_point
              The decimal-point used to format monetary quantities.
    char *mon_thousands_sep
              The separator for groups of digits before the decimal-point in formatted
              monetary quantities.
    char *mon_grouping
              A string whose elements indicate the size of each group of digits in
              formatted monetary quantities.
    char *positive_sign
              The string used to indicate a nonnegative-valued formatted monetary
              quantity.
    char *negative_sign
              The string used to indicate a negative-valued formatted monetary quantity.
    char *currency_symbol
              The local currency symbol applicable to the current locale.
    char frac_digits
              The number of fractional digits (those after the decimal-point) to be
              displayed in a locally formatted monetary quantity.
    char p_cs_precedes
              Set to 1 or 0 if the currency_symbol respectively precedes or
              succeeds the value for a nonnegative locally formatted monetary quantity.



[page 225]

char n_cs_precedes
          Set to 1 or 0 if the currency_symbol respectively precedes or
          succeeds the value for a negative locally formatted monetary quantity.
char p_sep_by_space
          Set to a value indicating the separation of the currency_symbol, the
          sign string, and the value for a nonnegative locally formatted monetary
          quantity.
char n_sep_by_space
          Set to a value indicating the separation of the currency_symbol, the
          sign string, and the value for a negative locally formatted monetary
          quantity.
char p_sign_posn
          Set to a value indicating the positioning of the positive_sign for a
          nonnegative locally formatted monetary quantity.
char n_sign_posn
          Set to a value indicating the positioning of the negative_sign for a
          negative locally formatted monetary quantity.
char *int_curr_symbol
          The international currency symbol applicable to the current locale. The
          first three characters contain the alphabetic international currency symbol
          in accordance with those specified in ISO 4217. The fourth character
          (immediately preceding the null character) is the character used to separate
          the international currency symbol from the monetary quantity.
char int_frac_digits
          The number of fractional digits (those after the decimal-point) to be
          displayed in an internationally formatted monetary quantity.
char int_p_cs_precedes
          Set to 1 or 0 if the int_curr_symbol respectively precedes or
          succeeds the value for a nonnegative internationally formatted monetary
          quantity.
char int_n_cs_precedes
          Set to 1 or 0 if the int_curr_symbol respectively precedes or
          succeeds the value for a negative internationally formatted monetary
          quantity.
char int_p_sep_by_space
          Set to a value indicating the separation of the int_curr_symbol, the
          sign string, and the value for a nonnegative internationally formatted
          monetary quantity.
[page 226]

    char int_n_sep_by_space
              Set to a value indicating the separation of the int_curr_symbol, the
              sign string, and the value for a negative internationally formatted monetary
              quantity.
    char int_p_sign_posn
              Set to a value indicating the positioning of the positive_sign for a
              nonnegative internationally formatted monetary quantity.
    char int_n_sign_posn
              Set to a value indicating the positioning of the negative_sign for a
              negative internationally formatted monetary quantity.
4   The elements of grouping and mon_grouping are interpreted according to the
    following:
    CHAR_MAX      No further grouping is to be performed.
    0             The previous element is to be repeatedly used for the remainder of the
                  digits.
    other         The integer value is the number of digits that compose the current group.
                  The next element is examined to determine the size of the next group of
                  digits before the current group.
5   The values of p_sep_by_space, n_sep_by_space, int_p_sep_by_space,
    and int_n_sep_by_space are interpreted according to the following:
    0   No space separates the currency symbol and value.
    1   If the currency symbol and sign string are adjacent, a space separates them from the
        value; otherwise, a space separates the currency symbol from the value.
    2   If the currency symbol and sign string are adjacent, a space separates them;
        otherwise, a space separates the sign string from the value.
    For int_p_sep_by_space and int_n_sep_by_space, the fourth character of
    int_curr_symbol is used instead of a space.
6   The values of p_sign_posn, n_sign_posn, int_p_sign_posn,                            and
    int_n_sign_posn are interpreted according to the following:
    0   Parentheses surround the quantity and currency symbol.
    1   The sign string precedes the quantity and currency symbol.
    2   The sign string succeeds the quantity and currency symbol.
    3   The sign string immediately precedes the currency symbol.
    4   The sign string immediately succeeds the currency symbol.


[page 227]

7    The implementation shall behave as if no library function calls the localeconv
     function.
     Returns
8    The localeconv function returns a pointer to the filled-in object. The structure
     pointed to by the return value shall not be modified by the program, but may be
     overwritten by a subsequent call to the localeconv function. In addition, calls to the
     setlocale function with categories LC_ALL, LC_MONETARY, or LC_NUMERIC may
     overwrite the contents of the structure.
9    EXAMPLE 1 The following table illustrates rules which may well be used by four countries to format
     monetary quantities.
                                   Local format                                     International format

     Country            Positive                  Negative                    Positive               Negative

     Country1     1.234,56 mk             -1.234,56 mk                  FIM   1.234,56         FIM -1.234,56
     Country2     L.1.234                 -L.1.234                      ITL   1.234            -ITL 1.234
     Country3     fl. 1.234,56              fl. -1.234,56                   NLG   1.234,56         NLG -1.234,56
     Country4     SFrs.1,234.56           SFrs.1,234.56C                CHF   1,234.56         CHF 1,234.56C
10   For these four countries, the respective values for the monetary members of the structure returned by
     localeconv could be:
                                       Country1              Country2              Country3            Country4

     mon_decimal_point                 ","                   ""                   ","                 "."
     mon_thousands_sep                 "."                   "."                  "."                 ","
     mon_grouping                      "\3"                  "\3"                 "\3"                "\3"
     positive_sign                     ""                    ""                   ""                  ""
     negative_sign                     "-"                   "-"                  "-"                 "C"
     currency_symbol                   "mk"                  "L."                 "\u0192"            "SFrs."
     frac_digits                       2                     0                    2                   2
     p_cs_precedes                     0                     1                    1                   1
     n_cs_precedes                     0                     1                    1                   1
     p_sep_by_space                    1                     0                    1                   0
     n_sep_by_space                    1                     0                    2                   0
     p_sign_posn                       1                     1                    1                   1
     n_sign_posn                       1                     1                    4                   2
     int_curr_symbol                   "FIM "                "ITL "               "NLG "              "CHF "
     int_frac_digits                   2                     0                    2                   2
     int_p_cs_precedes                 1                     1                    1                   1
     int_n_cs_precedes                 1                     1                    1                   1
     int_p_sep_by_space                1                     1                    1                   1
     int_n_sep_by_space                2                     1                    2                   1
     int_p_sign_posn                   1                     1                    1                   1
     int_n_sign_posn                   4                     1                    4                   2




[page 228]

11   EXAMPLE 2 The following table illustrates how the cs_precedes, sep_by_space, and sign_posn members
     affect the formatted value.
                                                                   p_sep_by_space

     p_cs_precedes           p_sign_posn                0                   1                  2

                     0                    0         (1.25$)            (1.25 $)            (1.25$)
                                          1         +1.25$             +1.25 $             + 1.25$
                                          2         1.25$+             1.25 $+             1.25$ +
                                          3         1.25+$             1.25 +$             1.25+ $
                                          4         1.25$+             1.25 $+             1.25$ +

                     1                    0         ($1.25)            ($ 1.25)            ($1.25)
                                          1         +$1.25             +$ 1.25             + $1.25
                                          2         $1.25+             $ 1.25+             $1.25 +
                                          3         +$1.25             +$ 1.25             + $1.25
                                          4         $+1.25             $+ 1.25             $ +1.25




[page 229]

    7.12 Mathematics <math.h>
1   The header <math.h> declares two types and many mathematical functions and defines
    several macros. Most synopses specify a family of functions consisting of a principal
    function with one or more double parameters, a double return value, or both; and
    other functions with the same name but with f and l suffixes, which are corresponding
    functions with float and long double parameters, return values, or both.223)
    Integer arithmetic functions and conversion functions are discussed later.
2   The types
            float_t
            double_t
    are floating types at least as wide as float and double, respectively, and such that
    double_t is at least as wide as float_t. If FLT_EVAL_METHOD equals 0,
    float_t and double_t are float and double, respectively; if
    FLT_EVAL_METHOD equals 1, they are both double; if FLT_EVAL_METHOD equals
    2, they are both long double; and for other values of FLT_EVAL_METHOD, they are
    otherwise implementation-defined.224)
3   The macro
            HUGE_VAL
    expands to a positive double constant expression, not necessarily representable as a
    float. The macros
            HUGE_VALF
            HUGE_VALL
    are respectively float and long double analogs of HUGE_VAL.225)
4   The macro
            INFINITY
    expands to a constant expression of type float representing positive or unsigned
    infinity, if available; else to a positive constant of type float that overflows at



    223) Particularly on systems with wide expression evaluation, a <math.h> function might pass arguments
         and return values in wider format than the synopsis prototype indicates.
    224) The types float_t and double_t are intended to be the implementation's most efficient types at
         least as wide as float and double, respectively. For FLT_EVAL_METHOD equal 0, 1, or 2, the
         type float_t is the narrowest type used by the implementation to evaluate floating expressions.
    225) HUGE_VAL, HUGE_VALF, and HUGE_VALL can be positive infinities in an implementation that
         supports infinities.

[page 230]

    translation time.226)
5   The macro
             NAN
    is defined if and only if the implementation supports quiet NaNs for the float type. It
    expands to a constant expression of type float representing a quiet NaN.
6   The number classification macros
             FP_INFINITE
             FP_NAN
             FP_NORMAL
             FP_SUBNORMAL
             FP_ZERO
    represent the mutually exclusive kinds of floating-point values. They expand to integer
    constant expressions with distinct values. Additional implementation-defined floating-
    point classifications, with macro definitions beginning with FP_ and an uppercase letter,
    may also be specified by the implementation.
7   The macro
             FP_FAST_FMA
    is optionally defined. If defined, it indicates that the fma function generally executes
    about as fast as, or faster than, a multiply and an add of double operands.227) The
    macros
             FP_FAST_FMAF
             FP_FAST_FMAL
    are, respectively, float and long double analogs of FP_FAST_FMA. If defined,
    these macros expand to the integer constant 1.
8   The macros
             FP_ILOGB0
             FP_ILOGBNAN
    expand to integer constant expressions whose values are returned by ilogb(x) if x is
    zero or NaN, respectively. The value of FP_ILOGB0 shall be either INT_MIN or
    -INT_MAX. The value of FP_ILOGBNAN shall be either INT_MAX or INT_MIN.


    226) In this case, using INFINITY will violate the constraint in 6.4.4 and thus require a diagnostic.
    227) Typically, the FP_FAST_FMA macro is defined if and only if the fma function is implemented
         directly with a hardware multiply-add instruction. Software implementations are expected to be
         substantially slower.

[page 231]

9   The macros
            MATH_ERRNO
            MATH_ERREXCEPT
    expand to the integer constants 1 and 2, respectively; the macro
            math_errhandling
    expands to an expression that has type int and the value MATH_ERRNO,
    MATH_ERREXCEPT, or the bitwise OR of both. The value of math_errhandling is
    constant for the duration of the program. It is unspecified whether
    math_errhandling is a macro or an identifier with external linkage. If a macro
    definition is suppressed or a program defines an identifier with the name
    math_errhandling, the behavior is undefined.               If the expression
    math_errhandling & MATH_ERREXCEPT can be nonzero, the implementation
    shall define the macros FE_DIVBYZERO, FE_INVALID, and FE_OVERFLOW in
    <fenv.h>.
    7.12.1 Treatment of error conditions
1   The behavior of each of the functions in <math.h> is specified for all representable
    values of its input arguments, except where stated otherwise. Each function shall execute
    as if it were a single operation without raising SIGFPE and without generating any of the
    floating-point exceptions ''invalid'', ''divide-by-zero'', or ''overflow'' except to reflect
    the result of the function.
2   For all functions, a domain error occurs if an input argument is outside the domain over
    which the mathematical function is defined. The description of each function lists any
    required domain errors; an implementation may define additional domain errors, provided
    that such errors are consistent with the mathematical definition of the function.228) On a
    domain error, the function returns an implementation-defined value; if the integer
    expression math_errhandling & MATH_ERRNO is nonzero, the integer expression
    errno acquires the value EDOM; if the integer expression math_errhandling &
    MATH_ERREXCEPT is nonzero, the ''invalid'' floating-point exception is raised.
3   Similarly, a pole error (also known as a singularity or infinitary) occurs if the
    mathematical function has an exact infinite result as the finite input argument(s) are
    approached in the limit (for example, log(0.0)). The description of each function lists
    any required pole errors; an implementation may define additional pole errors, provided
    that such errors are consistent with the mathematical definition of the function. On a pole
    error, the function returns an implementation-defined value; if the integer expression


    228) In an implementation that supports infinities, this allows an infinity as an argument to be a domain
         error if the mathematical domain of the function does not include the infinity.

[page 232]

    math_errhandling & MATH_ERRNO is nonzero, the integer expression errno
    acquires the value ERANGE; if the integer expression math_errhandling &
    MATH_ERREXCEPT is nonzero, the ''divide-by-zero'' floating-point exception is raised.
4   Likewise, a range error occurs if the mathematical result of the function cannot be
    represented in an object of the specified type, due to extreme magnitude.
5   A floating result overflows if the magnitude of the mathematical result is finite but so
    large that the mathematical result cannot be represented without extraordinary roundoff
    error in an object of the specified type. If a floating result overflows and default rounding
    is in effect, then the function returns the value of the macro HUGE_VAL, HUGE_VALF, or *
    HUGE_VALL according to the return type, with the same sign as the correct value of the
    function; if the integer expression math_errhandling & MATH_ERRNO is nonzero,
    the integer expression errno acquires the value ERANGE; if the integer expression
    math_errhandling & MATH_ERREXCEPT is nonzero, the ''overflow'' floating-
    point exception is raised.
6   The result underflows if the magnitude of the mathematical result is so small that the
    mathematical result cannot be represented, without extraordinary roundoff error, in an
    object of the specified type.229) If the result underflows, the function returns an
    implementation-defined value whose magnitude is no greater than the smallest
    normalized positive number in the specified type; if the integer expression
    math_errhandling & MATH_ERRNO is nonzero, whether errno acquires the
    value    ERANGE       is    implementation-defined;     if   the  integer   expression
    math_errhandling & MATH_ERREXCEPT is nonzero, whether the ''underflow''
    floating-point exception is raised is implementation-defined.
7   If a domain, pole, or range error occurs and the integer expression
    math_errhandling & MATH_ERRNO is zero,230) then errno shall either be set to
    the value corresponding to the error or left unmodified. If no such error occurs, errno
    shall be left unmodified regardless of the setting of math_errhandling.




    229) The term underflow here is intended to encompass both ''gradual underflow'' as in IEC 60559 and
         also ''flush-to-zero'' underflow.
    230) Math errors are being indicated by the floating-point exception flags rather than by errno.

[page 233]

    7.12.2 The FP_CONTRACT pragma
    Synopsis
1            #include <math.h>
             #pragma STDC FP_CONTRACT on-off-switch
    Description
2   The FP_CONTRACT pragma can be used to allow (if the state is ''on'') or disallow (if the
    state is ''off'') the implementation to contract expressions (6.5). Each pragma can occur
    either outside external declarations or preceding all explicit declarations and statements
    inside a compound statement. When outside external declarations, the pragma takes
    effect from its occurrence until another FP_CONTRACT pragma is encountered, or until
    the end of the translation unit. When inside a compound statement, the pragma takes
    effect from its occurrence until another FP_CONTRACT pragma is encountered
    (including within a nested compound statement), or until the end of the compound
    statement; at the end of a compound statement the state for the pragma is restored to its
    condition just before the compound statement. If this pragma is used in any other
    context, the behavior is undefined. The default state (''on'' or ''off'') for the pragma is
    implementation-defined.
    7.12.3 Classification macros
1   In the synopses in this subclause, real-floating indicates that the argument shall be an
    expression of real floating type.
    7.12.3.1 The fpclassify macro
    Synopsis
1            #include <math.h>
             int fpclassify(real-floating x);
    Description
2   The fpclassify macro classifies its argument value as NaN, infinite, normal,
    subnormal, zero, or into another implementation-defined category. First, an argument
    represented in a format wider than its semantic type is converted to its semantic type.
    Then classification is based on the type of the argument.231)
    Returns
3   The fpclassify macro returns the value of the number classification macro
    appropriate to the value of its argument.                                *


    231) Since an expression can be evaluated with more range and precision than its type has, it is important to
         know the type that classification is based on. For example, a normal long double value might
         become subnormal when converted to double, and zero when converted to float.

[page 234]

    7.12.3.2 The isfinite macro
    Synopsis
1           #include <math.h>
            int isfinite(real-floating x);
    Description
2   The isfinite macro determines whether its argument has a finite value (zero,
    subnormal, or normal, and not infinite or NaN). First, an argument represented in a
    format wider than its semantic type is converted to its semantic type. Then determination
    is based on the type of the argument.
    Returns
3   The isfinite macro returns a nonzero value if and only if its argument has a finite
    value.
    7.12.3.3 The isinf macro
    Synopsis
1           #include <math.h>
            int isinf(real-floating x);
    Description
2   The isinf macro determines whether its argument value is an infinity (positive or
    negative). First, an argument represented in a format wider than its semantic type is
    converted to its semantic type. Then determination is based on the type of the argument.
    Returns
3   The isinf macro returns a nonzero value if and only if its argument has an infinite
    value.
    7.12.3.4 The isnan macro
    Synopsis
1           #include <math.h>
            int isnan(real-floating x);
    Description
2   The isnan macro determines whether its argument value is a NaN. First, an argument
    represented in a format wider than its semantic type is converted to its semantic type.
    Then determination is based on the type of the argument.232)


    232) For the isnan macro, the type for determination does not matter unless the implementation supports
         NaNs in the evaluation type but not in the semantic type.

[page 235]

    Returns
3   The isnan macro returns a nonzero value if and only if its argument has a NaN value.
    7.12.3.5 The isnormal macro
    Synopsis
1           #include <math.h>
            int isnormal(real-floating x);
    Description
2   The isnormal macro determines whether its argument value is normal (neither zero,
    subnormal, infinite, nor NaN). First, an argument represented in a format wider than its
    semantic type is converted to its semantic type. Then determination is based on the type
    of the argument.
    Returns
3   The isnormal macro returns a nonzero value if and only if its argument has a normal
    value.
    7.12.3.6 The signbit macro
    Synopsis
1           #include <math.h>
            int signbit(real-floating x);
    Description
2   The signbit macro determines whether the sign of its argument value is negative.233)
    Returns
3   The signbit macro returns a nonzero value if and only if the sign of its argument value
    is negative.




    233) The signbit macro reports the sign of all values, including infinities, zeros, and NaNs. If zero is
         unsigned, it is treated as positive.

[page 236]

    7.12.4 Trigonometric functions
    7.12.4.1 The acos functions
    Synopsis
1           #include <math.h>
            double acos(double x);
            float acosf(float x);
            long double acosl(long double x);
    Description
2   The acos functions compute the principal value of the arc cosine of x. A domain error
    occurs for arguments not in the interval [-1, +1].
    Returns
3   The acos functions return arccos x in the interval [0, pi ] radians.
    7.12.4.2 The asin functions
    Synopsis
1           #include <math.h>
            double asin(double x);
            float asinf(float x);
            long double asinl(long double x);
    Description
2   The asin functions compute the principal value of the arc sine of x. A domain error
    occurs for arguments not in the interval [-1, +1].
    Returns
3   The asin functions return arcsin x in the interval [-pi /2, +pi /2] radians.
    7.12.4.3 The atan functions
    Synopsis
1           #include <math.h>
            double atan(double x);
            float atanf(float x);
            long double atanl(long double x);
    Description
2   The atan functions compute the principal value of the arc tangent of x.




[page 237]

    Returns
3   The atan functions return arctan x in the interval [-pi /2, +pi /2] radians.
    7.12.4.4 The atan2 functions
    Synopsis
1          #include <math.h>
           double atan2(double y, double x);
           float atan2f(float y, float x);
           long double atan2l(long double y, long double x);
    Description
2   The atan2 functions compute the value of the arc tangent of y/x, using the signs of both
    arguments to determine the quadrant of the return value. A domain error may occur if
    both arguments are zero.
    Returns
3   The atan2 functions return arctan y/x in the interval [-pi , +pi ] radians.
    7.12.4.5 The cos functions
    Synopsis
1          #include <math.h>
           double cos(double x);
           float cosf(float x);
           long double cosl(long double x);
    Description
2   The cos functions compute the cosine of x (measured in radians).
    Returns
3   The cos functions return cos x.
    7.12.4.6 The sin functions
    Synopsis
1          #include <math.h>
           double sin(double x);
           float sinf(float x);
           long double sinl(long double x);
    Description
2   The sin functions compute the sine of x (measured in radians).



[page 238]

    Returns
3   The sin functions return sin x.
    7.12.4.7 The tan functions
    Synopsis
1           #include <math.h>
            double tan(double x);
            float tanf(float x);
            long double tanl(long double x);
    Description
2   The tan functions return the tangent of x (measured in radians).
    Returns
3   The tan functions return tan x.
    7.12.5 Hyperbolic functions
    7.12.5.1 The acosh functions
    Synopsis
1           #include <math.h>
            double acosh(double x);
            float acoshf(float x);
            long double acoshl(long double x);
    Description
2   The acosh functions compute the (nonnegative) arc hyperbolic cosine of x. A domain
    error occurs for arguments less than 1.
    Returns
3   The acosh functions return arcosh x in the interval [0, +(inf)].
    7.12.5.2 The asinh functions
    Synopsis
1           #include <math.h>
            double asinh(double x);
            float asinhf(float x);
            long double asinhl(long double x);
    Description
2   The asinh functions compute the arc hyperbolic sine of x.


[page 239]

    Returns
3   The asinh functions return arsinh x.
    7.12.5.3 The atanh functions
    Synopsis
1          #include <math.h>
           double atanh(double x);
           float atanhf(float x);
           long double atanhl(long double x);
    Description
2   The atanh functions compute the arc hyperbolic tangent of x. A domain error occurs
    for arguments not in the interval [-1, +1]. A pole error may occur if the argument equals
    -1 or +1.
    Returns
3   The atanh functions return artanh x.
    7.12.5.4 The cosh functions
    Synopsis
1          #include <math.h>
           double cosh(double x);
           float coshf(float x);
           long double coshl(long double x);
    Description
2   The cosh functions compute the hyperbolic cosine of x. A range error occurs if the
    magnitude of x is too large.
    Returns
3   The cosh functions return cosh x.
    7.12.5.5 The sinh functions
    Synopsis
1          #include <math.h>
           double sinh(double x);
           float sinhf(float x);
           long double sinhl(long double x);
    Description
2   The sinh functions compute the hyperbolic sine of x. A range error occurs if the
    magnitude of x is too large.
[page 240]

    Returns
3   The sinh functions return sinh x.
    7.12.5.6 The tanh functions
    Synopsis
1           #include <math.h>
            double tanh(double x);
            float tanhf(float x);
            long double tanhl(long double x);
    Description
2   The tanh functions compute the hyperbolic tangent of x.
    Returns
3   The tanh functions return tanh x.
    7.12.6 Exponential and logarithmic functions
    7.12.6.1 The exp functions
    Synopsis
1           #include <math.h>
            double exp(double x);
            float expf(float x);
            long double expl(long double x);
    Description
2   The exp functions compute the base-e exponential of x. A range error occurs if the
    magnitude of x is too large.
    Returns
3   The exp functions return ex .
    7.12.6.2 The exp2 functions
    Synopsis
1           #include <math.h>
            double exp2(double x);
            float exp2f(float x);
            long double exp2l(long double x);
    Description
2   The exp2 functions compute the base-2 exponential of x. A range error occurs if the
    magnitude of x is too large.

[page 241]

    Returns
3   The exp2 functions return 2x .
    7.12.6.3 The expm1 functions
    Synopsis
1           #include <math.h>
            double expm1(double x);
            float expm1f(float x);
            long double expm1l(long double x);
    Description
2   The expm1 functions compute the base-e exponential of the argument, minus 1. A range
    error occurs if x is too large.234)
    Returns
3   The expm1 functions return ex - 1.
    7.12.6.4 The frexp functions
    Synopsis
1           #include <math.h>
            double frexp(double value, int *exp);
            float frexpf(float value, int *exp);
            long double frexpl(long double value, int *exp);
    Description
2   The frexp functions break a floating-point number into a normalized fraction and an
    integral power of 2. They store the integer in the int object pointed to by exp.
    Returns
3   If value is not a floating-point number or if the integral power of 2 is outside the range
    of int, the results are unspecified. Otherwise, the frexp functions return the value x,
    such that x has a magnitude in the interval [1/2, 1) or zero, and value equals x x 2*exp .
    If value is zero, both parts of the result are zero.




    234) For small magnitude x, expm1(x) is expected to be more accurate than exp(x) - 1.

[page 242]

    7.12.6.5 The ilogb functions
    Synopsis
1           #include <math.h>
            int ilogb(double x);
            int ilogbf(float x);
            int ilogbl(long double x);
    Description
2   The ilogb functions extract the exponent of x as a signed int value. If x is zero they
    compute the value FP_ILOGB0; if x is infinite they compute the value INT_MAX; if x is
    a NaN they compute the value FP_ILOGBNAN; otherwise, they are equivalent to calling
    the corresponding logb function and casting the returned value to type int. A domain
    error or range error may occur if x is zero, infinite, or NaN. If the correct value is outside
    the range of the return type, the numeric result is unspecified.
    Returns
3   The ilogb functions return the exponent of x as a signed int value.
    Forward references: the logb functions (7.12.6.11).
    7.12.6.6 The ldexp functions
    Synopsis
1           #include <math.h>
            double ldexp(double x, int exp);
            float ldexpf(float x, int exp);
            long double ldexpl(long double x, int exp);
    Description
2   The ldexp functions multiply a floating-point number by an integral power of 2. A
    range error may occur.
    Returns
3   The ldexp functions return x x 2exp .
    7.12.6.7 The log functions
    Synopsis
1           #include <math.h>
            double log(double x);
            float logf(float x);
            long double logl(long double x);



[page 243]

    Description
2   The log functions compute the base-e (natural) logarithm of x. A domain error occurs if
    the argument is negative. A pole error may occur if the argument is zero.
    Returns
3   The log functions return loge x.
    7.12.6.8 The log10 functions
    Synopsis
1           #include <math.h>
            double log10(double x);
            float log10f(float x);
            long double log10l(long double x);
    Description
2   The log10 functions compute the base-10 (common) logarithm of x. A domain error
    occurs if the argument is negative. A pole error may occur if the argument is zero.
    Returns
3   The log10 functions return log10 x.
    7.12.6.9 The log1p functions
    Synopsis
1           #include <math.h>
            double log1p(double x);
            float log1pf(float x);
            long double log1pl(long double x);
    Description
2   The log1p functions compute the base-e (natural) logarithm of 1 plus the argument.235)
    A domain error occurs if the argument is less than -1. A pole error may occur if the
    argument equals -1.
    Returns
3   The log1p functions return loge (1 + x).




    235) For small magnitude x, log1p(x) is expected to be more accurate than log(1 + x).

[page 244]

    7.12.6.10 The log2 functions
    Synopsis
1           #include <math.h>
            double log2(double x);
            float log2f(float x);
            long double log2l(long double x);
    Description
2   The log2 functions compute the base-2 logarithm of x. A domain error occurs if the
    argument is less than zero. A pole error may occur if the argument is zero.
    Returns
3   The log2 functions return log2 x.
    7.12.6.11 The logb functions
    Synopsis
1           #include <math.h>
            double logb(double x);
            float logbf(float x);
            long double logbl(long double x);
    Description
2   The logb functions extract the exponent of x, as a signed integer value in floating-point
    format. If x is subnormal it is treated as though it were normalized; thus, for positive
    finite x,
          1 <= x x FLT_RADIX-logb(x) < FLT_RADIX
    A domain error or pole error may occur if the argument is zero.
    Returns
3   The logb functions return the signed exponent of x.
    7.12.6.12 The modf functions
    Synopsis
1           #include <math.h>
            double modf(double value, double *iptr);
            float modff(float value, float *iptr);
            long double modfl(long double value, long double *iptr);
    Description
2   The modf functions break the argument value into integral and fractional parts, each of
    which has the same type and sign as the argument. They store the integral part (in
[page 245]

    floating-point format) in the object pointed to by iptr.
    Returns
3   The modf functions return the signed fractional part of value.
    7.12.6.13 The scalbn and scalbln functions
    Synopsis
1          #include <math.h>
           double scalbn(double x, int n);
           float scalbnf(float x, int n);
           long double scalbnl(long double x, int n);
           double scalbln(double x, long int n);
           float scalblnf(float x, long int n);
           long double scalblnl(long double x, long int n);
    Description
2   The scalbn and scalbln functions compute x x FLT_RADIXn efficiently, not
    normally by computing FLT_RADIXn explicitly. A range error may occur.
    Returns
3   The scalbn and scalbln functions return x x FLT_RADIXn .
    7.12.7 Power and absolute-value functions
    7.12.7.1 The cbrt functions
    Synopsis
1          #include <math.h>
           double cbrt(double x);
           float cbrtf(float x);
           long double cbrtl(long double x);
    Description
2   The cbrt functions compute the real cube root of x.
    Returns
3   The cbrt functions return x1/3 .




[page 246]

    7.12.7.2 The fabs functions
    Synopsis
1           #include <math.h>
            double fabs(double x);
            float fabsf(float x);
            long double fabsl(long double x);
    Description
2   The fabs functions compute the absolute value of a floating-point number x.
    Returns
3   The fabs functions return | x |.
    7.12.7.3 The hypot functions
    Synopsis
1           #include <math.h>
            double hypot(double x, double y);
            float hypotf(float x, float y);
            long double hypotl(long double x, long double y);
    Description
2   The hypot functions compute the square root of the sum of the squares of x and y,
    without undue overflow or underflow. A range error may occur.
3   Returns
4   The hypot functions return sqrt:x2 + y2 .
                               -
                               -----
    7.12.7.4 The pow functions
    Synopsis
1           #include <math.h>
            double pow(double x, double y);
            float powf(float x, float y);
            long double powl(long double x, long double y);
    Description
2   The pow functions compute x raised to the power y. A domain error occurs if x is finite
    and negative and y is finite and not an integer value. A range error may occur. A domain
    error may occur if x is zero and y is zero. A domain error or pole error may occur if x is
    zero and y is less than zero.




[page 247]

    Returns
3   The pow functions return xy .
    7.12.7.5 The sqrt functions
    Synopsis
1          #include <math.h>
           double sqrt(double x);
           float sqrtf(float x);
           long double sqrtl(long double x);
    Description
2   The sqrt functions compute the nonnegative square root of x. A domain error occurs if
    the argument is less than zero.
    Returns
3   The sqrt functions return sqrt:x.
                              -
                              -
    7.12.8 Error and gamma functions
    7.12.8.1 The erf functions
    Synopsis
1          #include <math.h>
           double erf(double x);
           float erff(float x);
           long double erfl(long double x);
    Description
2   The erf functions compute the error function of x.
    Returns
3                                      2        x
                                            (integral)       e-t dt.
                                                      2
    The erf functions return erf x =
                                       sqrt:pi
                                       -
                                       -    0

    7.12.8.2 The erfc functions
    Synopsis
1          #include <math.h>
           double erfc(double x);
           float erfcf(float x);
           long double erfcl(long double x);
    Description
2   The erfc functions compute the complementary error function of x. A range error
    occurs if x is too large.
[page 248]

    Returns
3                                                       2       (inf)
                                                            (integral)       e-t dt.
                                                                      2
    The erfc functions return erfc x = 1 - erf x =
                                                     sqrt:pi
                                                     -
                                                     -      x

    7.12.8.3 The lgamma functions
    Synopsis
1           #include <math.h>
            double lgamma(double x);
            float lgammaf(float x);
            long double lgammal(long double x);
    Description
2   The lgamma functions compute the natural logarithm of the absolute value of gamma of
    x. A range error occurs if x is too large. A pole error may occur if x is a negative integer
    or zero.
    Returns
3   The lgamma functions return loge | (Gamma)(x) |.
    7.12.8.4 The tgamma functions
    Synopsis
1           #include <math.h>
            double tgamma(double x);
            float tgammaf(float x);
            long double tgammal(long double x);
    Description
2   The tgamma functions compute the gamma function of x. A domain error or pole error
    may occur if x is a negative integer or zero. A range error occurs if the magnitude of x is
    too large and may occur if the magnitude of x is too small.
    Returns
3   The tgamma functions return (Gamma)(x).




[page 249]

    7.12.9 Nearest integer functions
    7.12.9.1 The ceil functions
    Synopsis
1          #include <math.h>
           double ceil(double x);
           float ceilf(float x);
           long double ceill(long double x);
    Description
2   The ceil functions compute the smallest integer value not less than x.
    Returns
3   The ceil functions return [^x^], expressed as a floating-point number.
    7.12.9.2 The floor functions
    Synopsis
1          #include <math.h>
           double floor(double x);
           float floorf(float x);
           long double floorl(long double x);
    Description
2   The floor functions compute the largest integer value not greater than x.
    Returns
3   The floor functions return [_x_], expressed as a floating-point number.
    7.12.9.3 The nearbyint functions
    Synopsis
1          #include <math.h>
           double nearbyint(double x);
           float nearbyintf(float x);
           long double nearbyintl(long double x);
    Description
2   The nearbyint functions round their argument to an integer value in floating-point
    format, using the current rounding direction and without raising the ''inexact'' floating-
    point exception.




[page 250]

    Returns
3   The nearbyint functions return the rounded integer value.
    7.12.9.4 The rint functions
    Synopsis
1           #include <math.h>
            double rint(double x);
            float rintf(float x);
            long double rintl(long double x);
    Description
2   The rint functions differ from the nearbyint functions (7.12.9.3) only in that the
    rint functions may raise the ''inexact'' floating-point exception if the result differs in
    value from the argument.
    Returns
3   The rint functions return the rounded integer value.
    7.12.9.5 The lrint and llrint functions
    Synopsis
1           #include <math.h>
            long int lrint(double x);
            long int lrintf(float x);
            long int lrintl(long double x);
            long long int llrint(double x);
            long long int llrintf(float x);
            long long int llrintl(long double x);
    Description
2   The lrint and llrint functions round their argument to the nearest integer value,
    rounding according to the current rounding direction. If the rounded value is outside the
    range of the return type, the numeric result is unspecified and a domain error or range
    error may occur.
    Returns
3   The lrint and llrint functions return the rounded integer value.




[page 251]

    7.12.9.6 The round functions
    Synopsis
1          #include <math.h>
           double round(double x);
           float roundf(float x);
           long double roundl(long double x);
    Description
2   The round functions round their argument to the nearest integer value in floating-point
    format, rounding halfway cases away from zero, regardless of the current rounding
    direction.
    Returns
3   The round functions return the rounded integer value.
    7.12.9.7 The lround and llround functions
    Synopsis
1          #include <math.h>
           long int lround(double x);
           long int lroundf(float x);
           long int lroundl(long double x);
           long long int llround(double x);
           long long int llroundf(float x);
           long long int llroundl(long double x);
    Description
2   The lround and llround functions round their argument to the nearest integer value,
    rounding halfway cases away from zero, regardless of the current rounding direction. If
    the rounded value is outside the range of the return type, the numeric result is unspecified
    and a domain error or range error may occur.
    Returns
3   The lround and llround functions return the rounded integer value.
    7.12.9.8 The trunc functions
    Synopsis
1          #include <math.h>
           double trunc(double x);
           float truncf(float x);
           long double truncl(long double x);


[page 252]

    Description
2   The trunc functions round their argument to the integer value, in floating format,
    nearest to but no larger in magnitude than the argument.
    Returns
3   The trunc functions return the truncated integer value.
    7.12.10 Remainder functions
    7.12.10.1 The fmod functions
    Synopsis
1            #include <math.h>
             double fmod(double x, double y);
             float fmodf(float x, float y);
             long double fmodl(long double x, long double y);
    Description
2   The fmod functions compute the floating-point remainder of x/y.
    Returns
3   The fmod functions return the value x - ny, for some integer n such that, if y is nonzero,
    the result has the same sign as x and magnitude less than the magnitude of y. If y is zero,
    whether a domain error occurs or the fmod functions return zero is implementation-
    defined.
    7.12.10.2 The remainder functions
    Synopsis
1            #include <math.h>
             double remainder(double x, double y);
             float remainderf(float x, float y);
             long double remainderl(long double x, long double y);
    Description
2   The remainder functions compute the remainder x REM y required by IEC 60559.236)




    236) ''When y != 0, the remainder r = x REM y is defined regardless of the rounding mode by the
         mathematical relation r = x - ny, where n is the integer nearest the exact value of x/y; whenever
         | n - x/y | = 1/2, then n is even. If r = 0, its sign shall be that of x.'' This definition is applicable for *
         all implementations.

[page 253]

    Returns
3   The remainder functions return x REM y. If y is zero, whether a domain error occurs
    or the functions return zero is implementation defined.
    7.12.10.3 The remquo functions
    Synopsis
1          #include <math.h>
           double remquo(double x, double y, int *quo);
           float remquof(float x, float y, int *quo);
           long double remquol(long double x, long double y,
                int *quo);
    Description
2   The remquo functions compute the same remainder as the remainder functions. In
    the object pointed to by quo they store a value whose sign is the sign of x/y and whose
    magnitude is congruent modulo 2n to the magnitude of the integral quotient of x/y, where
    n is an implementation-defined integer greater than or equal to 3.
    Returns
3   The remquo functions return x REM y. If y is zero, the value stored in the object
    pointed to by quo is unspecified and whether a domain error occurs or the functions
    return zero is implementation defined.
    7.12.11 Manipulation functions
    7.12.11.1 The copysign functions
    Synopsis
1          #include <math.h>
           double copysign(double x, double y);
           float copysignf(float x, float y);
           long double copysignl(long double x, long double y);
    Description
2   The copysign functions produce a value with the magnitude of x and the sign of y.
    They produce a NaN (with the sign of y) if x is a NaN. On implementations that
    represent a signed zero but do not treat negative zero consistently in arithmetic
    operations, the copysign functions regard the sign of zero as positive.
    Returns
3   The copysign functions return a value with the magnitude of x and the sign of y.



[page 254]

    7.12.11.2 The nan functions
    Synopsis
1           #include <math.h>
            double nan(const char *tagp);
            float nanf(const char *tagp);
            long double nanl(const char *tagp);
    Description
2   The call nan("n-char-sequence") is equivalent to strtod("NAN(n-char-
    sequence)",     (char**)       NULL); the call nan("") is equivalent to
    strtod("NAN()", (char**) NULL). If tagp does not point to an n-char
    sequence or an empty string, the call is equivalent to strtod("NAN", (char**)
    NULL). Calls to nanf and nanl are equivalent to the corresponding calls to strtof
    and strtold.
    Returns
3   The nan functions return a quiet NaN, if available, with content indicated through tagp.
    If the implementation does not support quiet NaNs, the functions return zero.
    Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
    7.12.11.3 The nextafter functions
    Synopsis
1           #include <math.h>
            double nextafter(double x, double y);
            float nextafterf(float x, float y);
            long double nextafterl(long double x, long double y);
    Description
2   The nextafter functions determine the next representable value, in the type of the
    function, after x in the direction of y, where x and y are first converted to the type of the
    function.237) The nextafter functions return y if x equals y. A range error may occur
    if the magnitude of x is the largest finite value representable in the type and the result is
    infinite or not representable in the type.
    Returns
3   The nextafter functions return the next representable value in the specified format
    after x in the direction of y.


    237) The argument values are converted to the type of the function, even by a macro implementation of the
         function.

[page 255]

    7.12.11.4 The nexttoward functions
    Synopsis
1           #include <math.h>
            double nexttoward(double x, long double y);
            float nexttowardf(float x, long double y);
            long double nexttowardl(long double x, long double y);
    Description
2   The nexttoward functions are equivalent to the nextafter functions except that the
    second parameter has type long double and the functions return y converted to the
    type of the function if x equals y.238)
    7.12.12 Maximum, minimum, and positive difference functions
    7.12.12.1 The fdim functions
    Synopsis
1           #include <math.h>
            double fdim(double x, double y);
            float fdimf(float x, float y);
            long double fdiml(long double x, long double y);
    Description
2   The fdim functions determine the positive difference between their arguments:
          {x - y if x > y
          {
          {+0     if x <= y
    A range error may occur.
    Returns
3   The fdim functions return the positive difference value.
    7.12.12.2 The fmax functions
    Synopsis
1           #include <math.h>
            double fmax(double x, double y);
            float fmaxf(float x, float y);
            long double fmaxl(long double x, long double y);



    238) The result of the nexttoward functions is determined in the type of the function, without loss of
         range or precision in a floating second argument.

[page 256]

    Description
2   The fmax functions determine the maximum numeric value of their arguments.239)
    Returns
3   The fmax functions return the maximum numeric value of their arguments.
    7.12.12.3 The fmin functions
    Synopsis
1           #include <math.h>
            double fmin(double x, double y);
            float fminf(float x, float y);
            long double fminl(long double x, long double y);
    Description
2   The fmin functions determine the minimum numeric value of their arguments.240)
    Returns
3   The fmin functions return the minimum numeric value of their arguments.
    7.12.13 Floating multiply-add
    7.12.13.1 The fma functions
    Synopsis
1           #include <math.h>
            double fma(double x, double y, double z);
            float fmaf(float x, float y, float z);
            long double fmal(long double x, long double y,
                 long double z);
    Description
2   The fma functions compute (x x y) + z, rounded as one ternary operation: they compute
    the value (as if) to infinite precision and round once to the result format, according to the
    current rounding mode. A range error may occur.
    Returns
3   The fma functions return (x x y) + z, rounded as one ternary operation.




    239) NaN arguments are treated as missing data: if one argument is a NaN and the other numeric, then the
         fmax functions choose the numeric value. See F.10.9.2.
    240) The fmin functions are analogous to the fmax functions in their treatment of NaNs.

[page 257]

    7.12.14 Comparison macros
1   The relational and equality operators support the usual mathematical relationships
    between numeric values. For any ordered pair of numeric values exactly one of the
    relationships -- less, greater, and equal -- is true. Relational operators may raise the
    ''invalid'' floating-point exception when argument values are NaNs. For a NaN and a
    numeric value, or for two NaNs, just the unordered relationship is true.241) The following
    subclauses provide macros that are quiet (non floating-point exception raising) versions
    of the relational operators, and other comparison macros that facilitate writing efficient
    code that accounts for NaNs without suffering the ''invalid'' floating-point exception. In
    the synopses in this subclause, real-floating indicates that the argument shall be an
    expression of real floating type242) (both arguments need not have the same type).243)
    7.12.14.1 The isgreater macro
    Synopsis
1            #include <math.h>
             int isgreater(real-floating x, real-floating y);
    Description
2   The isgreater macro determines whether its first argument is greater than its second
    argument. The value of isgreater(x, y) is always equal to (x) > (y); however,
    unlike (x) > (y), isgreater(x, y) does not raise the ''invalid'' floating-point
    exception when x and y are unordered.
    Returns
3   The isgreater macro returns the value of (x) > (y).
    7.12.14.2 The isgreaterequal macro
    Synopsis
1            #include <math.h>
             int isgreaterequal(real-floating x, real-floating y);




    241) IEC 60559 requires that the built-in relational operators raise the ''invalid'' floating-point exception if
         the operands compare unordered, as an error indicator for programs written without consideration of
         NaNs; the result in these cases is false.
    242) If any argument is of integer type, or any other type that is not a real floating type, the behavior is
         undefined.
    243) Whether an argument represented in a format wider than its semantic type is converted to the semantic
         type is unspecified.

[page 258]

    Description
2   The isgreaterequal macro determines whether its first argument is greater than or
    equal to its second argument. The value of isgreaterequal(x, y) is always equal
    to (x) >= (y); however, unlike (x) >= (y), isgreaterequal(x, y) does
    not raise the ''invalid'' floating-point exception when x and y are unordered.
    Returns
3   The isgreaterequal macro returns the value of (x) >= (y).
    7.12.14.3 The isless macro
    Synopsis
1           #include <math.h>
            int isless(real-floating x, real-floating y);
    Description
2   The isless macro determines whether its first argument is less than its second
    argument. The value of isless(x, y) is always equal to (x) < (y); however,
    unlike (x) < (y), isless(x, y) does not raise the ''invalid'' floating-point
    exception when x and y are unordered.
    Returns
3   The isless macro returns the value of (x) < (y).
    7.12.14.4 The islessequal macro
    Synopsis
1           #include <math.h>
            int islessequal(real-floating x, real-floating y);
    Description
2   The islessequal macro determines whether its first argument is less than or equal to
    its second argument. The value of islessequal(x, y) is always equal to
    (x) <= (y); however, unlike (x) <= (y), islessequal(x, y) does not raise
    the ''invalid'' floating-point exception when x and y are unordered.
    Returns
3   The islessequal macro returns the value of (x) <= (y).




[page 259]

    7.12.14.5 The islessgreater macro
    Synopsis
1          #include <math.h>
           int islessgreater(real-floating x, real-floating y);
    Description
2   The islessgreater macro determines whether its first argument is less than or
    greater than its second argument. The islessgreater(x, y) macro is similar to
    (x) < (y) || (x) > (y); however, islessgreater(x, y) does not raise
    the ''invalid'' floating-point exception when x and y are unordered (nor does it evaluate x
    and y twice).
    Returns
3   The islessgreater macro returns the value of (x) < (y) || (x) > (y).
    7.12.14.6 The isunordered macro
    Synopsis
1          #include <math.h>
           int isunordered(real-floating x, real-floating y);
    Description
2   The isunordered macro determines whether its arguments are unordered.
    Returns
3   The isunordered macro returns 1 if its arguments are unordered and 0 otherwise.




[page 260]

    7.13 Nonlocal jumps <setjmp.h>
1   The header <setjmp.h> defines the macro setjmp, and declares one function and
    one type, for bypassing the normal function call and return discipline.244)
2   The type declared is
            jmp_buf
    which is an array type suitable for holding the information needed to restore a calling
    environment. The environment of a call to the setjmp macro consists of information
    sufficient for a call to the longjmp function to return execution to the correct block and
    invocation of that block, were it called recursively. It does not include the state of the
    floating-point status flags, of open files, or of any other component of the abstract
    machine.
3   It is unspecified whether setjmp is a macro or an identifier declared with external
    linkage. If a macro definition is suppressed in order to access an actual function, or a
    program defines an external identifier with the name setjmp, the behavior is undefined.
    7.13.1 Save calling environment
    7.13.1.1 The setjmp macro
    Synopsis
1           #include <setjmp.h>
            int setjmp(jmp_buf env);
    Description
2   The setjmp macro saves its calling environment in its jmp_buf argument for later use
    by the longjmp function.
    Returns
3   If the return is from a direct invocation, the setjmp macro returns the value zero. If the
    return is from a call to the longjmp function, the setjmp macro returns a nonzero
    value.
    Environmental limits
4   An invocation of the setjmp macro shall appear only in one of the following contexts:
    -- the entire controlling expression of a selection or iteration statement;
    -- one operand of a relational or equality operator with the other operand an integer
      constant expression, with the resulting expression being the entire controlling


    244) These functions are useful for dealing with unusual conditions encountered in a low-level function of
         a program.

[page 261]

        expression of a selection or iteration statement;
    -- the operand of a unary ! operator with the resulting expression being the entire
      controlling expression of a selection or iteration statement; or
    -- the entire expression of an expression statement (possibly cast to void).
5   If the invocation appears in any other context, the behavior is undefined.
    7.13.2 Restore calling environment
    7.13.2.1 The longjmp function
    Synopsis
1            #include <setjmp.h>
             _Noreturn void longjmp(jmp_buf env, int val);
    Description
2   The longjmp function restores the environment saved by the most recent invocation of
    the setjmp macro in the same invocation of the program with the corresponding
    jmp_buf argument. If there has been no such invocation, or if the function containing
    the invocation of the setjmp macro has terminated execution245) in the interim, or if the
    invocation of the setjmp macro was within the scope of an identifier with variably
    modified type and execution has left that scope in the interim, the behavior is undefined.
3   All accessible objects have values, and all other components of the abstract machine246)
    have state, as of the time the longjmp function was called, except that the values of
    objects of automatic storage duration that are local to the function containing the
    invocation of the corresponding setjmp macro that do not have volatile-qualified type
    and have been changed between the setjmp invocation and longjmp call are
    indeterminate.
    Returns
4   After longjmp is completed, program execution continues as if the corresponding
    invocation of the setjmp macro had just returned the value specified by val. The
    longjmp function cannot cause the setjmp macro to return the value 0; if val is 0,
    the setjmp macro returns the value 1.
5   EXAMPLE The longjmp function that returns control back to the point of the setjmp invocation
    might cause memory associated with a variable length array object to be squandered.




    245) For example, by executing a return statement or because another longjmp call has caused a
         transfer to a setjmp invocation in a function earlier in the set of nested calls.
    246) This includes, but is not limited to, the floating-point status flags and the state of open files.

[page 262]

        #include <setjmp.h>
        jmp_buf buf;
        void g(int n);
        void h(int n);
        int n = 6;
        void f(void)
        {
              int x[n];          // valid: f is not terminated
              setjmp(buf);
              g(n);
        }
        void g(int n)
        {
              int a[n];          // a may remain allocated
              h(n);
        }
        void h(int n)
        {
              int b[n];          // b may remain allocated
              longjmp(buf, 2);   // might cause memory loss
        }




[page 263]

    7.14 Signal handling <signal.h>
1   The header <signal.h> declares a type and two functions and defines several macros,
    for handling various signals (conditions that may be reported during program execution).
2   The type defined is
             sig_atomic_t
    which is the (possibly volatile-qualified) integer type of an object that can be accessed as
    an atomic entity, even in the presence of asynchronous interrupts.
3   The macros defined are
             SIG_DFL
             SIG_ERR
             SIG_IGN
    which expand to constant expressions with distinct values that have type compatible with
    the second argument to, and the return value of, the signal function, and whose values
    compare unequal to the address of any declarable function; and the following, which
    expand to positive integer constant expressions with type int and distinct values that are
    the signal numbers, each corresponding to the specified condition:
             SIGABRT abnormal termination, such as is initiated by the abort function
             SIGFPE        an erroneous arithmetic operation, such as zero divide or an operation
                           resulting in overflow
             SIGILL        detection of an invalid function image, such as an invalid instruction
             SIGINT        receipt of an interactive attention signal
             SIGSEGV an invalid access to storage
             SIGTERM a termination request sent to the program
4   An implementation need not generate any of these signals, except as a result of explicit
    calls to the raise function. Additional signals and pointers to undeclarable functions,
    with macro definitions beginning, respectively, with the letters SIG and an uppercase
    letter or with SIG_ and an uppercase letter,247) may also be specified by the
    implementation. The complete set of signals, their semantics, and their default handling
    is implementation-defined; all signal numbers shall be positive.




    247) See ''future library directions'' (7.30.6). The names of the signal numbers reflect the following terms
         (respectively): abort, floating-point exception, illegal instruction, interrupt, segmentation violation,
         and termination.

[page 264]

    7.14.1 Specify signal handling
    7.14.1.1 The signal function
    Synopsis
1           #include <signal.h>
            void (*signal(int sig, void (*func)(int)))(int);
    Description
2   The signal function chooses one of three ways in which receipt of the signal number
    sig is to be subsequently handled. If the value of func is SIG_DFL, default handling
    for that signal will occur. If the value of func is SIG_IGN, the signal will be ignored.
    Otherwise, func shall point to a function to be called when that signal occurs. An
    invocation of such a function because of a signal, or (recursively) of any further functions
    called by that invocation (other than functions in the standard library),248) is called a
    signal handler.
3   When a signal occurs and func points to a function, it is implementation-defined
    whether the equivalent of signal(sig, SIG_DFL); is executed or the
    implementation prevents some implementation-defined set of signals (at least including
    sig) from occurring until the current signal handling has completed; in the case of
    SIGILL, the implementation may alternatively define that no action is taken. Then the
    equivalent of (*func)(sig); is executed. If and when the function returns, if the
    value of sig is SIGFPE, SIGILL, SIGSEGV, or any other implementation-defined
    value corresponding to a computational exception, the behavior is undefined; otherwise
    the program will resume execution at the point it was interrupted.
4   If the signal occurs as the result of calling the abort or raise function, the signal
    handler shall not call the raise function.
5   If the signal occurs other than as the result of calling the abort or raise function, the
    behavior is undefined if the signal handler refers to any object with static or thread
    storage duration that is not a lock-free atomic object other than by assigning a value to an
    object declared as volatile sig_atomic_t, or the signal handler calls any function
    in the standard library other than the abort function, the _Exit function, the
    quick_exit function, or the signal function with the first argument equal to the
    signal number corresponding to the signal that caused the invocation of the handler.
    Furthermore, if such a call to the signal function results in a SIG_ERR return, the
    value of errno is indeterminate.249)


    248) This includes functions called indirectly via standard library functions (e.g., a SIGABRT handler
         called via the abort function).
    249) If any signal is generated by an asynchronous signal handler, the behavior is undefined.

[page 265]

6   At program startup, the equivalent of
           signal(sig, SIG_IGN);
    may be executed for some signals selected in an implementation-defined manner; the
    equivalent of
           signal(sig, SIG_DFL);
    is executed for all other signals defined by the implementation.
7   The implementation shall behave as if no library function calls the signal function.
    Returns
8   If the request can be honored, the signal function returns the value of func for the
    most recent successful call to signal for the specified signal sig. Otherwise, a value of
    SIG_ERR is returned and a positive value is stored in errno.
    Forward references: the abort function (7.22.4.1), the exit function (7.22.4.4), the
    _Exit function (7.22.4.5), the quick_exit function (7.22.4.7).
    7.14.2 Send signal
    7.14.2.1 The raise function
    Synopsis
1          #include <signal.h>
           int raise(int sig);
    Description
2   The raise function carries out the actions described in 7.14.1.1 for the signal sig. If a
    signal handler is called, the raise function shall not return until after the signal handler
    does.
    Returns
3   The raise function returns zero if successful, nonzero if unsuccessful.




[page 266]

    7.15 Alignment <stdalign.h>
1   The header <stdalign.h> defines two macros.
2   The macro
            alignas
    expands to _Alignas.
3   The remaining macro is suitable for use in #if preprocessing directives. It is
            __alignas_is_defined
    which expands to the integer constant 1.




[page 267]

    7.16 Variable arguments <stdarg.h>
1   The header <stdarg.h> declares a type and defines four macros, for advancing
    through a list of arguments whose number and types are not known to the called function
    when it is translated.
2   A function may be called with a variable number of arguments of varying types. As
    described in 6.9.1, its parameter list contains one or more parameters. The rightmost
    parameter plays a special role in the access mechanism, and will be designated parmN in
    this description.
3   The type declared is
            va_list
    which is a complete object type suitable for holding information needed by the macros
    va_start, va_arg, va_end, and va_copy. If access to the varying arguments is
    desired, the called function shall declare an object (generally referred to as ap in this
    subclause) having type va_list. The object ap may be passed as an argument to
    another function; if that function invokes the va_arg macro with parameter ap, the
    value of ap in the calling function is indeterminate and shall be passed to the va_end
    macro prior to any further reference to ap.250)
    7.16.1 Variable argument list access macros
1   The va_start and va_arg macros described in this subclause shall be implemented
    as macros, not functions. It is unspecified whether va_copy and va_end are macros or
    identifiers declared with external linkage. If a macro definition is suppressed in order to
    access an actual function, or a program defines an external identifier with the same name,
    the behavior is undefined. Each invocation of the va_start and va_copy macros
    shall be matched by a corresponding invocation of the va_end macro in the same
    function.
    7.16.1.1 The va_arg macro
    Synopsis
1           #include <stdarg.h>
            type va_arg(va_list ap, type);
    Description
2   The va_arg macro expands to an expression that has the specified type and the value of
    the next argument in the call. The parameter ap shall have been initialized by the
    va_start or va_copy macro (without an intervening invocation of the va_end

    250) It is permitted to create a pointer to a va_list and pass that pointer to another function, in which
         case the original function may make further use of the original list after the other function returns.

[page 268]

    macro for the same ap). Each invocation of the va_arg macro modifies ap so that the
    values of successive arguments are returned in turn. The parameter type shall be a type
    name specified such that the type of a pointer to an object that has the specified type can
    be obtained simply by postfixing a * to type. If there is no actual next argument, or if
    type is not compatible with the type of the actual next argument (as promoted according
    to the default argument promotions), the behavior is undefined, except for the following
    cases:
    -- one type is a signed integer type, the other type is the corresponding unsigned integer
      type, and the value is representable in both types;
    -- one type is pointer to void and the other is a pointer to a character type.
    Returns
3   The first invocation of the va_arg macro after that of the va_start macro returns the
    value of the argument after that specified by parmN . Successive invocations return the
    values of the remaining arguments in succession.
    7.16.1.2 The va_copy macro
    Synopsis
1           #include <stdarg.h>
            void va_copy(va_list dest, va_list src);
    Description
2   The va_copy macro initializes dest as a copy of src, as if the va_start macro had
    been applied to dest followed by the same sequence of uses of the va_arg macro as
    had previously been used to reach the present state of src. Neither the va_copy nor
    va_start macro shall be invoked to reinitialize dest without an intervening
    invocation of the va_end macro for the same dest.
    Returns
3   The va_copy macro returns no value.
    7.16.1.3 The va_end macro
    Synopsis
1           #include <stdarg.h>
            void va_end(va_list ap);
    Description
2   The va_end macro facilitates a normal return from the function whose variable
    argument list was referred to by the expansion of the va_start macro, or the function
    containing the expansion of the va_copy macro, that initialized the va_list ap. The
    va_end macro may modify ap so that it is no longer usable (without being reinitialized

[page 269]

    by the va_start or va_copy macro). If there is no corresponding invocation of the
    va_start or va_copy macro, or if the va_end macro is not invoked before the
    return, the behavior is undefined.
    Returns
3   The va_end macro returns no value.
    7.16.1.4 The va_start macro
    Synopsis
1           #include <stdarg.h>
            void va_start(va_list ap, parmN);
    Description
2   The va_start macro shall be invoked before any access to the unnamed arguments.
3   The va_start macro initializes ap for subsequent use by the va_arg and va_end
    macros. Neither the va_start nor va_copy macro shall be invoked to reinitialize ap
    without an intervening invocation of the va_end macro for the same ap.
4   The parameter parmN is the identifier of the rightmost parameter in the variable
    parameter list in the function definition (the one just before the , ...). If the parameter
    parmN is declared with the register storage class, with a function or array type, or
    with a type that is not compatible with the type that results after application of the default
    argument promotions, the behavior is undefined.
    Returns
5   The va_start macro returns no value.
6   EXAMPLE 1 The function f1 gathers into an array a list of arguments that are pointers to strings (but not
    more than MAXARGS arguments), then passes the array as a single argument to function f2. The number of
    pointers is specified by the first argument to f1.
            #include <stdarg.h>
            #define MAXARGS   31
            void f1(int n_ptrs, ...)
            {
                  va_list ap;
                  char *array[MAXARGS];
                  int ptr_no = 0;




[page 270]

                      if (n_ptrs > MAXARGS)
                            n_ptrs = MAXARGS;
                      va_start(ap, n_ptrs);
                      while (ptr_no < n_ptrs)
                            array[ptr_no++] = va_arg(ap, char *);
                      va_end(ap);
                      f2(n_ptrs, array);
             }
    Each call to f1 is required to have visible the definition of the function or a declaration such as
             void f1(int, ...);

7   EXAMPLE 2 The function f3 is similar, but saves the status of the variable argument list after the
    indicated number of arguments; after f2 has been called once with the whole list, the trailing part of the list
    is gathered again and passed to function f4.
             #include <stdarg.h>
             #define MAXARGS 31
             void f3(int n_ptrs, int f4_after, ...)
             {
                   va_list ap, ap_save;
                   char *array[MAXARGS];
                   int ptr_no = 0;
                   if (n_ptrs > MAXARGS)
                         n_ptrs = MAXARGS;
                   va_start(ap, f4_after);
                   while (ptr_no < n_ptrs) {
                         array[ptr_no++] = va_arg(ap, char *);
                         if (ptr_no == f4_after)
                               va_copy(ap_save, ap);
                   }
                   va_end(ap);
                   f2(n_ptrs, array);
                      // Now process the saved copy.
                      n_ptrs -= f4_after;
                      ptr_no = 0;
                      while (ptr_no < n_ptrs)
                            array[ptr_no++] = va_arg(ap_save, char *);
                      va_end(ap_save);
                      f4(n_ptrs, array);
             }




[page 271]

    7.17 Atomics <stdatomic.h>
    7.17.1 Introduction
1   The header <stdatomic.h> defines several macros and declares several types and
    functions for performing atomic operations on data shared between threads.
2   Implementations that define the macro __STDC_NO_THREADS__ need not provide
    this header nor support any of its facilities.
3   The macros defined are the atomic lock-free macros
           ATOMIC_CHAR_LOCK_FREE
           ATOMIC_CHAR16_T_LOCK_FREE
           ATOMIC_CHAR32_T_LOCK_FREE
           ATOMIC_WCHAR_T_LOCK_FREE
           ATOMIC_SHORT_LOCK_FREE
           ATOMIC_INT_LOCK_FREE
           ATOMIC_LONG_LOCK_FREE
           ATOMIC_LLONG_LOCK_FREE
           ATOMIC_ADDRESS_LOCK_FREE
    which indicate the lock-free property of the corresponding atomic types (both signed and
    unsigned); and
           ATOMIC_FLAG_INIT
    which expands to an initializer for an object of type atomic_flag.
4   The types include
           memory_order
    which is an enumerated type whose enumerators identify memory ordering constraints;
           atomic_flag
    which is a structure type representing a lock-free, primitive atomic flag;
           atomic_bool
    which is a structure type representing the atomic analog of the type _Bool;
           atomic_address
    which is a structure type representing the atomic analog of a pointer type; and several
    atomic analogs of integer types.
5   In the following operation definitions:
    -- An A refers to one of the atomic types.


[page 272]

    -- A C refers to its corresponding non-atomic type. The atomic_address atomic
      type corresponds to the void * non-atomic type.
    -- An M refers to the type of the other argument for arithmetic operations. For atomic
      integer types, M is C. For atomic address types, M is ptrdiff_t.
    -- The functions not ending in _explicit have the same semantics as the
      corresponding _explicit function with memory_order_seq_cst for the
      memory_order argument.
6   NOTE Many operations are volatile-qualified. The ''volatile as device register'' semantics have not
    changed in the standard. This qualification means that volatility is preserved when applying these
    operations to volatile objects.

    7.17.2 Initialization
    7.17.2.1 The ATOMIC_VAR_INIT macro
    Synopsis
1           #include <stdatomic.h>
            #define ATOMIC_VAR_INIT(C value)
    Description
2   The ATOMIC_VAR_INIT macro expands to a token sequence suitable for initializing an
    atomic object of a type that is initialization-compatible with value. An atomic object
    with automatic storage duration that is not explicitly initialized using
    ATOMIC_VAR_INIT is initially in an indeterminate state; however, the default (zero)
    initialization for objects with static or thread-local storage duration is guaranteed to
    produce a valid state.
3   Concurrent access to the variable being initialized, even via an atomic operation,
    constitutes a data race.
4   EXAMPLE
            atomic_int guide = ATOMIC_VAR_INIT(42);

    7.17.2.2 The atomic_init generic function
    Synopsis
1           #include <stdatomic.h>
            void atomic_init(volatile A *obj, C value);
    Description
2   The atomic_init generic function initializes the atomic object pointed to by obj to
    the value value, while also initializing any additional state that the implementation
    might need to carry for the atomic object.



[page 273]

3   Although this function initializes an atomic object, it does not avoid data races;
    concurrent access to the variable being initialized, even via an atomic operation,
    constitutes a data race.
    Returns
4   The atomic_init generic function returns no value.
5   EXAMPLE
            atomic_int guide;
            atomic_init(&guide, 42);

    7.17.3 Order and consistency
1   The enumerated type memory_order specifies the detailed regular (non-atomic)
    memory synchronization operations as defined in 5.1.2.4 and may provide for operation
    ordering. Its enumeration constants are as follows:
            memory_order_relaxed
            memory_order_consume
            memory_order_acquire
            memory_order_release
            memory_order_acq_rel
            memory_order_seq_cst
2   For memory_order_relaxed, no operation orders memory.
3   For       memory_order_release,       memory_order_acq_rel,             and
    memory_order_seq_cst, a store operation performs a release operation on the
    affected memory location.
4   For       memory_order_acquire,       memory_order_acq_rel,             and
    memory_order_seq_cst, a load operation performs an acquire operation on the
    affected memory location.
5   For memory_order_consume, a load operation performs a consume operation on the
    affected memory location.
6   For memory_order_seq_cst, there shall be a single total order S on all operations,
    consistent with the ''happens before'' order and modification orders for all affected
    locations, such that each memory_order_seq_cst operation that loads a value
    observes either the last preceding modification according to this order S, or the result of
    an operation that is not memory_order_seq_cst.
7   NOTE 1 Although it is not explicitly required that S include lock operations, it can always be extended to
    an order that does include lock and unlock operations, since the ordering between those is already included
    in the ''happens before'' ordering.

8   NOTE 2 Atomic operations specifying memory_order_relaxed are relaxed only with respect to
    memory ordering. Implementations must still guarantee that any given atomic access to a particular atomic

[page 274]

     object be indivisible with respect to all other atomic accesses to that object.

9    For an atomic operation B that reads the value of an atomic object M, if there is a
     memory_order_seq_cst fence X sequenced before B, then B observes either the
     last memory_order_seq_cst modification of M preceding X in the total order S or
     a later modification of M in its modification order.
10   For atomic operations A and B on an atomic object M, where A modifies M and B takes
     its value, if there is a memory_order_seq_cst fence X such that A is sequenced
     before X and B follows X in S, then B observes either the effects of A or a later
     modification of M in its modification order.
11   For atomic operations A and B on an atomic object M, where A modifies M and B takes
     its value, if there are memory_order_seq_cst fences X and Y such that A is
     sequenced before X, Y is sequenced before B, and X precedes Y in S, then B observes
     either the effects of A or a later modification of M in its modification order.
12   Atomic read-modify-write operations shall always read the last value (in the modification
     order) stored before the write associated with the read-modify-write operation.
13   An atomic store shall only store a value that has been computed from constants and
     program input values by a finite sequence of program evaluations, such that each
     evaluation observes the values of variables as computed by the last prior assignment in
     the sequence.251) The ordering of evaluations in this sequence shall be such that
     -- If an evaluation B observes a value computed by A in a different thread, then B does
       not happen before A.
     -- If an evaluation A is included in the sequence, then all evaluations that assign to the
       same variable and happen before A are also included.
14   NOTE 3 The second requirement disallows ''out-of-thin-air'', or ''speculative'' stores of atomics when
     relaxed atomics are used. Since unordered operations are involved, evaluations may appear in this
     sequence out of thread order. For example, with x and y initially zero,
              // Thread 1:
              r1 = atomic_load_explicit(&y, memory_order_relaxed);
              atomic_store_explicit(&x, r1, memory_order_relaxed);

              // Thread 2:
              r2 = atomic_load_explicit(&x, memory_order_relaxed);
              atomic_store_explicit(&y, 42, memory_order_relaxed);
     is allowed to produce r1 == 42 && r2 == 42. The sequence of evaluations justifying this consists of:




     251) Among other implications, atomic variables shall not decay.

[page 275]

             atomic_store_explicit(&y, 42,               memory_order_relaxed);
             r1 = atomic_load_explicit(&y,               memory_order_relaxed);
             atomic_store_explicit(&x, r1,               memory_order_relaxed);
             r2 = atomic_load_explicit(&x,               memory_order_relaxed);
     On the other hand,
             // Thread 1:
             r1 = atomic_load_explicit(&y, memory_order_relaxed);
             atomic_store_explicit(&x, r1, memory_order_relaxed);

             // Thread 2:
             r2 = atomic_load_explicit(&x, memory_order_relaxed);
             atomic_store_explicit(&y, r2, memory_order_relaxed);
     is not allowed to produce r1 == 42 && r2 = 42, since there is no sequence of evaluations that results
     in the computation of 42. In the absence of ''relaxed'' operations and read-modify-write operations with
     weaker than memory_order_acq_rel ordering, the second requirement has no impact.

     Recommended practice
15   The requirements do not forbid r1 == 42 && r2 == 42 in the following example,
     with x and y initially zero:
             // Thread 1:
             r1 = atomic_load_explicit(&x, memory_order_relaxed);
             if (r1 == 42)
                  atomic_store_explicit(&y, r1, memory_order_relaxed);

             // Thread 2:
             r2 = atomic_load_explicit(&y, memory_order_relaxed);
             if (r2 == 42)
                  atomic_store_explicit(&x, 42, memory_order_relaxed);
     However, this is not useful behavior, and implementations should not allow it.
16   Implementations should make atomic stores visible to atomic loads within a reasonable
     amount of time.
     7.17.3.1 The kill_dependency macro
     Synopsis
1            #include <stdatomic.h>
             type kill_dependency(type y);
     Description
2    The kill_dependency macro terminates a dependency chain; the argument does not
     carry a dependency to the return value.



[page 276]

    Returns
3   The kill_dependency macro returns the value of y.
    7.17.4 Fences
1   This subclause introduces synchronization primitives called fences. Fences can have
    acquire semantics, release semantics, or both. A fence with acquire semantics is called
    an acquire fence; a fence with release semantics is called a release fence.
2   A release fence A synchronizes with an acquire fence B if there exist atomic operations
    X and Y , both operating on some atomic object M, such that A is sequenced before X, X
    modifies M, Y is sequenced before B, and Y reads the value written by X or a value
    written by any side effect in the hypothetical release sequence X would head if it were a
    release operation.
3   A release fence A synchronizes with an atomic operation B that performs an acquire
    operation on an atomic object M if there exists an atomic operation X such that A is
    sequenced before X, X modifies M, and B reads the value written by X or a value written
    by any side effect in the hypothetical release sequence X would head if it were a release
    operation.
4   An atomic operation A that is a release operation on an atomic object M synchronizes
    with an acquire fence B if there exists some atomic operation X on M such that X is
    sequenced before B and reads the value written by A or a value written by any side effect
    in the release sequence headed by A.
    7.17.4.1 The atomic_thread_fence function
    Synopsis
1           #include <stdatomic.h>
            void atomic_thread_fence(memory_order order);
    Description
2   Depending on the value of order, this operation:
    -- has no effects, if order == memory_order_relaxed;
    -- is an acquire fence, if order == memory_order_acquire or order ==
      memory_order_consume;
    -- is a release fence, if order == memory_order_release;
    -- is both an acquire fence              and   a    release   fence,    if   order     ==
      memory_order_acq_rel;
    -- is a sequentially consistent acquire and release fence, if order                    ==
      memory_order_seq_cst.


[page 277]

    Returns
3   The atomic_thread_fence function returns no value.
    7.17.4.2 The atomic_signal_fence function
    Synopsis
1           #include <stdatomic.h>
            void atomic_signal_fence(memory_order order);
    Description
2   Equivalent to atomic_thread_fence(order), except that ''synchronizes with''
    relationships are established only between a thread and a signal handler executed in the
    same thread.
3   NOTE 1 The atomic_signal_fence function can be used to specify the order in which actions
    performed by the thread become visible to the signal handler.

4   NOTE 2 Compiler optimizations and reorderings of loads and stores are inhibited in the same way as with
    atomic_thread_fence, but the hardware fence instructions that atomic_thread_fence would
    have inserted are not emitted.

    Returns
5   The atomic_signal_fence function returns no value.
    7.17.5 Lock-free property
1   The atomic lock-free macros indicate the lock-free property of integer and address atomic
    types. A value of 0 indicates that the type is never lock-free; a value of 1 indicates that
    the type is sometimes lock-free; a value of 2 indicates that the type is always lock-free.
2   NOTE Operations that are lock-free should also be address-free. That is, atomic operations on the same
    memory location via two different addresses will communicate atomically. The implementation should not
    depend on any per-process state. This restriction enables communication via memory mapped into a
    process more than once and memory shared between two processes.

    7.17.5.1 The atomic_is_lock_free generic function
    Synopsis
1           #include <stdatomic.h>
            _Bool atomic_is_lock_free(atomic_type const volatile *obj);
    Description
2   The atomic_is_lock_free generic function indicates whether or not the object
    pointed to by obj is lock-free. atomic_type can be any atomic type.
    Returns
3   The atomic_is_lock_free generic function returns nonzero (true) if and only if the
    object's operations are lock-free. The result of a lock-free query on one object cannot be

[page 278]

    inferred from the result of a lock-free query on another object.
    7.17.6 Atomic integer and address types
1   For each line in the following table, the atomic type name is declared as the
    corresponding direct type.




[page 279]

               Atomic type name                              Direct type
           atomic_char                           _Atomic    char
           atomic_schar                          _Atomic    signed char
           atomic_uchar                          _Atomic    unsigned char
           atomic_short                          _Atomic    short
           atomic_ushort                         _Atomic    unsigned short
           atomic_int                            _Atomic    int
           atomic_uint                           _Atomic    unsigned int
           atomic_long                           _Atomic    long
           atomic_ulong                          _Atomic    unsigned long
           atomic_llong                          _Atomic    long long
           atomic_ullong                         _Atomic    unsigned long long
           atomic_char16_t                       _Atomic    char16_t
           atomic_char32_t                       _Atomic    char32_t
           atomic_wchar_t                        _Atomic    wchar_t
           atomic_int_least8_t                   _Atomic    int_least8_t
           atomic_uint_least8_t                  _Atomic    uint_least8_t
           atomic_int_least16_t                  _Atomic    int_least16_t
           atomic_uint_least16_t                 _Atomic    uint_least16_t
           atomic_int_least32_t                  _Atomic    int_least32_t
           atomic_uint_least32_t                 _Atomic    uint_least32_t
           atomic_int_least64_t                  _Atomic    int_least64_t
           atomic_uint_least64_t                 _Atomic    uint_least64_t
           atomic_int_fast8_t                    _Atomic    int_fast8_t
           atomic_uint_fast8_t                   _Atomic    uint_fast8_t
           atomic_int_fast16_t                   _Atomic    int_fast16_t
           atomic_uint_fast16_t                  _Atomic    uint_fast16_t
           atomic_int_fast32_t                   _Atomic    int_fast32_t
           atomic_uint_fast32_t                  _Atomic    uint_fast32_t
           atomic_int_fast64_t                   _Atomic    int_fast64_t
           atomic_uint_fast64_t                  _Atomic    uint_fast64_t
           atomic_intptr_t                       _Atomic    intptr_t
           atomic_uintptr_t                      _Atomic    uintptr_t
           atomic_size_t                         _Atomic    size_t
           atomic_ptrdiff_t                      _Atomic    ptrdiff_t
           atomic_intmax_t                       _Atomic    intmax_t
           atomic_uintmax_t                      _Atomic    uintmax_t
2   The semantics of the operations on these types are defined in 7.17.7.
3   The atomic_bool type provides an atomic boolean.


[page 280]

4   The atomic_address type provides atomic void * operations. The unit of
    addition/subtraction shall be one byte.
5   NOTE The representation of atomic integer and address types need not have the same size as their
    corresponding regular types. They should have the same size whenever possible, as it eases effort required
    to port existing code.

    7.17.7 Operations on atomic types
1   There are only a few kinds of operations on atomic types, though there are many
    instances of those kinds. This subclause specifies each general kind.
    7.17.7.1 The atomic_store generic functions
    Synopsis
1           #include <stdatomic.h>
            void atomic_store(volatile A *object, C desired);
            void atomic_store_explicit(volatile A *object,
                 C desired, memory_order order);
    Description
2   The      order      argument    shall    not    be    memory_order_acquire,
    memory_order_consume, nor memory_order_acq_rel. Atomically replace the
    value pointed to by object with the value of desired. Memory is affected according
    to the value of order.
    Returns
3   The atomic_store generic functions return no value.
    7.17.7.2 The atomic_load generic functions
    Synopsis
1           #include <stdatomic.h>
            C atomic_load(volatile A *object);
            C atomic_load_explicit(volatile A *object,
                 memory_order order);
    Description
2   The order argument shall not be memory_order_release nor
    memory_order_acq_rel. Memory is affected according to the value of order.
    Returns
    Atomically returns the value pointed to by object.




[page 281]

    7.17.7.3 The atomic_exchange generic functions
    Synopsis
1            #include <stdatomic.h>
             C atomic_exchange(volatile A *object, C desired);
             C atomic_exchange_explicit(volatile A *object,
                  C desired, memory_order order);
    Description
2   Atomically replace the value pointed to by object with desired. Memory is affected
    according to the value of order. These operations are read-modify-write operations
    (5.1.2.4).
    Returns
3   Atomically returns the value pointed to by object immediately before the effects.
    7.17.7.4 The atomic_compare_exchange generic functions
    Synopsis
1            #include <stdatomic.h>
             _Bool atomic_compare_exchange_strong(volatile A *object,
                  C *expected, C desired);
             _Bool atomic_compare_exchange_strong_explicit(
                  volatile A *object, C *expected, C desired,
                  memory_order success, memory_order failure);
             _Bool atomic_compare_exchange_weak(volatile A *object,
                  C *expected, C desired);
             _Bool atomic_compare_exchange_weak_explicit(
                  volatile A *object, C *expected, C desired,
                  memory_order success, memory_order failure);
    Description
2   The failure argument shall not be memory_order_release nor
    memory_order_acq_rel. The failure argument shall be no stronger than the
    success argument. Atomically, compares the value pointed to by object for equality
    with that in expected, and if true, replaces the value pointed to by object with
    desired, and if false, updates the value in expected with the value pointed to by
    object. Further, if the comparison is true, memory is affected according to the value of
    success, and if the comparison is false, memory is affected according to the value of
    failure. These operations are atomic read-modify-write operations (5.1.2.4).
3   NOTE 1    The effect of the compare-and-exchange operations is




[page 282]

             if (*object == *expected)
                   *object = desired;
             else
                   *expected = *object;

4   The weak compare-and-exchange operations may fail spuriously, that is, return zero
    while leaving the value pointed to by expected unchanged.
5   NOTE 2 This spurious failure enables implementation of compare-and-exchange on a broader class of
    machines, e.g. load-locked store-conditional machines.

6   EXAMPLE         A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will
    be in a loop.
             exp = atomic_load(&cur);
             do {
                   des = function(exp);
             } while (!atomic_compare_exchange_weak(&cur, &exp, des));
    When a compare-and-exchange is in a loop, the weak version will yield better performance on some
    platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the
    strong one is preferable.

    Returns
7   The result of the comparison.
    7.17.7.5 The atomic_fetch and modify generic functions
1   The following operations perform arithmetic and bitwise computations. All of these
    operations are applicable to an object of any atomic integer type. Only addition and
    subtraction are applicable to atomic_address. None of these operations is applicable
    to atomic_bool. The key, operator, and computation correspondence is:
     key            op          computation
     add            +       addition
     sub            -       subtraction
     or             |       bitwise inclusive or
     xor            ^       bitwise exclusive or
     and            &       bitwise and
    Synopsis
2            #include <stdatomic.h>
             C atomic_fetch_key(volatile A *object, M operand);
             C atomic_fetch_key_explicit(volatile A *object,
                  M operand, memory_order order);
    Description
3   Atomically replaces the value pointed to by object with the result of the computation
    applied to the value pointed to by object and the given operand. Memory is affected
    according to the value of order. These operations are atomic read-modify-write
[page 283]

    operations (5.1.2.4). For signed integer types, arithmetic is defined to use two's
    complement representation with silent wrap-around on overflow; there are no undefined
    results. For address types, the result may be an undefined address, but the operations
    otherwise have no undefined behavior.
    Returns
4   Atomically, the value pointed to by object immediately before the effects.
5   NOTE The operation of the atomic_fetch and modify generic functions are nearly equivalent to the
    operation of the corresponding op= compound assignment operators. The only differences are that the
    compound assignment operators are not guaranteed to operate atomically, and the value yielded by a
    compound assignment operator is the updated value of the object, whereas the value returned by the
    atomic_fetch and modify generic functions is the previous value of the atomic object.

    7.17.8 Atomic flag type and operations
1   The atomic_flag type provides the classic test-and-set functionality. It has two
    states, set and clear.
2   Operations on an object of type atomic_flag shall be lock free.
3   NOTE Hence the operations should also be address-free. No other type requires lock-free operations, so
    the atomic_flag type is the minimum hardware-implemented type needed to conform to this
    International standard. The remaining types can be emulated with atomic_flag, though with less than
    ideal properties.

4   The macro ATOMIC_FLAG_INIT may be used to initialize an atomic_flag to the
    clear state. An atomic_flag that is not explicitly initialized with
    ATOMIC_FLAG_INIT is initially in an indeterminate state.
5   EXAMPLE
            atomic_flag guard = ATOMIC_FLAG_INIT;

    7.17.8.1 The atomic_flag_test_and_set functions
    Synopsis
1           #include <stdatomic.h>
            bool atomic_flag_test_and_set(
                 volatile atomic_flag *object);
            bool atomic_flag_test_and_set_explicit(
                 volatile atomic_flag *object, memory_order order);
    Description
2   Atomically sets the value pointed to by object to true. Memory is affected according
    to the value of order. These operations are atomic read-modify-write operations
    (5.1.2.4).




[page 284]

    Returns
3   Atomically, the value of the object immediately before the effects.
    7.17.8.2 The atomic_flag_clear functions
    Synopsis
1           #include <stdatomic.h>
            void atomic_flag_clear(volatile atomic_flag *object);
            void atomic_flag_clear_explicit(
                 volatile atomic_flag *object, memory_order order);
    Description
2   The order argument shall not be memory_order_acquire nor
    memory_order_acq_rel. Atomically sets the value pointed to by object to false.
    Memory is affected according to the value of order.
    Returns
3   The atomic_flag_clear functions return no value.




[page 285]

    7.18 Boolean type and values <stdbool.h>
1   The header <stdbool.h> defines four macros.
2   The macro
             bool
    expands to _Bool.
3   The remaining three macros are suitable for use in #if preprocessing directives. They
    are
             true
    which expands to the integer constant 1,
             false
    which expands to the integer constant 0, and
             __bool_true_false_are_defined
    which expands to the integer constant 1.
4   Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then
    redefine the macros bool, true, and false.252)




    252) See ''future library directions'' (7.30.7).

[page 286]

    7.19 Common definitions <stddef.h>
1   The header <stddef.h> defines the following macros and declares the following types.
    Some are also defined in other headers, as noted in their respective subclauses.
2   The types are
            ptrdiff_t
    which is the signed integer type of the result of subtracting two pointers;
            size_t
    which is the unsigned integer type of the result of the sizeof operator;
            max_align_t
    which is an object type whose alignment is as great as is supported by the implementation
    in all contexts; and
            wchar_t
    which is an integer type whose range of values can represent distinct codes for all
    members of the largest extended character set specified among the supported locales; the
    null character shall have the code value zero. Each member of the basic character set
    shall have a code value equal to its value when used as the lone character in an integer
    character      constant     if     an      implementation      does      not      define
    __STDC_MB_MIGHT_NEQ_WC__.
3   The macros are
            NULL
    which expands to an implementation-defined null pointer constant; and
            offsetof(type, member-designator)
    which expands to an integer constant expression that has type size_t, the value of
    which is the offset in bytes, to the structure member (designated by member-designator),
    from the beginning of its structure (designated by type). The type and member designator
    shall be such that given
            static type t;
    then the expression &(t.member-designator) evaluates to an address constant. (If the
    specified member is a bit-field, the behavior is undefined.)
    Recommended practice
4   The types used for size_t and ptrdiff_t should not have an integer conversion rank
    greater than that of signed long int unless the implementation supports objects
    large enough to make this necessary.

[page 287]

Forward references: localization (7.11).




[page 288]

    7.20 Integer types <stdint.h>
1   The header <stdint.h> declares sets of integer types having specified widths, and
    defines corresponding sets of macros.253) It also defines macros that specify limits of
    integer types corresponding to types defined in other standard headers.
2   Types are defined in the following categories:
    -- integer types having certain exact widths;
    -- integer types having at least certain specified widths;
    -- fastest integer types having at least certain specified widths;
    -- integer types wide enough to hold pointers to objects;
    -- integer types having greatest width.
    (Some of these types may denote the same type.)
3   Corresponding macros specify limits of the declared types and construct suitable
    constants.
4   For each type described herein that the implementation provides,254) <stdint.h> shall
    declare that typedef name and define the associated macros. Conversely, for each type
    described herein that the implementation does not provide, <stdint.h> shall not
    declare that typedef name nor shall it define the associated macros. An implementation
    shall provide those types described as ''required'', but need not provide any of the others
    (described as ''optional'').
    7.20.1 Integer types
1   When typedef names differing only in the absence or presence of the initial u are defined,
    they shall denote corresponding signed and unsigned types as described in 6.2.5; an
    implementation providing one of these corresponding types shall also provide the other.
2   In the following descriptions, the symbol N represents an unsigned decimal integer with
    no leading zeros (e.g., 8 or 24, but not 04 or 048).




    253) See ''future library directions'' (7.30.8).
    254) Some of these types may denote implementation-defined extended integer types.

[page 289]

    7.20.1.1 Exact-width integer types
1   The typedef name intN_t designates a signed integer type with width N , no padding
    bits, and a two's complement representation. Thus, int8_t denotes such a signed
    integer type with a width of exactly 8 bits.
2   The typedef name uintN_t designates an unsigned integer type with width N and no
    padding bits. Thus, uint24_t denotes such an unsigned integer type with a width of
    exactly 24 bits.
3   These types are optional. However, if an implementation provides integer types with
    widths of 8, 16, 32, or 64 bits, no padding bits, and (for the signed types) that have a
    two's complement representation, it shall define the corresponding typedef names.
    7.20.1.2 Minimum-width integer types
1   The typedef name int_leastN_t designates a signed integer type with a width of at
    least N , such that no signed integer type with lesser size has at least the specified width.
    Thus, int_least32_t denotes a signed integer type with a width of at least 32 bits.
2   The typedef name uint_leastN_t designates an unsigned integer type with a width
    of at least N , such that no unsigned integer type with lesser size has at least the specified
    width. Thus, uint_least16_t denotes an unsigned integer type with a width of at
    least 16 bits.
3   The following types are required:
             int_least8_t                                      uint_least8_t
             int_least16_t                                     uint_least16_t
             int_least32_t                                     uint_least32_t
             int_least64_t                                     uint_least64_t
    All other types of this form are optional.
    7.20.1.3 Fastest minimum-width integer types
1   Each of the following types designates an integer type that is usually fastest255) to operate
    with among all integer types that have at least the specified width.
2   The typedef name int_fastN_t designates the fastest signed integer type with a width
    of at least N . The typedef name uint_fastN_t designates the fastest unsigned integer
    type with a width of at least N .




    255) The designated type is not guaranteed to be fastest for all purposes; if the implementation has no clear
         grounds for choosing one type over another, it will simply pick some integer type satisfying the
         signedness and width requirements.

[page 290]

3   The following types are required:
            int_fast8_t                                    uint_fast8_t
            int_fast16_t                                   uint_fast16_t
            int_fast32_t                                   uint_fast32_t
            int_fast64_t                                   uint_fast64_t
    All other types of this form are optional.
    7.20.1.4 Integer types capable of holding object pointers
1   The following type designates a signed integer type with the property that any valid
    pointer to void can be converted to this type, then converted back to pointer to void,
    and the result will compare equal to the original pointer:
            intptr_t
    The following type designates an unsigned integer type with the property that any valid
    pointer to void can be converted to this type, then converted back to pointer to void,
    and the result will compare equal to the original pointer:
            uintptr_t
    These types are optional.
    7.20.1.5 Greatest-width integer types
1   The following type designates a signed integer type capable of representing any value of
    any signed integer type:
            intmax_t
    The following type designates an unsigned integer type capable of representing any value
    of any unsigned integer type:
            uintmax_t
    These types are required.
    7.20.2 Limits of specified-width integer types
1   The following object-like macros specify the minimum and maximum limits of the types *
    declared in <stdint.h>. Each macro name corresponds to a similar type name in
    7.20.1.
2   Each instance of any defined macro shall be replaced by a constant expression suitable
    for use in #if preprocessing directives, and this expression shall have the same type as
    would an expression that is an object of the corresponding type converted according to
    the integer promotions. Its implementation-defined value shall be equal to or greater in
    magnitude (absolute value) than the corresponding value given below, with the same sign,
    except where stated to be exactly the given value.

[page 291]

    7.20.2.1 Limits of exact-width integer types
1   -- minimum values of exact-width signed integer types
          INTN_MIN                                  exactly -(2 N -1 )
    -- maximum values of exact-width signed integer types
          INTN_MAX                                  exactly 2 N -1 - 1
    -- maximum values of exact-width unsigned integer types
       UINTN_MAX                                    exactly 2 N - 1
    7.20.2.2 Limits of minimum-width integer types
1   -- minimum values of minimum-width signed integer types
          INT_LEASTN_MIN                                    -(2 N -1 - 1)
    -- maximum values of minimum-width signed integer types
          INT_LEASTN_MAX                                    2 N -1 - 1
    -- maximum values of minimum-width unsigned integer types
       UINT_LEASTN_MAX                                      2N - 1
    7.20.2.3 Limits of fastest minimum-width integer types
1   -- minimum values of fastest minimum-width signed integer types
          INT_FASTN_MIN                                     -(2 N -1 - 1)
    -- maximum values of fastest minimum-width signed integer types
       INT_FASTN_MAX                                        2 N -1 - 1
    -- maximum values of fastest minimum-width unsigned integer types
       UINT_FASTN_MAX                                       2N - 1
    7.20.2.4 Limits of integer types capable of holding object pointers
1   -- minimum value of pointer-holding signed integer type
          INTPTR_MIN                                        -(215 - 1)
    -- maximum value of pointer-holding signed integer type
       INTPTR_MAX                                           215 - 1
    -- maximum value of pointer-holding unsigned integer type
       UINTPTR_MAX                                          216 - 1



[page 292]

    7.20.2.5 Limits of greatest-width integer types
1   -- minimum value of greatest-width signed integer type
        INTMAX_MIN                                                    -(263 - 1)
    -- maximum value of greatest-width signed integer type
        INTMAX_MAX                                                    263 - 1
    -- maximum value of greatest-width unsigned integer type
        UINTMAX_MAX                                                   264 - 1
    7.20.3 Limits of other integer types
1   The following object-like macros specify the minimum and maximum limits of integer *
    types corresponding to types defined in other standard headers.
2   Each instance of these macros shall be replaced by a constant expression suitable for use
    in #if preprocessing directives, and this expression shall have the same type as would an
    expression that is an object of the corresponding type converted according to the integer
    promotions. Its implementation-defined value shall be equal to or greater in magnitude
    (absolute value) than the corresponding value given below, with the same sign. An
    implementation shall define only the macros corresponding to those typedef names it
    actually provides.256)
    -- limits of ptrdiff_t
        PTRDIFF_MIN                                                 -65535
        PTRDIFF_MAX                                                 +65535
    -- limits of sig_atomic_t
        SIG_ATOMIC_MIN                                              see below
        SIG_ATOMIC_MAX                                              see below
    -- limit of size_t
        SIZE_MAX                                                      65535
    -- limits of wchar_t
        WCHAR_MIN                                                   see below
        WCHAR_MAX                                                   see below
    -- limits of wint_t




    256) A freestanding implementation need not provide all of these types.

[page 293]

        WINT_MIN                                              see below
        WINT_MAX                                              see below
3   If sig_atomic_t (see 7.14) is defined as a signed integer type, the value of
    SIG_ATOMIC_MIN shall be no greater than -127 and the value of SIG_ATOMIC_MAX
    shall be no less than 127; otherwise, sig_atomic_t is defined as an unsigned integer
    type, and the value of SIG_ATOMIC_MIN shall be 0 and the value of
    SIG_ATOMIC_MAX shall be no less than 255.
4   If wchar_t (see 7.19) is defined as a signed integer type, the value of WCHAR_MIN
    shall be no greater than -127 and the value of WCHAR_MAX shall be no less than 127;
    otherwise, wchar_t is defined as an unsigned integer type, and the value of
    WCHAR_MIN shall be 0 and the value of WCHAR_MAX shall be no less than 255.257)
5   If wint_t (see 7.28) is defined as a signed integer type, the value of WINT_MIN shall
    be no greater than -32767 and the value of WINT_MAX shall be no less than 32767;
    otherwise, wint_t is defined as an unsigned integer type, and the value of WINT_MIN
    shall be 0 and the value of WINT_MAX shall be no less than 65535.
    7.20.4 Macros for integer constants
1   The following function-like macros expand to integer constants suitable for initializing *
    objects that have integer types corresponding to types defined in <stdint.h>. Each
    macro name corresponds to a similar type name in 7.20.1.2 or 7.20.1.5.
2   The argument in any instance of these macros shall be an unsuffixed integer constant (as
    defined in 6.4.4.1) with a value that does not exceed the limits for the corresponding type.
3   Each invocation of one of these macros shall expand to an integer constant expression
    suitable for use in #if preprocessing directives. The type of the expression shall have
    the same type as would an expression of the corresponding type converted according to
    the integer promotions. The value of the expression shall be that of the argument.
    7.20.4.1 Macros for minimum-width integer constants
1   The macro INTN_C(value) shall expand to an integer constant expression
    corresponding to the type int_leastN_t. The macro UINTN_C(value) shall expand
    to an integer constant expression corresponding to the type uint_leastN_t. For
    example, if uint_least64_t is a name for the type unsigned long long int,
    then UINT64_C(0x123) might expand to the integer constant 0x123ULL.




    257) The values WCHAR_MIN and WCHAR_MAX do not necessarily correspond to members of the extended
         character set.

[page 294]

    7.20.4.2 Macros for greatest-width integer constants
1   The following macro expands to an integer constant expression having the value specified
    by its argument and the type intmax_t:
            INTMAX_C(value)
    The following macro expands to an integer constant expression having the value specified
    by its argument and the type uintmax_t:
            UINTMAX_C(value)




[page 295]

    7.21 Input/output <stdio.h>
    7.21.1 Introduction
1   The header <stdio.h> defines several macros, and declares three types and many
    functions for performing input and output.
2   The types declared are size_t (described in 7.19);
           FILE
    which is an object type capable of recording all the information needed to control a
    stream, including its file position indicator, a pointer to its associated buffer (if any), an
    error indicator that records whether a read/write error has occurred, and an end-of-file
    indicator that records whether the end of the file has been reached; and
           fpos_t
    which is a complete object type other than an array type capable of recording all the
    information needed to specify uniquely every position within a file.
3   The macros are NULL (described in 7.19);
           _IOFBF
           _IOLBF
           _IONBF
    which expand to integer constant expressions with distinct values, suitable for use as the
    third argument to the setvbuf function;
           BUFSIZ
    which expands to an integer constant expression that is the size of the buffer used by the
    setbuf function;
           EOF
    which expands to an integer constant expression, with type int and a negative value, that
    is returned by several functions to indicate end-of-file, that is, no more input from a
    stream;
           FOPEN_MAX
    which expands to an integer constant expression that is the minimum number of files that
    the implementation guarantees can be open simultaneously;
           FILENAME_MAX
    which expands to an integer constant expression that is the size needed for an array of
    char large enough to hold the longest file name string that the implementation



[page 296]

    guarantees can be opened;258)
            L_tmpnam
    which expands to an integer constant expression that is the size needed for an array of
    char large enough to hold a temporary file name string generated by the tmpnam
    function;
            SEEK_CUR
            SEEK_END
            SEEK_SET
    which expand to integer constant expressions with distinct values, suitable for use as the
    third argument to the fseek function;
            TMP_MAX
    which expands to an integer constant expression that is the minimum number of unique
    file names that can be generated by the tmpnam function;
            stderr
            stdin
            stdout
    which are expressions of type ''pointer to FILE'' that point to the FILE objects
    associated, respectively, with the standard error, input, and output streams.
4   The header <wchar.h> declares a number of functions useful for wide character input
    and output. The wide character input/output functions described in that subclause
    provide operations analogous to most of those described here, except that the
    fundamental units internal to the program are wide characters. The external
    representation (in the file) is a sequence of ''generalized'' multibyte characters, as
    described further in 7.21.3.
5   The input/output functions are given the following collective terms:
    -- The wide character input functions -- those functions described in 7.28 that perform
      input into wide characters and wide strings: fgetwc, fgetws, getwc, getwchar,
      fwscanf, wscanf, vfwscanf, and vwscanf.
    -- The wide character output functions -- those functions described in 7.28 that perform
      output from wide characters and wide strings: fputwc, fputws, putwc,
      putwchar, fwprintf, wprintf, vfwprintf, and vwprintf.


    258) If the implementation imposes no practical limit on the length of file name strings, the value of
         FILENAME_MAX should instead be the recommended size of an array intended to hold a file name
         string. Of course, file name string contents are subject to other system-specific constraints; therefore
         all possible strings of length FILENAME_MAX cannot be expected to be opened successfully.

[page 297]

    -- The wide character input/output functions -- the union of the ungetwc function, the
      wide character input functions, and the wide character output functions.
    -- The byte input/output functions -- those functions described in this subclause that
      perform input/output: fgetc, fgets, fprintf, fputc, fputs, fread,
      fscanf, fwrite, getc, getchar, printf, putc, putchar, puts, scanf, *
      ungetc, vfprintf, vfscanf, vprintf, and vscanf.
    Forward references: files (7.21.3), the fseek function (7.21.9.2), streams (7.21.2), the
    tmpnam function (7.21.4.4), <wchar.h> (7.28).
    7.21.2 Streams
1   Input and output, whether to or from physical devices such as terminals and tape drives,
    or whether to or from files supported on structured storage devices, are mapped into
    logical data streams, whose properties are more uniform than their various inputs and
    outputs. Two forms of mapping are supported, for text streams and for binary
    streams.259)
2   A text stream is an ordered sequence of characters composed into lines, each line
    consisting of zero or more characters plus a terminating new-line character. Whether the
    last line requires a terminating new-line character is implementation-defined. Characters
    may have to be added, altered, or deleted on input and output to conform to differing
    conventions for representing text in the host environment. Thus, there need not be a one-
    to-one correspondence between the characters in a stream and those in the external
    representation. Data read in from a text stream will necessarily compare equal to the data
    that were earlier written out to that stream only if: the data consist only of printing
    characters and the control characters horizontal tab and new-line; no new-line character is
    immediately preceded by space characters; and the last character is a new-line character.
    Whether space characters that are written out immediately before a new-line character
    appear when read in is implementation-defined.
3   A binary stream is an ordered sequence of characters that can transparently record
    internal data. Data read in from a binary stream shall compare equal to the data that were
    earlier written out to that stream, under the same implementation. Such a stream may,
    however, have an implementation-defined number of null characters appended to the end
    of the stream.
4   Each stream has an orientation. After a stream is associated with an external file, but
    before any operations are performed on it, the stream is without orientation. Once a wide
    character input/output function has been applied to a stream without orientation, the


    259) An implementation need not distinguish between text streams and binary streams. In such an
         implementation, there need be no new-line characters in a text stream nor any limit to the length of a
         line.

[page 298]

    stream becomes a wide-oriented stream. Similarly, once a byte input/output function has
    been applied to a stream without orientation, the stream becomes a byte-oriented stream.
    Only a call to the freopen function or the fwide function can otherwise alter the
    orientation of a stream. (A successful call to freopen removes any orientation.)260)
5   Byte input/output functions shall not be applied to a wide-oriented stream and wide
    character input/output functions shall not be applied to a byte-oriented stream. The
    remaining stream operations do not affect, and are not affected by, a stream's orientation,
    except for the following additional restrictions:
    -- Binary wide-oriented streams have the file-positioning restrictions ascribed to both
      text and binary streams.
    -- For wide-oriented streams, after a successful call to a file-positioning function that
      leaves the file position indicator prior to the end-of-file, a wide character output
      function can overwrite a partial multibyte character; any file contents beyond the
      byte(s) written are henceforth indeterminate.
6   Each wide-oriented stream has an associated mbstate_t object that stores the current
    parse state of the stream. A successful call to fgetpos stores a representation of the
    value of this mbstate_t object as part of the value of the fpos_t object. A later
    successful call to fsetpos using the same stored fpos_t value restores the value of
    the associated mbstate_t object as well as the position within the controlled stream.
    Environmental limits
7   An implementation shall support text files with lines containing at least 254 characters,
    including the terminating new-line character. The value of the macro BUFSIZ shall be at
    least 256.
    Forward references: the freopen function (7.21.5.4), the fwide function (7.28.3.5),
    mbstate_t (7.29.1), the fgetpos function (7.21.9.1), the fsetpos function
    (7.21.9.3).




    260) The three predefined streams stdin, stdout, and stderr are unoriented at program startup.

[page 299]

    7.21.3 Files
1   A stream is associated with an external file (which may be a physical device) by opening
    a file, which may involve creating a new file. Creating an existing file causes its former
    contents to be discarded, if necessary. If a file can support positioning requests (such as a
    disk file, as opposed to a terminal), then a file position indicator associated with the
    stream is positioned at the start (character number zero) of the file, unless the file is
    opened with append mode in which case it is implementation-defined whether the file
    position indicator is initially positioned at the beginning or the end of the file. The file
    position indicator is maintained by subsequent reads, writes, and positioning requests, to
    facilitate an orderly progression through the file.
2   Binary files are not truncated, except as defined in 7.21.5.3. Whether a write on a text
    stream causes the associated file to be truncated beyond that point is implementation-
    defined.
3   When a stream is unbuffered, characters are intended to appear from the source or at the
    destination as soon as possible. Otherwise characters may be accumulated and
    transmitted to or from the host environment as a block. When a stream is fully buffered,
    characters are intended to be transmitted to or from the host environment as a block when
    a buffer is filled. When a stream is line buffered, characters are intended to be
    transmitted to or from the host environment as a block when a new-line character is
    encountered. Furthermore, characters are intended to be transmitted as a block to the host
    environment when a buffer is filled, when input is requested on an unbuffered stream, or
    when input is requested on a line buffered stream that requires the transmission of
    characters from the host environment. Support for these characteristics is
    implementation-defined, and may be affected via the setbuf and setvbuf functions.
4   A file may be disassociated from a controlling stream by closing the file. Output streams
    are flushed (any unwritten buffer contents are transmitted to the host environment) before
    the stream is disassociated from the file. The value of a pointer to a FILE object is
    indeterminate after the associated file is closed (including the standard text streams).
    Whether a file of zero length (on which no characters have been written by an output
    stream) actually exists is implementation-defined.
5   The file may be subsequently reopened, by the same or another program execution, and
    its contents reclaimed or modified (if it can be repositioned at its start). If the main
    function returns to its original caller, or if the exit function is called, all open files are
    closed (hence all output streams are flushed) before program termination. Other paths to
    program termination, such as calling the abort function, need not close all files
    properly.
6   The address of the FILE object used to control a stream may be significant; a copy of a
    FILE object need not serve in place of the original.

[page 300]

7    At program startup, three text streams are predefined and need not be opened explicitly
     -- standard input (for reading conventional input), standard output (for writing
     conventional output), and standard error (for writing diagnostic output). As initially
     opened, the standard error stream is not fully buffered; the standard input and standard
     output streams are fully buffered if and only if the stream can be determined not to refer
     to an interactive device.
8    Functions that open additional (nontemporary) files require a file name, which is a string.
     The rules for composing valid file names are implementation-defined. Whether the same
     file can be simultaneously open multiple times is also implementation-defined.
9    Although both text and binary wide-oriented streams are conceptually sequences of wide
     characters, the external file associated with a wide-oriented stream is a sequence of
     multibyte characters, generalized as follows:
     -- Multibyte encodings within files may contain embedded null bytes (unlike multibyte
       encodings valid for use internal to the program).
     -- A file need not begin nor end in the initial shift state.261)
10   Moreover, the encodings used for multibyte characters may differ among files. Both the
     nature and choice of such encodings are implementation-defined.
11   The wide character input functions read multibyte characters from the stream and convert
     them to wide characters as if they were read by successive calls to the fgetwc function.
     Each conversion occurs as if by a call to the mbrtowc function, with the conversion state
     described by the stream's own mbstate_t object. The byte input functions read
     characters from the stream as if by successive calls to the fgetc function.
12   The wide character output functions convert wide characters to multibyte characters and
     write them to the stream as if they were written by successive calls to the fputwc
     function. Each conversion occurs as if by a call to the wcrtomb function, with the
     conversion state described by the stream's own mbstate_t object. The byte output
     functions write characters to the stream as if by successive calls to the fputc function.
13   In some cases, some of the byte input/output functions also perform conversions between
     multibyte characters and wide characters. These conversions also occur as if by calls to
     the mbrtowc and wcrtomb functions.
14   An encoding error occurs if the character sequence presented to the underlying
     mbrtowc function does not form a valid (generalized) multibyte character, or if the code
     value passed to the underlying wcrtomb does not correspond to a valid (generalized)


     261) Setting the file position indicator to end-of-file, as with fseek(file, 0, SEEK_END), has
          undefined behavior for a binary stream (because of possible trailing null characters) or for any stream
          with state-dependent encoding that does not assuredly end in the initial shift state.

[page 301]

     multibyte character. The wide character input/output functions and the byte input/output
     functions store the value of the macro EILSEQ in errno if and only if an encoding error
     occurs.
     Environmental limits
15   The value of FOPEN_MAX shall be at least eight, including the three standard text
     streams.
     Forward references: the exit function (7.22.4.4), the fgetc function (7.21.7.1), the
     fopen function (7.21.5.3), the fputc function (7.21.7.3), the setbuf function
     (7.21.5.5), the setvbuf function (7.21.5.6), the fgetwc function (7.28.3.1), the
     fputwc function (7.28.3.3), conversion state (7.28.6), the mbrtowc function
     (7.28.6.3.2), the wcrtomb function (7.28.6.3.3).
     7.21.4 Operations on files
     7.21.4.1 The remove function
     Synopsis
1           #include <stdio.h>
            int remove(const char *filename);
     Description
2    The remove function causes the file whose name is the string pointed to by filename
     to be no longer accessible by that name. A subsequent attempt to open that file using that
     name will fail, unless it is created anew. If the file is open, the behavior of the remove
     function is implementation-defined.
     Returns
3    The remove function returns zero if the operation succeeds, nonzero if it fails.
     7.21.4.2 The rename function
     Synopsis
1           #include <stdio.h>
            int rename(const char *old, const char *new);
     Description
2    The rename function causes the file whose name is the string pointed to by old to be
     henceforth known by the name given by the string pointed to by new. The file named
     old is no longer accessible by that name. If a file named by the string pointed to by new
     exists prior to the call to the rename function, the behavior is implementation-defined.




[page 302]

    Returns
3   The rename function returns zero if the operation succeeds, nonzero if it fails,262) in
    which case if the file existed previously it is still known by its original name.
    7.21.4.3 The tmpfile function
    Synopsis
1           #include <stdio.h>
            FILE *tmpfile(void);
    Description
2   The tmpfile function creates a temporary binary file that is different from any other
    existing file and that will automatically be removed when it is closed or at program
    termination. If the program terminates abnormally, whether an open temporary file is
    removed is implementation-defined. The file is opened for update with "wb+" mode.
    Recommended practice
3   It should be possible to open at least TMP_MAX temporary files during the lifetime of the
    program (this limit may be shared with tmpnam) and there should be no limit on the
    number simultaneously open other than this limit and any limit on the number of open
    files (FOPEN_MAX).
    Returns
4   The tmpfile function returns a pointer to the stream of the file that it created. If the file
    cannot be created, the tmpfile function returns a null pointer.
    Forward references: the fopen function (7.21.5.3).
    7.21.4.4 The tmpnam function
    Synopsis
1           #include <stdio.h>
            char *tmpnam(char *s);
    Description
2   The tmpnam function generates a string that is a valid file name and that is not the same
    as the name of an existing file.263) The function is potentially capable of generating at


    262) Among the reasons the implementation may cause the rename function to fail are that the file is open
         or that it is necessary to copy its contents to effectuate its renaming.
    263) Files created using strings generated by the tmpnam function are temporary only in the sense that
         their names should not collide with those generated by conventional naming rules for the
         implementation. It is still necessary to use the remove function to remove such files when their use
         is ended, and before program termination.

[page 303]

    least TMP_MAX different strings, but any or all of them may already be in use by existing
    files and thus not be suitable return values.
3   The tmpnam function generates a different string each time it is called.
4   Calls to the tmpnam function with a null pointer argument may introduce data races with
    each other. The implementation shall behave as if no library function calls the tmpnam
    function.
    Returns
5   If no suitable string can be generated, the tmpnam function returns a null pointer.
    Otherwise, if the argument is a null pointer, the tmpnam function leaves its result in an
    internal static object and returns a pointer to that object (subsequent calls to the tmpnam
    function may modify the same object). If the argument is not a null pointer, it is assumed
    to point to an array of at least L_tmpnam chars; the tmpnam function writes its result
    in that array and returns the argument as its value.
    Environmental limits
6   The value of the macro TMP_MAX shall be at least 25.
    7.21.5 File access functions
    7.21.5.1 The fclose function
    Synopsis
1          #include <stdio.h>
           int fclose(FILE *stream);
    Description
2   A successful call to the fclose function causes the stream pointed to by stream to be
    flushed and the associated file to be closed. Any unwritten buffered data for the stream
    are delivered to the host environment to be written to the file; any unread buffered data
    are discarded. Whether or not the call succeeds, the stream is disassociated from the file
    and any buffer set by the setbuf or setvbuf function is disassociated from the stream
    (and deallocated if it was automatically allocated).
    Returns
3   The fclose function returns zero if the stream was successfully closed, or EOF if any
    errors were detected.




[page 304]

    7.21.5.2 The fflush function
    Synopsis
1           #include <stdio.h>
            int fflush(FILE *stream);
    Description
2   If stream points to an output stream or an update stream in which the most recent
    operation was not input, the fflush function causes any unwritten data for that stream
    to be delivered to the host environment to be written to the file; otherwise, the behavior is
    undefined.
3   If stream is a null pointer, the fflush function performs this flushing action on all
    streams for which the behavior is defined above.
    Returns
4   The fflush function sets the error indicator for the stream and returns EOF if a write
    error occurs, otherwise it returns zero.
    Forward references: the fopen function (7.21.5.3).
    7.21.5.3 The fopen function
    Synopsis
1           #include <stdio.h>
            FILE *fopen(const char * restrict filename,
                 const char * restrict mode);
    Description
2   The fopen function opens the file whose name is the string pointed to by filename,
    and associates a stream with it.
3   The argument mode points to a string. If the string is one of the following, the file is
    open in the indicated mode. Otherwise, the behavior is undefined.264)
    r                     open text file for reading
    w                     truncate to zero length or create text file for writing
    wx                    create text file for writing
    a                     append; open or create text file for writing at end-of-file
    rb                    open binary file for reading
    wb                    truncate to zero length or create binary file for writing


    264) If the string begins with one of the above sequences, the implementation might choose to ignore the
         remaining characters, or it might use them to select different kinds of a file (some of which might not
         conform to the properties in 7.21.2).

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    wbx               create binary file for writing
    ab                append; open or create binary file for writing at end-of-file
    r+                open text file for update (reading and writing)
    w+                truncate to zero length or create text file for update
    w+x               create text file for update
    a+                append; open or create text file for update, writing at end-of-file
    r+b or rb+        open binary file for update (reading and writing)
    w+b or wb+        truncate to zero length or create binary file for update
    w+bx or wb+x      create binary file for update
    a+b or ab+        append; open or create binary file for update, writing at end-of-file
4   Opening a file with read mode ('r' as the first character in the mode argument) fails if
    the file does not exist or cannot be read.
5   Opening a file with exclusive mode ('x' as the last character in the mode argument)
    fails if the file already exists or cannot be created. Otherwise, the file is created with
    exclusive (also known as non-shared) access to the extent that the underlying system
    supports exclusive access.
6   Opening a file with append mode ('a' as the first character in the mode argument)
    causes all subsequent writes to the file to be forced to the then current end-of-file,
    regardless of intervening calls to the fseek function. In some implementations, opening
    a binary file with append mode ('b' as the second or third character in the above list of
    mode argument values) may initially position the file position indicator for the stream
    beyond the last data written, because of null character padding.
7   When a file is opened with update mode ('+' as the second or third character in the
    above list of mode argument values), both input and output may be performed on the
    associated stream. However, output shall not be directly followed by input without an
    intervening call to the fflush function or to a file positioning function (fseek,
    fsetpos, or rewind), and input shall not be directly followed by output without an
    intervening call to a file positioning function, unless the input operation encounters end-
    of-file. Opening (or creating) a text file with update mode may instead open (or create) a
    binary stream in some implementations.
8   When opened, a stream is fully buffered if and only if it can be determined not to refer to
    an interactive device. The error and end-of-file indicators for the stream are cleared.
    Returns
9   The fopen function returns a pointer to the object controlling the stream. If the open
    operation fails, fopen returns a null pointer.
    Forward references: file positioning functions (7.21.9).



[page 306]

    7.21.5.4 The freopen function
    Synopsis
1           #include <stdio.h>
            FILE *freopen(const char * restrict filename,
                 const char * restrict mode,
                 FILE * restrict stream);
    Description
2   The freopen function opens the file whose name is the string pointed to by filename
    and associates the stream pointed to by stream with it. The mode argument is used just
    as in the fopen function.265)
3   If filename is a null pointer, the freopen function attempts to change the mode of
    the stream to that specified by mode, as if the name of the file currently associated with
    the stream had been used. It is implementation-defined which changes of mode are
    permitted (if any), and under what circumstances.
4   The freopen function first attempts to close any file that is associated with the specified
    stream. Failure to close the file is ignored. The error and end-of-file indicators for the
    stream are cleared.
    Returns
5   The freopen function returns a null pointer if the open operation fails. Otherwise,
    freopen returns the value of stream.
    7.21.5.5 The setbuf function
    Synopsis
1           #include <stdio.h>
            void setbuf(FILE * restrict stream,
                 char * restrict buf);
    Description
2   Except that it returns no value, the setbuf function is equivalent to the setvbuf
    function invoked with the values _IOFBF for mode and BUFSIZ for size, or (if buf
    is a null pointer), with the value _IONBF for mode.




    265) The primary use of the freopen function is to change the file associated with a standard text stream
         (stderr, stdin, or stdout), as those identifiers need not be modifiable lvalues to which the value
         returned by the fopen function may be assigned.

[page 307]

    Returns
3   The setbuf function returns no value.
    Forward references: the setvbuf function (7.21.5.6).
    7.21.5.6 The setvbuf function
    Synopsis
1           #include <stdio.h>
            int setvbuf(FILE * restrict stream,
                 char * restrict buf,
                 int mode, size_t size);
    Description
2   The setvbuf function may be used only after the stream pointed to by stream has
    been associated with an open file and before any other operation (other than an
    unsuccessful call to setvbuf) is performed on the stream. The argument mode
    determines how stream will be buffered, as follows: _IOFBF causes input/output to be
    fully buffered; _IOLBF causes input/output to be line buffered; _IONBF causes
    input/output to be unbuffered. If buf is not a null pointer, the array it points to may be
    used instead of a buffer allocated by the setvbuf function266) and the argument size
    specifies the size of the array; otherwise, size may determine the size of a buffer
    allocated by the setvbuf function. The contents of the array at any time are
    indeterminate.
    Returns
3   The setvbuf function returns zero on success, or nonzero if an invalid value is given
    for mode or if the request cannot be honored.




    266) The buffer has to have a lifetime at least as great as the open stream, so the stream should be closed
         before a buffer that has automatic storage duration is deallocated upon block exit.

[page 308]

    7.21.6 Formatted input/output functions
1   The formatted input/output functions shall behave as if there is a sequence point after the
    actions associated with each specifier.267)
    7.21.6.1 The fprintf function
    Synopsis
1            #include <stdio.h>
             int fprintf(FILE * restrict stream,
                  const char * restrict format, ...);
    Description
2   The fprintf function writes output to the stream pointed to by stream, under control
    of the string pointed to by format that specifies how subsequent arguments are
    converted for output. If there are insufficient arguments for the format, the behavior is
    undefined. If the format is exhausted while arguments remain, the excess arguments are
    evaluated (as always) but are otherwise ignored. The fprintf function returns when
    the end of the format string is encountered.
3   The format shall be a multibyte character sequence, beginning and ending in its initial
    shift state. The format is composed of zero or more directives: ordinary multibyte
    characters (not %), which are copied unchanged to the output stream; and conversion
    specifications, each of which results in fetching zero or more subsequent arguments,
    converting them, if applicable, according to the corresponding conversion specifier, and
    then writing the result to the output stream.
4   Each conversion specification is introduced by the character %. After the %, the following
    appear in sequence:
    -- Zero or more flags (in any order) that modify the meaning of the conversion
      specification.
    -- An optional minimum field width. If the converted value has fewer characters than the
      field width, it is padded with spaces (by default) on the left (or right, if the left
      adjustment flag, described later, has been given) to the field width. The field width
      takes the form of an asterisk * (described later) or a nonnegative decimal integer.268)
    -- An optional precision that gives the minimum number of digits to appear for the d, i,
      o, u, x, and X conversions, the number of digits to appear after the decimal-point
      character for a, A, e, E, f, and F conversions, the maximum number of significant
      digits for the g and G conversions, or the maximum number of bytes to be written for


    267) The fprintf functions perform writes to memory for the %n specifier.
    268) Note that 0 is taken as a flag, not as the beginning of a field width.

[page 309]

        s conversions. The precision takes the form of a period (.) followed either by an
        asterisk * (described later) or by an optional decimal integer; if only the period is
        specified, the precision is taken as zero. If a precision appears with any other
        conversion specifier, the behavior is undefined.
    -- An optional length modifier that specifies the size of the argument.
    -- A conversion specifier character that specifies the type of conversion to be applied.
5   As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
    this case, an int argument supplies the field width or precision. The arguments
    specifying field width, or precision, or both, shall appear (in that order) before the
    argument (if any) to be converted. A negative field width argument is taken as a - flag
    followed by a positive field width. A negative precision argument is taken as if the
    precision were omitted.
6   The flag characters and their meanings are:
    -       The result of the conversion is left-justified within the field. (It is right-justified if
            this flag is not specified.)
    +       The result of a signed conversion always begins with a plus or minus sign. (It
            begins with a sign only when a negative value is converted if this flag is not
            specified.)269)
    space If the first character of a signed conversion is not a sign, or if a signed conversion
          results in no characters, a space is prefixed to the result. If the space and + flags
          both appear, the space flag is ignored.
    #       The result is converted to an ''alternative form''. For o conversion, it increases
            the precision, if and only if necessary, to force the first digit of the result to be a
            zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
            conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,
            and G conversions, the result of converting a floating-point number always
            contains a decimal-point character, even if no digits follow it. (Normally, a
            decimal-point character appears in the result of these conversions only if a digit
            follows it.) For g and G conversions, trailing zeros are not removed from the
            result. For other conversions, the behavior is undefined.
    0       For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
            (following any indication of sign or base) are used to pad to the field width rather
            than performing space padding, except when converting an infinity or NaN. If the
            0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X


    269) The results of all floating conversions of a negative zero, and of negative values that round to zero,
         include a minus sign.

[page 310]

              conversions, if a precision is specified, the 0 flag is ignored. For other
              conversions, the behavior is undefined.
7   The length modifiers and their meanings are:
    hh            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  signed char or unsigned char argument (the argument will have
                  been promoted according to the integer promotions, but its value shall be
                  converted to signed char or unsigned char before printing); or that
                  a following n conversion specifier applies to a pointer to a signed char
                  argument.
    h             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  short int or unsigned short int argument (the argument will
                  have been promoted according to the integer promotions, but its value shall
                  be converted to short int or unsigned short int before printing);
                  or that a following n conversion specifier applies to a pointer to a short
                  int argument.
    l (ell)       Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  long int or unsigned long int argument; that a following n
                  conversion specifier applies to a pointer to a long int argument; that a
                  following c conversion specifier applies to a wint_t argument; that a
                  following s conversion specifier applies to a pointer to a wchar_t
                  argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
                  specifier.
    ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 long long int or unsigned long long int argument; or that a
                 following n conversion specifier applies to a pointer to a long long int
                 argument.
    j             Specifies that a following d, i, o, u, x, or X conversion specifier applies to
                  an intmax_t or uintmax_t argument; or that a following n conversion
                  specifier applies to a pointer to an intmax_t argument.
    z             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  size_t or the corresponding signed integer type argument; or that a
                  following n conversion specifier applies to a pointer to a signed integer type
                  corresponding to size_t argument.
    t             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                  ptrdiff_t or the corresponding unsigned integer type argument; or that a
                  following n conversion specifier applies to a pointer to a ptrdiff_t
                  argument.


[page 311]

    L              Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                   applies to a long double argument.
    If a length modifier appears with any conversion specifier other than as specified above,
    the behavior is undefined.
8   The conversion specifiers and their meanings are:
    d,i          The int argument is converted to signed decimal in the style [-]dddd. The
                 precision specifies the minimum number of digits to appear; if the value
                 being converted can be represented in fewer digits, it is expanded with
                 leading zeros. The default precision is 1. The result of converting a zero
                 value with a precision of zero is no characters.
    o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
            decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
            letters abcdef are used for x conversion and the letters ABCDEF for X
            conversion. The precision specifies the minimum number of digits to appear;
            if the value being converted can be represented in fewer digits, it is expanded
            with leading zeros. The default precision is 1. The result of converting a
            zero value with a precision of zero is no characters.
    f,F          A double argument representing a floating-point number is converted to
                 decimal notation in the style [-]ddd.ddd, where the number of digits after
                 the decimal-point character is equal to the precision specification. If the
                 precision is missing, it is taken as 6; if the precision is zero and the # flag is
                 not specified, no decimal-point character appears. If a decimal-point
                 character appears, at least one digit appears before it. The value is rounded to
                 the appropriate number of digits.
                 A double argument representing an infinity is converted in one of the styles
                 [-]inf or [-]infinity -- which style is implementation-defined. A
                 double argument representing a NaN is converted in one of the styles
                 [-]nan or [-]nan(n-char-sequence) -- which style, and the meaning of
                 any n-char-sequence, is implementation-defined. The F conversion specifier
                 produces INF, INFINITY, or NAN instead of inf, infinity, or nan,
                 respectively.270)
    e,E          A double argument representing a floating-point number is converted in the
                 style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
                 argument is nonzero) before the decimal-point character and the number of
                 digits after it is equal to the precision; if the precision is missing, it is taken as


    270) When applied to infinite and NaN values, the -, +, and space flag characters have their usual meaning;
         the # and 0 flag characters have no effect.

[page 312]

              6; if the precision is zero and the # flag is not specified, no decimal-point
              character appears. The value is rounded to the appropriate number of digits.
              The E conversion specifier produces a number with E instead of e
              introducing the exponent. The exponent always contains at least two digits,
              and only as many more digits as necessary to represent the exponent. If the
              value is zero, the exponent is zero.
              A double argument representing an infinity or NaN is converted in the style
              of an f or F conversion specifier.
g,G           A double argument representing a floating-point number is converted in
              style f or e (or in style F or E in the case of a G conversion specifier),
              depending on the value converted and the precision. Let P equal the
              precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
              Then, if a conversion with style E would have an exponent of X:
              -- if P > X >= -4, the conversion is with style f (or F) and precision
                P - (X + 1).
              -- otherwise, the conversion is with style e (or E) and precision P - 1.
              Finally, unless the # flag is used, any trailing zeros are removed from the
              fractional portion of the result and the decimal-point character is removed if
              there is no fractional portion remaining.
              A double argument representing an infinity or NaN is converted in the style
              of an f or F conversion specifier.
a,A           A double argument representing a floating-point number is converted in the
              style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
              nonzero if the argument is a normalized floating-point number and is
              otherwise unspecified) before the decimal-point character271) and the number
              of hexadecimal digits after it is equal to the precision; if the precision is
              missing and FLT_RADIX is a power of 2, then the precision is sufficient for
              an exact representation of the value; if the precision is missing and
              FLT_RADIX is not a power of 2, then the precision is sufficient to




271) Binary implementations can choose the hexadecimal digit to the left of the decimal-point character so
     that subsequent digits align to nibble (4-bit) boundaries.

[page 313]

              distinguish272) values of type double, except that trailing zeros may be
              omitted; if the precision is zero and the # flag is not specified, no decimal-
              point character appears. The letters abcdef are used for a conversion and
              the letters ABCDEF for A conversion. The A conversion specifier produces a
              number with X and P instead of x and p. The exponent always contains at
              least one digit, and only as many more digits as necessary to represent the
              decimal exponent of 2. If the value is zero, the exponent is zero.
              A double argument representing an infinity or NaN is converted in the style
              of an f or F conversion specifier.
c             If no l length modifier is present, the int argument is converted to an
              unsigned char, and the resulting character is written.
              If an l length modifier is present, the wint_t argument is converted as if by
              an ls conversion specification with no precision and an argument that points
              to the initial element of a two-element array of wchar_t, the first element
              containing the wint_t argument to the lc conversion specification and the
              second a null wide character.
s             If no l length modifier is present, the argument shall be a pointer to the initial
              element of an array of character type.273) Characters from the array are
              written up to (but not including) the terminating null character. If the
              precision is specified, no more than that many bytes are written. If the
              precision is not specified or is greater than the size of the array, the array shall
              contain a null character.
              If an l length modifier is present, the argument shall be a pointer to the initial
              element of an array of wchar_t type. Wide characters from the array are
              converted to multibyte characters (each as if by a call to the wcrtomb
              function, with the conversion state described by an mbstate_t object
              initialized to zero before the first wide character is converted) up to and
              including a terminating null wide character. The resulting multibyte
              characters are written up to (but not including) the terminating null character
              (byte). If no precision is specified, the array shall contain a null wide
              character. If a precision is specified, no more than that many bytes are
              written (including shift sequences, if any), and the array shall contain a null
              wide character if, to equal the multibyte character sequence length given by

272) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
     FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
     might suffice depending on the implementation's scheme for determining the digit to the left of the
     decimal-point character.
273) No special provisions are made for multibyte characters.

[page 314]

                    the precision, the function would need to access a wide character one past the
                    end of the array. In no case is a partial multibyte character written.274)
     p              The argument shall be a pointer to void. The value of the pointer is
                    converted to a sequence of printing characters, in an implementation-defined
                    manner.
     n              The argument shall be a pointer to signed integer into which is written the
                    number of characters written to the output stream so far by this call to
                    fprintf. No argument is converted, but one is consumed. If the conversion
                    specification includes any flags, a field width, or a precision, the behavior is
                    undefined.
     %              A % character is written. No argument is converted. The complete
                    conversion specification shall be %%.
9    If a conversion specification is invalid, the behavior is undefined.275) If any argument is
     not the correct type for the corresponding conversion specification, the behavior is
     undefined.
10   In no case does a nonexistent or small field width cause truncation of a field; if the result
     of a conversion is wider than the field width, the field is expanded to contain the
     conversion result.
11   For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
     to a hexadecimal floating number with the given precision.
     Recommended practice
12   For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
     representable in the given precision, the result should be one of the two adjacent numbers
     in hexadecimal floating style with the given precision, with the extra stipulation that the
     error should have a correct sign for the current rounding direction.
13   For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
     DECIMAL_DIG, then the result should be correctly rounded.276) If the number of
     significant decimal digits is more than DECIMAL_DIG but the source value is exactly
     representable with DECIMAL_DIG digits, then the result should be an exact
     representation with trailing zeros. Otherwise, the source value is bounded by two
     adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value


     274) Redundant shift sequences may result if multibyte characters have a state-dependent encoding.
     275) See ''future library directions'' (7.30.9).
     276) For binary-to-decimal conversion, the result format's values are the numbers representable with the
          given format specifier. The number of significant digits is determined by the format specifier, and in
          the case of fixed-point conversion by the source value as well.

[page 315]

     of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
     the error should have a correct sign for the current rounding direction.
     Returns
14   The fprintf function returns the number of characters transmitted, or a negative value
     if an output or encoding error occurred.
     Environmental limits
15   The number of characters that can be produced by any single conversion shall be at least
     4095.
16   EXAMPLE 1         To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
     places:
              #include <math.h>
              #include <stdio.h>
              /* ... */
              char *weekday, *month;      // pointers to strings
              int day, hour, min;
              fprintf(stdout, "%s, %s %d, %.2d:%.2d\n",
                      weekday, month, day, hour, min);
              fprintf(stdout, "pi = %.5f\n", 4 * atan(1.0));

17   EXAMPLE 2 In this example, multibyte characters do not have a state-dependent encoding, and the
     members of the extended character set that consist of more than one byte each consist of exactly two bytes,
     the first of which is denoted here by a and the second by an uppercase letter.
18   Given the following wide string with length seven,
              static wchar_t wstr[] = L" X Yabc Z W";
     the seven calls
              fprintf(stdout,          "|1234567890123|\n");
              fprintf(stdout,          "|%13ls|\n", wstr);
              fprintf(stdout,          "|%-13.9ls|\n", wstr);
              fprintf(stdout,          "|%13.10ls|\n", wstr);
              fprintf(stdout,          "|%13.11ls|\n", wstr);
              fprintf(stdout,          "|%13.15ls|\n", &wstr[2]);
              fprintf(stdout,          "|%13lc|\n", (wint_t) wstr[5]);
     will print the following seven lines:
              |1234567890123|
              |   X Yabc Z W|
              | X Yabc Z    |
              |     X Yabc Z|
              |   X Yabc Z W|
              |      abc Z W|
              |            Z|

     Forward references: conversion state (7.28.6), the wcrtomb function (7.28.6.3.3).



[page 316]

    7.21.6.2 The fscanf function
    Synopsis
1           #include <stdio.h>
            int fscanf(FILE * restrict stream,
                 const char * restrict format, ...);
    Description
2   The fscanf function reads input from the stream pointed to by stream, under control
    of the string pointed to by format that specifies the admissible input sequences and how
    they are to be converted for assignment, using subsequent arguments as pointers to the
    objects to receive the converted input. If there are insufficient arguments for the format,
    the behavior is undefined. If the format is exhausted while arguments remain, the excess
    arguments are evaluated (as always) but are otherwise ignored.
3   The format shall be a multibyte character sequence, beginning and ending in its initial
    shift state. The format is composed of zero or more directives: one or more white-space
    characters, an ordinary multibyte character (neither % nor a white-space character), or a
    conversion specification. Each conversion specification is introduced by the character %.
    After the %, the following appear in sequence:
    -- An optional assignment-suppressing character *.
    -- An optional decimal integer greater than zero that specifies the maximum field width
      (in characters).
    -- An optional length modifier that specifies the size of the receiving object.
    -- A conversion specifier character that specifies the type of conversion to be applied.
4   The fscanf function executes each directive of the format in turn. When all directives
    have been executed, or if a directive fails (as detailed below), the function returns.
    Failures are described as input failures (due to the occurrence of an encoding error or the
    unavailability of input characters), or matching failures (due to inappropriate input).
5   A directive composed of white-space character(s) is executed by reading input up to the
    first non-white-space character (which remains unread), or until no more characters can
    be read.
6   A directive that is an ordinary multibyte character is executed by reading the next
    characters of the stream. If any of those characters differ from the ones composing the
    directive, the directive fails and the differing and subsequent characters remain unread.
    Similarly, if end-of-file, an encoding error, or a read error prevents a character from being
    read, the directive fails.
7   A directive that is a conversion specification defines a set of matching input sequences, as
    described below for each specifier. A conversion specification is executed in the

[page 317]

     following steps:
8    Input white-space characters (as specified by the isspace function) are skipped, unless
     the specification includes a [, c, or n specifier.277)
9    An input item is read from the stream, unless the specification includes an n specifier. An
     input item is defined as the longest sequence of input characters which does not exceed
     any specified field width and which is, or is a prefix of, a matching input sequence.278)
     The first character, if any, after the input item remains unread. If the length of the input
     item is zero, the execution of the directive fails; this condition is a matching failure unless
     end-of-file, an encoding error, or a read error prevented input from the stream, in which
     case it is an input failure.
10   Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
     count of input characters) is converted to a type appropriate to the conversion specifier. If
     the input item is not a matching sequence, the execution of the directive fails: this
     condition is a matching failure. Unless assignment suppression was indicated by a *, the
     result of the conversion is placed in the object pointed to by the first argument following
     the format argument that has not already received a conversion result. If this object
     does not have an appropriate type, or if the result of the conversion cannot be represented
     in the object, the behavior is undefined.
11   The length modifiers and their meanings are:
     hh             Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                    to an argument with type pointer to signed char or unsigned char.
     h              Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                    to an argument with type pointer to short int or unsigned short
                    int.
     l (ell)        Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                    to an argument with type pointer to long int or unsigned long
                    int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
                    an argument with type pointer to double; or that a following c, s, or [
                    conversion specifier applies to an argument with type pointer to wchar_t.
     ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to long long int or unsigned
                  long long int.



     277) These white-space characters are not counted against a specified field width.
     278) fscanf pushes back at most one input character onto the input stream. Therefore, some sequences
          that are acceptable to strtod, strtol, etc., are unacceptable to fscanf.

[page 318]

     j            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to intmax_t or uintmax_t.
     z            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to size_t or the corresponding signed
                  integer type.
     t            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to ptrdiff_t or the corresponding
                  unsigned integer type.
     L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                  applies to an argument with type pointer to long double.
     If a length modifier appears with any conversion specifier other than as specified above,
     the behavior is undefined.
12   The conversion specifiers and their meanings are:
     d           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the strtol function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 signed integer.
     i           Matches an optionally signed integer, whose format is the same as expected
                 for the subject sequence of the strtol function with the value 0 for the
                 base argument. The corresponding argument shall be a pointer to signed
                 integer.
     o           Matches an optionally signed octal integer, whose format is the same as
                 expected for the subject sequence of the strtoul function with the value 8
                 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     u           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the strtoul function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     x           Matches an optionally signed hexadecimal integer, whose format is the same
                 as expected for the subject sequence of the strtoul function with the value
                 16 for the base argument. The corresponding argument shall be a pointer to
                 unsigned integer.
     a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
             format is the same as expected for the subject sequence of the strtod
             function. The corresponding argument shall be a pointer to floating.


[page 319]

c             Matches a sequence of characters of exactly the number specified by the field
              width (1 if no field width is present in the directive).279)
              If no l length modifier is present, the corresponding argument shall be a
              pointer to the initial element of a character array large enough to accept the
              sequence. No null character is added.
              If an l length modifier is present, the input shall be a sequence of multibyte
              characters that begins in the initial shift state. Each multibyte character in the
              sequence is converted to a wide character as if by a call to the mbrtowc
              function, with the conversion state described by an mbstate_t object
              initialized to zero before the first multibyte character is converted. The
              corresponding argument shall be a pointer to the initial element of an array of
              wchar_t large enough to accept the resulting sequence of wide characters.
              No null wide character is added.
s             Matches a sequence of non-white-space characters.279)
              If no l length modifier is present, the corresponding argument shall be a
              pointer to the initial element of a character array large enough to accept the
              sequence and a terminating null character, which will be added automatically.
              If an l length modifier is present, the input shall be a sequence of multibyte
              characters that begins in the initial shift state. Each multibyte character is
              converted to a wide character as if by a call to the mbrtowc function, with
              the conversion state described by an mbstate_t object initialized to zero
              before the first multibyte character is converted. The corresponding argument
              shall be a pointer to the initial element of an array of wchar_t large enough
              to accept the sequence and the terminating null wide character, which will be
              added automatically.
[             Matches a nonempty sequence of characters from a set of expected characters
              (the scanset).279)
              If no l length modifier is present, the corresponding argument shall be a
              pointer to the initial element of a character array large enough to accept the
              sequence and a terminating null character, which will be added automatically.
              If an l length modifier is present, the input shall be a sequence of multibyte
              characters that begins in the initial shift state. Each multibyte character is
              converted to a wide character as if by a call to the mbrtowc function, with
              the conversion state described by an mbstate_t object initialized to zero

279) No special provisions are made for multibyte characters in the matching rules used by the c, s, and [
     conversion specifiers -- the extent of the input field is determined on a byte-by-byte basis. The
     resulting field is nevertheless a sequence of multibyte characters that begins in the initial shift state.

[page 320]

                    before the first multibyte character is converted. The corresponding argument
                    shall be a pointer to the initial element of an array of wchar_t large enough
                    to accept the sequence and the terminating null wide character, which will be
                    added automatically.
                    The conversion specifier includes all subsequent characters in the format
                    string, up to and including the matching right bracket (]). The characters
                    between the brackets (the scanlist) compose the scanset, unless the character
                    after the left bracket is a circumflex (^), in which case the scanset contains all
                    characters that do not appear in the scanlist between the circumflex and the
                    right bracket. If the conversion specifier begins with [] or [^], the right
                    bracket character is in the scanlist and the next following right bracket
                    character is the matching right bracket that ends the specification; otherwise
                    the first following right bracket character is the one that ends the
                    specification. If a - character is in the scanlist and is not the first, nor the
                    second where the first character is a ^, nor the last character, the behavior is
                    implementation-defined.
     p              Matches an implementation-defined set of sequences, which should be the
                    same as the set of sequences that may be produced by the %p conversion of
                    the fprintf function. The corresponding argument shall be a pointer to a
                    pointer to void. The input item is converted to a pointer value in an
                    implementation-defined manner. If the input item is a value converted earlier
                    during the same program execution, the pointer that results shall compare
                    equal to that value; otherwise the behavior of the %p conversion is undefined.
     n              No input is consumed. The corresponding argument shall be a pointer to
                    signed integer into which is to be written the number of characters read from
                    the input stream so far by this call to the fscanf function. Execution of a
                    %n directive does not increment the assignment count returned at the
                    completion of execution of the fscanf function. No argument is converted,
                    but one is consumed. If the conversion specification includes an assignment-
                    suppressing character or a field width, the behavior is undefined.
     %              Matches a single % character; no conversion or assignment occurs. The
                    complete conversion specification shall be %%.
13   If a conversion specification is invalid, the behavior is undefined.280)
14   The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
     respectively, a, e, f, g, and x.



     280) See ''future library directions'' (7.30.9).

[page 321]

15   Trailing white space (including new-line characters) is left unread unless matched by a
     directive. The success of literal matches and suppressed assignments is not directly
     determinable other than via the %n directive.
     Returns
16   The fscanf function returns the value of the macro EOF if an input failure occurs
     before the first conversion (if any) has completed. Otherwise, the function returns the
     number of input items assigned, which can be fewer than provided for, or even zero, in
     the event of an early matching failure.
17   EXAMPLE 1        The call:
              #include <stdio.h>
              /* ... */
              int n, i; float x; char name[50];
              n = fscanf(stdin, "%d%f%s", &i, &x, name);
     with the input line:
              25 54.32E-1 thompson
     will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
     thompson\0.

18   EXAMPLE 2        The call:
              #include <stdio.h>
              /* ... */
              int i; float x; char name[50];
              fscanf(stdin, "%2d%f%*d %[0123456789]", &i, &x, name);
     with input:
              56789 0123 56a72
     will assign to i the value 56 and to x the value 789.0, will skip 0123, and will assign to name the
     sequence 56\0. The next character read from the input stream will be a.

19   EXAMPLE 3        To accept repeatedly from stdin a quantity, a unit of measure, and an item name:
              #include <stdio.h>
              /* ... */
              int count; float quant; char units[21], item[21];
              do {
                      count = fscanf(stdin, "%f%20s of %20s", &quant, units, item);
                      fscanf(stdin,"%*[^\n]");
              } while (!feof(stdin) && !ferror(stdin));
20   If the stdin stream contains the following lines:
              2 quarts of oil
              -12.8degrees Celsius
              lots of luck
              10.0LBS     of
              dirt
              100ergs of energy

[page 322]

     the execution of the above example will be analogous to the following assignments:
               quant     =   2; strcpy(units, "quarts"); strcpy(item, "oil");
               count     =   3;
               quant     =   -12.8; strcpy(units, "degrees");
               count     =   2; // "C" fails to match "o"
               count     =   0; // "l" fails to match "%f"
               quant     =   10.0; strcpy(units, "LBS"); strcpy(item, "dirt");
               count     =   3;
               count     =   0; // "100e" fails to match "%f"
               count     =   EOF;

21   EXAMPLE 4         In:
               #include <stdio.h>
               /* ... */
               int d1, d2, n1, n2, i;
               i = sscanf("123", "%d%n%n%d", &d1, &n1, &n2, &d2);
     the value 123 is assigned to d1 and the value 3 to n1. Because %n can never get an input failure the value
     of 3 is also assigned to n2. The value of d2 is not affected. The value 1 is assigned to i.

22   EXAMPLE 5 In these examples, multibyte characters do have a state-dependent encoding, and the
     members of the extended character set that consist of more than one byte each consist of exactly two bytes,
     the first of which is denoted here by a and the second by an uppercase letter, but are only recognized as
     such when in the alternate shift state. The shift sequences are denoted by (uparrow) and (downarrow), in which the first causes
     entry into the alternate shift state.
23   After the call:
               #include <stdio.h>
               /* ... */
               char str[50];
               fscanf(stdin, "a%s", str);
     with the input line:
               a(uparrow) X Y(downarrow) bc
     str will contain (uparrow) X Y(downarrow)\0 assuming that none of the bytes of the shift sequences (or of the multibyte
     characters, in the more general case) appears to be a single-byte white-space character.
24   In contrast, after the call:
               #include <stdio.h>
               #include <stddef.h>
               /* ... */
               wchar_t wstr[50];
               fscanf(stdin, "a%ls", wstr);
     with the same input line, wstr will contain the two wide characters that correspond to X and Y and a
     terminating null wide character.
25   However, the call:




[page 323]

             #include <stdio.h>
             #include <stddef.h>
             /* ... */
             wchar_t wstr[50];
             fscanf(stdin, "a(uparrow) X(downarrow)%ls", wstr);
     with the same input line will return zero due to a matching failure against the (downarrow) sequence in the format
     string.
26   Assuming that the first byte of the multibyte character X is the same as the first byte of the multibyte
     character Y, after the call:
             #include <stdio.h>
             #include <stddef.h>
             /* ... */
             wchar_t wstr[50];
             fscanf(stdin, "a(uparrow) Y(downarrow)%ls", wstr);
     with the same input line, zero will again be returned, but stdin will be left with a partially consumed
     multibyte character.

     Forward references: the strtod, strtof, and strtold functions (7.22.1.3), the
     strtol, strtoll, strtoul, and strtoull functions (7.22.1.4), conversion state
     (7.28.6), the wcrtomb function (7.28.6.3.3).
     7.21.6.3 The printf function
     Synopsis
1            #include <stdio.h>
             int printf(const char * restrict format, ...);
     Description
2    The printf function is equivalent to fprintf with the argument stdout interposed
     before the arguments to printf.
     Returns
3    The printf function returns the number of characters transmitted, or a negative value if
     an output or encoding error occurred.
     7.21.6.4 The scanf function
     Synopsis
1            #include <stdio.h>
             int scanf(const char * restrict format, ...);
     Description
2    The scanf function is equivalent to fscanf with the argument stdin interposed
     before the arguments to scanf.



[page 324]

    Returns
3   The scanf function returns the value of the macro EOF if an input failure occurs before
    the first conversion (if any) has completed. Otherwise, the scanf function returns the
    number of input items assigned, which can be fewer than provided for, or even zero, in
    the event of an early matching failure.
    7.21.6.5 The snprintf function
    Synopsis
1           #include <stdio.h>
            int snprintf(char * restrict s, size_t n,
                 const char * restrict format, ...);
    Description
2   The snprintf function is equivalent to fprintf, except that the output is written into
    an array (specified by argument s) rather than to a stream. If n is zero, nothing is written,
    and s may be a null pointer. Otherwise, output characters beyond the n-1st are
    discarded rather than being written to the array, and a null character is written at the end
    of the characters actually written into the array. If copying takes place between objects
    that overlap, the behavior is undefined.
    Returns
3   The snprintf function returns the number of characters that would have been written
    had n been sufficiently large, not counting the terminating null character, or a negative
    value if an encoding error occurred. Thus, the null-terminated output has been
    completely written if and only if the returned value is nonnegative and less than n.
    7.21.6.6 The sprintf function
    Synopsis
1           #include <stdio.h>
            int sprintf(char * restrict s,
                 const char * restrict format, ...);
    Description
2   The sprintf function is equivalent to fprintf, except that the output is written into
    an array (specified by the argument s) rather than to a stream. A null character is written
    at the end of the characters written; it is not counted as part of the returned value. If
    copying takes place between objects that overlap, the behavior is undefined.
    Returns
3   The sprintf function returns the number of characters written in the array, not
    counting the terminating null character, or a negative value if an encoding error occurred.

[page 325]

    7.21.6.7 The sscanf function
    Synopsis
1          #include <stdio.h>
           int sscanf(const char * restrict s,
                const char * restrict format, ...);
    Description
2   The sscanf function is equivalent to fscanf, except that input is obtained from a
    string (specified by the argument s) rather than from a stream. Reaching the end of the
    string is equivalent to encountering end-of-file for the fscanf function. If copying
    takes place between objects that overlap, the behavior is undefined.
    Returns
3   The sscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the sscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.21.6.8 The vfprintf function
    Synopsis
1          #include <stdarg.h>
           #include <stdio.h>
           int vfprintf(FILE * restrict stream,
                const char * restrict format,
                va_list arg);
    Description
2   The vfprintf function is equivalent to fprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfprintf function does not invoke the
    va_end macro.281)
    Returns
3   The vfprintf function returns the number of characters transmitted, or a negative
    value if an output or encoding error occurred.
4   EXAMPLE       The following shows the use of the vfprintf function in a general error-reporting routine.




    281) As the functions vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf, and
         vsscanf invoke the va_arg macro, the value of arg after the return is indeterminate.

[page 326]

            #include <stdarg.h>
            #include <stdio.h>
            void error(char *function_name, char *format, ...)
            {
                  va_list args;
                  va_start(args, format);
                  // print out name of function causing error
                  fprintf(stderr, "ERROR in %s: ", function_name);
                  // print out remainder of message
                  vfprintf(stderr, format, args);
                  va_end(args);
            }

    7.21.6.9 The vfscanf function
    Synopsis
1           #include <stdarg.h>
            #include <stdio.h>
            int vfscanf(FILE * restrict stream,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vfscanf function is equivalent to fscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfscanf function does not invoke the
    va_end macro.281)
    Returns
3   The vfscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vfscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.21.6.10 The vprintf function
    Synopsis
1           #include <stdarg.h>
            #include <stdio.h>
            int vprintf(const char * restrict format,
                 va_list arg);
    Description
2   The vprintf function is equivalent to printf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and

[page 327]

    possibly subsequent va_arg calls). The vprintf function does not invoke the
    va_end macro.281)
    Returns
3   The vprintf function returns the number of characters transmitted, or a negative value
    if an output or encoding error occurred.
    7.21.6.11 The vscanf function
    Synopsis
1          #include <stdarg.h>
           #include <stdio.h>
           int vscanf(const char * restrict format,
                va_list arg);
    Description
2   The vscanf function is equivalent to scanf, with the variable argument list replaced
    by arg, which shall have been initialized by the va_start macro (and possibly
    subsequent va_arg calls). The vscanf function does not invoke the va_end
    macro.281)
    Returns
3   The vscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.21.6.12 The vsnprintf function
    Synopsis
1          #include <stdarg.h>
           #include <stdio.h>
           int vsnprintf(char * restrict s, size_t n,
                const char * restrict format,
                va_list arg);
    Description
2   The vsnprintf function is equivalent to snprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsnprintf function does not invoke the
    va_end macro.281) If copying takes place between objects that overlap, the behavior is
    undefined.



[page 328]

    Returns
3   The vsnprintf function returns the number of characters that would have been written
    had n been sufficiently large, not counting the terminating null character, or a negative
    value if an encoding error occurred. Thus, the null-terminated output has been
    completely written if and only if the returned value is nonnegative and less than n.
    7.21.6.13 The vsprintf function
    Synopsis
1           #include <stdarg.h>
            #include <stdio.h>
            int vsprintf(char * restrict s,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vsprintf function is equivalent to sprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsprintf function does not invoke the
    va_end macro.281) If copying takes place between objects that overlap, the behavior is
    undefined.
    Returns
3   The vsprintf function returns the number of characters written in the array, not
    counting the terminating null character, or a negative value if an encoding error occurred.
    7.21.6.14 The vsscanf function
    Synopsis
1           #include <stdarg.h>
            #include <stdio.h>
            int vsscanf(const char * restrict s,
                 const char * restrict format,
                 va_list arg);
    Description
2   The vsscanf function is equivalent to sscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsscanf function does not invoke the
    va_end macro.281)
    Returns
3   The vsscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vsscanf function
[page 329]

    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.21.7 Character input/output functions
    7.21.7.1 The fgetc function
    Synopsis
1           #include <stdio.h>
            int fgetc(FILE *stream);
    Description
2   If the end-of-file indicator for the input stream pointed to by stream is not set and a
    next character is present, the fgetc function obtains that character as an unsigned
    char converted to an int and advances the associated file position indicator for the
    stream (if defined).
    Returns
3   If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
    of-file indicator for the stream is set and the fgetc function returns EOF. Otherwise, the
    fgetc function returns the next character from the input stream pointed to by stream.
    If a read error occurs, the error indicator for the stream is set and the fgetc function
    returns EOF.282)
    7.21.7.2 The fgets function
    Synopsis
1           #include <stdio.h>
            char *fgets(char * restrict s, int n,
                 FILE * restrict stream);
    Description
2   The fgets function reads at most one less than the number of characters specified by n
    from the stream pointed to by stream into the array pointed to by s. No additional
    characters are read after a new-line character (which is retained) or after end-of-file. A
    null character is written immediately after the last character read into the array.
    Returns
3   The fgets function returns s if successful. If end-of-file is encountered and no
    characters have been read into the array, the contents of the array remain unchanged and a
    null pointer is returned. If a read error occurs during the operation, the array contents are
    indeterminate and a null pointer is returned.

    282) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.

[page 330]

    7.21.7.3 The fputc function
    Synopsis
1           #include <stdio.h>
            int fputc(int c, FILE *stream);
    Description
2   The fputc function writes the character specified by c (converted to an unsigned
    char) to the output stream pointed to by stream, at the position indicated by the
    associated file position indicator for the stream (if defined), and advances the indicator
    appropriately. If the file cannot support positioning requests, or if the stream was opened
    with append mode, the character is appended to the output stream.
    Returns
3   The fputc function returns the character written. If a write error occurs, the error
    indicator for the stream is set and fputc returns EOF.
    7.21.7.4 The fputs function
    Synopsis
1           #include <stdio.h>
            int fputs(const char * restrict s,
                 FILE * restrict stream);
    Description
2   The fputs function writes the string pointed to by s to the stream pointed to by
    stream. The terminating null character is not written.
    Returns
3   The fputs function returns EOF if a write error occurs; otherwise it returns a
    nonnegative value.
    7.21.7.5 The getc function
    Synopsis
1           #include <stdio.h>
            int getc(FILE *stream);
    Description
2   The getc function is equivalent to fgetc, except that if it is implemented as a macro, it
    may evaluate stream more than once, so the argument should never be an expression
    with side effects.




[page 331]

    Returns
3   The getc function returns the next character from the input stream pointed to by
    stream. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
    getc returns EOF. If a read error occurs, the error indicator for the stream is set and
    getc returns EOF.
    7.21.7.6 The getchar function
    Synopsis
1          #include <stdio.h>
           int getchar(void);
    Description
2   The getchar function is equivalent to getc with the argument stdin.
    Returns
3   The getchar function returns the next character from the input stream pointed to by
    stdin. If the stream is at end-of-file, the end-of-file indicator for the stream is set and
    getchar returns EOF. If a read error occurs, the error indicator for the stream is set and
    getchar returns EOF.                                                                       *
    7.21.7.7 The putc function
    Synopsis
1          #include <stdio.h>
           int putc(int c, FILE *stream);
    Description
2   The putc function is equivalent to fputc, except that if it is implemented as a macro, it
    may evaluate stream more than once, so that argument should never be an expression
    with side effects.
    Returns
3   The putc function returns the character written. If a write error occurs, the error
    indicator for the stream is set and putc returns EOF.
    7.21.7.8 The putchar function
    Synopsis
1          #include <stdio.h>
           int putchar(int c);
    Description
2   The putchar function is equivalent to putc with the second argument stdout.


[page 332]

    Returns
3   The putchar function returns the character written. If a write error occurs, the error
    indicator for the stream is set and putchar returns EOF.
    7.21.7.9 The puts function
    Synopsis
1           #include <stdio.h>
            int puts(const char *s);
    Description
2   The puts function writes the string pointed to by s to the stream pointed to by stdout,
    and appends a new-line character to the output. The terminating null character is not
    written.
    Returns
3   The puts function returns EOF if a write error occurs; otherwise it returns a nonnegative
    value.
    7.21.7.10 The ungetc function
    Synopsis
1           #include <stdio.h>
            int ungetc(int c, FILE *stream);
    Description
2   The ungetc function pushes the character specified by c (converted to an unsigned
    char) back onto the input stream pointed to by stream. Pushed-back characters will be
    returned by subsequent reads on that stream in the reverse order of their pushing. A
    successful intervening call (with the stream pointed to by stream) to a file positioning
    function (fseek, fsetpos, or rewind) discards any pushed-back characters for the
    stream. The external storage corresponding to the stream is unchanged.
3   One character of pushback is guaranteed. If the ungetc function is called too many
    times on the same stream without an intervening read or file positioning operation on that
    stream, the operation may fail.
4   If the value of c equals that of the macro EOF, the operation fails and the input stream is
    unchanged.
5   A successful call to the ungetc function clears the end-of-file indicator for the stream.
    The value of the file position indicator for the stream after reading or discarding all
    pushed-back characters shall be the same as it was before the characters were pushed
    back. For a text stream, the value of its file position indicator after a successful call to the
    ungetc function is unspecified until all pushed-back characters are read or discarded.

[page 333]

    For a binary stream, its file position indicator is decremented by each successful call to
    the ungetc function; if its value was zero before a call, it is indeterminate after the
    call.283)
    Returns
6   The ungetc function returns the character pushed back after conversion, or EOF if the
    operation fails.
    Forward references: file positioning functions (7.21.9).
    7.21.8 Direct input/output functions
    7.21.8.1 The fread function
    Synopsis
1            #include <stdio.h>
             size_t fread(void * restrict ptr,
                  size_t size, size_t nmemb,
                  FILE * restrict stream);
    Description
2   The fread function reads, into the array pointed to by ptr, up to nmemb elements
    whose size is specified by size, from the stream pointed to by stream. For each
    object, size calls are made to the fgetc function and the results stored, in the order
    read, in an array of unsigned char exactly overlaying the object. The file position
    indicator for the stream (if defined) is advanced by the number of characters successfully
    read. If an error occurs, the resulting value of the file position indicator for the stream is
    indeterminate. If a partial element is read, its value is indeterminate.
    Returns
3   The fread function returns the number of elements successfully read, which may be
    less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero,
    fread returns zero and the contents of the array and the state of the stream remain
    unchanged.




    283) See ''future library directions'' (7.30.9).

[page 334]

    7.21.8.2 The fwrite function
    Synopsis
1           #include <stdio.h>
            size_t fwrite(const void * restrict ptr,
                 size_t size, size_t nmemb,
                 FILE * restrict stream);
    Description
2   The fwrite function writes, from the array pointed to by ptr, up to nmemb elements
    whose size is specified by size, to the stream pointed to by stream. For each object,
    size calls are made to the fputc function, taking the values (in order) from an array of
    unsigned char exactly overlaying the object. The file position indicator for the
    stream (if defined) is advanced by the number of characters successfully written. If an
    error occurs, the resulting value of the file position indicator for the stream is
    indeterminate.
    Returns
3   The fwrite function returns the number of elements successfully written, which will be
    less than nmemb only if a write error is encountered. If size or nmemb is zero,
    fwrite returns zero and the state of the stream remains unchanged.
    7.21.9 File positioning functions
    7.21.9.1 The fgetpos function
    Synopsis
1           #include <stdio.h>
            int fgetpos(FILE * restrict stream,
                 fpos_t * restrict pos);
    Description
2   The fgetpos function stores the current values of the parse state (if any) and file
    position indicator for the stream pointed to by stream in the object pointed to by pos.
    The values stored contain unspecified information usable by the fsetpos function for
    repositioning the stream to its position at the time of the call to the fgetpos function.
    Returns
3   If successful, the fgetpos function returns zero; on failure, the fgetpos function
    returns nonzero and stores an implementation-defined positive value in errno.
    Forward references: the fsetpos function (7.21.9.3).




[page 335]

    7.21.9.2 The fseek function
    Synopsis
1          #include <stdio.h>
           int fseek(FILE *stream, long int offset, int whence);
    Description
2   The fseek function sets the file position indicator for the stream pointed to by stream.
    If a read or write error occurs, the error indicator for the stream is set and fseek fails.
3   For a binary stream, the new position, measured in characters from the beginning of the
    file, is obtained by adding offset to the position specified by whence. The specified
    position is the beginning of the file if whence is SEEK_SET, the current value of the file
    position indicator if SEEK_CUR, or end-of-file if SEEK_END. A binary stream need not
    meaningfully support fseek calls with a whence value of SEEK_END.
4   For a text stream, either offset shall be zero, or offset shall be a value returned by
    an earlier successful call to the ftell function on a stream associated with the same file
    and whence shall be SEEK_SET.
5   After determining the new position, a successful call to the fseek function undoes any
    effects of the ungetc function on the stream, clears the end-of-file indicator for the
    stream, and then establishes the new position. After a successful fseek call, the next
    operation on an update stream may be either input or output.
    Returns
6   The fseek function returns nonzero only for a request that cannot be satisfied.
    Forward references: the ftell function (7.21.9.4).
    7.21.9.3 The fsetpos function
    Synopsis
1          #include <stdio.h>
           int fsetpos(FILE *stream, const fpos_t *pos);
    Description
2   The fsetpos function sets the mbstate_t object (if any) and file position indicator
    for the stream pointed to by stream according to the value of the object pointed to by
    pos, which shall be a value obtained from an earlier successful call to the fgetpos
    function on a stream associated with the same file. If a read or write error occurs, the
    error indicator for the stream is set and fsetpos fails.
3   A successful call to the fsetpos function undoes any effects of the ungetc function
    on the stream, clears the end-of-file indicator for the stream, and then establishes the new
    parse state and position. After a successful fsetpos call, the next operation on an

[page 336]

    update stream may be either input or output.
    Returns
4   If successful, the fsetpos function returns zero; on failure, the fsetpos function
    returns nonzero and stores an implementation-defined positive value in errno.
    7.21.9.4 The ftell function
    Synopsis
1           #include <stdio.h>
            long int ftell(FILE *stream);
    Description
2   The ftell function obtains the current value of the file position indicator for the stream
    pointed to by stream. For a binary stream, the value is the number of characters from
    the beginning of the file. For a text stream, its file position indicator contains unspecified
    information, usable by the fseek function for returning the file position indicator for the
    stream to its position at the time of the ftell call; the difference between two such
    return values is not necessarily a meaningful measure of the number of characters written
    or read.
    Returns
3   If successful, the ftell function returns the current value of the file position indicator
    for the stream. On failure, the ftell function returns -1L and stores an
    implementation-defined positive value in errno.
    7.21.9.5 The rewind function
    Synopsis
1           #include <stdio.h>
            void rewind(FILE *stream);
    Description
2   The rewind function sets the file position indicator for the stream pointed to by
    stream to the beginning of the file. It is equivalent to
            (void)fseek(stream, 0L, SEEK_SET)
    except that the error indicator for the stream is also cleared.
    Returns
3   The rewind function returns no value.




[page 337]

    7.21.10 Error-handling functions
    7.21.10.1 The clearerr function
    Synopsis
1          #include <stdio.h>
           void clearerr(FILE *stream);
    Description
2   The clearerr function clears the end-of-file and error indicators for the stream pointed
    to by stream.
    Returns
3   The clearerr function returns no value.
    7.21.10.2 The feof function
    Synopsis
1          #include <stdio.h>
           int feof(FILE *stream);
    Description
2   The feof function tests the end-of-file indicator for the stream pointed to by stream.
    Returns
3   The feof function returns nonzero if and only if the end-of-file indicator is set for
    stream.
    7.21.10.3 The ferror function
    Synopsis
1          #include <stdio.h>
           int ferror(FILE *stream);
    Description
2   The ferror function tests the error indicator for the stream pointed to by stream.
    Returns
3   The ferror function returns nonzero if and only if the error indicator is set for
    stream.




[page 338]

    7.21.10.4 The perror function
    Synopsis
1           #include <stdio.h>
            void perror(const char *s);
    Description
2   The perror function maps the error number in the integer expression errno to an
    error message. It writes a sequence of characters to the standard error stream thus: first
    (if s is not a null pointer and the character pointed to by s is not the null character), the
    string pointed to by s followed by a colon (:) and a space; then an appropriate error
    message string followed by a new-line character. The contents of the error message
    strings are the same as those returned by the strerror function with argument errno.
    Returns
3   The perror function returns no value.
    Forward references: the strerror function (7.23.6.2).




[page 339]

    7.22 General utilities <stdlib.h>
1   The header <stdlib.h> declares five types and several functions of general utility, and
    defines several macros.284)
2   The types declared are size_t and wchar_t (both described in 7.19),
             div_t
    which is a structure type that is the type of the value returned by the div function,
             ldiv_t
    which is a structure type that is the type of the value returned by the ldiv function, and
             lldiv_t
    which is a structure type that is the type of the value returned by the lldiv function.
3   The macros defined are NULL (described in 7.19);
             EXIT_FAILURE
    and
             EXIT_SUCCESS
    which expand to integer constant expressions that can be used as the argument to the
    exit function to return unsuccessful or successful termination status, respectively, to the
    host environment;
             RAND_MAX
    which expands to an integer constant expression that is the maximum value returned by
    the rand function; and
             MB_CUR_MAX
    which expands to a positive integer expression with type size_t that is the maximum
    number of bytes in a multibyte character for the extended character set specified by the
    current locale (category LC_CTYPE), which is never greater than MB_LEN_MAX.




    284) See ''future library directions'' (7.30.10).

[page 340]

    7.22.1 Numeric conversion functions
1   The functions atof, atoi, atol, and atoll need not affect the value of the integer
    expression errno on an error. If the value of the result cannot be represented, the
    behavior is undefined.
    7.22.1.1 The atof function
    Synopsis
1           #include <stdlib.h>
            double atof(const char *nptr);
    Description
2   The atof function converts the initial portion of the string pointed to by nptr to
    double representation. Except for the behavior on error, it is equivalent to
            strtod(nptr, (char **)NULL)
    Returns
3   The atof function returns the converted value.
    Forward references: the strtod, strtof, and strtold functions (7.22.1.3).
    7.22.1.2 The atoi, atol, and atoll functions
    Synopsis
1           #include <stdlib.h>
            int atoi(const char *nptr);
            long int atol(const char *nptr);
            long long int atoll(const char *nptr);
    Description
2   The atoi, atol, and atoll functions convert the initial portion of the string pointed
    to by nptr to int, long int, and long long int representation, respectively.
    Except for the behavior on error, they are equivalent to
            atoi: (int)strtol(nptr, (char **)NULL, 10)
            atol: strtol(nptr, (char **)NULL, 10)
            atoll: strtoll(nptr, (char **)NULL, 10)
    Returns
3   The atoi, atol, and atoll functions return the converted value.
    Forward references: the strtol, strtoll, strtoul, and strtoull functions
    (7.22.1.4).



[page 341]

    7.22.1.3 The strtod, strtof, and strtold functions
    Synopsis
1          #include <stdlib.h>
           double strtod(const char * restrict nptr,
                char ** restrict endptr);
           float strtof(const char * restrict nptr,
                char ** restrict endptr);
           long double strtold(const char * restrict nptr,
                char ** restrict endptr);
    Description
2   The strtod, strtof, and strtold functions convert the initial portion of the string
    pointed to by nptr to double, float, and long double representation,
    respectively. First, they decompose the input string into three parts: an initial, possibly
    empty, sequence of white-space characters (as specified by the isspace function), a
    subject sequence resembling a floating-point constant or representing an infinity or NaN;
    and a final string of one or more unrecognized characters, including the terminating null
    character of the input string. Then, they attempt to convert the subject sequence to a
    floating-point number, and return the result.
3   The expected form of the subject sequence is an optional plus or minus sign, then one of
    the following:
    -- a nonempty sequence of decimal digits optionally containing a decimal-point
      character, then an optional exponent part as defined in 6.4.4.2;
    -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
      decimal-point character, then an optional binary exponent part as defined in 6.4.4.2;
    -- INF or INFINITY, ignoring case
    -- NAN or NAN(n-char-sequenceopt), ignoring case in the NAN part, where:
               n-char-sequence:
                      digit
                      nondigit
                      n-char-sequence digit
                      n-char-sequence nondigit
    The subject sequence is defined as the longest initial subsequence of the input string,
    starting with the first non-white-space character, that is of the expected form. The subject
    sequence contains no characters if the input string is not of the expected form.
4   If the subject sequence has the expected form for a floating-point number, the sequence of
    characters starting with the first digit or the decimal-point character (whichever occurs
    first) is interpreted as a floating constant according to the rules of 6.4.4.2, except that the
[page 342]

    decimal-point character is used in place of a period, and that if neither an exponent part
    nor a decimal-point character appears in a decimal floating point number, or if a binary
    exponent part does not appear in a hexadecimal floating point number, an exponent part
    of the appropriate type with value zero is assumed to follow the last digit in the string. If
    the subject sequence begins with a minus sign, the sequence is interpreted as negated.285)
    A character sequence INF or INFINITY is interpreted as an infinity, if representable in
    the return type, else like a floating constant that is too large for the range of the return
    type. A character sequence NAN or NAN(n-char-sequenceopt), is interpreted as a quiet
    NaN, if supported in the return type, else like a subject sequence part that does not have
    the expected form; the meaning of the n-char sequences is implementation-defined.286) A
    pointer to the final string is stored in the object pointed to by endptr, provided that
    endptr is not a null pointer.
5   If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
    value resulting from the conversion is correctly rounded.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Recommended practice
8   If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
    the result is not exactly representable, the result should be one of the two numbers in the
    appropriate internal format that are adjacent to the hexadecimal floating source value,
    with the extra stipulation that the error should have a correct sign for the current rounding
    direction.
9   If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
    <float.h>) significant digits, the result should be correctly rounded. If the subject
    sequence D has the decimal form and more than DECIMAL_DIG significant digits,
    consider the two bounding, adjacent decimal strings L and U, both having
    DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
    The result should be one of the (equal or adjacent) values that would be obtained by
    correctly rounding L and U according to the current rounding direction, with the extra

    285) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
         negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
         methods may yield different results if rounding is toward positive or negative infinity. In either case,
         the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
    286) An implementation may use the n-char sequence to determine extra information to be represented in
         the NaN's significand.

[page 343]

     stipulation that the error with respect to D should have a correct sign for the current
     rounding direction.287)
     Returns
10   The functions return the converted value, if any. If no conversion could be performed,
     zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
     plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
     return type and sign of the value), and the value of the macro ERANGE is stored in
     errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
     no greater than the smallest normalized positive number in the return type; whether
     errno acquires the value ERANGE is implementation-defined.
     7.22.1.4 The strtol, strtoll, strtoul, and strtoull functions
     Synopsis
1            #include <stdlib.h>
             long int strtol(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
             long long int strtoll(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
             unsigned long int strtoul(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
             unsigned long long int strtoull(
                  const char * restrict nptr,
                  char ** restrict endptr,
                  int base);
     Description
2    The strtol, strtoll, strtoul, and strtoull functions convert the initial
     portion of the string pointed to by nptr to long int, long long int, unsigned
     long int, and unsigned long long int representation, respectively. First,
     they decompose the input string into three parts: an initial, possibly empty, sequence of
     white-space characters (as specified by the isspace function), a subject sequence


     287) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
          to the same internal floating value, but if not will round to adjacent values.

[page 344]

    resembling an integer represented in some radix determined by the value of base, and a
    final string of one or more unrecognized characters, including the terminating null
    character of the input string. Then, they attempt to convert the subject sequence to an
    integer, and return the result.
3   If the value of base is zero, the expected form of the subject sequence is that of an
    integer constant as described in 6.4.4.1, optionally preceded by a plus or minus sign, but
    not including an integer suffix. If the value of base is between 2 and 36 (inclusive), the
    expected form of the subject sequence is a sequence of letters and digits representing an
    integer with the radix specified by base, optionally preceded by a plus or minus sign,
    but not including an integer suffix. The letters from a (or A) through z (or Z) are
    ascribed the values 10 through 35; only letters and digits whose ascribed values are less
    than that of base are permitted. If the value of base is 16, the characters 0x or 0X may
    optionally precede the sequence of letters and digits, following the sign if present.
4   The subject sequence is defined as the longest initial subsequence of the input string,
    starting with the first non-white-space character, that is of the expected form. The subject
    sequence contains no characters if the input string is empty or consists entirely of white
    space, or if the first non-white-space character is other than a sign or a permissible letter
    or digit.
5   If the subject sequence has the expected form and the value of base is zero, the sequence
    of characters starting with the first digit is interpreted as an integer constant according to
    the rules of 6.4.4.1. If the subject sequence has the expected form and the value of base
    is between 2 and 36, it is used as the base for conversion, ascribing to each letter its value
    as given above. If the subject sequence begins with a minus sign, the value resulting from
    the conversion is negated (in the return type). A pointer to the final string is stored in the
    object pointed to by endptr, provided that endptr is not a null pointer.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Returns
8   The strtol, strtoll, strtoul, and strtoull functions return the converted
    value, if any. If no conversion could be performed, zero is returned. If the correct value
    is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
    LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
    and sign of the value, if any), and the value of the macro ERANGE is stored in errno.




[page 345]

    7.22.2 Pseudo-random sequence generation functions
    7.22.2.1 The rand function
    Synopsis
1           #include <stdlib.h>
            int rand(void);
    Description
2   The rand function computes a sequence of pseudo-random integers in the range 0 to
    RAND_MAX.288)
3   The rand function is not required to avoid data races. The implementation shall behave
    as if no library function calls the rand function.
    Returns
4   The rand function returns a pseudo-random integer.
    Environmental limits
5   The value of the RAND_MAX macro shall be at least 32767.
    7.22.2.2 The srand function
    Synopsis
1           #include <stdlib.h>
            void srand(unsigned int seed);
    Description
2   The srand function uses the argument as a seed for a new sequence of pseudo-random
    numbers to be returned by subsequent calls to rand. If srand is then called with the
    same seed value, the sequence of pseudo-random numbers shall be repeated. If rand is
    called before any calls to srand have been made, the same sequence shall be generated
    as when srand is first called with a seed value of 1.
3   The implementation shall behave as if no library function calls the srand function.
    Returns
4   The srand function returns no value.




    288) There are no guarantees as to the quality of the random sequence produced and some implementations
         are known to produce sequences with distressingly non-random low-order bits. Applications with
         particular requirements should use a generator that is known to be sufficient for their needs.

[page 346]

5   EXAMPLE       The following functions define a portable implementation of rand and srand.
            static unsigned long int next = 1;
            int rand(void)   // RAND_MAX assumed to be 32767
            {
                  next = next * 1103515245 + 12345;
                  return (unsigned int)(next/65536) % 32768;
            }
            void srand(unsigned int seed)
            {
                  next = seed;
            }

    7.22.3 Memory management functions
1   The order and contiguity of storage allocated by successive calls to the
    aligned_alloc, calloc, malloc, and realloc functions is unspecified. The
    pointer returned if the allocation succeeds is suitably aligned so that it may be assigned to
    a pointer to any type of object with a fundamental alignment requirement and then used
    to access such an object or an array of such objects in the space allocated (until the space
    is explicitly deallocated). The lifetime of an allocated object extends from the allocation
    until the deallocation. Each such allocation shall yield a pointer to an object disjoint from
    any other object. The pointer returned points to the start (lowest byte address) of the
    allocated space. If the space cannot be allocated, a null pointer is returned. If the size of
    the space requested is zero, the behavior is implementation-defined: either a null pointer
    is returned, or the behavior is as if the size were some nonzero value, except that the
    returned pointer shall not be used to access an object.
    7.22.3.1 The aligned_alloc function
    Synopsis
1           #include <stdlib.h>
            void *aligned_alloc(size_t alignment, size_t size);
    Description
2   The aligned_alloc function allocates space for an object whose alignment is
    specified by alignment, whose size is specified by size, and whose value is
    indeterminate. The value of alignment shall be a valid alignment supported by the
    implementation and the value of size shall be an integral multiple of alignment.
    Returns
3   The aligned_alloc function returns either a null pointer or a pointer to the allocated
    space.




[page 347]

    7.22.3.2 The calloc function
    Synopsis
1           #include <stdlib.h>
            void *calloc(size_t nmemb, size_t size);
    Description
2   The calloc function allocates space for an array of nmemb objects, each of whose size
    is size. The space is initialized to all bits zero.289)
    Returns
3   The calloc function returns either a null pointer or a pointer to the allocated space.
    7.22.3.3 The free function
    Synopsis
1           #include <stdlib.h>
            void free(void *ptr);
    Description
2   The free function causes the space pointed to by ptr to be deallocated, that is, made
    available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if
    the argument does not match a pointer earlier returned by a memory management
    function, or if the space has been deallocated by a call to free or realloc, the
    behavior is undefined.
    Returns
3   The free function returns no value.
    7.22.3.4 The malloc function
    Synopsis
1           #include <stdlib.h>
            void *malloc(size_t size);
    Description
2   The malloc function allocates space for an object whose size is specified by size and
    whose value is indeterminate.




    289) Note that this need not be the same as the representation of floating-point zero or a null pointer
         constant.

[page 348]

    Returns
3   The malloc function returns either a null pointer or a pointer to the allocated space.
    7.22.3.5 The realloc function
    Synopsis
1           #include <stdlib.h>
            void *realloc(void *ptr, size_t size);
    Description
2   The realloc function deallocates the old object pointed to by ptr and returns a
    pointer to a new object that has the size specified by size. The contents of the new
    object shall be the same as that of the old object prior to deallocation, up to the lesser of
    the new and old sizes. Any bytes in the new object beyond the size of the old object have
    indeterminate values.
3   If ptr is a null pointer, the realloc function behaves like the malloc function for the
    specified size. Otherwise, if ptr does not match a pointer earlier returned by a memory
    management function, or if the space has been deallocated by a call to the free or
    realloc function, the behavior is undefined. If memory for the new object cannot be
    allocated, the old object is not deallocated and its value is unchanged.
    Returns
4   The realloc function returns a pointer to the new object (which may have the same
    value as a pointer to the old object), or a null pointer if the new object could not be
    allocated.
    7.22.4 Communication with the environment
    7.22.4.1 The abort function
    Synopsis
1           #include <stdlib.h>
            _Noreturn void abort(void);
    Description
2   The abort function causes abnormal program termination to occur, unless the signal
    SIGABRT is being caught and the signal handler does not return. Whether open streams
    with unwritten buffered data are flushed, open streams are closed, or temporary files are
    removed is implementation-defined. An implementation-defined form of the status
    unsuccessful termination is returned to the host environment by means of the function
    call raise(SIGABRT).




[page 349]

    Returns
3   The abort function does not return to its caller.
    7.22.4.2 The atexit function
    Synopsis
1          #include <stdlib.h>
           int atexit(void (*func)(void));
    Description
2   The atexit function registers the function pointed to by func, to be called without
    arguments at normal program termination.290)
    Environmental limits
3   The implementation shall support the registration of at least 32 functions.
    Returns
4   The atexit function returns zero if the registration succeeds, nonzero if it fails.
    Forward references: the at_quick_exit function (7.22.4.3), the exit function
    (7.22.4.4).
    7.22.4.3 The at_quick_exit function
    Synopsis
1          #include <stdlib.h>
           int at_quick_exit(void (*func)(void));
    Description
2   The at_quick_exit function registers the function pointed to by func, to be called
    without arguments should quick_exit be called.291)
    Environmental limits
3   The implementation shall support the registration of at least 32 functions.
    Returns
4   The at_quick_exit function returns zero if the registration succeeds, nonzero if it
    fails.
    Forward references: the quick_exit function (7.22.4.7).


    290) The atexit function registrations are distinct from the at_quick_exit registrations, so
         applications may need to call both registration functions with the same argument.
    291) The at_quick_exit function registrations are distinct from the atexit registrations, so
         applications may need to call both registration functions with the same argument.

[page 350]

    7.22.4.4 The exit function
    Synopsis
1           #include <stdlib.h>
            _Noreturn void exit(int status);
    Description
2   The exit function causes normal program termination to occur. No functions registered
    by the at_quick_exit function are called. If a program calls the exit function
    more than once, or calls the quick_exit function in addition to the exit function, the
    behavior is undefined.
3   First, all functions registered by the atexit function are called, in the reverse order of
    their registration,292) except that a function is called after any previously registered
    functions that had already been called at the time it was registered. If, during the call to
    any such function, a call to the longjmp function is made that would terminate the call
    to the registered function, the behavior is undefined.
4   Next, all open streams with unwritten buffered data are flushed, all open streams are
    closed, and all files created by the tmpfile function are removed.
5   Finally, control is returned to the host environment. If the value of status is zero or
    EXIT_SUCCESS, an implementation-defined form of the status successful termination is
    returned. If the value of status is EXIT_FAILURE, an implementation-defined form
    of the status unsuccessful termination is returned. Otherwise the status returned is
    implementation-defined.
    Returns
6   The exit function cannot return to its caller.
    7.22.4.5 The _Exit function
    Synopsis
1           #include <stdlib.h>
            _Noreturn void _Exit(int status);
    Description
2   The _Exit function causes normal program termination to occur and control to be
    returned to the host environment. No functions registered by the atexit function, the
    at_quick_exit function, or signal handlers registered by the signal function are
    called. The status returned to the host environment is determined in the same way as for


    292) Each function is called as many times as it was registered, and in the correct order with respect to
         other registered functions.

[page 351]

    the exit function (7.22.4.4). Whether open streams with unwritten buffered data are
    flushed, open streams are closed, or temporary files are removed is implementation-
    defined.
    Returns
3   The _Exit function cannot return to its caller.
    7.22.4.6 The getenv function
    Synopsis
1           #include <stdlib.h>
            char *getenv(const char *name);
    Description
2   The getenv function searches an environment list, provided by the host environment,
    for a string that matches the string pointed to by name. The set of environment names
    and the method for altering the environment list are implementation-defined. The
    getenv function need not avoid data races with other threads of execution that modify
    the environment list.293)
3   The implementation shall behave as if no library function calls the getenv function.
    Returns
4   The getenv function returns a pointer to a string associated with the matched list
    member. The string pointed to shall not be modified by the program, but may be
    overwritten by a subsequent call to the getenv function. If the specified name cannot
    be found, a null pointer is returned.
    7.22.4.7 The quick_exit function
    Synopsis
1           #include <stdlib.h>
            _Noreturn void quick_exit(int status);
    Description
2   The quick_exit function causes normal program termination to occur. No functions
    registered by the atexit function or signal handlers registered by the signal function
    are called. If a program calls the quick_exit function more than once, or calls the
    exit function in addition to the quick_exit function, the behavior is undefined.
3   The quick_exit function first calls all functions registered by the at_quick_exit
    function, in the reverse order of their registration,294) except that a function is called after


    293) Many implementations provide non-standard functions that modify the environment list.

[page 352]

    any previously registered functions that had already been called at the time it was
    registered. If, during the call to any such function, a call to the longjmp function is
    made that would terminate the call to the registered function, the behavior is undefined.
4   Then control is returned to the host environment by means of the function call
    _Exit(status).
    Returns
5   The quick_exit function cannot return to its caller.
    7.22.4.8 The system function
    Synopsis
1           #include <stdlib.h>
            int system(const char *string);
    Description
2   If string is a null pointer, the system function determines whether the host
    environment has a command processor. If string is not a null pointer, the system
    function passes the string pointed to by string to that command processor to be
    executed in a manner which the implementation shall document; this might then cause the
    program calling system to behave in a non-conforming manner or to terminate.
    Returns
3   If the argument is a null pointer, the system function returns nonzero only if a
    command processor is available. If the argument is not a null pointer, and the system
    function does return, it returns an implementation-defined value.
    7.22.5 Searching and sorting utilities
1   These utilities make use of a comparison function to search or sort arrays of unspecified
    type. Where an argument declared as size_t nmemb specifies the length of the array
    for a function, nmemb can have the value zero on a call to that function; the comparison
    function is not called, a search finds no matching element, and sorting performs no
    rearrangement. Pointer arguments on such a call shall still have valid values, as described
    in 7.1.4.
2   The implementation shall ensure that the second argument of the comparison function
    (when called from bsearch), or both arguments (when called from qsort), are
    pointers to elements of the array.295) The first argument when called from bsearch
    shall equal key.



    294) Each function is called as many times as it was registered, and in the correct order with respect to
         other registered functions.

[page 353]

3   The comparison function shall not alter the contents of the array. The implementation
    may reorder elements of the array between calls to the comparison function, but shall not
    alter the contents of any individual element.
4   When the same objects (consisting of size bytes, irrespective of their current positions
    in the array) are passed more than once to the comparison function, the results shall be
    consistent with one another. That is, for qsort they shall define a total ordering on the
    array, and for bsearch the same object shall always compare the same way with the
    key.
5   A sequence point occurs immediately before and immediately after each call to the
    comparison function, and also between any call to the comparison function and any
    movement of the objects passed as arguments to that call.
    7.22.5.1 The bsearch function
    Synopsis
1            #include <stdlib.h>
             void *bsearch(const void *key, const void *base,
                  size_t nmemb, size_t size,
                  int (*compar)(const void *, const void *));
    Description
2   The bsearch function searches an array of nmemb objects, the initial element of which
    is pointed to by base, for an element that matches the object pointed to by key. The
    size of each element of the array is specified by size.
3   The comparison function pointed to by compar is called with two arguments that point
    to the key object and to an array element, in that order. The function shall return an
    integer less than, equal to, or greater than zero if the key object is considered,
    respectively, to be less than, to match, or to be greater than the array element. The array
    shall consist of: all the elements that compare less than, all the elements that compare
    equal to, and all the elements that compare greater than the key object, in that order.296)
    Returns
4   The bsearch function returns a pointer to a matching element of the array, or a null
    pointer if no match is found. If two elements compare as equal, which element is


    295) That is, if the value passed is p, then the following expressions are always nonzero:
                  ((char *)p - (char *)base) % size == 0
                  (char *)p >= (char *)base
                  (char *)p < (char *)base + nmemb * size

    296) In practice, the entire array is sorted according to the comparison function.

[page 354]

    matched is unspecified.
    7.22.5.2 The qsort function
    Synopsis
1           #include <stdlib.h>
            void qsort(void *base, size_t nmemb, size_t size,
                 int (*compar)(const void *, const void *));
    Description
2   The qsort function sorts an array of nmemb objects, the initial element of which is
    pointed to by base. The size of each object is specified by size.
3   The contents of the array are sorted into ascending order according to a comparison
    function pointed to by compar, which is called with two arguments that point to the
    objects being compared. The function shall return an integer less than, equal to, or
    greater than zero if the first argument is considered to be respectively less than, equal to,
    or greater than the second.
4   If two elements compare as equal, their order in the resulting sorted array is unspecified.
    Returns
5   The qsort function returns no value.
    7.22.6 Integer arithmetic functions
    7.22.6.1 The abs, labs and llabs functions
    Synopsis
1           #include <stdlib.h>
            int abs(int j);
            long int labs(long int j);
            long long int llabs(long long int j);
    Description
2   The abs, labs, and llabs functions compute the absolute value of an integer j. If the
    result cannot be represented, the behavior is undefined.297)
    Returns
3   The abs, labs, and llabs, functions return the absolute value.




    297) The absolute value of the most negative number cannot be represented in two's complement.

[page 355]

    7.22.6.2 The div, ldiv, and lldiv functions
    Synopsis
1            #include <stdlib.h>
             div_t div(int numer, int denom);
             ldiv_t ldiv(long int numer, long int denom);
             lldiv_t lldiv(long long int numer, long long int denom);
    Description
2   The div, ldiv, and lldiv, functions compute numer / denom and numer %
    denom in a single operation.
    Returns
3   The div, ldiv, and lldiv functions return a structure of type div_t, ldiv_t, and
    lldiv_t, respectively, comprising both the quotient and the remainder. The structures
    shall contain (in either order) the members quot (the quotient) and rem (the remainder),
    each of which has the same type as the arguments numer and denom. If either part of
    the result cannot be represented, the behavior is undefined.
    7.22.7 Multibyte/wide character conversion functions
1   The behavior of the multibyte character functions is affected by the LC_CTYPE category
    of the current locale. For a state-dependent encoding, each function is placed into its
    initial conversion state at program startup and can be returned to that state by a call for
    which its character pointer argument, s, is a null pointer. Subsequent calls with s as
    other than a null pointer cause the internal conversion state of the function to be altered as
    necessary. A call with s as a null pointer causes these functions to return a nonzero value
    if encodings have state dependency, and zero otherwise.298) Changing the LC_CTYPE
    category causes the conversion state of these functions to be indeterminate.
    7.22.7.1 The mblen function
    Synopsis
1            #include <stdlib.h>
             int mblen(const char *s, size_t n);
    Description
2   If s is not a null pointer, the mblen function determines the number of bytes contained
    in the multibyte character pointed to by s. Except that the conversion state of the
    mbtowc function is not affected, it is equivalent to



    298) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
         character codes, but are grouped with an adjacent multibyte character.

[page 356]

            mbtowc((wchar_t *)0, (const char *)0, 0);
            mbtowc((wchar_t *)0, s, n);
3   The implementation shall behave as if no library function calls the mblen function.
    Returns
4   If s is a null pointer, the mblen function returns a nonzero or zero value, if multibyte
    character encodings, respectively, do or do not have state-dependent encodings. If s is
    not a null pointer, the mblen function either returns 0 (if s points to the null character),
    or returns the number of bytes that are contained in the multibyte character (if the next n
    or fewer bytes form a valid multibyte character), or returns -1 (if they do not form a valid
    multibyte character).
    Forward references: the mbtowc function (7.22.7.2).
    7.22.7.2 The mbtowc function
    Synopsis
1           #include <stdlib.h>
            int mbtowc(wchar_t * restrict pwc,
                 const char * restrict s,
                 size_t n);
    Description
2   If s is not a null pointer, the mbtowc function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the value of the
    corresponding wide character and then, if pwc is not a null pointer, stores that value in
    the object pointed to by pwc. If the corresponding wide character is the null wide
    character, the function is left in the initial conversion state.
3   The implementation shall behave as if no library function calls the mbtowc function.
    Returns
4   If s is a null pointer, the mbtowc function returns a nonzero or zero value, if multibyte
    character encodings, respectively, do or do not have state-dependent encodings. If s is
    not a null pointer, the mbtowc function either returns 0 (if s points to the null character),
    or returns the number of bytes that are contained in the converted multibyte character (if
    the next n or fewer bytes form a valid multibyte character), or returns -1 (if they do not
    form a valid multibyte character).
5   In no case will the value returned be greater than n or the value of the MB_CUR_MAX
    macro.


[page 357]

    7.22.7.3 The wctomb function
    Synopsis
1          #include <stdlib.h>
           int wctomb(char *s, wchar_t wc);
    Description
2   The wctomb function determines the number of bytes needed to represent the multibyte
    character corresponding to the wide character given by wc (including any shift
    sequences), and stores the multibyte character representation in the array whose first
    element is pointed to by s (if s is not a null pointer). At most MB_CUR_MAX characters
    are stored. If wc is a null wide character, a null byte is stored, preceded by any shift
    sequence needed to restore the initial shift state, and the function is left in the initial
    conversion state.
3   The implementation shall behave as if no library function calls the wctomb function.
    Returns
4   If s is a null pointer, the wctomb function returns a nonzero or zero value, if multibyte
    character encodings, respectively, do or do not have state-dependent encodings. If s is
    not a null pointer, the wctomb function returns -1 if the value of wc does not correspond
    to a valid multibyte character, or returns the number of bytes that are contained in the
    multibyte character corresponding to the value of wc.
5   In no case will the value returned be greater than the value of the MB_CUR_MAX macro.
    7.22.8 Multibyte/wide string conversion functions
1   The behavior of the multibyte string functions is affected by the LC_CTYPE category of
    the current locale.
    7.22.8.1 The mbstowcs function
    Synopsis
1          #include <stdlib.h>
           size_t mbstowcs(wchar_t * restrict pwcs,
                const char * restrict s,
                size_t n);
    Description
2   The mbstowcs function converts a sequence of multibyte characters that begins in the
    initial shift state from the array pointed to by s into a sequence of corresponding wide
    characters and stores not more than n wide characters into the array pointed to by pwcs.
    No multibyte characters that follow a null character (which is converted into a null wide
    character) will be examined or converted. Each multibyte character is converted as if by
    a call to the mbtowc function, except that the conversion state of the mbtowc function is
[page 358]

    not affected.
3   No more than n elements will be modified in the array pointed to by pwcs. If copying
    takes place between objects that overlap, the behavior is undefined.
    Returns
4   If an invalid multibyte character is encountered, the mbstowcs function returns
    (size_t)(-1). Otherwise, the mbstowcs function returns the number of array
    elements modified, not including a terminating null wide character, if any.299)
    7.22.8.2 The wcstombs function
    Synopsis
1            #include <stdlib.h>
             size_t wcstombs(char * restrict s,
                  const wchar_t * restrict pwcs,
                  size_t n);
    Description
2   The wcstombs function converts a sequence of wide characters from the array pointed
    to by pwcs into a sequence of corresponding multibyte characters that begins in the
    initial shift state, and stores these multibyte characters into the array pointed to by s,
    stopping if a multibyte character would exceed the limit of n total bytes or if a null
    character is stored. Each wide character is converted as if by a call to the wctomb
    function, except that the conversion state of the wctomb function is not affected.
3   No more than n bytes will be modified in the array pointed to by s. If copying takes place
    between objects that overlap, the behavior is undefined.
    Returns
4   If a wide character is encountered that does not correspond to a valid multibyte character,
    the wcstombs function returns (size_t)(-1). Otherwise, the wcstombs function
    returns the number of bytes modified, not including a terminating null character, if
    any.299)




    299) The array will not be null-terminated if the value returned is n.

[page 359]

    7.23 String handling <string.h>
    7.23.1 String function conventions
1   The header <string.h> declares one type and several functions, and defines one
    macro useful for manipulating arrays of character type and other objects treated as arrays
    of character type.300) The type is size_t and the macro is NULL (both described in
    7.19). Various methods are used for determining the lengths of the arrays, but in all cases
    a char * or void * argument points to the initial (lowest addressed) character of the
    array. If an array is accessed beyond the end of an object, the behavior is undefined.
2   Where an argument declared as size_t n specifies the length of the array for a
    function, n can have the value zero on a call to that function. Unless explicitly stated
    otherwise in the description of a particular function in this subclause, pointer arguments
    on such a call shall still have valid values, as described in 7.1.4. On such a call, a
    function that locates a character finds no occurrence, a function that compares two
    character sequences returns zero, and a function that copies characters copies zero
    characters.
3   For all functions in this subclause, each character shall be interpreted as if it had the type
    unsigned char (and therefore every possible object representation is valid and has a
    different value).
    7.23.2 Copying functions
    7.23.2.1 The memcpy function
    Synopsis
1            #include <string.h>
             void *memcpy(void * restrict s1,
                  const void * restrict s2,
                  size_t n);
    Description
2   The memcpy function copies n characters from the object pointed to by s2 into the
    object pointed to by s1. If copying takes place between objects that overlap, the behavior
    is undefined.
    Returns
3   The memcpy function returns the value of s1.




    300) See ''future library directions'' (7.30.11).

[page 360]

    7.23.2.2 The memmove function
    Synopsis
1           #include <string.h>
            void *memmove(void *s1, const void *s2, size_t n);
    Description
2   The memmove function copies n characters from the object pointed to by s2 into the
    object pointed to by s1. Copying takes place as if the n characters from the object
    pointed to by s2 are first copied into a temporary array of n characters that does not
    overlap the objects pointed to by s1 and s2, and then the n characters from the
    temporary array are copied into the object pointed to by s1.
    Returns
3   The memmove function returns the value of s1.
    7.23.2.3 The strcpy function
    Synopsis
1           #include <string.h>
            char *strcpy(char * restrict s1,
                 const char * restrict s2);
    Description
2   The strcpy function copies the string pointed to by s2 (including the terminating null
    character) into the array pointed to by s1. If copying takes place between objects that
    overlap, the behavior is undefined.
    Returns
3   The strcpy function returns the value of s1.
    7.23.2.4 The strncpy function
    Synopsis
1           #include <string.h>
            char *strncpy(char * restrict s1,
                 const char * restrict s2,
                 size_t n);
    Description
2   The strncpy function copies not more than n characters (characters that follow a null
    character are not copied) from the array pointed to by s2 to the array pointed to by




[page 361]

    s1.301) If copying takes place between objects that overlap, the behavior is undefined.
3   If the array pointed to by s2 is a string that is shorter than n characters, null characters
    are appended to the copy in the array pointed to by s1, until n characters in all have been
    written.
    Returns
4   The strncpy function returns the value of s1.
    7.23.3 Concatenation functions
    7.23.3.1 The strcat function
    Synopsis
1            #include <string.h>
             char *strcat(char * restrict s1,
                  const char * restrict s2);
    Description
2   The strcat function appends a copy of the string pointed to by s2 (including the
    terminating null character) to the end of the string pointed to by s1. The initial character
    of s2 overwrites the null character at the end of s1. If copying takes place between
    objects that overlap, the behavior is undefined.
    Returns
3   The strcat function returns the value of s1.
    7.23.3.2 The strncat function
    Synopsis
1            #include <string.h>
             char *strncat(char * restrict s1,
                  const char * restrict s2,
                  size_t n);
    Description
2   The strncat function appends not more than n characters (a null character and
    characters that follow it are not appended) from the array pointed to by s2 to the end of
    the string pointed to by s1. The initial character of s2 overwrites the null character at the
    end of s1. A terminating null character is always appended to the result.302) If copying

    301) Thus, if there is no null character in the first n characters of the array pointed to by s2, the result will
         not be null-terminated.
    302) Thus, the maximum number of characters that can end up in the array pointed to by s1 is
         strlen(s1)+n+1.

[page 362]

    takes place between objects that overlap, the behavior is undefined.
    Returns
3   The strncat function returns the value of s1.
    Forward references: the strlen function (7.23.6.3).
    7.23.4 Comparison functions
1   The sign of a nonzero value returned by the comparison functions memcmp, strcmp,
    and strncmp is determined by the sign of the difference between the values of the first
    pair of characters (both interpreted as unsigned char) that differ in the objects being
    compared.
    7.23.4.1 The memcmp function
    Synopsis
1           #include <string.h>
            int memcmp(const void *s1, const void *s2, size_t n);
    Description
2   The memcmp function compares the first n characters of the object pointed to by s1 to
    the first n characters of the object pointed to by s2.303)
    Returns
3   The memcmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
    pointed to by s2.
    7.23.4.2 The strcmp function
    Synopsis
1           #include <string.h>
            int strcmp(const char *s1, const char *s2);
    Description
2   The strcmp function compares the string pointed to by s1 to the string pointed to by
    s2.
    Returns
3   The strcmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the string pointed to by s1 is greater than, equal to, or less than the string

    303) The contents of ''holes'' used as padding for purposes of alignment within structure objects are
         indeterminate. Strings shorter than their allocated space and unions may also cause problems in
         comparison.

[page 363]

    pointed to by s2.
    7.23.4.3 The strcoll function
    Synopsis
1          #include <string.h>
           int strcoll(const char *s1, const char *s2);
    Description
2   The strcoll function compares the string pointed to by s1 to the string pointed to by
    s2, both interpreted as appropriate to the LC_COLLATE category of the current locale.
    Returns
3   The strcoll function returns an integer greater than, equal to, or less than zero,
    accordingly as the string pointed to by s1 is greater than, equal to, or less than the string
    pointed to by s2 when both are interpreted as appropriate to the current locale.
    7.23.4.4 The strncmp function
    Synopsis
1          #include <string.h>
           int strncmp(const char *s1, const char *s2, size_t n);
    Description
2   The strncmp function compares not more than n characters (characters that follow a
    null character are not compared) from the array pointed to by s1 to the array pointed to
    by s2.
    Returns
3   The strncmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
    to, or less than the possibly null-terminated array pointed to by s2.
    7.23.4.5 The strxfrm function
    Synopsis
1          #include <string.h>
           size_t strxfrm(char * restrict s1,
                const char * restrict s2,
                size_t n);
    Description
2   The strxfrm function transforms the string pointed to by s2 and places the resulting
    string into the array pointed to by s1. The transformation is such that if the strcmp
    function is applied to two transformed strings, it returns a value greater than, equal to, or

[page 364]

    less than zero, corresponding to the result of the strcoll function applied to the same
    two original strings. No more than n characters are placed into the resulting array
    pointed to by s1, including the terminating null character. If n is zero, s1 is permitted to
    be a null pointer. If copying takes place between objects that overlap, the behavior is
    undefined.
    Returns
3   The strxfrm function returns the length of the transformed string (not including the
    terminating null character). If the value returned is n or more, the contents of the array
    pointed to by s1 are indeterminate.
4   EXAMPLE The value of the following expression is the size of the array needed to hold the
    transformation of the string pointed to by s.
            1 + strxfrm(NULL, s, 0)

    7.23.5 Search functions
    7.23.5.1 The memchr function
    Synopsis
1           #include <string.h>
            void *memchr(const void *s, int c, size_t n);
    Description
2   The memchr function locates the first occurrence of c (converted to an unsigned
    char) in the initial n characters (each interpreted as unsigned char) of the object
    pointed to by s. The implementation shall behave as if it reads the characters sequentially
    and stops as soon as a matching character is found.
    Returns
3   The memchr function returns a pointer to the located character, or a null pointer if the
    character does not occur in the object.
    7.23.5.2 The strchr function
    Synopsis
1           #include <string.h>
            char *strchr(const char *s, int c);
    Description
2   The strchr function locates the first occurrence of c (converted to a char) in the
    string pointed to by s. The terminating null character is considered to be part of the
    string.



[page 365]

    Returns
3   The strchr function returns a pointer to the located character, or a null pointer if the
    character does not occur in the string.
    7.23.5.3 The strcspn function
    Synopsis
1          #include <string.h>
           size_t strcspn(const char *s1, const char *s2);
    Description
2   The strcspn function computes the length of the maximum initial segment of the string
    pointed to by s1 which consists entirely of characters not from the string pointed to by
    s2.
    Returns
3   The strcspn function returns the length of the segment.
    7.23.5.4 The strpbrk function
    Synopsis
1          #include <string.h>
           char *strpbrk(const char *s1, const char *s2);
    Description
2   The strpbrk function locates the first occurrence in the string pointed to by s1 of any
    character from the string pointed to by s2.
    Returns
3   The strpbrk function returns a pointer to the character, or a null pointer if no character
    from s2 occurs in s1.
    7.23.5.5 The strrchr function
    Synopsis
1          #include <string.h>
           char *strrchr(const char *s, int c);
    Description
2   The strrchr function locates the last occurrence of c (converted to a char) in the
    string pointed to by s. The terminating null character is considered to be part of the
    string.




[page 366]

    Returns
3   The strrchr function returns a pointer to the character, or a null pointer if c does not
    occur in the string.
    7.23.5.6 The strspn function
    Synopsis
1           #include <string.h>
            size_t strspn(const char *s1, const char *s2);
    Description
2   The strspn function computes the length of the maximum initial segment of the string
    pointed to by s1 which consists entirely of characters from the string pointed to by s2.
    Returns
3   The strspn function returns the length of the segment.
    7.23.5.7 The strstr function
    Synopsis
1           #include <string.h>
            char *strstr(const char *s1, const char *s2);
    Description
2   The strstr function locates the first occurrence in the string pointed to by s1 of the
    sequence of characters (excluding the terminating null character) in the string pointed to
    by s2.
    Returns
3   The strstr function returns a pointer to the located string, or a null pointer if the string
    is not found. If s2 points to a string with zero length, the function returns s1.
    7.23.5.8 The strtok function
    Synopsis
1           #include <string.h>
            char *strtok(char * restrict s1,
                 const char * restrict s2);
    Description
2   A sequence of calls to the strtok function breaks the string pointed to by s1 into a
    sequence of tokens, each of which is delimited by a character from the string pointed to
    by s2. The first call in the sequence has a non-null first argument; subsequent calls in the
    sequence have a null first argument. The separator string pointed to by s2 may be
    different from call to call.
[page 367]

3   The first call in the sequence searches the string pointed to by s1 for the first character
    that is not contained in the current separator string pointed to by s2. If no such character
    is found, then there are no tokens in the string pointed to by s1 and the strtok function
    returns a null pointer. If such a character is found, it is the start of the first token.
4   The strtok function then searches from there for a character that is contained in the
    current separator string. If no such character is found, the current token extends to the
    end of the string pointed to by s1, and subsequent searches for a token will return a null
    pointer. If such a character is found, it is overwritten by a null character, which
    terminates the current token. The strtok function saves a pointer to the following
    character, from which the next search for a token will start.
5   Each subsequent call, with a null pointer as the value of the first argument, starts
    searching from the saved pointer and behaves as described above.
6   The strtok function is not required to avoid data races. The implementation shall
    behave as if no library function calls the strtok function.
    Returns
7   The strtok function returns a pointer to the first character of a token, or a null pointer
    if there is no token.
8   EXAMPLE
           #include <string.h>
           static char str[] = "?a???b,,,#c";
           char *t;
           t   =   strtok(str, "?");      //   t   points to the token "a"
           t   =   strtok(NULL, ",");     //   t   points to the token "??b"
           t   =   strtok(NULL, "#,");    //   t   points to the token "c"
           t   =   strtok(NULL, "?");     //   t   is a null pointer

    7.23.6 Miscellaneous functions
    7.23.6.1 The memset function
    Synopsis
1          #include <string.h>
           void *memset(void *s, int c, size_t n);
    Description
2   The memset function copies the value of c (converted to an unsigned char) into
    each of the first n characters of the object pointed to by s.
    Returns
3   The memset function returns the value of s.



[page 368]

    7.23.6.2 The strerror function
    Synopsis
1           #include <string.h>
            char *strerror(int errnum);
    Description
2   The strerror function maps the number in errnum to a message string. Typically,
    the values for errnum come from errno, but strerror shall map any value of type
    int to a message.
3   The strerror function is not required to avoid data races. The implementation shall
    behave as if no library function calls the strerror function.
    Returns
4   The strerror function returns a pointer to the string, the contents of which are locale-
    specific. The array pointed to shall not be modified by the program, but may be
    overwritten by a subsequent call to the strerror function.
    7.23.6.3 The strlen function
    Synopsis
1           #include <string.h>
            size_t strlen(const char *s);
    Description
2   The strlen function computes the length of the string pointed to by s.
    Returns
3   The strlen function returns the number of characters that precede the terminating null
    character.




[page 369]

    7.24 Type-generic math <tgmath.h>
1   The header <tgmath.h> includes the headers <math.h> and <complex.h> and
    defines several type-generic macros.
2   Of the <math.h> and <complex.h> functions without an f (float) or l (long
    double) suffix, several have one or more parameters whose corresponding real type is
    double. For each such function, except modf, there is a corresponding type-generic
    macro.304) The parameters whose corresponding real type is double in the function
    synopsis are generic parameters. Use of the macro invokes a function whose
    corresponding real type and type domain are determined by the arguments for the generic
    parameters.305)
3   Use of the macro invokes a function whose generic parameters have the corresponding
    real type determined as follows:
    -- First, if any argument for generic parameters has type long double, the type
      determined is long double.
    -- Otherwise, if any argument for generic parameters has type double or is of integer
      type, the type determined is double.
    -- Otherwise, the type determined is float.
4   For each unsuffixed function in <math.h> for which there is a function in
    <complex.h> with the same name except for a c prefix, the corresponding type-
    generic macro (for both functions) has the same name as the function in <math.h>. The
    corresponding type-generic macro for fabs and cabs is fabs.




    304) Like other function-like macros in Standard libraries, each type-generic macro can be suppressed to
         make available the corresponding ordinary function.
    305) If the type of the argument is not compatible with the type of the parameter for the selected function,
         the behavior is undefined.

[page 370]

             <math.h>         <complex.h>              type-generic
              function           function                 macro
               acos              cacos                   acos
               asin              casin                   asin
               atan              catan                   atan
               acosh             cacosh                  acosh
               asinh             casinh                  asinh
               atanh             catanh                  atanh
               cos               ccos                    cos
               sin               csin                    sin
               tan               ctan                    tan
               cosh              ccosh                   cosh
               sinh              csinh                   sinh
               tanh              ctanh                   tanh
               exp               cexp                    exp
               log               clog                    log
               pow               cpow                    pow
               sqrt              csqrt                   sqrt
               fabs              cabs                    fabs
    If at least one argument for a generic parameter is complex, then use of the macro invokes
    a complex function; otherwise, use of the macro invokes a real function.
5   For each unsuffixed function in <math.h> without a c-prefixed counterpart in
    <complex.h> (except modf), the corresponding type-generic macro has the same
    name as the function. These type-generic macros are:
            atan2              fma                  llround              remainder
            cbrt               fmax                 log10                remquo
            ceil               fmin                 log1p                rint
            copysign           fmod                 log2                 round
            erf                frexp                logb                 scalbn
            erfc               hypot                lrint                scalbln
            exp2               ilogb                lround               tgamma
            expm1              ldexp                nearbyint            trunc
            fdim               lgamma               nextafter
            floor              llrint               nexttoward
    If all arguments for generic parameters are real, then use of the macro invokes a real
    function; otherwise, use of the macro results in undefined behavior.




[page 371]

6   For each unsuffixed function in <complex.h> that is not a c-prefixed counterpart to a
    function in <math.h>, the corresponding type-generic macro has the same name as the
    function. These type-generic macros are:
           carg                     conj                     creal
           cimag                    cproj
    Use of the macro with any real or complex argument invokes a complex function.
7   EXAMPLE       With the declarations
            #include <tgmath.h>
            int n;
            float f;
            double d;
            long double ld;
            float complex fc;
            double complex dc;
            long double complex ldc;
    functions invoked by use of type-generic macros are shown in the following table:
                     macro use                                  invokes
                exp(n)                              exp(n), the function
                acosh(f)                            acoshf(f)
                sin(d)                              sin(d), the function
                atan(ld)                            atanl(ld)
                log(fc)                             clogf(fc)
                sqrt(dc)                            csqrt(dc)
                pow(ldc, f)                         cpowl(ldc, f)
                remainder(n, n)                     remainder(n, n), the function
                nextafter(d, f)                     nextafter(d, f), the function
                nexttoward(f, ld)                   nexttowardf(f, ld)
                copysign(n, ld)                     copysignl(n, ld)
                ceil(fc)                            undefined behavior
                rint(dc)                            undefined behavior
                fmax(ldc, ld)                       undefined behavior
                carg(n)                             carg(n), the function
                cproj(f)                            cprojf(f)
                creal(d)                            creal(d), the function
                cimag(ld)                           cimagl(ld)
                fabs(fc)                            cabsf(fc)
                carg(dc)                            carg(dc), the function
                cproj(ldc)                          cprojl(ldc)




[page 372]

    7.25 Threads <threads.h>
    7.25.1 Introduction
1   The header <threads.h> defines macros, and declares types, enumeration constants,
    and functions that support multiple threads of execution.
2   Implementations that define the macro __STDC_NO_THREADS__ need not provide
    this header nor support any of its facilities.
3   The macros are
            ONCE_FLAG_INIT
    which expands to a value that can be used to initialize an object of type once_flag;
    and
            TSS_DTOR_ITERATIONS
    which expands to an integer constant expression representing the maximum number of
    times that destructors will be called when a thread terminates.
4   The types are
            cnd_t
    which is a complete object type that holds an identifier for a condition variable;
            thrd_t
    which is a complete object type that holds an identifier for a thread;
            tss_t
    which is a complete object type that holds an identifier for a thread-specific storage
    pointer;
            mtx_t
    which is a complete object type that holds an identifier for a mutex;
            tss_dtor_t
    which is the function pointer type void (*)(void*), used for a destructor for a
    thread-specific storage pointer;
            thrd_start_t
    which is the function pointer type int (*)(void*) that is passed to thrd_create
    to create a new thread;
            once_flag
    which is a complete object type that holds a flag for use by call_once; and


[page 373]

           xtime
    which is a structure type that holds a time specified in seconds and nanoseconds. The
    structure shall contain at least the following members, in any order.
           time_t sec;
           long nsec;
5   The enumeration constants are
           mtx_plain
    which is passed to mtx_init to create a mutex object that supports neither timeout nor
    test and return;
           mtx_recursive
    which is passed to mtx_init to create a mutex object that supports recursive locking;
           mtx_timed
    which is passed to mtx_init to create a mutex object that supports timeout;
           mtx_try
    which is passed to mtx_init to create a mutex object that supports test and return;
           thrd_timeout
    which is returned by a timed wait function to indicate that the time specified in the call
    was reached without acquiring the requested resource;
           thrd_success
    which is returned by a function to indicate that the requested operation succeeded;
           thrd_busy
    which is returned by a function to indicate that the requested operation failed because a
    resource requested by a test and return function is already in use;
           thrd_error
    which is returned by a function to indicate that the requested operation failed; and
           thrd_nomem
    which is returned by a function to indicate that the requested operation failed because it
    was unable to allocate memory.




[page 374]

    7.25.2 Initialization functions
    7.25.2.1 The call_once function
    Synopsis
1           #include <threads.h>
            void call_once(once_flag *flag, void (*func)(void));
    Description
2   The call_once function uses the once_flag pointed to by flag to ensure that
    func is called exactly once, the first time the call_once function is called with that
    value of flag. Completion of an effective call to the call_once function synchronizes
    with all subsequent calls to the call_once function with the same value of flag.
    Returns
3   The call_once function returns no value.
    7.25.3 Condition variable functions
    7.25.3.1 The cnd_broadcast function
    Synopsis
1           #include <threads.h>
            int cnd_broadcast(cnd_t *cond);
    Description
2   The cnd_broadcast function unblocks all of the threads that are blocked on the
    condition variable pointed to by cond at the time of the call. If no threads are blocked
    on the condition variable pointed to by cond at the time of the call, the function does
    nothing.
    Returns
3   The cnd_broadcast function returns thrd_success on success, or thrd_error
    if the request could not be honored.
    7.25.3.2 The cnd_destroy function
    Synopsis
1           #include <threads.h>
            void cnd_destroy(cnd_t *cond);
    Description
2   The cnd_destroy function releases all resources used by the condition variable
    pointed to by cond. The cnd_destroy function requires that no threads be blocked
    waiting for the condition variable pointed to by cond.

[page 375]

    Returns
3   The cnd_destroy function returns no value.
    7.25.3.3 The cnd_init function
    Synopsis
1          #include <threads.h>
           int cnd_init(cnd_t *cond);
    Description
2   The cnd_init function creates a condition variable. If it succeeds it sets the variable
    pointed to by cond to a value that uniquely identifies the newly created condition
    variable. A thread that calls cnd_wait on a newly created condition variable will
    block.
    Returns
3   The cnd_init function returns thrd_success on success, or thrd_nomem if no
    memory could be allocated for the newly created condition, or thrd_error if the
    request could not be honored.
    7.25.3.4 The cnd_signal function
    Synopsis
1          #include <threads.h>
           int cnd_signal(cnd_t *cond);
    Description
2   The cnd_signal function unblocks one of the threads that are blocked on the
    condition variable pointed to by cond at the time of the call. If no threads are blocked
    on the condition variable at the time of the call, the function does nothing and return
    success.
    Returns
3   The cnd_signal function returns thrd_success on success or thrd_error if
    the request could not be honored.
    7.25.3.5 The cnd_timedwait function
    Synopsis
1          #include <threads.h>
           int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
                const xtime *xt);




[page 376]

    Description
2   The cnd_timedwait function atomically unlocks the mutex pointed to by mtx and
    endeavors to block until the condition variable pointed to by cond is signaled by a call to
    cnd_signal or to cnd_broadcast, or until after the time specified by the xtime
    object pointed to by xt. When the calling thread becomes unblocked it locks the variable
    pointed to by mtx before it returns. The cnd_timedwait function requires that the
    mutex pointed to by mtx be locked by the calling thread.
    Returns
3   The cnd_timedwait function returns thrd_success upon success, or
    thrd_timeout if the time specified in the call was reached without acquiring the
    requested resource, or thrd_error if the request could not be honored.
    7.25.3.6 The cnd_wait function
    Synopsis
1           #include <threads.h>
            int cnd_wait(cnd_t *cond, mtx_t *mtx);
    Description
2   The cnd_wait function atomically unlocks the mutex pointed to by mtx and endeavors
    to block until the condition variable pointed to by cond is signaled by a call to
    cnd_signal or to cnd_broadcast. When the calling thread becomes unblocked it
    locks the mutex pointed to by mtx before it returns. If the mutex pointed to by mtx is
    not locked by the calling thread, the cnd_wait function will act as if the abort
    function is called.
    Returns
3   The cnd_wait function returns thrd_success on success or thrd_error if the
    request could not be honored.
    7.25.4 Mutex functions
    7.25.4.1 The mtx_destroy function
    Synopsis
1           #include <threads.h>
            void mtx_destroy(mtx_t *mtx);
    Description
2   The mtx_destroy function releases any resources used by the mutex pointed to by
    mtx. No threads can be blocked waiting for the mutex pointed to by mtx.



[page 377]

    Returns
3   The mtx_destroy function returns no value.
    7.25.4.2 The mtx_init function
    Synopsis
1          #include <threads.h>
           int mtx_init(mtx_t *mtx, int type);
    Description
2   The mtx_init function creates a mutex object with properties indicated by type,
    which must have one of the six values:
    mtx_plain for a simple non-recursive mutex,
    mtx_timed for a non-recursive mutex that supports timeout,
    mtx_try      for a non-recursive mutex that supports test and return,
    mtx_plain | mtx_recursive for a simple recursive mutex,
    mtx_timed | mtx_recursive for a recursive mutex that supports timeout, or
    mtx_try | mtx_recursive for a recursive mutex that supports test and return.
3   If the mtx_init function succeeds, it sets the mutex pointed to by mtx to a value that
    uniquely identifies the newly created mutex.
    Returns
4   The mtx_init function returns thrd_success on success, or thrd_error if the
    request could not be honored.
    7.25.4.3 The mtx_lock function
    Synopsis
1          #include <threads.h>
           int mtx_lock(mtx_t *mtx);
    Description
2   The mtx_lock function blocks until it locks the mutex pointed to by mtx. If the mutex
    is non-recursive, it shall not be locked by the calling thread. Prior calls to mtx_unlock
    on the same mutex shall synchronize with this operation.
    Returns
3   The mtx_lock function returns thrd_success on success, or thrd_busy if the
    resource requested is already in use, or thrd_error if the request could not be
    honored.




[page 378]

    7.25.4.4 The mtx_timedlock function
    Synopsis
1           #include <threads.h>
            int mtx_timedlock(mtx_t *mtx, const xtime *xt);
    Description
2   The mtx_timedlock function endeavors to block until it locks the mutex pointed to by
    mtx or until the time specified by the xtime object xt has passed. The specified mutex
    shall support timeout. If the operation succeeds, prior calls to mtx_unlock on the same
    mutex shall synchronize with this operation.
    Returns
3   The mtx_timedlock function returns thrd_success on success, or thrd_busy
    if the resource requested is already in use, or thrd_timeout if the time specified was
    reached without acquiring the requested resource, or thrd_error if the request could
    not be honored.
    7.25.4.5 The mtx_trylock function
    Synopsis
1           #include <threads.h>
            int mtx_trylock(mtx_t *mtx);
    Description
2   The mtx_trylock function endeavors to lock the mutex pointed to by mtx. The
    specified mutex shall support either test and return or timeout. If the mutex is already
    locked, the function returns without blocking. If the operation succeeds, prior calls to
    mtx_unlock on the same mutex shall synchronize with this operation.
    Returns
3   The mtx_trylock function returns thrd_success on success, or thrd_busy if
    the resource requested is already in use, or thrd_error if the request could not be
    honored.
    7.25.4.6 The mtx_unlock function
    Synopsis
1           #include <threads.h>
            int mtx_unlock(mtx_t *mtx);
    Description
2   The mtx_unlock function unlocks the mutex pointed to by mtx. The mutex pointed to
    by mtx shall be locked by the calling thread.

[page 379]

    Returns
3   The mtx_unlock function returns thrd_success on success or thrd_error if
    the request could not be honored.
    7.25.5 Thread functions
    7.25.5.1 The thrd_create function
    Synopsis
1          #include <threads.h>
           int thrd_create(thrd_t *thr, thrd_start_t func,
                void *arg);
    Description
2   The thrd_create function creates a new thread executing func(arg). If the
    thrd_create function succeeds, it sets the object pointed to by thr to the identifier of
    the newly created thread. (A thread's identifier may be reused for a different thread once
    the original thread has exited and either been detached or joined to another thread.) The
    completion of the thrd_create function synchronizes with the beginning of the
    execution of the new thread.
    Returns
3   The thrd_create function returns thrd_success on success, or thrd_nomem if
    no memory could be allocated for the thread requested, or thrd_error if the request
    could not be honored.
    7.25.5.2 The thrd_current function
    Synopsis
1          #include <threads.h>
           thrd_t thrd_current(void);
    Description
2   The thrd_current function identifies the thread that called it.
    Returns
3   The thrd_current function returns the identifier of the thread that called it.
    7.25.5.3 The thrd_detach function
    Synopsis
1          #include <threads.h>
           int thrd_detach(thrd_t thr);



[page 380]

    Description
2   The thrd_detach function tells the operating system to dispose of any resources
    allocated to the thread identified by thr when that thread terminates. The thread
    identified by thr shall not have been previously detached or joined with another thread.
    Returns
3   The thrd_detach function returns thrd_success on success or thrd_error if
    the request could not be honored.
    7.25.5.4 The thrd_equal function
    Synopsis
1           #include <threads.h>
            int thrd_equal(thrd_t thr0, thrd_t thr1);
    Description
2   The thrd_equal function will determine whether the thread identified by thr0 refers
    to the thread identified by thr1.
    Returns
3   The thrd_equal function returns zero if the thread thr0 and the thread thr1 refer to
    different threads. Otherwise the thrd_equal function returns a nonzero value.
    7.25.5.5 The thrd_exit function
    Synopsis
1           #include <threads.h>
            void thrd_exit(int res);
    Description
2   The thrd_exit function terminates execution of the calling thread and sets its result
    code to res.
    Returns
3   The thrd_exit function returns no value.
    7.25.5.6 The thrd_join function
    Synopsis
1           #include <threads.h>
            int thrd_join(thrd_t thr, int *res);
    Description
2   The thrd_join function joins the thread identified by thr with the current thread by
    blocking until the other thread has terminated. If the parameter res is not a null pointer,

[page 381]

    it stores the thread's result code in the integer pointed to by res. The termination of the
    other thread synchronizes with the completion of the thrd_join function. The thread
    identified by thr shall not have been previously detached or joined with another thread.
    Returns
3   The thrd_join function returns thrd_success on success or thrd_error if the
    request could not be honored.
    7.25.5.7 The thrd_sleep function
    Synopsis
1          #include <threads.h>
           void thrd_sleep(const xtime *xt);
    Description
2   The thrd_sleep function suspends execution of the calling thread until after the time
    specified by the xtime object pointed to by xt.
    Returns
3   The thrd_sleep function returns no value.
    7.25.5.8 The thrd_yield function
    Synopsis
1          #include <threads.h>
           void thrd_yield(void);
    Description
2   The thrd_yield function endeavors to permit other threads to run, even if the current
    thread would ordinarily continue to run.
    Returns
3   The thrd_yield function returns no value.
    7.25.6 Thread-specific storage functions
    7.25.6.1 The tss_create function
    Synopsis
1          #include <threads.h>
           int tss_create(tss_t *key, tss_dtor_t dtor);
    Description
2   The tss_create function creates a thread-specific storage pointer with destructor
    dtor, which may be null.


[page 382]

    Returns
3   If the tss_create function is successful, it sets the thread-specific storage pointed to
    by key to a value that uniquely identifies the newly created pointer and returns
    thrd_success; otherwise, thrd_error is returned and the thread-specific storage
    pointed to by key is set to an undefined value.
    7.25.6.2 The tss_delete function
    Synopsis
1           #include <threads.h>
            void tss_delete(tss_t key);
    Description
2   The tss_delete function releases any resources used by the thread-specific storage
    identified by key.
    Returns
3   The tss_delete function returns no value.
    7.25.6.3 The tss_get function
    Synopsis
1           #include <threads.h>
            void *tss_get(tss_t key);
    Description
2   The tss_get function returns the value for the current thread held in the thread-specific
    storage identified by key.
    Returns
3   The tss_get function returns the value for the current thread if successful, or zero if
    unsuccessful.
    7.25.6.4 The tss_set function
    Synopsis
1           #include <threads.h>
            int tss_set(tss_t key, void *val);
    Description
2   The tss_set function sets the value for the current thread held in the thread-specific
    storage identified by key to val.




[page 383]

    Returns
3   The tss_set function returns thrd_success on success or thrd_error if the
    request could not be honored.
    7.25.7 Time functions
    7.25.7.1 The xtime_get function
    Synopsis
1           #include <threads.h>
            int xtime_get(xtime *xt, int base);
    Description
2   The xtime_get function sets the xtime object pointed to by xt to hold the current
    time based on the time base base.
    Returns
3   If the xtime_get function is successful it returns the nonzero value base, which must
    be TIME_UTC; otherwise, it returns zero.306)




    306) Although an xtime object describes times with nanosecond resolution, the actual resolution in an
         xtime object is system dependent.

[page 384]

    7.26 Date and time <time.h>
    7.26.1 Components of time
1   The header <time.h> defines two macros, and declares several types and functions for
    manipulating time. Many functions deal with a calendar time that represents the current
    date (according to the Gregorian calendar) and time. Some functions deal with local
    time, which is the calendar time expressed for some specific time zone, and with Daylight
    Saving Time, which is a temporary change in the algorithm for determining local time.
    The local time zone and Daylight Saving Time are implementation-defined.
2   The macros defined are NULL (described in 7.19); and
            CLOCKS_PER_SEC
    which expands to an expression with type clock_t (described below) that is the
    number per second of the value returned by the clock function.
3   The types declared are size_t (described in 7.19);
            clock_t
    and
            time_t
    which are arithmetic types capable of representing times; and
            struct tm
    which holds the components of a calendar time, called the broken-down time.
4   The range and precision of times representable in clock_t and time_t are
    implementation-defined. The tm structure shall contain at least the following members,
    in any order. The semantics of the members and their normal ranges are expressed in the
    comments.307)
            int    tm_sec;           //   seconds after the minute -- [0, 60]
            int    tm_min;           //   minutes after the hour -- [0, 59]
            int    tm_hour;          //   hours since midnight -- [0, 23]
            int    tm_mday;          //   day of the month -- [1, 31]
            int    tm_mon;           //   months since January -- [0, 11]
            int    tm_year;          //   years since 1900
            int    tm_wday;          //   days since Sunday -- [0, 6]
            int    tm_yday;          //   days since January 1 -- [0, 365]
            int    tm_isdst;         //   Daylight Saving Time flag



    307) The range [0, 60] for tm_sec allows for a positive leap second.

[page 385]

    The value of tm_isdst is positive if Daylight Saving Time is in effect, zero if Daylight
    Saving Time is not in effect, and negative if the information is not available.
    7.26.2 Time manipulation functions
    7.26.2.1 The clock function
    Synopsis
1           #include <time.h>
            clock_t clock(void);
    Description
2   The clock function determines the processor time used.
    Returns
3   The clock function returns the implementation's best approximation to the processor
    time used by the program since the beginning of an implementation-defined era related
    only to the program invocation. To determine the time in seconds, the value returned by
    the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If
    the processor time used is not available or its value cannot be represented, the function
    returns the value (clock_t)(-1).308)
    7.26.2.2 The difftime function
    Synopsis
1           #include <time.h>
            double difftime(time_t time1, time_t time0);
    Description
2   The difftime function computes the difference between two calendar times: time1 -
    time0.
    Returns
3   The difftime function returns the difference expressed in seconds as a double.




    308) In order to measure the time spent in a program, the clock function should be called at the start of
         the program and its return value subtracted from the value returned by subsequent calls.

[page 386]

    7.26.2.3 The mktime function
    Synopsis
1           #include <time.h>
            time_t mktime(struct tm *timeptr);
    Description
2   The mktime function converts the broken-down time, expressed as local time, in the
    structure pointed to by timeptr into a calendar time value with the same encoding as
    that of the values returned by the time function. The original values of the tm_wday
    and tm_yday components of the structure are ignored, and the original values of the
    other components are not restricted to the ranges indicated above.309) On successful
    completion, the values of the tm_wday and tm_yday components of the structure are
    set appropriately, and the other components are set to represent the specified calendar
    time, but with their values forced to the ranges indicated above; the final value of
    tm_mday is not set until tm_mon and tm_year are determined.
    Returns
3   The mktime function returns the specified calendar time encoded as a value of type
    time_t. If the calendar time cannot be represented, the function returns the value
    (time_t)(-1).
4   EXAMPLE       What day of the week is July 4, 2001?
            #include <stdio.h>
            #include <time.h>
            static const char *const wday[] = {
                    "Sunday", "Monday", "Tuesday", "Wednesday",
                    "Thursday", "Friday", "Saturday", "-unknown-"
            };
            struct tm time_str;
            /* ... */




    309) Thus, a positive or zero value for tm_isdst causes the mktime function to presume initially that
         Daylight Saving Time, respectively, is or is not in effect for the specified time. A negative value
         causes it to attempt to determine whether Daylight Saving Time is in effect for the specified time.

[page 387]

           time_str.tm_year   = 2001 - 1900;
           time_str.tm_mon    = 7 - 1;
           time_str.tm_mday   = 4;
           time_str.tm_hour   = 0;
           time_str.tm_min    = 0;
           time_str.tm_sec    = 1;
           time_str.tm_isdst = -1;
           if (mktime(&time_str) == (time_t)(-1))
                 time_str.tm_wday = 7;
           printf("%s\n", wday[time_str.tm_wday]);

    7.26.2.4 The time function
    Synopsis
1          #include <time.h>
           time_t time(time_t *timer);
    Description
2   The time function determines the current calendar time. The encoding of the value is
    unspecified.
    Returns
3   The time function returns the implementation's best approximation to the current
    calendar time. The value (time_t)(-1) is returned if the calendar time is not
    available. If timer is not a null pointer, the return value is also assigned to the object it
    points to.
    7.26.3 Time conversion functions
1   Except for the strftime function, these functions each return a pointer to one of two
    types of static objects: a broken-down time structure or an array of char. Execution of
    any of the functions that return a pointer to one of these object types may overwrite the
    information in any object of the same type pointed to by the value returned from any
    previous call to any of them and the functions are not required to avoid data races. The
    implementation shall behave as if no other library functions call these functions.
    7.26.3.1 The asctime function
    Synopsis
1          #include <time.h>
           char *asctime(const struct tm *timeptr);
    Description
2   The asctime function converts the broken-down time in the structure pointed to by
    timeptr into a string in the form
           Sun Sep 16 01:03:52 1973\n\0

[page 388]

    using the equivalent of the following algorithm.
    char *asctime(const struct tm *timeptr)
    {
         static const char wday_name[7][3] = {
              "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
         };
         static const char mon_name[12][3] = {
              "Jan", "Feb", "Mar", "Apr", "May", "Jun",
              "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
         };
         static char result[26];
            sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
                 wday_name[timeptr->tm_wday],
                 mon_name[timeptr->tm_mon],
                 timeptr->tm_mday, timeptr->tm_hour,
                 timeptr->tm_min, timeptr->tm_sec,
                 1900 + timeptr->tm_year);
            return result;
    }
3   If any of the fields of the broken-down time contain values that are outside their normal
    ranges,310) the behavior of the asctime function is undefined. Likewise, if the
    calculated year exceeds four digits or is less than the year 1000, the behavior is
    undefined.
    Returns
4   The asctime function returns a pointer to the string.
    7.26.3.2 The ctime function
    Synopsis
1           #include <time.h>
            char *ctime(const time_t *timer);
    Description
2   The ctime function converts the calendar time pointed to by timer to local time in the
    form of a string. It is equivalent to
            asctime(localtime(timer))



    310) See 7.26.1.

[page 389]

    Returns
3   The ctime function returns the pointer returned by the asctime function with that
    broken-down time as argument.
    Forward references: the localtime function (7.26.3.4).
    7.26.3.3 The gmtime function
    Synopsis
1          #include <time.h>
           struct tm *gmtime(const time_t *timer);
    Description
2   The gmtime function converts the calendar time pointed to by timer into a broken-
    down time, expressed as UTC.
    Returns
3   The gmtime function returns a pointer to the broken-down time, or a null pointer if the
    specified time cannot be converted to UTC.
    7.26.3.4 The localtime function
    Synopsis
1          #include <time.h>
           struct tm *localtime(const time_t *timer);
    Description
2   The localtime function converts the calendar time pointed to by timer into a
    broken-down time, expressed as local time.
    Returns
3   The localtime function returns a pointer to the broken-down time, or a null pointer if
    the specified time cannot be converted to local time.
    7.26.3.5 The strftime function
    Synopsis
1          #include <time.h>
           size_t strftime(char * restrict s,
                size_t maxsize,
                const char * restrict format,
                const struct tm * restrict timeptr);




[page 390]

    Description
2   The strftime function places characters into the array pointed to by s as controlled by
    the string pointed to by format. The format shall be a multibyte character sequence,
    beginning and ending in its initial shift state. The format string consists of zero or
    more conversion specifiers and ordinary multibyte characters. A conversion specifier
    consists of a % character, possibly followed by an E or O modifier character (described
    below), followed by a character that determines the behavior of the conversion specifier.
    All ordinary multibyte characters (including the terminating null character) are copied
    unchanged into the array. If copying takes place between objects that overlap, the
    behavior is undefined. No more than maxsize characters are placed into the array.
3   Each conversion specifier is replaced by appropriate characters as described in the
    following list. The appropriate characters are determined using the LC_TIME category
    of the current locale and by the values of zero or more members of the broken-down time
    structure pointed to by timeptr, as specified in brackets in the description. If any of
    the specified values is outside the normal range, the characters stored are unspecified.
    %a   is replaced by the locale's abbreviated weekday name. [tm_wday]
    %A   is replaced by the locale's full weekday name. [tm_wday]
    %b   is replaced by the locale's abbreviated month name. [tm_mon]
    %B   is replaced by the locale's full month name. [tm_mon]
    %c   is replaced by the locale's appropriate date and time representation. [all specified
         in 7.26.1]
    %C   is replaced by the year divided by 100 and truncated to an integer, as a decimal
         number (00-99). [tm_year]
    %d   is replaced by the day of the month as a decimal number (01-31). [tm_mday]
    %D   is equivalent to ''%m/%d/%y''. [tm_mon, tm_mday, tm_year]
    %e   is replaced by the day of the month as a decimal number (1-31); a single digit is
         preceded by a space. [tm_mday]
    %F   is equivalent to ''%Y-%m-%d'' (the ISO 8601 date format). [tm_year, tm_mon,
         tm_mday]
    %g   is replaced by the last 2 digits of the week-based year (see below) as a decimal
         number (00-99). [tm_year, tm_wday, tm_yday]
    %G   is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
         [tm_year, tm_wday, tm_yday]
    %h   is equivalent to ''%b''. [tm_mon]
    %H   is replaced by the hour (24-hour clock) as a decimal number (00-23). [tm_hour]
    %I   is replaced by the hour (12-hour clock) as a decimal number (01-12). [tm_hour]
    %j   is replaced by the day of the year as a decimal number (001-366). [tm_yday]
    %m   is replaced by the month as a decimal number (01-12). [tm_mon]
    %M   is replaced by the minute as a decimal number (00-59). [tm_min]
    %n   is replaced by a new-line character.

[page 391]

    %p    is replaced by the locale's equivalent of the AM/PM designations associated with a
          12-hour clock. [tm_hour]
    %r    is replaced by the locale's 12-hour clock time. [tm_hour, tm_min, tm_sec]
    %R    is equivalent to ''%H:%M''. [tm_hour, tm_min]
    %S    is replaced by the second as a decimal number (00-60). [tm_sec]
    %t    is replaced by a horizontal-tab character.
    %T    is equivalent to ''%H:%M:%S'' (the ISO 8601 time format). [tm_hour, tm_min,
          tm_sec]
    %u    is replaced by the ISO 8601 weekday as a decimal number (1-7), where Monday
          is 1. [tm_wday]
    %U    is replaced by the week number of the year (the first Sunday as the first day of week
          1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
    %V    is replaced by the ISO 8601 week number (see below) as a decimal number
          (01-53). [tm_year, tm_wday, tm_yday]
    %w    is replaced by the weekday as a decimal number (0-6), where Sunday is 0.
          [tm_wday]
    %W    is replaced by the week number of the year (the first Monday as the first day of
          week 1) as a decimal number (00-53). [tm_year, tm_wday, tm_yday]
    %x    is replaced by the locale's appropriate date representation. [all specified in 7.26.1]
    %X    is replaced by the locale's appropriate time representation. [all specified in 7.26.1]
    %y    is replaced by the last 2 digits of the year as a decimal number (00-99).
          [tm_year]
    %Y    is replaced by the year as a decimal number (e.g., 1997). [tm_year]
    %z    is replaced by the offset from UTC in the ISO 8601 format ''-0430'' (meaning 4
          hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time
          zone is determinable. [tm_isdst]
    %Z    is replaced by the locale's time zone name or abbreviation, or by no characters if no
          time zone is determinable. [tm_isdst]
    %%    is replaced by %.
4   Some conversion specifiers can be modified by the inclusion of an E or O modifier
    character to indicate an alternative format or specification. If the alternative format or
    specification does not exist for the current locale, the modifier is ignored.
    %Ec is replaced by the locale's alternative date and time representation.
    %EC is replaced by the name of the base year (period) in the locale's alternative
        representation.
    %Ex is replaced by the locale's alternative date representation.
    %EX is replaced by the locale's alternative time representation.
    %Ey is replaced by the offset from %EC (year only) in the locale's alternative
        representation.
    %EY is replaced by the locale's full alternative year representation.

[page 392]

    %Od is replaced by the day of the month, using the locale's alternative numeric symbols
        (filled as needed with leading zeros, or with leading spaces if there is no alternative
        symbol for zero).
    %Oe is replaced by the day of the month, using the locale's alternative numeric symbols
        (filled as needed with leading spaces).
    %OH is replaced by the hour (24-hour clock), using the locale's alternative numeric
        symbols.
    %OI is replaced by the hour (12-hour clock), using the locale's alternative numeric
        symbols.
    %Om is replaced by the month, using the locale's alternative numeric symbols.
    %OM is replaced by the minutes, using the locale's alternative numeric symbols.
    %OS is replaced by the seconds, using the locale's alternative numeric symbols.
    %Ou is replaced by the ISO 8601 weekday as a number in the locale's alternative
        representation, where Monday is 1.
    %OU is replaced by the week number, using the locale's alternative numeric symbols.
    %OV is replaced by the ISO 8601 week number, using the locale's alternative numeric
        symbols.
    %Ow is replaced by the weekday as a number, using the locale's alternative numeric
        symbols.
    %OW is replaced by the week number of the year, using the locale's alternative numeric
        symbols.
    %Oy is replaced by the last 2 digits of the year, using the locale's alternative numeric
        symbols.
5   %g, %G, and %V give values according to the ISO 8601 week-based year. In this system,
    weeks begin on a Monday and week 1 of the year is the week that includes January 4th,
    which is also the week that includes the first Thursday of the year, and is also the first
    week that contains at least four days in the year. If the first Monday of January is the
    2nd, 3rd, or 4th, the preceding days are part of the last week of the preceding year; thus,
    for Saturday 2nd January 1999, %G is replaced by 1998 and %V is replaced by 53. If
    December 29th, 30th, or 31st is a Monday, it and any following days are part of week 1 of
    the following year. Thus, for Tuesday 30th December 1997, %G is replaced by 1998 and
    %V is replaced by 01.
6   If a conversion specifier is not one of the above, the behavior is undefined.
7   In the "C" locale, the E and O modifiers are ignored and the replacement strings for the
    following specifiers are:
    %a the first three characters of %A.
    %A one of ''Sunday'', ''Monday'', ... , ''Saturday''.
    %b the first three characters of %B.
    %B one of ''January'', ''February'', ... , ''December''.
    %c equivalent to ''%a %b %e %T %Y''.
[page 393]

    %p    one of ''AM'' or ''PM''.
    %r    equivalent to ''%I:%M:%S %p''.
    %x    equivalent to ''%m/%d/%y''.
    %X    equivalent to %T.
    %Z    implementation-defined.
    Returns
8   If the total number of resulting characters including the terminating null character is not
    more than maxsize, the strftime function returns the number of characters placed
    into the array pointed to by s not including the terminating null character. Otherwise,
    zero is returned and the contents of the array are indeterminate.




[page 394]

    7.27 Unicode utilities <uchar.h>
1   The header <uchar.h> declares types and functions for manipulating Unicode
    characters.
2   The types declared are mbstate_t (described in 7.29.1) and size_t (described in
    7.19);
            char16_t
    which is an unsigned integer type used for 16-bit characters and is the same type as
    uint_least16_t (described in 7.20.1.2); and
            char32_t
    which is an unsigned integer type used for 32-bit characters and is the same type as
    uint_least32_t (also described in 7.20.1.2).
    7.27.1 Restartable multibyte/wide character conversion functions
1   These functions have a parameter, ps, of type pointer to mbstate_t that points to an
    object that can completely describe the current conversion state of the associated
    multibyte character sequence, which the functions alter as necessary. If ps is a null
    pointer, each function uses its own internal mbstate_t object instead, which is
    initialized at program startup to the initial conversion state; the functions are not required
    to avoid data races in this case. The implementation behaves as if no library function
    calls these functions with a null pointer for ps.
    7.27.1.1 The mbrtoc16 function
    Synopsis
1           #include <uchar.h>
            size_t mbrtoc16(char16_t * restrict pc16,
                 const char * restrict s, size_t n,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the mbrtoc16 function is equivalent to the call:
                   mbrtoc16(NULL, "", 1, ps)
    In this case, the values of the parameters pc16 and n are ignored.
3   If s is not a null pointer, the mbrtoc16 function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the values of the
    corresponding wide characters and then, if pc16 is not a null pointer, stores the value of
    the first (or only) such character in the object pointed to by pc16. Subsequent calls will
[page 395]

    store successive wide characters without consuming any additional input until all the
    characters have been stored. If the corresponding wide character is the null wide
    character, the resulting state described is the initial conversion state.
    Returns
4   The mbrtoc16 function returns the first of the following that applies (given the current
    conversion state):
    0                     if the next n or fewer bytes complete the multibyte character that
                          corresponds to the null wide character (which is the value stored).
    between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                       character (which is the value stored); the value returned is the number
                       of bytes that complete the multibyte character.
    (size_t)(-3) if the next character resulting from a previous call has been stored (no
                 bytes from the input have been consumed by this call).
    (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                 multibyte character, and all n bytes have been processed (no value is
                 stored).311)
    (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                 do not contribute to a complete and valid multibyte character (no
                 value is stored); the value of the macro EILSEQ is stored in errno,
                 and the conversion state is unspecified.
    7.27.1.2 The c16rtomb function
    Synopsis
1           #include <uchar.h>
            size_t c16rtomb(char * restrict s, char16_t c16,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the c16rtomb function is equivalent to the call
                    c16rtomb(buf, L'\0', ps)
    where buf is an internal buffer.
3   If s is not a null pointer, the c16rtomb function determines the number of bytes needed
    to represent the multibyte character that corresponds to the wide character given by c16
    (including any shift sequences), and stores the multibyte character representation in the


    311) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
         sequence of redundant shift sequences (for implementations with state-dependent encodings).

[page 396]

    array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
    c16 is a null wide character, a null byte is stored, preceded by any shift sequence needed
    to restore the initial shift state; the resulting state described is the initial conversion state.
    Returns
4   The c16rtomb function returns the number of bytes stored in the array object (including
    any shift sequences). When c16 is not a valid wide character, an encoding error occurs:
    the function stores the value of the macro EILSEQ in errno and returns
    (size_t)(-1); the conversion state is unspecified.
    7.27.1.3 The mbrtoc32 function
    Synopsis
1           #include <uchar.h>
            size_t mbrtoc32(char32_t * restrict pc32,
                 const char * restrict s, size_t n,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the mbrtoc32 function is equivalent to the call:
                    mbrtoc32(NULL, "", 1, ps)
    In this case, the values of the parameters pc32 and n are ignored.
3   If s is not a null pointer, the mbrtoc32 function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the values of the
    corresponding wide characters and then, if pc32 is not a null pointer, stores the value of
    the first (or only) such character in the object pointed to by pc32. Subsequent calls will
    store successive wide characters without consuming any additional input until all the
    characters have been stored. If the corresponding wide character is the null wide
    character, the resulting state described is the initial conversion state.
    Returns
4   The mbrtoc32 function returns the first of the following that applies (given the current
    conversion state):
    0                    if the next n or fewer bytes complete the multibyte character that
                         corresponds to the null wide character (which is the value stored).
    between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                       character (which is the value stored); the value returned is the number
                       of bytes that complete the multibyte character.


[page 397]

    (size_t)(-3) if the next character resulting from a previous call has been stored (no
                 bytes from the input have been consumed by this call).
    (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                 multibyte character, and all n bytes have been processed (no value is
                 stored).312)
    (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                 do not contribute to a complete and valid multibyte character (no
                 value is stored); the value of the macro EILSEQ is stored in errno,
                 and the conversion state is unspecified.
    7.27.1.4 The c32rtomb function
    Synopsis
1           #include <uchar.h>
            size_t c32rtomb(char * restrict s, char32_t c32,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the c32rtomb function is equivalent to the call
                    c32rtomb(buf, L'\0', ps)
    where buf is an internal buffer.
3   If s is not a null pointer, the c32rtomb function determines the number of bytes needed
    to represent the multibyte character that corresponds to the wide character given by c32
    (including any shift sequences), and stores the multibyte character representation in the
    array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
    c32 is a null wide character, a null byte is stored, preceded by any shift sequence needed
    to restore the initial shift state; the resulting state described is the initial conversion state.
    Returns
4   The c32rtomb function returns the number of bytes stored in the array object (including
    any shift sequences). When c32 is not a valid wide character, an encoding error occurs:
    the function stores the value of the macro EILSEQ in errno and returns
    (size_t)(-1); the conversion state is unspecified.




    312) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
         sequence of redundant shift sequences (for implementations with state-dependent encodings).

[page 398]

    7.28 Extended multibyte and wide character utilities <wchar.h>
    7.28.1 Introduction
1   The header <wchar.h> defines four macros, and declares four data types, one tag, and
    many functions.313)
2   The types declared are wchar_t and size_t (both described in 7.19);
              mbstate_t
    which is a complete object type other than an array type that can hold the conversion state
    information necessary to convert between sequences of multibyte characters and wide
    characters;
             wint_t
    which is an integer type unchanged by default argument promotions that can hold any
    value corresponding to members of the extended character set, as well as at least one
    value that does not correspond to any member of the extended character set (see WEOF
    below);314) and
             struct tm
    which is declared as an incomplete structure type (the contents are described in 7.26.1).
3   The macros defined are NULL (described in 7.19); WCHAR_MIN and WCHAR_MAX
    (described in 7.20.3); and
             WEOF
    which expands to a constant expression of type wint_t whose value does not
    correspond to any member of the extended character set.315) It is accepted (and returned)
    by several functions in this subclause to indicate end-of-file, that is, no more input from a
    stream. It is also used as a wide character value that does not correspond to any member
    of the extended character set.
4   The functions declared are grouped as follows:
    -- Functions that perform input and output of wide characters, or multibyte characters,
      or both;
    -- Functions that provide wide string numeric conversion;
    -- Functions that perform general wide string manipulation;


    313) See ''future library directions'' (7.30.12).
    314) wchar_t and wint_t can be the same integer type.
    315) The value of the macro WEOF may differ from that of EOF and need not be negative.

[page 399]

    -- Functions for wide string date and time conversion; and
    -- Functions that provide extended capabilities for conversion between multibyte and
      wide character sequences.
5   Unless explicitly stated otherwise, if the execution of a function described in this
    subclause causes copying to take place between objects that overlap, the behavior is
    undefined.
    7.28.2 Formatted wide character input/output functions
1   The formatted wide character input/output functions shall behave as if there is a sequence
    point after the actions associated with each specifier.316)
    7.28.2.1 The fwprintf function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            int fwprintf(FILE * restrict stream,
                 const wchar_t * restrict format, ...);
    Description
2   The fwprintf function writes output to the stream pointed to by stream, under
    control of the wide string pointed to by format that specifies how subsequent arguments
    are converted for output. If there are insufficient arguments for the format, the behavior
    is undefined. If the format is exhausted while arguments remain, the excess arguments
    are evaluated (as always) but are otherwise ignored. The fwprintf function returns
    when the end of the format string is encountered.
3   The format is composed of zero or more directives: ordinary wide characters (not %),
    which are copied unchanged to the output stream; and conversion specifications, each of
    which results in fetching zero or more subsequent arguments, converting them, if
    applicable, according to the corresponding conversion specifier, and then writing the
    result to the output stream.
4   Each conversion specification is introduced by the wide character %. After the %, the
    following appear in sequence:
    -- Zero or more flags (in any order) that modify the meaning of the conversion
      specification.
    -- An optional minimum field width. If the converted value has fewer wide characters
      than the field width, it is padded with spaces (by default) on the left (or right, if the


    316) The fwprintf functions perform writes to memory for the %n specifier.

[page 400]

        left adjustment flag, described later, has been given) to the field width. The field
        width takes the form of an asterisk * (described later) or a nonnegative decimal
        integer.317)
    -- An optional precision that gives the minimum number of digits to appear for the d, i,
      o, u, x, and X conversions, the number of digits to appear after the decimal-point
      wide character for a, A, e, E, f, and F conversions, the maximum number of
      significant digits for the g and G conversions, or the maximum number of wide
      characters to be written for s conversions. The precision takes the form of a period
      (.) followed either by an asterisk * (described later) or by an optional decimal
      integer; if only the period is specified, the precision is taken as zero. If a precision
      appears with any other conversion specifier, the behavior is undefined.
    -- An optional length modifier that specifies the size of the argument.
    -- A conversion specifier wide character that specifies the type of conversion to be
      applied.
5   As noted above, a field width, or precision, or both, may be indicated by an asterisk. In
    this case, an int argument supplies the field width or precision. The arguments
    specifying field width, or precision, or both, shall appear (in that order) before the
    argument (if any) to be converted. A negative field width argument is taken as a - flag
    followed by a positive field width. A negative precision argument is taken as if the
    precision were omitted.
6   The flag wide characters and their meanings are:
    -        The result of the conversion is left-justified within the field. (It is right-justified if
             this flag is not specified.)
    +        The result of a signed conversion always begins with a plus or minus sign. (It
             begins with a sign only when a negative value is converted if this flag is not
             specified.)318)
    space If the first wide character of a signed conversion is not a sign, or if a signed
          conversion results in no wide characters, a space is prefixed to the result. If the
          space and + flags both appear, the space flag is ignored.
    #        The result is converted to an ''alternative form''. For o conversion, it increases
             the precision, if and only if necessary, to force the first digit of the result to be a
             zero (if the value and precision are both 0, a single 0 is printed). For x (or X)
             conversion, a nonzero result has 0x (or 0X) prefixed to it. For a, A, e, E, f, F, g,


    317) Note that 0 is taken as a flag, not as the beginning of a field width.
    318) The results of all floating conversions of a negative zero, and of negative values that round to zero,
         include a minus sign.

[page 401]

              and G conversions, the result of converting a floating-point number always
              contains a decimal-point wide character, even if no digits follow it. (Normally, a
              decimal-point wide character appears in the result of these conversions only if a
              digit follows it.) For g and G conversions, trailing zeros are not removed from the
              result. For other conversions, the behavior is undefined.
    0         For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, leading zeros
              (following any indication of sign or base) are used to pad to the field width rather
              than performing space padding, except when converting an infinity or NaN. If the
              0 and - flags both appear, the 0 flag is ignored. For d, i, o, u, x, and X
              conversions, if a precision is specified, the 0 flag is ignored. For other
              conversions, the behavior is undefined.
7   The length modifiers and their meanings are:
    hh             Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                   signed char or unsigned char argument (the argument will have
                   been promoted according to the integer promotions, but its value shall be
                   converted to signed char or unsigned char before printing); or that
                   a following n conversion specifier applies to a pointer to a signed char
                   argument.
    h              Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                   short int or unsigned short int argument (the argument will
                   have been promoted according to the integer promotions, but its value shall
                   be converted to short int or unsigned short int before printing);
                   or that a following n conversion specifier applies to a pointer to a short
                   int argument.
    l (ell)        Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                   long int or unsigned long int argument; that a following n
                   conversion specifier applies to a pointer to a long int argument; that a
                   following c conversion specifier applies to a wint_t argument; that a
                   following s conversion specifier applies to a pointer to a wchar_t
                   argument; or has no effect on a following a, A, e, E, f, F, g, or G conversion
                   specifier.
    ll (ell-ell) Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 long long int or unsigned long long int argument; or that a
                 following n conversion specifier applies to a pointer to a long long int
                 argument.
    j              Specifies that a following d, i, o, u, x, or X conversion specifier applies to
                   an intmax_t or uintmax_t argument; or that a following n conversion
                   specifier applies to a pointer to an intmax_t argument.

[page 402]

    z            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 size_t or the corresponding signed integer type argument; or that a
                 following n conversion specifier applies to a pointer to a signed integer type
                 corresponding to size_t argument.
    t            Specifies that a following d, i, o, u, x, or X conversion specifier applies to a
                 ptrdiff_t or the corresponding unsigned integer type argument; or that a
                 following n conversion specifier applies to a pointer to a ptrdiff_t
                 argument.
    L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                 applies to a long double argument.
    If a length modifier appears with any conversion specifier other than as specified above,
    the behavior is undefined.
8   The conversion specifiers and their meanings are:
    d,i         The int argument is converted to signed decimal in the style [-]dddd. The
                precision specifies the minimum number of digits to appear; if the value
                being converted can be represented in fewer digits, it is expanded with
                leading zeros. The default precision is 1. The result of converting a zero
                value with a precision of zero is no wide characters.
    o,u,x,X The unsigned int argument is converted to unsigned octal (o), unsigned
            decimal (u), or unsigned hexadecimal notation (x or X) in the style dddd; the
            letters abcdef are used for x conversion and the letters ABCDEF for X
            conversion. The precision specifies the minimum number of digits to appear;
            if the value being converted can be represented in fewer digits, it is expanded
            with leading zeros. The default precision is 1. The result of converting a
            zero value with a precision of zero is no wide characters.
    f,F         A double argument representing a floating-point number is converted to
                decimal notation in the style [-]ddd.ddd, where the number of digits after
                the decimal-point wide character is equal to the precision specification. If the
                precision is missing, it is taken as 6; if the precision is zero and the # flag is
                not specified, no decimal-point wide character appears. If a decimal-point
                wide character appears, at least one digit appears before it. The value is
                rounded to the appropriate number of digits.
                A double argument representing an infinity is converted in one of the styles
                [-]inf or [-]infinity -- which style is implementation-defined. A
                double argument representing a NaN is converted in one of the styles
                [-]nan or [-]nan(n-wchar-sequence) -- which style, and the meaning of
                any n-wchar-sequence, is implementation-defined. The F conversion
                specifier produces INF, INFINITY, or NAN instead of inf, infinity, or

[page 403]

             nan, respectively.319)
e,E          A double argument representing a floating-point number is converted in the
             style [-]d.ddd e(+-)dd, where there is one digit (which is nonzero if the
             argument is nonzero) before the decimal-point wide character and the number
             of digits after it is equal to the precision; if the precision is missing, it is taken
             as 6; if the precision is zero and the # flag is not specified, no decimal-point
             wide character appears. The value is rounded to the appropriate number of
             digits. The E conversion specifier produces a number with E instead of e
             introducing the exponent. The exponent always contains at least two digits,
             and only as many more digits as necessary to represent the exponent. If the
             value is zero, the exponent is zero.
             A double argument representing an infinity or NaN is converted in the style
             of an f or F conversion specifier.
g,G          A double argument representing a floating-point number is converted in
             style f or e (or in style F or E in the case of a G conversion specifier),
             depending on the value converted and the precision. Let P equal the
             precision if nonzero, 6 if the precision is omitted, or 1 if the precision is zero.
             Then, if a conversion with style E would have an exponent of X:
             -- if P > X >= -4, the conversion is with style f (or F) and precision
               P - (X + 1).
             -- otherwise, the conversion is with style e (or E) and precision P - 1.
             Finally, unless the # flag is used, any trailing zeros are removed from the
             fractional portion of the result and the decimal-point wide character is
             removed if there is no fractional portion remaining.
             A double argument representing an infinity or NaN is converted in the style
             of an f or F conversion specifier.
a,A          A double argument representing a floating-point number is converted in the
             style [-]0xh.hhhh p(+-)d, where there is one hexadecimal digit (which is
             nonzero if the argument is a normalized floating-point number and is
             otherwise unspecified) before the decimal-point wide character320) and the
             number of hexadecimal digits after it is equal to the precision; if the precision
             is missing and FLT_RADIX is a power of 2, then the precision is sufficient


319) When applied to infinite and NaN values, the -, +, and space flag wide characters have their usual
     meaning; the # and 0 flag wide characters have no effect.
320) Binary implementations can choose the hexadecimal digit to the left of the decimal-point wide
     character so that subsequent digits align to nibble (4-bit) boundaries.

[page 404]

             for an exact representation of the value; if the precision is missing and
             FLT_RADIX is not a power of 2, then the precision is sufficient to
             distinguish321) values of type double, except that trailing zeros may be
             omitted; if the precision is zero and the # flag is not specified, no decimal-
             point wide character appears. The letters abcdef are used for a conversion
             and the letters ABCDEF for A conversion. The A conversion specifier
             produces a number with X and P instead of x and p. The exponent always
             contains at least one digit, and only as many more digits as necessary to
             represent the decimal exponent of 2. If the value is zero, the exponent is
             zero.
             A double argument representing an infinity or NaN is converted in the style
             of an f or F conversion specifier.
c            If no l length modifier is present, the int argument is converted to a wide
             character as if by calling btowc and the resulting wide character is written.
             If an l length modifier is present, the wint_t argument is converted to
             wchar_t and written.
s            If no l length modifier is present, the argument shall be a pointer to the initial
             element of a character array containing a multibyte character sequence
             beginning in the initial shift state. Characters from the array are converted as
             if by repeated calls to the mbrtowc function, with the conversion state
             described by an mbstate_t object initialized to zero before the first
             multibyte character is converted, and written up to (but not including) the
             terminating null wide character. If the precision is specified, no more than
             that many wide characters are written. If the precision is not specified or is
             greater than the size of the converted array, the converted array shall contain a
             null wide character.
             If an l length modifier is present, the argument shall be a pointer to the initial
             element of an array of wchar_t type. Wide characters from the array are
             written up to (but not including) a terminating null wide character. If the
             precision is specified, no more than that many wide characters are written. If
             the precision is not specified or is greater than the size of the array, the array
             shall contain a null wide character.
p            The argument shall be a pointer to void. The value of the pointer is
             converted to a sequence of printing wide characters, in an implementation-

321) The precision p is sufficient to distinguish values of the source type if 16 p-1 > b n where b is
     FLT_RADIX and n is the number of base-b digits in the significand of the source type. A smaller p
     might suffice depending on the implementation's scheme for determining the digit to the left of the
     decimal-point wide character.

[page 405]

                    defined manner.
     n              The argument shall be a pointer to signed integer into which is written the
                    number of wide characters written to the output stream so far by this call to
                    fwprintf. No argument is converted, but one is consumed. If the
                    conversion specification includes any flags, a field width, or a precision, the
                    behavior is undefined.
     %              A % wide character is written. No argument is converted. The complete
                    conversion specification shall be %%.
9    If a conversion specification is invalid, the behavior is undefined.322) If any argument is
     not the correct type for the corresponding conversion specification, the behavior is
     undefined.
10   In no case does a nonexistent or small field width cause truncation of a field; if the result
     of a conversion is wider than the field width, the field is expanded to contain the
     conversion result.
11   For a and A conversions, if FLT_RADIX is a power of 2, the value is correctly rounded
     to a hexadecimal floating number with the given precision.
     Recommended practice
12   For a and A conversions, if FLT_RADIX is not a power of 2 and the result is not exactly
     representable in the given precision, the result should be one of the two adjacent numbers
     in hexadecimal floating style with the given precision, with the extra stipulation that the
     error should have a correct sign for the current rounding direction.
13   For e, E, f, F, g, and G conversions, if the number of significant decimal digits is at most
     DECIMAL_DIG, then the result should be correctly rounded.323) If the number of
     significant decimal digits is more than DECIMAL_DIG but the source value is exactly
     representable with DECIMAL_DIG digits, then the result should be an exact
     representation with trailing zeros. Otherwise, the source value is bounded by two
     adjacent decimal strings L < U, both having DECIMAL_DIG significant digits; the value
     of the resultant decimal string D should satisfy L <= D <= U, with the extra stipulation that
     the error should have a correct sign for the current rounding direction.
     Returns
14   The fwprintf function returns the number of wide characters transmitted, or a negative
     value if an output or encoding error occurred.

     322) See ''future library directions'' (7.30.12).
     323) For binary-to-decimal conversion, the result format's values are the numbers representable with the
          given format specifier. The number of significant digits is determined by the format specifier, and in
          the case of fixed-point conversion by the source value as well.

[page 406]

     Environmental limits
15   The number of wide characters that can be produced by any single conversion shall be at
     least 4095.
16   EXAMPLE       To print a date and time in the form ''Sunday, July 3, 10:02'' followed by pi to five decimal
     places:
             #include <math.h>
             #include <stdio.h>
             #include <wchar.h>
             /* ... */
             wchar_t *weekday, *month; // pointers to wide strings
             int day, hour, min;
             fwprintf(stdout, L"%ls, %ls %d, %.2d:%.2d\n",
                     weekday, month, day, hour, min);
             fwprintf(stdout, L"pi = %.5f\n", 4 * atan(1.0));

     Forward references:          the btowc function (7.28.6.1.1), the mbrtowc function
     (7.28.6.3.2).
     7.28.2.2 The fwscanf function
     Synopsis
1            #include <stdio.h>
             #include <wchar.h>
             int fwscanf(FILE * restrict stream,
                  const wchar_t * restrict format, ...);
     Description
2    The fwscanf function reads input from the stream pointed to by stream, under
     control of the wide string pointed to by format that specifies the admissible input
     sequences and how they are to be converted for assignment, using subsequent arguments
     as pointers to the objects to receive the converted input. If there are insufficient
     arguments for the format, the behavior is undefined. If the format is exhausted while
     arguments remain, the excess arguments are evaluated (as always) but are otherwise
     ignored.
3    The format is composed of zero or more directives: one or more white-space wide
     characters, an ordinary wide character (neither % nor a white-space wide character), or a
     conversion specification. Each conversion specification is introduced by the wide
     character %. After the %, the following appear in sequence:
     -- An optional assignment-suppressing wide character *.
     -- An optional decimal integer greater than zero that specifies the maximum field width
       (in wide characters).



[page 407]

     -- An optional length modifier that specifies the size of the receiving object.
     -- A conversion specifier wide character that specifies the type of conversion to be
       applied.
4    The fwscanf function executes each directive of the format in turn. When all directives
     have been executed, or if a directive fails (as detailed below), the function returns.
     Failures are described as input failures (due to the occurrence of an encoding error or the
     unavailability of input characters), or matching failures (due to inappropriate input).
5    A directive composed of white-space wide character(s) is executed by reading input up to
     the first non-white-space wide character (which remains unread), or until no more wide
     characters can be read.
6    A directive that is an ordinary wide character is executed by reading the next wide
     character of the stream. If that wide character differs from the directive, the directive
     fails and the differing and subsequent wide characters remain unread. Similarly, if end-
     of-file, an encoding error, or a read error prevents a wide character from being read, the
     directive fails.
7    A directive that is a conversion specification defines a set of matching input sequences, as
     described below for each specifier. A conversion specification is executed in the
     following steps:
8    Input white-space wide characters (as specified by the iswspace function) are skipped,
     unless the specification includes a [, c, or n specifier.324)
9    An input item is read from the stream, unless the specification includes an n specifier. An
     input item is defined as the longest sequence of input wide characters which does not
     exceed any specified field width and which is, or is a prefix of, a matching input
     sequence.325) The first wide character, if any, after the input item remains unread. If the
     length of the input item is zero, the execution of the directive fails; this condition is a
     matching failure unless end-of-file, an encoding error, or a read error prevented input
     from the stream, in which case it is an input failure.
10   Except in the case of a % specifier, the input item (or, in the case of a %n directive, the
     count of input wide characters) is converted to a type appropriate to the conversion
     specifier. If the input item is not a matching sequence, the execution of the directive fails:
     this condition is a matching failure. Unless assignment suppression was indicated by a *,
     the result of the conversion is placed in the object pointed to by the first argument
     following the format argument that has not already received a conversion result. If this


     324) These white-space wide characters are not counted against a specified field width.
     325) fwscanf pushes back at most one input wide character onto the input stream. Therefore, some
          sequences that are acceptable to wcstod, wcstol, etc., are unacceptable to fwscanf.

[page 408]

     object does not have an appropriate type, or if the result of the conversion cannot be
     represented in the object, the behavior is undefined.
11   The length modifiers and their meanings are:
     hh           Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to signed char or unsigned char.
     h            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to short int or unsigned short
                  int.
     l (ell)      Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to long int or unsigned long
                  int; that a following a, A, e, E, f, F, g, or G conversion specifier applies to
                  an argument with type pointer to double; or that a following c, s, or [
                  conversion specifier applies to an argument with type pointer to wchar_t.
     ll (ell-ell) Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to long long int or unsigned
                  long long int.
     j            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to intmax_t or uintmax_t.
     z            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to size_t or the corresponding signed
                  integer type.
     t            Specifies that a following d, i, o, u, x, X, or n conversion specifier applies
                  to an argument with type pointer to ptrdiff_t or the corresponding
                  unsigned integer type.
     L            Specifies that a following a, A, e, E, f, F, g, or G conversion specifier
                  applies to an argument with type pointer to long double.
     If a length modifier appears with any conversion specifier other than as specified above,
     the behavior is undefined.
12   The conversion specifiers and their meanings are:
     d           Matches an optionally signed decimal integer, whose format is the same as
                 expected for the subject sequence of the wcstol function with the value 10
                 for the base argument. The corresponding argument shall be a pointer to
                 signed integer.
     i           Matches an optionally signed integer, whose format is the same as expected
                 for the subject sequence of the wcstol function with the value 0 for the
                 base argument. The corresponding argument shall be a pointer to signed

[page 409]

          integer.
o         Matches an optionally signed octal integer, whose format is the same as
          expected for the subject sequence of the wcstoul function with the value 8
          for the base argument. The corresponding argument shall be a pointer to
          unsigned integer.
u         Matches an optionally signed decimal integer, whose format is the same as
          expected for the subject sequence of the wcstoul function with the value 10
          for the base argument. The corresponding argument shall be a pointer to
          unsigned integer.
x         Matches an optionally signed hexadecimal integer, whose format is the same
          as expected for the subject sequence of the wcstoul function with the value
          16 for the base argument. The corresponding argument shall be a pointer to
          unsigned integer.
a,e,f,g Matches an optionally signed floating-point number, infinity, or NaN, whose
        format is the same as expected for the subject sequence of the wcstod
        function. The corresponding argument shall be a pointer to floating.
c         Matches a sequence of wide characters of exactly the number specified by the
          field width (1 if no field width is present in the directive).
          If no l length modifier is present, characters from the input field are
          converted as if by repeated calls to the wcrtomb function, with the
          conversion state described by an mbstate_t object initialized to zero
          before the first wide character is converted. The corresponding argument
          shall be a pointer to the initial element of a character array large enough to
          accept the sequence. No null character is added.
          If an l length modifier is present, the corresponding argument shall be a
          pointer to the initial element of an array of wchar_t large enough to accept
          the sequence. No null wide character is added.
s         Matches a sequence of non-white-space wide characters.
          If no l length modifier is present, characters from the input field are
          converted as if by repeated calls to the wcrtomb function, with the
          conversion state described by an mbstate_t object initialized to zero
          before the first wide character is converted. The corresponding argument
          shall be a pointer to the initial element of a character array large enough to
          accept the sequence and a terminating null character, which will be added
          automatically.
          If an l length modifier is present, the corresponding argument shall be a
          pointer to the initial element of an array of wchar_t large enough to accept

[page 410]

            the sequence and the terminating null wide character, which will be added
            automatically.
[           Matches a nonempty sequence of wide characters from a set of expected
            characters (the scanset).
            If no l length modifier is present, characters from the input field are
            converted as if by repeated calls to the wcrtomb function, with the
            conversion state described by an mbstate_t object initialized to zero
            before the first wide character is converted. The corresponding argument
            shall be a pointer to the initial element of a character array large enough to
            accept the sequence and a terminating null character, which will be added
            automatically.
            If an l length modifier is present, the corresponding argument shall be a
            pointer to the initial element of an array of wchar_t large enough to accept
            the sequence and the terminating null wide character, which will be added
            automatically.
            The conversion specifier includes all subsequent wide characters in the
            format string, up to and including the matching right bracket (]). The wide
            characters between the brackets (the scanlist) compose the scanset, unless the
            wide character after the left bracket is a circumflex (^), in which case the
            scanset contains all wide characters that do not appear in the scanlist between
            the circumflex and the right bracket. If the conversion specifier begins with
            [] or [^], the right bracket wide character is in the scanlist and the next
            following right bracket wide character is the matching right bracket that ends
            the specification; otherwise the first following right bracket wide character is
            the one that ends the specification. If a - wide character is in the scanlist and
            is not the first, nor the second where the first wide character is a ^, nor the
            last character, the behavior is implementation-defined.
p           Matches an implementation-defined set of sequences, which should be the
            same as the set of sequences that may be produced by the %p conversion of
            the fwprintf function. The corresponding argument shall be a pointer to a
            pointer to void. The input item is converted to a pointer value in an
            implementation-defined manner. If the input item is a value converted earlier
            during the same program execution, the pointer that results shall compare
            equal to that value; otherwise the behavior of the %p conversion is undefined.
n           No input is consumed. The corresponding argument shall be a pointer to
            signed integer into which is to be written the number of wide characters read
            from the input stream so far by this call to the fwscanf function. Execution
            of a %n directive does not increment the assignment count returned at the
            completion of execution of the fwscanf function. No argument is
[page 411]

                    converted, but one is consumed. If the conversion specification includes an
                    assignment-suppressing wide character or a field width, the behavior is
                    undefined.
     %              Matches a single % wide character; no conversion or assignment occurs. The
                    complete conversion specification shall be %%.
13   If a conversion specification is invalid, the behavior is undefined.326)
14   The conversion specifiers A, E, F, G, and X are also valid and behave the same as,
     respectively, a, e, f, g, and x.
15   Trailing white space (including new-line wide characters) is left unread unless matched
     by a directive. The success of literal matches and suppressed assignments is not directly
     determinable other than via the %n directive.
     Returns
16   The fwscanf function returns the value of the macro EOF if an input failure occurs
     before the first conversion (if any) has completed. Otherwise, the function returns the
     number of input items assigned, which can be fewer than provided for, or even zero, in
     the event of an early matching failure.
17   EXAMPLE 1        The call:
              #include <stdio.h>
              #include <wchar.h>
              /* ... */
              int n, i; float x; wchar_t name[50];
              n = fwscanf(stdin, L"%d%f%ls", &i, &x, name);
     with the input line:
              25 54.32E-1 thompson
     will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
     thompson\0.

18   EXAMPLE 2        The call:
              #include <stdio.h>
              #include <wchar.h>
              /* ... */
              int i; float x; double y;
              fwscanf(stdin, L"%2d%f%*d %lf", &i, &x, &y);
     with input:
              56789 0123 56a72
     will assign to i the value 56 and to x the value 789.0, will skip past 0123, and will assign to y the value
     56.0. The next wide character read from the input stream will be a.


     326) See ''future library directions'' (7.30.12).

[page 412]

    Forward references: the wcstod, wcstof, and wcstold functions (7.28.4.1.1), the
    wcstol, wcstoll, wcstoul, and wcstoull functions (7.28.4.1.2), the wcrtomb
    function (7.28.6.3.3).
    7.28.2.3 The swprintf function
    Synopsis
1           #include <wchar.h>
            int swprintf(wchar_t * restrict s,
                 size_t n,
                 const wchar_t * restrict format, ...);
    Description
2   The swprintf function is equivalent to fwprintf, except that the argument s
    specifies an array of wide characters into which the generated output is to be written,
    rather than written to a stream. No more than n wide characters are written, including a
    terminating null wide character, which is always added (unless n is zero).
    Returns
3   The swprintf function returns the number of wide characters written in the array, not
    counting the terminating null wide character, or a negative value if an encoding error
    occurred or if n or more wide characters were requested to be written.
    7.28.2.4 The swscanf function
    Synopsis
1           #include <wchar.h>
            int swscanf(const wchar_t * restrict s,
                 const wchar_t * restrict format, ...);
    Description
2   The swscanf function is equivalent to fwscanf, except that the argument s specifies a
    wide string from which the input is to be obtained, rather than from a stream. Reaching
    the end of the wide string is equivalent to encountering end-of-file for the fwscanf
    function.
    Returns
3   The swscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the swscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.




[page 413]

    7.28.2.5 The vfwprintf function
    Synopsis
1          #include <stdarg.h>
           #include <stdio.h>
           #include <wchar.h>
           int vfwprintf(FILE * restrict stream,
                const wchar_t * restrict format,
                va_list arg);
    Description
2   The vfwprintf function is equivalent to fwprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfwprintf function does not invoke the
    va_end macro.327)
    Returns
3   The vfwprintf function returns the number of wide characters transmitted, or a
    negative value if an output or encoding error occurred.
4   EXAMPLE       The following shows the use of the vfwprintf function in a general error-reporting
    routine.
           #include <stdarg.h>
           #include <stdio.h>
           #include <wchar.h>
           void error(char *function_name, wchar_t *format, ...)
           {
                 va_list args;
                    va_start(args, format);
                    // print out name of function causing error
                    fwprintf(stderr, L"ERROR in %s: ", function_name);
                    // print out remainder of message
                    vfwprintf(stderr, format, args);
                    va_end(args);
           }




    327) As the functions vfwprintf, vswprintf, vfwscanf, vwprintf, vwscanf, and vswscanf
         invoke the va_arg macro, the value of arg after the return is indeterminate.

[page 414]

    7.28.2.6 The vfwscanf function
    Synopsis
1           #include <stdarg.h>
            #include <stdio.h>
            #include <wchar.h>
            int vfwscanf(FILE * restrict stream,
                 const wchar_t * restrict format,
                 va_list arg);
    Description
2   The vfwscanf function is equivalent to fwscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfwscanf function does not invoke the
    va_end macro.327)
    Returns
3   The vfwscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vfwscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.28.2.7 The vswprintf function
    Synopsis
1           #include <stdarg.h>
            #include <wchar.h>
            int vswprintf(wchar_t * restrict s,
                 size_t n,
                 const wchar_t * restrict format,
                 va_list arg);
    Description
2   The vswprintf function is equivalent to swprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vswprintf function does not invoke the
    va_end macro.327)
    Returns
3   The vswprintf function returns the number of wide characters written in the array, not
    counting the terminating null wide character, or a negative value if an encoding error
    occurred or if n or more wide characters were requested to be generated.


[page 415]

    7.28.2.8 The vswscanf function
    Synopsis
1          #include <stdarg.h>
           #include <wchar.h>
           int vswscanf(const wchar_t * restrict s,
                const wchar_t * restrict format,
                va_list arg);
    Description
2   The vswscanf function is equivalent to swscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vswscanf function does not invoke the
    va_end macro.327)
    Returns
3   The vswscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vswscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.28.2.9 The vwprintf function
    Synopsis
1          #include <stdarg.h>
           #include <wchar.h>
           int vwprintf(const wchar_t * restrict format,
                va_list arg);
    Description
2   The vwprintf function is equivalent to wprintf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vwprintf function does not invoke the
    va_end macro.327)
    Returns
3   The vwprintf function returns the number of wide characters transmitted, or a negative
    value if an output or encoding error occurred.




[page 416]

    7.28.2.10 The vwscanf function
    Synopsis
1           #include <stdarg.h>
            #include <wchar.h>
            int vwscanf(const wchar_t * restrict format,
                 va_list arg);
    Description
2   The vwscanf function is equivalent to wscanf, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vwscanf function does not invoke the
    va_end macro.327)
    Returns
3   The vwscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the vwscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.28.2.11 The wprintf function
    Synopsis
1           #include <wchar.h>
            int wprintf(const wchar_t * restrict format, ...);
    Description
2   The wprintf function is equivalent to fwprintf with the argument stdout
    interposed before the arguments to wprintf.
    Returns
3   The wprintf function returns the number of wide characters transmitted, or a negative
    value if an output or encoding error occurred.
    7.28.2.12 The wscanf function
    Synopsis
1           #include <wchar.h>
            int wscanf(const wchar_t * restrict format, ...);
    Description
2   The wscanf function is equivalent to fwscanf with the argument stdin interposed
    before the arguments to wscanf.


[page 417]

    Returns
3   The wscanf function returns the value of the macro EOF if an input failure occurs
    before the first conversion (if any) has completed. Otherwise, the wscanf function
    returns the number of input items assigned, which can be fewer than provided for, or even
    zero, in the event of an early matching failure.
    7.28.3 Wide character input/output functions
    7.28.3.1 The fgetwc function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            wint_t fgetwc(FILE *stream);
    Description
2   If the end-of-file indicator for the input stream pointed to by stream is not set and a
    next wide character is present, the fgetwc function obtains that wide character as a
    wchar_t converted to a wint_t and advances the associated file position indicator for
    the stream (if defined).
    Returns
3   If the end-of-file indicator for the stream is set, or if the stream is at end-of-file, the end-
    of-file indicator for the stream is set and the fgetwc function returns WEOF. Otherwise,
    the fgetwc function returns the next wide character from the input stream pointed to by
    stream. If a read error occurs, the error indicator for the stream is set and the fgetwc
    function returns WEOF. If an encoding error occurs (including too few bytes), the value of
    the macro EILSEQ is stored in errno and the fgetwc function returns WEOF.328)
    7.28.3.2 The fgetws function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            wchar_t *fgetws(wchar_t * restrict s,
                 int n, FILE * restrict stream);
    Description
2   The fgetws function reads at most one less than the number of wide characters
    specified by n from the stream pointed to by stream into the array pointed to by s. No


    328) An end-of-file and a read error can be distinguished by use of the feof and ferror functions.
         Also, errno will be set to EILSEQ by input/output functions only if an encoding error occurs.

[page 418]

    additional wide characters are read after a new-line wide character (which is retained) or
    after end-of-file. A null wide character is written immediately after the last wide
    character read into the array.
    Returns
3   The fgetws function returns s if successful. If end-of-file is encountered and no
    characters have been read into the array, the contents of the array remain unchanged and a
    null pointer is returned. If a read or encoding error occurs during the operation, the array
    contents are indeterminate and a null pointer is returned.
    7.28.3.3 The fputwc function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            wint_t fputwc(wchar_t c, FILE *stream);
    Description
2   The fputwc function writes the wide character specified by c to the output stream
    pointed to by stream, at the position indicated by the associated file position indicator
    for the stream (if defined), and advances the indicator appropriately. If the file cannot
    support positioning requests, or if the stream was opened with append mode, the
    character is appended to the output stream.
    Returns
3   The fputwc function returns the wide character written. If a write error occurs, the
    error indicator for the stream is set and fputwc returns WEOF. If an encoding error
    occurs, the value of the macro EILSEQ is stored in errno and fputwc returns WEOF.
    7.28.3.4 The fputws function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            int fputws(const wchar_t * restrict s,
                 FILE * restrict stream);
    Description
2   The fputws function writes the wide string pointed to by s to the stream pointed to by
    stream. The terminating null wide character is not written.
    Returns
3   The fputws function returns EOF if a write or encoding error occurs; otherwise, it
    returns a nonnegative value.

[page 419]

    7.28.3.5 The fwide function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            int fwide(FILE *stream, int mode);
    Description
2   The fwide function determines the orientation of the stream pointed to by stream. If
    mode is greater than zero, the function first attempts to make the stream wide oriented. If
    mode is less than zero, the function first attempts to make the stream byte oriented.329)
    Otherwise, mode is zero and the function does not alter the orientation of the stream.
    Returns
3   The fwide function returns a value greater than zero if, after the call, the stream has
    wide orientation, a value less than zero if the stream has byte orientation, or zero if the
    stream has no orientation.
    7.28.3.6 The getwc function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            wint_t getwc(FILE *stream);
    Description
2   The getwc function is equivalent to fgetwc, except that if it is implemented as a
    macro, it may evaluate stream more than once, so the argument should never be an
    expression with side effects.
    Returns
3   The getwc function returns the next wide character from the input stream pointed to by
    stream, or WEOF.
    7.28.3.7 The getwchar function
    Synopsis
1           #include <wchar.h>
            wint_t getwchar(void);




    329) If the orientation of the stream has already been determined, fwide does not change it.

[page 420]

    Description
2   The getwchar function is equivalent to getwc with the argument stdin.
    Returns
3   The getwchar function returns the next wide character from the input stream pointed to
    by stdin, or WEOF.
    7.28.3.8 The putwc function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            wint_t putwc(wchar_t c, FILE *stream);
    Description
2   The putwc function is equivalent to fputwc, except that if it is implemented as a
    macro, it may evaluate stream more than once, so that argument should never be an
    expression with side effects.
    Returns
3   The putwc function returns the wide character written, or WEOF.
    7.28.3.9 The putwchar function
    Synopsis
1           #include <wchar.h>
            wint_t putwchar(wchar_t c);
    Description
2   The putwchar function is equivalent to putwc with the second argument stdout.
    Returns
3   The putwchar function returns the character written, or WEOF.
    7.28.3.10 The ungetwc function
    Synopsis
1           #include <stdio.h>
            #include <wchar.h>
            wint_t ungetwc(wint_t c, FILE *stream);
    Description
2   The ungetwc function pushes the wide character specified by c back onto the input
    stream pointed to by stream. Pushed-back wide characters will be returned by
    subsequent reads on that stream in the reverse order of their pushing. A successful

[page 421]

    intervening call (with the stream pointed to by stream) to a file positioning function
    (fseek, fsetpos, or rewind) discards any pushed-back wide characters for the
    stream. The external storage corresponding to the stream is unchanged.
3   One wide character of pushback is guaranteed, even if the call to the ungetwc function
    follows just after a call to a formatted wide character input function fwscanf,
    vfwscanf, vwscanf, or wscanf. If the ungetwc function is called too many times
    on the same stream without an intervening read or file positioning operation on that
    stream, the operation may fail.
4   If the value of c equals that of the macro WEOF, the operation fails and the input stream is
    unchanged.
5   A successful call to the ungetwc function clears the end-of-file indicator for the stream.
    The value of the file position indicator for the stream after reading or discarding all
    pushed-back wide characters is the same as it was before the wide characters were pushed
    back. For a text or binary stream, the value of its file position indicator after a successful
    call to the ungetwc function is unspecified until all pushed-back wide characters are
    read or discarded.
    Returns
6   The ungetwc function returns the wide character pushed back, or WEOF if the operation
    fails.
    7.28.4 General wide string utilities
1   The header <wchar.h> declares a number of functions useful for wide string
    manipulation. Various methods are used for determining the lengths of the arrays, but in
    all cases a wchar_t * argument points to the initial (lowest addressed) element of the
    array. If an array is accessed beyond the end of an object, the behavior is undefined.
2   Where an argument declared as size_t n determines the length of the array for a
    function, n can have the value zero on a call to that function. Unless explicitly stated
    otherwise in the description of a particular function in this subclause, pointer arguments
    on such a call shall still have valid values, as described in 7.1.4. On such a call, a
    function that locates a wide character finds no occurrence, a function that compares two
    wide character sequences returns zero, and a function that copies wide characters copies
    zero wide characters.




[page 422]

    7.28.4.1 Wide string numeric conversion functions
    7.28.4.1.1 The wcstod, wcstof, and wcstold functions
    Synopsis
1           #include <wchar.h>
            double wcstod(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr);
            float wcstof(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr);
            long double wcstold(const wchar_t * restrict nptr,
                 wchar_t ** restrict endptr);
    Description
2   The wcstod, wcstof, and wcstold functions convert the initial portion of the wide
    string pointed to by nptr to double, float, and long double representation,
    respectively. First, they decompose the input string into three parts: an initial, possibly
    empty, sequence of white-space wide characters (as specified by the iswspace
    function), a subject sequence resembling a floating-point constant or representing an
    infinity or NaN; and a final wide string of one or more unrecognized wide characters,
    including the terminating null wide character of the input wide string. Then, they attempt
    to convert the subject sequence to a floating-point number, and return the result.
3   The expected form of the subject sequence is an optional plus or minus sign, then one of
    the following:
    -- a nonempty sequence of decimal digits optionally containing a decimal-point wide
      character, then an optional exponent part as defined for the corresponding single-byte
      characters in 6.4.4.2;
    -- a 0x or 0X, then a nonempty sequence of hexadecimal digits optionally containing a
      decimal-point wide character, then an optional binary exponent part as defined in
      6.4.4.2;
    -- INF or INFINITY, or any other wide string equivalent except for case
    -- NAN or NAN(n-wchar-sequenceopt), or any other wide string equivalent except for
      case in the NAN part, where:
               n-wchar-sequence:
                     digit
                     nondigit
                     n-wchar-sequence digit
                     n-wchar-sequence nondigit
    The subject sequence is defined as the longest initial subsequence of the input wide
    string, starting with the first non-white-space wide character, that is of the expected form.
[page 423]

    The subject sequence contains no wide characters if the input wide string is not of the
    expected form.
4   If the subject sequence has the expected form for a floating-point number, the sequence of
    wide characters starting with the first digit or the decimal-point wide character
    (whichever occurs first) is interpreted as a floating constant according to the rules of
    6.4.4.2, except that the decimal-point wide character is used in place of a period, and that
    if neither an exponent part nor a decimal-point wide character appears in a decimal
    floating point number, or if a binary exponent part does not appear in a hexadecimal
    floating point number, an exponent part of the appropriate type with value zero is
    assumed to follow the last digit in the string. If the subject sequence begins with a minus
    sign, the sequence is interpreted as negated.330) A wide character sequence INF or
    INFINITY is interpreted as an infinity, if representable in the return type, else like a
    floating constant that is too large for the range of the return type. A wide character
    sequence NAN or NAN(n-wchar-sequenceopt) is interpreted as a quiet NaN, if supported
    in the return type, else like a subject sequence part that does not have the expected form;
    the meaning of the n-wchar sequences is implementation-defined.331) A pointer to the
    final wide string is stored in the object pointed to by endptr, provided that endptr is
    not a null pointer.
5   If the subject sequence has the hexadecimal form and FLT_RADIX is a power of 2, the
    value resulting from the conversion is correctly rounded.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Recommended practice
8   If the subject sequence has the hexadecimal form, FLT_RADIX is not a power of 2, and
    the result is not exactly representable, the result should be one of the two numbers in the
    appropriate internal format that are adjacent to the hexadecimal floating source value,
    with the extra stipulation that the error should have a correct sign for the current rounding
    direction.



    330) It is unspecified whether a minus-signed sequence is converted to a negative number directly or by
         negating the value resulting from converting the corresponding unsigned sequence (see F.5); the two
         methods may yield different results if rounding is toward positive or negative infinity. In either case,
         the functions honor the sign of zero if floating-point arithmetic supports signed zeros.
    331) An implementation may use the n-wchar sequence to determine extra information to be represented in
         the NaN's significand.

[page 424]

9    If the subject sequence has the decimal form and at most DECIMAL_DIG (defined in
     <float.h>) significant digits, the result should be correctly rounded. If the subject
     sequence D has the decimal form and more than DECIMAL_DIG significant digits,
     consider the two bounding, adjacent decimal strings L and U, both having
     DECIMAL_DIG significant digits, such that the values of L, D, and U satisfy L <= D <= U.
     The result should be one of the (equal or adjacent) values that would be obtained by
     correctly rounding L and U according to the current rounding direction, with the extra
     stipulation that the error with respect to D should have a correct sign for the current
     rounding direction.332)
     Returns
10   The functions return the converted value, if any. If no conversion could be performed,
     zero is returned. If the correct value overflows and default rounding is in effect (7.12.1),
     plus or minus HUGE_VAL, HUGE_VALF, or HUGE_VALL is returned (according to the
     return type and sign of the value), and the value of the macro ERANGE is stored in
     errno. If the result underflows (7.12.1), the functions return a value whose magnitude is
     no greater than the smallest normalized positive number in the return type; whether
     errno acquires the value ERANGE is implementation-defined.




     332) DECIMAL_DIG, defined in <float.h>, should be sufficiently large that L and U will usually round
          to the same internal floating value, but if not will round to adjacent values.

[page 425]

    7.28.4.1.2 The wcstol, wcstoll, wcstoul, and wcstoull functions
    Synopsis
1          #include <wchar.h>
           long int wcstol(
                const wchar_t * restrict nptr,
                wchar_t ** restrict endptr,
                int base);
           long long int wcstoll(
                const wchar_t * restrict nptr,
                wchar_t ** restrict endptr,
                int base);
           unsigned long int wcstoul(
                const wchar_t * restrict nptr,
                wchar_t ** restrict endptr,
                int base);
           unsigned long long int wcstoull(
                const wchar_t * restrict nptr,
                wchar_t ** restrict endptr,
                int base);
    Description
2   The wcstol, wcstoll, wcstoul, and wcstoull functions convert the initial
    portion of the wide string pointed to by nptr to long int, long long int,
    unsigned long int, and unsigned long long int representation,
    respectively. First, they decompose the input string into three parts: an initial, possibly
    empty, sequence of white-space wide characters (as specified by the iswspace
    function), a subject sequence resembling an integer represented in some radix determined
    by the value of base, and a final wide string of one or more unrecognized wide
    characters, including the terminating null wide character of the input wide string. Then,
    they attempt to convert the subject sequence to an integer, and return the result.
3   If the value of base is zero, the expected form of the subject sequence is that of an
    integer constant as described for the corresponding single-byte characters in 6.4.4.1,
    optionally preceded by a plus or minus sign, but not including an integer suffix. If the
    value of base is between 2 and 36 (inclusive), the expected form of the subject sequence
    is a sequence of letters and digits representing an integer with the radix specified by
    base, optionally preceded by a plus or minus sign, but not including an integer suffix.
    The letters from a (or A) through z (or Z) are ascribed the values 10 through 35; only
    letters and digits whose ascribed values are less than that of base are permitted. If the
    value of base is 16, the wide characters 0x or 0X may optionally precede the sequence
    of letters and digits, following the sign if present.

[page 426]

4   The subject sequence is defined as the longest initial subsequence of the input wide
    string, starting with the first non-white-space wide character, that is of the expected form.
    The subject sequence contains no wide characters if the input wide string is empty or
    consists entirely of white space, or if the first non-white-space wide character is other
    than a sign or a permissible letter or digit.
5   If the subject sequence has the expected form and the value of base is zero, the sequence
    of wide characters starting with the first digit is interpreted as an integer constant
    according to the rules of 6.4.4.1. If the subject sequence has the expected form and the
    value of base is between 2 and 36, it is used as the base for conversion, ascribing to each
    letter its value as given above. If the subject sequence begins with a minus sign, the value
    resulting from the conversion is negated (in the return type). A pointer to the final wide
    string is stored in the object pointed to by endptr, provided that endptr is not a null
    pointer.
6   In other than the "C" locale, additional locale-specific subject sequence forms may be
    accepted.
7   If the subject sequence is empty or does not have the expected form, no conversion is
    performed; the value of nptr is stored in the object pointed to by endptr, provided
    that endptr is not a null pointer.
    Returns
8   The wcstol, wcstoll, wcstoul, and wcstoull functions return the converted
    value, if any. If no conversion could be performed, zero is returned. If the correct value
    is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN,
    LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type
    sign of the value, if any), and the value of the macro ERANGE is stored in errno.
    7.28.4.2 Wide string copying functions
    7.28.4.2.1 The wcscpy function
    Synopsis
1           #include <wchar.h>
            wchar_t *wcscpy(wchar_t * restrict s1,
                 const wchar_t * restrict s2);
    Description
2   The wcscpy function copies the wide string pointed to by s2 (including the terminating
    null wide character) into the array pointed to by s1.
    Returns
3   The wcscpy function returns the value of s1.


[page 427]

    7.28.4.2.2 The wcsncpy function
    Synopsis
1            #include <wchar.h>
             wchar_t *wcsncpy(wchar_t * restrict s1,
                  const wchar_t * restrict s2,
                  size_t n);
    Description
2   The wcsncpy function copies not more than n wide characters (those that follow a null
    wide character are not copied) from the array pointed to by s2 to the array pointed to by
    s1.333)
3   If the array pointed to by s2 is a wide string that is shorter than n wide characters, null
    wide characters are appended to the copy in the array pointed to by s1, until n wide
    characters in all have been written.
    Returns
4   The wcsncpy function returns the value of s1.
    7.28.4.2.3 The wmemcpy function
    Synopsis
1            #include <wchar.h>
             wchar_t *wmemcpy(wchar_t * restrict s1,
                  const wchar_t * restrict s2,
                  size_t n);
    Description
2   The wmemcpy function copies n wide characters from the object pointed to by s2 to the
    object pointed to by s1.
    Returns
3   The wmemcpy function returns the value of s1.




    333) Thus, if there is no null wide character in the first n wide characters of the array pointed to by s2, the
         result will not be null-terminated.

[page 428]

    7.28.4.2.4 The wmemmove function
    Synopsis
1           #include <wchar.h>
            wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
                 size_t n);
    Description
2   The wmemmove function copies n wide characters from the object pointed to by s2 to
    the object pointed to by s1. Copying takes place as if the n wide characters from the
    object pointed to by s2 are first copied into a temporary array of n wide characters that
    does not overlap the objects pointed to by s1 or s2, and then the n wide characters from
    the temporary array are copied into the object pointed to by s1.
    Returns
3   The wmemmove function returns the value of s1.
    7.28.4.3 Wide string concatenation functions
    7.28.4.3.1 The wcscat function
    Synopsis
1           #include <wchar.h>
            wchar_t *wcscat(wchar_t * restrict s1,
                 const wchar_t * restrict s2);
    Description
2   The wcscat function appends a copy of the wide string pointed to by s2 (including the
    terminating null wide character) to the end of the wide string pointed to by s1. The initial
    wide character of s2 overwrites the null wide character at the end of s1.
    Returns
3   The wcscat function returns the value of s1.
    7.28.4.3.2 The wcsncat function
    Synopsis
1           #include <wchar.h>
            wchar_t *wcsncat(wchar_t * restrict s1,
                 const wchar_t * restrict s2,
                 size_t n);
    Description
2   The wcsncat function appends not more than n wide characters (a null wide character
    and those that follow it are not appended) from the array pointed to by s2 to the end of

[page 429]

    the wide string pointed to by s1. The initial wide character of s2 overwrites the null
    wide character at the end of s1. A terminating null wide character is always appended to
    the result.334)
    Returns
3   The wcsncat function returns the value of s1.
    7.28.4.4 Wide string comparison functions
1   Unless explicitly stated otherwise, the functions described in this subclause order two
    wide characters the same way as two integers of the underlying integer type designated
    by wchar_t.
    7.28.4.4.1 The wcscmp function
    Synopsis
1           #include <wchar.h>
            int wcscmp(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcscmp function compares the wide string pointed to by s1 to the wide string
    pointed to by s2.
    Returns
3   The wcscmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the
    wide string pointed to by s2.
    7.28.4.4.2 The wcscoll function
    Synopsis
1           #include <wchar.h>
            int wcscoll(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcscoll function compares the wide string pointed to by s1 to the wide string
    pointed to by s2, both interpreted as appropriate to the LC_COLLATE category of the
    current locale.
    Returns
3   The wcscoll function returns an integer greater than, equal to, or less than zero,
    accordingly as the wide string pointed to by s1 is greater than, equal to, or less than the


    334) Thus, the maximum number of wide characters that can end up in the array pointed to by s1 is
         wcslen(s1)+n+1.

[page 430]

    wide string pointed to by s2 when both are interpreted as appropriate to the current
    locale.
    7.28.4.4.3 The wcsncmp function
    Synopsis
1           #include <wchar.h>
            int wcsncmp(const wchar_t *s1, const wchar_t *s2,
                 size_t n);
    Description
2   The wcsncmp function compares not more than n wide characters (those that follow a
    null wide character are not compared) from the array pointed to by s1 to the array
    pointed to by s2.
    Returns
3   The wcsncmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal
    to, or less than the possibly null-terminated array pointed to by s2.
    7.28.4.4.4 The wcsxfrm function
    Synopsis
1           #include <wchar.h>
            size_t wcsxfrm(wchar_t * restrict s1,
                 const wchar_t * restrict s2,
                 size_t n);
    Description
2   The wcsxfrm function transforms the wide string pointed to by s2 and places the
    resulting wide string into the array pointed to by s1. The transformation is such that if
    the wcscmp function is applied to two transformed wide strings, it returns a value greater
    than, equal to, or less than zero, corresponding to the result of the wcscoll function
    applied to the same two original wide strings. No more than n wide characters are placed
    into the resulting array pointed to by s1, including the terminating null wide character. If
    n is zero, s1 is permitted to be a null pointer.
    Returns
3   The wcsxfrm function returns the length of the transformed wide string (not including
    the terminating null wide character). If the value returned is n or greater, the contents of
    the array pointed to by s1 are indeterminate.
4   EXAMPLE The value of the following expression is the length of the array needed to hold the
    transformation of the wide string pointed to by s:


[page 431]

           1 + wcsxfrm(NULL, s, 0)

    7.28.4.4.5 The wmemcmp function
    Synopsis
1          #include <wchar.h>
           int wmemcmp(const wchar_t *s1, const wchar_t *s2,
                size_t n);
    Description
2   The wmemcmp function compares the first n wide characters of the object pointed to by
    s1 to the first n wide characters of the object pointed to by s2.
    Returns
3   The wmemcmp function returns an integer greater than, equal to, or less than zero,
    accordingly as the object pointed to by s1 is greater than, equal to, or less than the object
    pointed to by s2.
    7.28.4.5 Wide string search functions
    7.28.4.5.1 The wcschr function
    Synopsis
1          #include <wchar.h>
           wchar_t *wcschr(const wchar_t *s, wchar_t c);
    Description
2   The wcschr function locates the first occurrence of c in the wide string pointed to by s.
    The terminating null wide character is considered to be part of the wide string.
    Returns
3   The wcschr function returns a pointer to the located wide character, or a null pointer if
    the wide character does not occur in the wide string.
    7.28.4.5.2 The wcscspn function
    Synopsis
1          #include <wchar.h>
           size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcscspn function computes the length of the maximum initial segment of the wide
    string pointed to by s1 which consists entirely of wide characters not from the wide
    string pointed to by s2.



[page 432]

    Returns
3   The wcscspn function returns the length of the segment.
    7.28.4.5.3 The wcspbrk function
    Synopsis
1           #include <wchar.h>
            wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcspbrk function locates the first occurrence in the wide string pointed to by s1 of
    any wide character from the wide string pointed to by s2.
    Returns
3   The wcspbrk function returns a pointer to the wide character in s1, or a null pointer if
    no wide character from s2 occurs in s1.
    7.28.4.5.4 The wcsrchr function
    Synopsis
1           #include <wchar.h>
            wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
    Description
2   The wcsrchr function locates the last occurrence of c in the wide string pointed to by
    s. The terminating null wide character is considered to be part of the wide string.
    Returns
3   The wcsrchr function returns a pointer to the wide character, or a null pointer if c does
    not occur in the wide string.
    7.28.4.5.5 The wcsspn function
    Synopsis
1           #include <wchar.h>
            size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcsspn function computes the length of the maximum initial segment of the wide
    string pointed to by s1 which consists entirely of wide characters from the wide string
    pointed to by s2.
    Returns
3   The wcsspn function returns the length of the segment.


[page 433]

    7.28.4.5.6 The wcsstr function
    Synopsis
1          #include <wchar.h>
           wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
    Description
2   The wcsstr function locates the first occurrence in the wide string pointed to by s1 of
    the sequence of wide characters (excluding the terminating null wide character) in the
    wide string pointed to by s2.
    Returns
3   The wcsstr function returns a pointer to the located wide string, or a null pointer if the
    wide string is not found. If s2 points to a wide string with zero length, the function
    returns s1.
    7.28.4.5.7 The wcstok function
    Synopsis
1          #include <wchar.h>
           wchar_t *wcstok(wchar_t * restrict s1,
                const wchar_t * restrict s2,
                wchar_t ** restrict ptr);
    Description
2   A sequence of calls to the wcstok function breaks the wide string pointed to by s1 into
    a sequence of tokens, each of which is delimited by a wide character from the wide string
    pointed to by s2. The third argument points to a caller-provided wchar_t pointer into
    which the wcstok function stores information necessary for it to continue scanning the
    same wide string.
3   The first call in a sequence has a non-null first argument and stores an initial value in the
    object pointed to by ptr. Subsequent calls in the sequence have a null first argument and
    the object pointed to by ptr is required to have the value stored by the previous call in
    the sequence, which is then updated. The separator wide string pointed to by s2 may be
    different from call to call.
4   The first call in the sequence searches the wide string pointed to by s1 for the first wide
    character that is not contained in the current separator wide string pointed to by s2. If no
    such wide character is found, then there are no tokens in the wide string pointed to by s1
    and the wcstok function returns a null pointer. If such a wide character is found, it is
    the start of the first token.
5   The wcstok function then searches from there for a wide character that is contained in
    the current separator wide string. If no such wide character is found, the current token
[page 434]

    extends to the end of the wide string pointed to by s1, and subsequent searches in the
    same wide string for a token return a null pointer. If such a wide character is found, it is
    overwritten by a null wide character, which terminates the current token.
6   In all cases, the wcstok function stores sufficient information in the pointer pointed to
    by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
    value for ptr, shall start searching just past the element overwritten by a null wide
    character (if any).
    Returns
7   The wcstok function returns a pointer to the first wide character of a token, or a null
    pointer if there is no token.
8   EXAMPLE
            #include <wchar.h>
            static wchar_t str1[] = L"?a???b,,,#c";
            static wchar_t str2[] = L"\t \t";
            wchar_t *t, *ptr1, *ptr2;
            t   =   wcstok(str1,   L"?", &ptr1);         //   t   points to the token L"a"
            t   =   wcstok(NULL,   L",", &ptr1);         //   t   points to the token L"??b"
            t   =   wcstok(str2,   L" \t", &ptr2);       //   t   is a null pointer
            t   =   wcstok(NULL,   L"#,", &ptr1);        //   t   points to the token L"c"
            t   =   wcstok(NULL,   L"?", &ptr1);         //   t   is a null pointer

    7.28.4.5.8 The wmemchr function
    Synopsis
1           #include <wchar.h>
            wchar_t *wmemchr(const wchar_t *s, wchar_t c,
                 size_t n);
    Description
2   The wmemchr function locates the first occurrence of c in the initial n wide characters of
    the object pointed to by s.
    Returns
3   The wmemchr function returns a pointer to the located wide character, or a null pointer if
    the wide character does not occur in the object.




[page 435]

    7.28.4.6 Miscellaneous functions
    7.28.4.6.1 The wcslen function
    Synopsis
1          #include <wchar.h>
           size_t wcslen(const wchar_t *s);
    Description
2   The wcslen function computes the length of the wide string pointed to by s.
    Returns
3   The wcslen function returns the number of wide characters that precede the terminating
    null wide character.
    7.28.4.6.2 The wmemset function
    Synopsis
1          #include <wchar.h>
           wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
    Description
2   The wmemset function copies the value of c into each of the first n wide characters of
    the object pointed to by s.
    Returns
3   The wmemset function returns the value of s.
    7.28.5 Wide character time conversion functions
    7.28.5.1 The wcsftime function
    Synopsis
1          #include <time.h>
           #include <wchar.h>
           size_t wcsftime(wchar_t * restrict s,
                size_t maxsize,
                const wchar_t * restrict format,
                const struct tm * restrict timeptr);
    Description
2   The wcsftime function is equivalent to the strftime function, except that:
    -- The argument s points to the initial element of an array of wide characters into which
      the generated output is to be placed.


[page 436]

    -- The argument maxsize indicates the limiting number of wide characters.
    -- The argument format is a wide string and the conversion specifiers are replaced by
      corresponding sequences of wide characters.
    -- The return value indicates the number of wide characters.
    Returns
3   If the total number of resulting wide characters including the terminating null wide
    character is not more than maxsize, the wcsftime function returns the number of
    wide characters placed into the array pointed to by s not including the terminating null
    wide character. Otherwise, zero is returned and the contents of the array are
    indeterminate.
    7.28.6 Extended multibyte/wide character conversion utilities
1   The header <wchar.h> declares an extended set of functions useful for conversion
    between multibyte characters and wide characters.
2   Most of the following functions -- those that are listed as ''restartable'', 7.28.6.3 and
    7.28.6.4 -- take as a last argument a pointer to an object of type mbstate_t that is used
    to describe the current conversion state from a particular multibyte character sequence to
    a wide character sequence (or the reverse) under the rules of a particular setting for the
    LC_CTYPE category of the current locale.
3   The initial conversion state corresponds, for a conversion in either direction, to the
    beginning of a new multibyte character in the initial shift state. A zero-valued
    mbstate_t object is (at least) one way to describe an initial conversion state. A zero-
    valued mbstate_t object can be used to initiate conversion involving any multibyte
    character sequence, in any LC_CTYPE category setting. If an mbstate_t object has
    been altered by any of the functions described in this subclause, and is then used with a
    different multibyte character sequence, or in the other conversion direction, or with a
    different LC_CTYPE category setting than on earlier function calls, the behavior is
    undefined.335)
4   On entry, each function takes the described conversion state (either internal or pointed to
    by an argument) as current. The conversion state described by the referenced object is
    altered as needed to track the shift state, and the position within a multibyte character, for
    the associated multibyte character sequence.




    335) Thus, a particular mbstate_t object can be used, for example, with both the mbrtowc and
         mbsrtowcs functions as long as they are used to step sequentially through the same multibyte
         character string.

[page 437]

    7.28.6.1 Single-byte/wide character conversion functions
    7.28.6.1.1 The btowc function
    Synopsis
1          #include <wchar.h>                                                                        *
           wint_t btowc(int c);
    Description
2   The btowc function determines whether c constitutes a valid single-byte character in the
    initial shift state.
    Returns
3   The btowc function returns WEOF if c has the value EOF or if (unsigned char)c
    does not constitute a valid single-byte character in the initial shift state. Otherwise, it
    returns the wide character representation of that character.
    7.28.6.1.2 The wctob function
    Synopsis
1          #include <wchar.h>                                                                        *
           int wctob(wint_t c);
    Description
2   The wctob function determines whether c corresponds to a member of the extended
    character set whose multibyte character representation is a single byte when in the initial
    shift state.
    Returns
3   The wctob function returns EOF if c does not correspond to a multibyte character with
    length one in the initial shift state. Otherwise, it returns the single-byte representation of
    that character as an unsigned char converted to an int.
    7.28.6.2 Conversion state functions
    7.28.6.2.1 The mbsinit function
    Synopsis
1          #include <wchar.h>
           int mbsinit(const mbstate_t *ps);
    Description
2   If ps is not a null pointer, the mbsinit function determines whether the referenced
    mbstate_t object describes an initial conversion state.



[page 438]

    Returns
3   The mbsinit function returns nonzero if ps is a null pointer or if the referenced object
    describes an initial conversion state; otherwise, it returns zero.
    7.28.6.3 Restartable multibyte/wide character conversion functions
1   These functions differ from the corresponding multibyte character functions of 7.22.7
    (mblen, mbtowc, and wctomb) in that they have an extra parameter, ps, of type
    pointer to mbstate_t that points to an object that can completely describe the current
    conversion state of the associated multibyte character sequence. If ps is a null pointer,
    each function uses its own internal mbstate_t object instead, which is initialized at
    program startup to the initial conversion state; the functions are not required to avoid data
    races in this case. The implementation behaves as if no library function calls these
    functions with a null pointer for ps.
2   Also unlike their corresponding functions, the return value does not represent whether the
    encoding is state-dependent.
    7.28.6.3.1 The mbrlen function
    Synopsis
1           #include <wchar.h>
            size_t mbrlen(const char * restrict s,
                 size_t n,
                 mbstate_t * restrict ps);
    Description
2   The mbrlen function is equivalent to the call:
            mbrtowc(NULL, s, n, ps != NULL ? ps : &internal)
    where internal is the mbstate_t object for the mbrlen function, except that the
    expression designated by ps is evaluated only once.
    Returns
3   The mbrlen function returns a value between zero and n, inclusive, (size_t)(-2),
    or (size_t)(-1).
    Forward references: the mbrtowc function (7.28.6.3.2).




[page 439]

    7.28.6.3.2 The mbrtowc function
    Synopsis
1           #include <wchar.h>
            size_t mbrtowc(wchar_t * restrict pwc,
                 const char * restrict s,
                 size_t n,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the mbrtowc function is equivalent to the call:
                    mbrtowc(NULL, "", 1, ps)
    In this case, the values of the parameters pwc and n are ignored.
3   If s is not a null pointer, the mbrtowc function inspects at most n bytes beginning with
    the byte pointed to by s to determine the number of bytes needed to complete the next
    multibyte character (including any shift sequences). If the function determines that the
    next multibyte character is complete and valid, it determines the value of the
    corresponding wide character and then, if pwc is not a null pointer, stores that value in
    the object pointed to by pwc. If the corresponding wide character is the null wide
    character, the resulting state described is the initial conversion state.
    Returns
4   The mbrtowc function returns the first of the following that applies (given the current
    conversion state):
    0                     if the next n or fewer bytes complete the multibyte character that
                          corresponds to the null wide character (which is the value stored).
    between 1 and n inclusive if the next n or fewer bytes complete a valid multibyte
                       character (which is the value stored); the value returned is the number
                       of bytes that complete the multibyte character.
    (size_t)(-2) if the next n bytes contribute to an incomplete (but potentially valid)
                 multibyte character, and all n bytes have been processed (no value is
                 stored).336)
    (size_t)(-1) if an encoding error occurs, in which case the next n or fewer bytes
                 do not contribute to a complete and valid multibyte character (no
                 value is stored); the value of the macro EILSEQ is stored in errno,
                 and the conversion state is unspecified.

    336) When n has at least the value of the MB_CUR_MAX macro, this case can only occur if s points at a
         sequence of redundant shift sequences (for implementations with state-dependent encodings).

[page 440]

    7.28.6.3.3 The wcrtomb function
    Synopsis
1           #include <wchar.h>
            size_t wcrtomb(char * restrict s,
                 wchar_t wc,
                 mbstate_t * restrict ps);
    Description
2   If s is a null pointer, the wcrtomb function is equivalent to the call
                    wcrtomb(buf, L'\0', ps)
    where buf is an internal buffer.
3   If s is not a null pointer, the wcrtomb function determines the number of bytes needed
    to represent the multibyte character that corresponds to the wide character given by wc
    (including any shift sequences), and stores the multibyte character representation in the
    array whose first element is pointed to by s. At most MB_CUR_MAX bytes are stored. If
    wc is a null wide character, a null byte is stored, preceded by any shift sequence needed
    to restore the initial shift state; the resulting state described is the initial conversion state.
    Returns
4   The wcrtomb function returns the number of bytes stored in the array object (including
    any shift sequences). When wc is not a valid wide character, an encoding error occurs:
    the function stores the value of the macro EILSEQ in errno and returns
    (size_t)(-1); the conversion state is unspecified.
    7.28.6.4 Restartable multibyte/wide string conversion functions
1   These functions differ from the corresponding multibyte string functions of 7.22.8
    (mbstowcs and wcstombs) in that they have an extra parameter, ps, of type pointer to
    mbstate_t that points to an object that can completely describe the current conversion
    state of the associated multibyte character sequence. If ps is a null pointer, each function
    uses its own internal mbstate_t object instead, which is initialized at program startup
    to the initial conversion state; the functions are not required to avoid data races in this
    case. The implementation behaves as if no library function calls these functions with a
    null pointer for ps.
2   Also unlike their corresponding functions, the conversion source parameter, src, has a
    pointer-to-pointer type. When the function is storing the results of conversions (that is,
    when dst is not a null pointer), the pointer object pointed to by this parameter is updated
    to reflect the amount of the source processed by that invocation.




[page 441]

    7.28.6.4.1 The mbsrtowcs function
    Synopsis
1            #include <wchar.h>
             size_t mbsrtowcs(wchar_t * restrict dst,
                  const char ** restrict src,
                  size_t len,
                  mbstate_t * restrict ps);
    Description
2   The mbsrtowcs function converts a sequence of multibyte characters that begins in the
    conversion state described by the object pointed to by ps, from the array indirectly
    pointed to by src into a sequence of corresponding wide characters. If dst is not a null
    pointer, the converted characters are stored into the array pointed to by dst. Conversion
    continues up to and including a terminating null character, which is also stored.
    Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
    not form a valid multibyte character, or (if dst is not a null pointer) when len wide
    characters have been stored into the array pointed to by dst.337) Each conversion takes
    place as if by a call to the mbrtowc function.
3   If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
    pointer (if conversion stopped due to reaching a terminating null character) or the address
    just past the last multibyte character converted (if any). If conversion stopped due to
    reaching a terminating null character and if dst is not a null pointer, the resulting state
    described is the initial conversion state.
    Returns
4   If the input conversion encounters a sequence of bytes that do not form a valid multibyte
    character, an encoding error occurs: the mbsrtowcs function stores the value of the
    macro EILSEQ in errno and returns (size_t)(-1); the conversion state is
    unspecified. Otherwise, it returns the number of multibyte characters successfully
    converted, not including the terminating null character (if any).




    337) Thus, the value of len is ignored if dst is a null pointer.

[page 442]

    7.28.6.4.2 The wcsrtombs function
    Synopsis
1           #include <wchar.h>
            size_t wcsrtombs(char * restrict dst,
                 const wchar_t ** restrict src,
                 size_t len,
                 mbstate_t * restrict ps);
    Description
2   The wcsrtombs function converts a sequence of wide characters from the array
    indirectly pointed to by src into a sequence of corresponding multibyte characters that
    begins in the conversion state described by the object pointed to by ps. If dst is not a
    null pointer, the converted characters are then stored into the array pointed to by dst.
    Conversion continues up to and including a terminating null wide character, which is also
    stored. Conversion stops earlier in two cases: when a wide character is reached that does
    not correspond to a valid multibyte character, or (if dst is not a null pointer) when the
    next multibyte character would exceed the limit of len total bytes to be stored into the
    array pointed to by dst. Each conversion takes place as if by a call to the wcrtomb
    function.338)
3   If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
    pointer (if conversion stopped due to reaching a terminating null wide character) or the
    address just past the last wide character converted (if any). If conversion stopped due to
    reaching a terminating null wide character, the resulting state described is the initial
    conversion state.
    Returns
4   If conversion stops because a wide character is reached that does not correspond to a
    valid multibyte character, an encoding error occurs: the wcsrtombs function stores the
    value of the macro EILSEQ in errno and returns (size_t)(-1); the conversion
    state is unspecified. Otherwise, it returns the number of bytes in the resulting multibyte
    character sequence, not including the terminating null character (if any).




    338) If conversion stops because a terminating null wide character has been reached, the bytes stored
         include those necessary to reach the initial shift state immediately before the null byte.

[page 443]

    7.29 Wide character classification and mapping utilities <wctype.h>
    7.29.1 Introduction
1   The header <wctype.h> defines one macro, and declares three data types and many
    functions.339)
2   The types declared are
             wint_t
    described in 7.28.1;
             wctrans_t
    which is a scalar type that can hold values which represent locale-specific character
    mappings; and
             wctype_t
    which is a scalar type that can hold values which represent locale-specific character
    classifications.
3   The macro defined is WEOF (described in 7.28.1).
4   The functions declared are grouped as follows:
    -- Functions that provide wide character classification;
    -- Extensible functions that provide wide character classification;
    -- Functions that provide wide character case mapping;
    -- Extensible functions that provide wide character mapping.
5   For all functions described in this subclause that accept an argument of type wint_t, the
    value shall be representable as a wchar_t or shall equal the value of the macro WEOF. If
    this argument has any other value, the behavior is undefined.
6   The behavior of these functions is affected by the LC_CTYPE category of the current
    locale.




    339) See ''future library directions'' (7.30.13).

[page 444]

    7.29.2 Wide character classification utilities
1   The header <wctype.h> declares several functions useful for classifying wide
    characters.
2   The term printing wide character refers to a member of a locale-specific set of wide
    characters, each of which occupies at least one printing position on a display device. The
    term control wide character refers to a member of a locale-specific set of wide characters
    that are not printing wide characters.
    7.29.2.1 Wide character classification functions
1   The functions in this subclause return nonzero (true) if and only if the value of the
    argument wc conforms to that in the description of the function.
2   Each of the following functions returns true for each wide character that corresponds (as
    if by a call to the wctob function) to a single-byte character for which the corresponding
    character classification function from 7.4.1 returns true, except that the iswgraph and
    iswpunct functions may differ with respect to wide characters other than L' ' that are
    both printing and white-space wide characters.340)
    Forward references: the wctob function (7.28.6.1.2).
    7.29.2.1.1 The iswalnum function
    Synopsis
1           #include <wctype.h>
            int iswalnum(wint_t wc);
    Description
2   The iswalnum function tests for any wide character for which iswalpha or
    iswdigit is true.
    7.29.2.1.2 The iswalpha function
    Synopsis
1           #include <wctype.h>
            int iswalpha(wint_t wc);
    Description
2   The iswalpha function tests for any wide character for which iswupper or
    iswlower is true, or any wide character that is one of a locale-specific set of alphabetic

    340) For example, if the expression isalpha(wctob(wc)) evaluates to true, then the call
         iswalpha(wc) also returns true. But, if the expression isgraph(wctob(wc)) evaluates to true
         (which cannot occur for wc == L' ' of course), then either iswgraph(wc) or iswprint(wc)
         && iswspace(wc) is true, but not both.

[page 445]

    wide characters for which none of iswcntrl, iswdigit, iswpunct, or iswspace
    is true.341)
    7.29.2.1.3 The iswblank function
    Synopsis
1           #include <wctype.h>
            int iswblank(wint_t wc);
    Description
2   The iswblank function tests for any wide character that is a standard blank wide
    character or is one of a locale-specific set of wide characters for which iswspace is true
    and that is used to separate words within a line of text. The standard blank wide
    characters are the following: space (L' '), and horizontal tab (L'\t'). In the "C"
    locale, iswblank returns true only for the standard blank characters.
    7.29.2.1.4 The iswcntrl function
    Synopsis
1           #include <wctype.h>
            int iswcntrl(wint_t wc);
    Description
2   The iswcntrl function tests for any control wide character.
    7.29.2.1.5 The iswdigit function
    Synopsis
1           #include <wctype.h>
            int iswdigit(wint_t wc);
    Description
2   The iswdigit function tests for any wide character that corresponds to a decimal-digit
    character (as defined in 5.2.1).
    7.29.2.1.6 The iswgraph function
    Synopsis
1           #include <wctype.h>
            int iswgraph(wint_t wc);




    341) The functions iswlower and iswupper test true or false separately for each of these additional
         wide characters; all four combinations are possible.

[page 446]

    Description
2   The iswgraph function tests for any wide character for which iswprint is true and
    iswspace is false.342)
    7.29.2.1.7 The iswlower function
    Synopsis
1           #include <wctype.h>
            int iswlower(wint_t wc);
    Description
2   The iswlower function tests for any wide character that corresponds to a lowercase
    letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
    iswdigit, iswpunct, or iswspace is true.
    7.29.2.1.8 The iswprint function
    Synopsis
1           #include <wctype.h>
            int iswprint(wint_t wc);
    Description
2   The iswprint function tests for any printing wide character.
    7.29.2.1.9 The iswpunct function
    Synopsis
1           #include <wctype.h>
            int iswpunct(wint_t wc);
    Description
2   The iswpunct function tests for any printing wide character that is one of a locale-
    specific set of punctuation wide characters for which neither iswspace nor iswalnum
    is true.342)
    7.29.2.1.10 The iswspace function
    Synopsis
1           #include <wctype.h>
            int iswspace(wint_t wc);



    342) Note that the behavior of the iswgraph and iswpunct functions may differ from their
         corresponding functions in 7.4.1 with respect to printing, white-space, single-byte execution
         characters other than ' '.

[page 447]

    Description
2   The iswspace function tests for any wide character that corresponds to a locale-specific
    set of white-space wide characters for which none of iswalnum, iswgraph, or
    iswpunct is true.
    7.29.2.1.11 The iswupper function
    Synopsis
1          #include <wctype.h>
           int iswupper(wint_t wc);
    Description
2   The iswupper function tests for any wide character that corresponds to an uppercase
    letter or is one of a locale-specific set of wide characters for which none of iswcntrl,
    iswdigit, iswpunct, or iswspace is true.
    7.29.2.1.12 The iswxdigit function
    Synopsis
1          #include <wctype.h>
           int iswxdigit(wint_t wc);
    Description
2   The iswxdigit function tests for any wide character that corresponds to a
    hexadecimal-digit character (as defined in 6.4.4.1).
    7.29.2.2 Extensible wide character classification functions
1   The functions wctype and iswctype provide extensible wide character classification
    as well as testing equivalent to that performed by the functions described in the previous
    subclause (7.29.2.1).
    7.29.2.2.1 The iswctype function
    Synopsis
1          #include <wctype.h>
           int iswctype(wint_t wc, wctype_t desc);
    Description
2   The iswctype function determines whether the wide character wc has the property
    described by desc. The current setting of the LC_CTYPE category shall be the same as
    during the call to wctype that returned the value desc.
3   Each of the following expressions has a truth-value equivalent to the call to the wide
    character classification function (7.29.2.1) in the comment that follows the expression:


[page 448]

            iswctype(wc,      wctype("alnum"))              //   iswalnum(wc)
            iswctype(wc,      wctype("alpha"))              //   iswalpha(wc)
            iswctype(wc,      wctype("blank"))              //   iswblank(wc)
            iswctype(wc,      wctype("cntrl"))              //   iswcntrl(wc)
            iswctype(wc,      wctype("digit"))              //   iswdigit(wc)
            iswctype(wc,      wctype("graph"))              //   iswgraph(wc)
            iswctype(wc,      wctype("lower"))              //   iswlower(wc)
            iswctype(wc,      wctype("print"))              //   iswprint(wc)
            iswctype(wc,      wctype("punct"))              //   iswpunct(wc)
            iswctype(wc,      wctype("space"))              //   iswspace(wc)
            iswctype(wc,      wctype("upper"))              //   iswupper(wc)
            iswctype(wc,      wctype("xdigit"))             //   iswxdigit(wc)
    Returns
4   The iswctype function returns nonzero (true) if and only if the value of the wide
    character wc has the property described by desc. If desc is zero, the iswctype
    function returns zero (false).
    Forward references: the wctype function (7.29.2.2.2).
    7.29.2.2.2 The wctype function
    Synopsis
1           #include <wctype.h>
            wctype_t wctype(const char *property);
    Description
2   The wctype function constructs a value with type wctype_t that describes a class of
    wide characters identified by the string argument property.
3   The strings listed in the description of the iswctype function shall be valid in all
    locales as property arguments to the wctype function.
    Returns
4   If property identifies a valid class of wide characters according to the LC_CTYPE
    category of the current locale, the wctype function returns a nonzero value that is valid
    as the second argument to the iswctype function; otherwise, it returns zero.




[page 449]

    7.29.3 Wide character case mapping utilities
1   The header <wctype.h> declares several functions useful for mapping wide characters.
    7.29.3.1 Wide character case mapping functions
    7.29.3.1.1 The towlower function
    Synopsis
1          #include <wctype.h>
           wint_t towlower(wint_t wc);
    Description
2   The towlower function converts an uppercase letter to a corresponding lowercase letter.
    Returns
3   If the argument is a wide character for which iswupper is true and there are one or
    more corresponding wide characters, as specified by the current locale, for which
    iswlower is true, the towlower function returns one of the corresponding wide
    characters (always the same one for any given locale); otherwise, the argument is
    returned unchanged.
    7.29.3.1.2 The towupper function
    Synopsis
1          #include <wctype.h>
           wint_t towupper(wint_t wc);
    Description
2   The towupper function converts a lowercase letter to a corresponding uppercase letter.
    Returns
3   If the argument is a wide character for which iswlower is true and there are one or
    more corresponding wide characters, as specified by the current locale, for which
    iswupper is true, the towupper function returns one of the corresponding wide
    characters (always the same one for any given locale); otherwise, the argument is
    returned unchanged.
    7.29.3.2 Extensible wide character case mapping functions
1   The functions wctrans and towctrans provide extensible wide character mapping as
    well as case mapping equivalent to that performed by the functions described in the
    previous subclause (7.29.3.1).




[page 450]

    7.29.3.2.1 The towctrans function
    Synopsis
1           #include <wctype.h>
            wint_t towctrans(wint_t wc, wctrans_t desc);
    Description
2   The towctrans function maps the wide character wc using the mapping described by
    desc. The current setting of the LC_CTYPE category shall be the same as during the call
    to wctrans that returned the value desc.
3   Each of the following expressions behaves the same as the call to the wide character case
    mapping function (7.29.3.1) in the comment that follows the expression:
            towctrans(wc, wctrans("tolower"))                     // towlower(wc)
            towctrans(wc, wctrans("toupper"))                     // towupper(wc)
    Returns
4   The towctrans function returns the mapped value of wc using the mapping described
    by desc. If desc is zero, the towctrans function returns the value of wc.
    7.29.3.2.2 The wctrans function
    Synopsis
1           #include <wctype.h>
            wctrans_t wctrans(const char *property);
    Description
2   The wctrans function constructs a value with type wctrans_t that describes a
    mapping between wide characters identified by the string argument property.
3   The strings listed in the description of the towctrans function shall be valid in all
    locales as property arguments to the wctrans function.
    Returns
4   If property identifies a valid mapping of wide characters according to the LC_CTYPE
    category of the current locale, the wctrans function returns a nonzero value that is valid
    as the second argument to the towctrans function; otherwise, it returns zero.




[page 451]

    7.30 Future library directions
1   The following names are grouped under individual headers for convenience. All external
    names described below are reserved no matter what headers are included by the program.
    7.30.1 Complex arithmetic <complex.h>
1   The function names
          cerf               cexpm1              clog2
          cerfc              clog10              clgamma
          cexp2              clog1p              ctgamma
    and the same names suffixed with f or l may be added to the declarations in the
    <complex.h> header.
    7.30.2 Character handling <ctype.h>
1   Function names that begin with either is or to, and a lowercase letter may be added to
    the declarations in the <ctype.h> header.
    7.30.3 Errors <errno.h>
1   Macros that begin with E and a digit or E and an uppercase letter may be added to the
    declarations in the <errno.h> header.
    7.30.4 Format conversion of integer types <inttypes.h>
1   Macro names beginning with PRI or SCN followed by any lowercase letter or X may be
    added to the macros defined in the <inttypes.h> header.
    7.30.5 Localization <locale.h>
1   Macros that begin with LC_ and an uppercase letter may be added to the definitions in
    the <locale.h> header.
    7.30.6 Signal handling <signal.h>
1   Macros that begin with either SIG and an uppercase letter or SIG_ and an uppercase
    letter may be added to the definitions in the <signal.h> header.
    7.30.7 Boolean type and values <stdbool.h>
1   The ability to undefine and perhaps then redefine the macros bool, true, and false is
    an obsolescent feature.
    7.30.8 Integer types <stdint.h>
1   Typedef names beginning with int or uint and ending with _t may be added to the
    types defined in the <stdint.h> header. Macro names beginning with INT or UINT
    and ending with _MAX, _MIN, or _C may be added to the macros defined in the
    <stdint.h> header.

[page 452]

    7.30.9 Input/output <stdio.h>
1   Lowercase letters may be added to the conversion specifiers and length modifiers in
    fprintf and fscanf. Other characters may be used in extensions.
2   The use of ungetc on a binary stream where the file position indicator is zero prior to *
    the call is an obsolescent feature.
    7.30.10 General utilities <stdlib.h>
1   Function names that begin with str and a lowercase letter may be added to the
    declarations in the <stdlib.h> header.
    7.30.11 String handling <string.h>
1   Function names that begin with str, mem, or wcs and a lowercase letter may be added
    to the declarations in the <string.h> header.
    7.30.12 Extended multibyte and wide character utilities <wchar.h>
1   Function names that begin with wcs and a lowercase letter may be added to the
    declarations in the <wchar.h> header.
2   Lowercase letters may be added to the conversion specifiers and length modifiers in
    fwprintf and fwscanf. Other characters may be used in extensions.
    7.30.13 Wide character classification and mapping utilities
    <wctype.h>
1   Function names that begin with is or to and a lowercase letter may be added to the
    declarations in the <wctype.h> header.




[page 453]

                                                 Annex A
                                               (informative)
                                Language syntax summary
1   NOTE   The notation is described in 6.1.

    A.1 Lexical grammar
    A.1.1 Lexical elements
    (6.4) token:
                   keyword
                   identifier
                   constant
                   string-literal
                   punctuator
    (6.4) preprocessing-token:
                  header-name
                  identifier
                  pp-number
                  character-constant
                  string-literal
                  punctuator
                  each non-white-space character that cannot be one of the above




[page 454]

A.1.2 Keywords
(6.4.1) keyword: one of
              alignof                     goto                  union
              auto                        if                    unsigned
              break                       inline                void
              case                        int                   volatile
              char                        long                  while
              const                       register              _Alignas
              continue                    restrict              _Atomic
              default                     return                _Bool
              do                          short                 _Complex
              double                      signed                _Generic
              else                        sizeof                _Imaginary
              enum                        static                _Noreturn
              extern                      struct                _Static_assert
              float                       switch                _Thread_local
              for                         typedef
A.1.3 Identifiers
(6.4.2.1) identifier:
               identifier-nondigit
               identifier identifier-nondigit
               identifier digit
(6.4.2.1) identifier-nondigit:
               nondigit
               universal-character-name
               other implementation-defined characters
(6.4.2.1) nondigit: one of
              _ a b          c    d   e    f   g   h    i   j   k   l   m
                   n o       p    q   r    s   t   u    v   w   x   y   z
                   A B       C    D   E    F   G   H    I   J   K   L   M
                   N O       P    Q   R    S   T   U    V   W   X   Y   Z
(6.4.2.1) digit: one of
               0 1 2         3    4   5    6   7   8    9




[page 455]

A.1.4 Universal character names
(6.4.3) universal-character-name:
              \u hex-quad
              \U hex-quad hex-quad
(6.4.3) hex-quad:
              hexadecimal-digit hexadecimal-digit
                           hexadecimal-digit hexadecimal-digit
A.1.5 Constants
(6.4.4) constant:
              integer-constant
              floating-constant
              enumeration-constant
              character-constant
(6.4.4.1) integer-constant:
               decimal-constant integer-suffixopt
               octal-constant integer-suffixopt
               hexadecimal-constant integer-suffixopt
(6.4.4.1) decimal-constant:
              nonzero-digit
              decimal-constant digit
(6.4.4.1) octal-constant:
               0
               octal-constant octal-digit
(6.4.4.1) hexadecimal-constant:
              hexadecimal-prefix hexadecimal-digit
              hexadecimal-constant hexadecimal-digit
(6.4.4.1) hexadecimal-prefix: one of
              0x 0X
(6.4.4.1) nonzero-digit: one of
              1 2 3 4 5              6      7   8   9
(6.4.4.1) octal-digit: one of
               0 1 2 3           4   5      6   7




[page 456]

(6.4.4.1) hexadecimal-digit: one of
              0 1 2 3 4 5                6    7    8   9
              a b c d e f
              A B C D E F
(6.4.4.1) integer-suffix:
               unsigned-suffix long-suffixopt
               unsigned-suffix long-long-suffix
               long-suffix unsigned-suffixopt
               long-long-suffix unsigned-suffixopt
(6.4.4.1) unsigned-suffix: one of
               u U
(6.4.4.1) long-suffix: one of
               l L
(6.4.4.1) long-long-suffix: one of
               ll LL
(6.4.4.2) floating-constant:
               decimal-floating-constant
               hexadecimal-floating-constant
(6.4.4.2) decimal-floating-constant:
              fractional-constant exponent-partopt floating-suffixopt
              digit-sequence exponent-part floating-suffixopt
(6.4.4.2) hexadecimal-floating-constant:
              hexadecimal-prefix hexadecimal-fractional-constant
                            binary-exponent-part floating-suffixopt
              hexadecimal-prefix hexadecimal-digit-sequence
                            binary-exponent-part floating-suffixopt
(6.4.4.2) fractional-constant:
               digit-sequenceopt . digit-sequence
               digit-sequence .
(6.4.4.2) exponent-part:
              e signopt digit-sequence
              E signopt digit-sequence
(6.4.4.2) sign: one of
               + -



[page 457]

(6.4.4.2) digit-sequence:
               digit
               digit-sequence digit
(6.4.4.2) hexadecimal-fractional-constant:
              hexadecimal-digit-sequenceopt .
                             hexadecimal-digit-sequence
              hexadecimal-digit-sequence .
(6.4.4.2) binary-exponent-part:
               p signopt digit-sequence
               P signopt digit-sequence
(6.4.4.2) hexadecimal-digit-sequence:
              hexadecimal-digit
              hexadecimal-digit-sequence hexadecimal-digit
(6.4.4.2) floating-suffix: one of
               f l F L
(6.4.4.3) enumeration-constant:
              identifier
(6.4.4.4) character-constant:
              ' c-char-sequence '
              L' c-char-sequence '
              u' c-char-sequence '
              U' c-char-sequence '
(6.4.4.4) c-char-sequence:
               c-char
               c-char-sequence c-char
(6.4.4.4) c-char:
               any member of the source character set except
                            the single-quote ', backslash \, or new-line character
               escape-sequence
(6.4.4.4) escape-sequence:
              simple-escape-sequence
              octal-escape-sequence
              hexadecimal-escape-sequence
              universal-character-name




[page 458]

(6.4.4.4) simple-escape-sequence: one of
              \' \" \? \\
              \a \b \f \n \r \t                   \v
(6.4.4.4) octal-escape-sequence:
               \ octal-digit
               \ octal-digit octal-digit
               \ octal-digit octal-digit octal-digit
(6.4.4.4) hexadecimal-escape-sequence:
              \x hexadecimal-digit
              hexadecimal-escape-sequence hexadecimal-digit
A.1.6 String literals
(6.4.5) string-literal:
               encoding-prefixopt " s-char-sequenceopt "
(6.4.5) encoding-prefix:
              u8
              u
              U
              L
(6.4.5) s-char-sequence:
               s-char
               s-char-sequence s-char
(6.4.5) s-char:
               any member of the source character set except
                            the double-quote ", backslash \, or new-line character
               escape-sequence
A.1.7 Punctuators
(6.4.6) punctuator: one of
              [ ] ( ) { } . ->
              ++ -- & * + - ~ !
              / % << >> < > <= >=                      ==    !=    ^    |   &&   ||
              ? : ; ...
              = *= /= %= += -= <<=                     >>=    &=       ^=   |=
              , # ##
              <: :> <% %> %: %:%:




[page 459]

A.1.8 Header names
(6.4.7) header-name:
              < h-char-sequence >
              " q-char-sequence "
(6.4.7) h-char-sequence:
              h-char
              h-char-sequence h-char
(6.4.7) h-char:
              any member of the source character set except
                           the new-line character and >
(6.4.7) q-char-sequence:
              q-char
              q-char-sequence q-char
(6.4.7) q-char:
              any member of the source character set except
                           the new-line character and "
A.1.9 Preprocessing numbers
(6.4.8) pp-number:
              digit
              . digit
              pp-number   digit
              pp-number   identifier-nondigit
              pp-number   e sign
              pp-number   E sign
              pp-number   p sign
              pp-number   P sign
              pp-number   .




[page 460]

A.2 Phrase structure grammar
A.2.1 Expressions
(6.5.1) primary-expression:
              identifier
              constant
              string-literal
              ( expression )
              generic-selection
(6.5.1.1) generic-selection:
              _Generic ( assignment-expression , generic-assoc-list )
(6.5.1.1) generic-assoc-list:
              generic-association
              generic-assoc-list , generic-association
(6.5.1.1) generic-association:
              type-name : assignment-expression
              default : assignment-expression
(6.5.2) postfix-expression:
              primary-expression
              postfix-expression [ expression ]
              postfix-expression ( argument-expression-listopt )
              postfix-expression . identifier
              postfix-expression -> identifier
              postfix-expression ++
              postfix-expression --
              ( type-name ) { initializer-list }
              ( type-name ) { initializer-list , }
(6.5.2) argument-expression-list:
             assignment-expression
             argument-expression-list , assignment-expression
(6.5.3) unary-expression:
              postfix-expression
              ++ unary-expression
              -- unary-expression
              unary-operator cast-expression
              sizeof unary-expression
              sizeof ( type-name )
              alignof ( type-name )

[page 461]

(6.5.3) unary-operator: one of
              & * + - ~                !
(6.5.4) cast-expression:
               unary-expression
               ( type-name ) cast-expression
(6.5.5) multiplicative-expression:
               cast-expression
               multiplicative-expression * cast-expression
               multiplicative-expression / cast-expression
               multiplicative-expression % cast-expression
(6.5.6) additive-expression:
               multiplicative-expression
               additive-expression + multiplicative-expression
               additive-expression - multiplicative-expression
(6.5.7) shift-expression:
                additive-expression
                shift-expression << additive-expression
                shift-expression >> additive-expression
(6.5.8) relational-expression:
               shift-expression
               relational-expression   <    shift-expression
               relational-expression   >    shift-expression
               relational-expression   <=   shift-expression
               relational-expression   >=   shift-expression
(6.5.9) equality-expression:
               relational-expression
               equality-expression == relational-expression
               equality-expression != relational-expression
(6.5.10) AND-expression:
             equality-expression
             AND-expression & equality-expression
(6.5.11) exclusive-OR-expression:
              AND-expression
              exclusive-OR-expression ^ AND-expression




[page 462]

(6.5.12) inclusive-OR-expression:
               exclusive-OR-expression
               inclusive-OR-expression | exclusive-OR-expression
(6.5.13) logical-AND-expression:
              inclusive-OR-expression
              logical-AND-expression && inclusive-OR-expression
(6.5.14) logical-OR-expression:
              logical-AND-expression
              logical-OR-expression || logical-AND-expression
(6.5.15) conditional-expression:
              logical-OR-expression
              logical-OR-expression ? expression : conditional-expression
(6.5.16) assignment-expression:
              conditional-expression
              unary-expression assignment-operator assignment-expression
(6.5.16) assignment-operator: one of
              = *= /= %= +=                -=    <<=    >>=      &=    ^=   |=
(6.5.17) expression:
              assignment-expression
              expression , assignment-expression
(6.6) constant-expression:
              conditional-expression
A.2.2 Declarations
(6.7) declaration:
               declaration-specifiers init-declarator-listopt ;
               static_assert-declaration
(6.7) declaration-specifiers:
               storage-class-specifier declaration-specifiersopt
               type-specifier declaration-specifiersopt
               type-qualifier declaration-specifiersopt
               function-specifier declaration-specifiersopt
               alignment-specifier declaration-specifiersopt
(6.7) init-declarator-list:
               init-declarator
               init-declarator-list , init-declarator


[page 463]

(6.7) init-declarator:
               declarator
               declarator = initializer
(6.7.1) storage-class-specifier:
              typedef
              extern
              static
              _Thread_local
              auto
              register
(6.7.2) type-specifier:
               void
               char
               short
               int
               long
               float
               double
               signed
               unsigned
               _Bool
               _Complex
               atomic-type-specifier
               struct-or-union-specifier
               enum-specifier
               typedef-name
(6.7.2.1) struct-or-union-specifier:
               struct-or-union identifieropt { struct-declaration-list }
               struct-or-union identifier
(6.7.2.1) struct-or-union:
               struct
               union
(6.7.2.1) struct-declaration-list:
               struct-declaration
               struct-declaration-list struct-declaration
(6.7.2.1) struct-declaration:
               specifier-qualifier-list struct-declarator-listopt ;
               static_assert-declaration

[page 464]

(6.7.2.1) specifier-qualifier-list:
               type-specifier specifier-qualifier-listopt
               type-qualifier specifier-qualifier-listopt
(6.7.2.1) struct-declarator-list:
               struct-declarator
               struct-declarator-list , struct-declarator
(6.7.2.1) struct-declarator:
               declarator
               declaratoropt : constant-expression
(6.7.2.2) enum-specifier:
              enum identifieropt { enumerator-list }
              enum identifieropt { enumerator-list , }
              enum identifier
(6.7.2.2) enumerator-list:
              enumerator
              enumerator-list , enumerator
(6.7.2.2) enumerator:
              enumeration-constant
              enumeration-constant = constant-expression
(6.7.2.4) atomic-type-specifier:
              _Atomic ( type-name )
(6.7.3) type-qualifier:
              const
              restrict
              volatile
              _Atomic
(6.7.4) function-specifier:
               inline
               _Noreturn
(6.7.5) alignment-specifier:
              _Alignas ( type-name )
              _Alignas ( constant-expression )
(6.7.6) declarator:
              pointeropt direct-declarator



[page 465]

(6.7.6) direct-declarator:
               identifier
               ( declarator )
               direct-declarator [ type-qualifier-listopt assignment-expressionopt ]
               direct-declarator [ static type-qualifier-listopt assignment-expression ]
               direct-declarator [ type-qualifier-list static assignment-expression ]
               direct-declarator [ type-qualifier-listopt * ]
               direct-declarator ( parameter-type-list )
               direct-declarator ( identifier-listopt )
(6.7.6) pointer:
               * type-qualifier-listopt
               * type-qualifier-listopt pointer
(6.7.6) type-qualifier-list:
              type-qualifier
              type-qualifier-list type-qualifier
(6.7.6) parameter-type-list:
             parameter-list
             parameter-list , ...
(6.7.6) parameter-list:
             parameter-declaration
             parameter-list , parameter-declaration
(6.7.6) parameter-declaration:
             declaration-specifiers declarator
             declaration-specifiers abstract-declaratoropt
(6.7.6) identifier-list:
               identifier
               identifier-list , identifier
(6.7.7) type-name:
              specifier-qualifier-list abstract-declaratoropt
(6.7.7) abstract-declarator:
              pointer
              pointeropt direct-abstract-declarator




[page 466]

(6.7.7) direct-abstract-declarator:
               ( abstract-declarator )
               direct-abstract-declaratoropt [ type-qualifier-listopt
                              assignment-expressionopt ]
               direct-abstract-declaratoropt [ static type-qualifier-listopt
                              assignment-expression ]
               direct-abstract-declaratoropt [ type-qualifier-list static
                              assignment-expression ]
               direct-abstract-declaratoropt [ * ]
               direct-abstract-declaratoropt ( parameter-type-listopt )
(6.7.8) typedef-name:
              identifier
(6.7.9) initializer:
                assignment-expression
                { initializer-list }
                { initializer-list , }
(6.7.9) initializer-list:
                designationopt initializer
                initializer-list , designationopt initializer
(6.7.9) designation:
              designator-list =
(6.7.9) designator-list:
              designator
              designator-list designator
(6.7.9) designator:
              [ constant-expression ]
              . identifier
(6.7.10) static_assert-declaration:
               _Static_assert ( constant-expression , string-literal ) ;




[page 467]

A.2.3 Statements
(6.8) statement:
              labeled-statement
              compound-statement
              expression-statement
              selection-statement
              iteration-statement
              jump-statement
(6.8.1) labeled-statement:
               identifier : statement
               case constant-expression : statement
               default : statement
(6.8.2) compound-statement:
             { block-item-listopt }
(6.8.2) block-item-list:
               block-item
               block-item-list block-item
(6.8.2) block-item:
               declaration
               statement
(6.8.3) expression-statement:
              expressionopt ;
(6.8.4) selection-statement:
               if ( expression ) statement
               if ( expression ) statement else statement
               switch ( expression ) statement
(6.8.5) iteration-statement:
                while ( expression ) statement
                do statement while ( expression ) ;
                for ( expressionopt ; expressionopt ; expressionopt ) statement
                for ( declaration expressionopt ; expressionopt ) statement
(6.8.6) jump-statement:
              goto identifier ;
              continue ;
              break ;
              return expressionopt ;

[page 468]

A.2.4 External definitions
(6.9) translation-unit:
               external-declaration
               translation-unit external-declaration
(6.9) external-declaration:
               function-definition
               declaration
(6.9.1) function-definition:
               declaration-specifiers declarator declaration-listopt compound-statement
(6.9.1) declaration-list:
              declaration
              declaration-list declaration
A.3 Preprocessing directives
(6.10) preprocessing-file:
              groupopt
(6.10) group:
                group-part
                group group-part
(6.10) group-part:
              if-section
              control-line
              text-line
              # non-directive
(6.10) if-section:
                if-group elif-groupsopt else-groupopt endif-line
(6.10) if-group:
               # if     constant-expression new-line groupopt
               # ifdef identifier new-line groupopt
               # ifndef identifier new-line groupopt
(6.10) elif-groups:
               elif-group
               elif-groups elif-group
(6.10) elif-group:
               # elif       constant-expression new-line groupopt


[page 469]

(6.10) else-group:
               # else        new-line groupopt
(6.10) endif-line:
               # endif       new-line
(6.10) control-line:
              # include pp-tokens new-line
              # define identifier replacement-list new-line
              # define identifier lparen identifier-listopt )
                                              replacement-list new-line
              # define identifier lparen ... ) replacement-list new-line
              # define identifier lparen identifier-list , ... )
                                              replacement-list new-line
              # undef   identifier new-line
              # line    pp-tokens new-line
              # error   pp-tokensopt new-line
              # pragma pp-tokensopt new-line
              #         new-line
(6.10) text-line:
               pp-tokensopt new-line
(6.10) non-directive:
              pp-tokens new-line
(6.10) lparen:
                 a ( character not immediately preceded by white-space
(6.10) replacement-list:
              pp-tokensopt
(6.10) pp-tokens:
              preprocessing-token
              pp-tokens preprocessing-token
(6.10) new-line:
              the new-line character




[page 470]

                               Annex B
                             (informative)
                         Library summary
B.1 Diagnostics <assert.h>
        NDEBUG
        static_assert
        void assert(scalar expression);
B.2 Complex <complex.h>
        __STDC_NO_COMPLEX__           imaginary
        complex                         _Imaginary_I
        _Complex_I                      I
        #pragma STDC CX_LIMITED_RANGE on-off-switch
        double complex cacos(double complex z);
        float complex cacosf(float complex z);
        long double complex cacosl(long double complex z);
        double complex casin(double complex z);
        float complex casinf(float complex z);
        long double complex casinl(long double complex z);
        double complex catan(double complex z);
        float complex catanf(float complex z);
        long double complex catanl(long double complex z);
        double complex ccos(double complex z);
        float complex ccosf(float complex z);
        long double complex ccosl(long double complex z);
        double complex csin(double complex z);
        float complex csinf(float complex z);
        long double complex csinl(long double complex z);
        double complex ctan(double complex z);
        float complex ctanf(float complex z);
        long double complex ctanl(long double complex z);
        double complex cacosh(double complex z);
        float complex cacoshf(float complex z);
        long double complex cacoshl(long double complex z);
        double complex casinh(double complex z);
        float complex casinhf(float complex z);
        long double complex casinhl(long double complex z);

[page 471]

      double complex catanh(double complex z);
      float complex catanhf(float complex z);
      long double complex catanhl(long double complex z);
      double complex ccosh(double complex z);
      float complex ccoshf(float complex z);
      long double complex ccoshl(long double complex z);
      double complex csinh(double complex z);
      float complex csinhf(float complex z);
      long double complex csinhl(long double complex z);
      double complex ctanh(double complex z);
      float complex ctanhf(float complex z);
      long double complex ctanhl(long double complex z);
      double complex cexp(double complex z);
      float complex cexpf(float complex z);
      long double complex cexpl(long double complex z);
      double complex clog(double complex z);
      float complex clogf(float complex z);
      long double complex clogl(long double complex z);
      double cabs(double complex z);
      float cabsf(float complex z);
      long double cabsl(long double complex z);
      double complex cpow(double complex x, double complex y);
      float complex cpowf(float complex x, float complex y);
      long double complex cpowl(long double complex x,
           long double complex y);
      double complex csqrt(double complex z);
      float complex csqrtf(float complex z);
      long double complex csqrtl(long double complex z);
      double carg(double complex z);
      float cargf(float complex z);
      long double cargl(long double complex z);
      double cimag(double complex z);
      float cimagf(float complex z);
      long double cimagl(long double complex z);
      double complex CMPLX(double x, double y);
      float complex CMPLXF(float x, float y);
      long double complex CMPLXL(long double x, long double y);
      double complex conj(double complex z);
      float complex conjf(float complex z);
      long double complex conjl(long double complex z);
      double complex cproj(double complex z);

[page 472]

        float complex cprojf(float complex z);
        long double complex cprojl(long double complex z);
        double creal(double complex z);
        float crealf(float complex z);
        long double creall(long double complex z);
B.3 Character handling <ctype.h>
        int   isalnum(int c);
        int   isalpha(int c);
        int   isblank(int c);
        int   iscntrl(int c);
        int   isdigit(int c);
        int   isgraph(int c);
        int   islower(int c);
        int   isprint(int c);
        int   ispunct(int c);
        int   isspace(int c);
        int   isupper(int c);
        int   isxdigit(int c);
        int   tolower(int c);
        int   toupper(int c);
B.4 Errors <errno.h>
        EDOM           EILSEQ            ERANGE           errno
        __STDC_WANT_LIB_EXT1__
        errno_t
B.5 Floating-point environment <fenv.h>
        fenv_t               FE_OVERFLOW             FE_TOWARDZERO
        fexcept_t            FE_UNDERFLOW            FE_UPWARD
        FE_DIVBYZERO         FE_ALL_EXCEPT           FE_DFL_ENV
        FE_INEXACT           FE_DOWNWARD
        FE_INVALID           FE_TONEAREST
        #pragma STDC FENV_ACCESS on-off-switch
        int feclearexcept(int excepts);
        int fegetexceptflag(fexcept_t *flagp, int excepts);
        int feraiseexcept(int excepts);
        int fesetexceptflag(const fexcept_t *flagp,
             int excepts);
        int fetestexcept(int excepts);

[page 473]

      int   fegetround(void);
      int   fesetround(int round);
      int   fegetenv(fenv_t *envp);
      int   feholdexcept(fenv_t *envp);
      int   fesetenv(const fenv_t *envp);
      int   feupdateenv(const fenv_t *envp);
B.6 Characteristics of floating types <float.h>
      FLT_ROUNDS              DBL_DIG                 FLT_MAX
      FLT_EVAL_METHOD         LDBL_DIG                DBL_MAX
      FLT_HAS_SUBNORM         FLT_MIN_EXP             LDBL_MAX
      DBL_HAS_SUBNORM         DBL_MIN_EXP             FLT_EPSILON
      LDBL_HAS_SUBNORM        LDBL_MIN_EXP            DBL_EPSILON
      FLT_RADIX               FLT_MIN_10_EXP          LDBL_EPSILON
      FLT_MANT_DIG            DBL_MIN_10_EXP          FLT_MIN
      DBL_MANT_DIG            LDBL_MIN_10_EXP         DBL_MIN
      LDBL_MANT_DIG           FLT_MAX_EXP             LDBL_MIN
      FLT_DECIMAL_DIG         DBL_MAX_EXP             FLT_TRUE_MIN
      DBL_DECIMAL_DIG         LDBL_MAX_EXP            DBL_TRUE_MIN
      LDBL_DECIMAL_DIG        FLT_MAX_10_EXP          LDBL_TRUE_MIN
      DECIMAL_DIG             DBL_MAX_10_EXP
      FLT_DIG                 LDBL_MAX_10_EXP
B.7 Format conversion of integer types <inttypes.h>
      imaxdiv_t
      PRIdN         PRIdLEASTN       PRIdFASTN        PRIdMAX    PRIdPTR
      PRIiN         PRIiLEASTN       PRIiFASTN        PRIiMAX    PRIiPTR
      PRIoN         PRIoLEASTN       PRIoFASTN        PRIoMAX    PRIoPTR
      PRIuN         PRIuLEASTN       PRIuFASTN        PRIuMAX    PRIuPTR
      PRIxN         PRIxLEASTN       PRIxFASTN        PRIxMAX    PRIxPTR
      PRIXN         PRIXLEASTN       PRIXFASTN        PRIXMAX    PRIXPTR
      SCNdN         SCNdLEASTN       SCNdFASTN        SCNdMAX    SCNdPTR
      SCNiN         SCNiLEASTN       SCNiFASTN        SCNiMAX    SCNiPTR
      SCNoN         SCNoLEASTN       SCNoFASTN        SCNoMAX    SCNoPTR
      SCNuN         SCNuLEASTN       SCNuFASTN        SCNuMAX    SCNuPTR
      SCNxN         SCNxLEASTN       SCNxFASTN        SCNxMAX    SCNxPTR
      intmax_t imaxabs(intmax_t j);
      imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
      intmax_t strtoimax(const char * restrict nptr,
              char ** restrict endptr, int base);

[page 474]

        uintmax_t strtoumax(const char * restrict nptr,
                char ** restrict endptr, int base);
        intmax_t wcstoimax(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr, int base);
        uintmax_t wcstoumax(const wchar_t * restrict nptr,
                wchar_t ** restrict endptr, int base);
B.8 Alternative spellings <iso646.h>
        and            bitor             not_eq           xor
        and_eq         compl             or               xor_eq
        bitand         not               or_eq
B.9 Sizes of integer types <limits.h>
        CHAR_BIT       CHAR_MAX          INT_MIN          ULONG_MAX
        SCHAR_MIN      MB_LEN_MAX        INT_MAX          LLONG_MIN
        SCHAR_MAX      SHRT_MIN          UINT_MAX         LLONG_MAX
        UCHAR_MAX      SHRT_MAX          LONG_MIN         ULLONG_MAX
        CHAR_MIN       USHRT_MAX         LONG_MAX
B.10 Localization <locale.h>
        struct lconv   LC_ALL            LC_CTYPE         LC_NUMERIC
        NULL           LC_COLLATE        LC_MONETARY      LC_TIME
        char *setlocale(int category, const char *locale);
        struct lconv *localeconv(void);
B.11 Mathematics <math.h>
        float_t              FP_INFINITE             FP_FAST_FMAL
        double_t             FP_NAN                  FP_ILOGB0
        HUGE_VAL             FP_NORMAL               FP_ILOGBNAN
        HUGE_VALF            FP_SUBNORMAL            MATH_ERRNO
        HUGE_VALL            FP_ZERO                 MATH_ERREXCEPT
        INFINITY             FP_FAST_FMA             math_errhandling
        NAN                  FP_FAST_FMAF
        #pragma STDC FP_CONTRACT on-off-switch
        int fpclassify(real-floating x);
        int isfinite(real-floating x);
        int isinf(real-floating x);
        int isnan(real-floating x);
        int isnormal(real-floating x);
        int signbit(real-floating x);
[page 475]

      double acos(double x);
      float acosf(float x);
      long double acosl(long double x);
      double asin(double x);
      float asinf(float x);
      long double asinl(long double x);
      double atan(double x);
      float atanf(float x);
      long double atanl(long double x);
      double atan2(double y, double x);
      float atan2f(float y, float x);
      long double atan2l(long double y, long double x);
      double cos(double x);
      float cosf(float x);
      long double cosl(long double x);
      double sin(double x);
      float sinf(float x);
      long double sinl(long double x);
      double tan(double x);
      float tanf(float x);
      long double tanl(long double x);
      double acosh(double x);
      float acoshf(float x);
      long double acoshl(long double x);
      double asinh(double x);
      float asinhf(float x);
      long double asinhl(long double x);
      double atanh(double x);
      float atanhf(float x);
      long double atanhl(long double x);
      double cosh(double x);
      float coshf(float x);
      long double coshl(long double x);
      double sinh(double x);
      float sinhf(float x);
      long double sinhl(long double x);
      double tanh(double x);
      float tanhf(float x);
      long double tanhl(long double x);
      double exp(double x);
      float expf(float x);

[page 476]

        long double expl(long double x);
        double exp2(double x);
        float exp2f(float x);
        long double exp2l(long double x);
        double expm1(double x);
        float expm1f(float x);
        long double expm1l(long double x);
        double frexp(double value, int *exp);
        float frexpf(float value, int *exp);
        long double frexpl(long double value, int *exp);
        int ilogb(double x);
        int ilogbf(float x);
        int ilogbl(long double x);
        double ldexp(double x, int exp);
        float ldexpf(float x, int exp);
        long double ldexpl(long double x, int exp);
        double log(double x);
        float logf(float x);
        long double logl(long double x);
        double log10(double x);
        float log10f(float x);
        long double log10l(long double x);
        double log1p(double x);
        float log1pf(float x);
        long double log1pl(long double x);
        double log2(double x);
        float log2f(float x);
        long double log2l(long double x);
        double logb(double x);
        float logbf(float x);
        long double logbl(long double x);
        double modf(double value, double *iptr);
        float modff(float value, float *iptr);
        long double modfl(long double value, long double *iptr);
        double scalbn(double x, int n);
        float scalbnf(float x, int n);
        long double scalbnl(long double x, int n);
        double scalbln(double x, long int n);
        float scalblnf(float x, long int n);
        long double scalblnl(long double x, long int n);
        double cbrt(double x);

[page 477]

      float cbrtf(float x);
      long double cbrtl(long double x);
      double fabs(double x);
      float fabsf(float x);
      long double fabsl(long double x);
      double hypot(double x, double y);
      float hypotf(float x, float y);
      long double hypotl(long double x, long double y);
      double pow(double x, double y);
      float powf(float x, float y);
      long double powl(long double x, long double y);
      double sqrt(double x);
      float sqrtf(float x);
      long double sqrtl(long double x);
      double erf(double x);
      float erff(float x);
      long double erfl(long double x);
      double erfc(double x);
      float erfcf(float x);
      long double erfcl(long double x);
      double lgamma(double x);
      float lgammaf(float x);
      long double lgammal(long double x);
      double tgamma(double x);
      float tgammaf(float x);
      long double tgammal(long double x);
      double ceil(double x);
      float ceilf(float x);
      long double ceill(long double x);
      double floor(double x);
      float floorf(float x);
      long double floorl(long double x);
      double nearbyint(double x);
      float nearbyintf(float x);
      long double nearbyintl(long double x);
      double rint(double x);
      float rintf(float x);
      long double rintl(long double x);
      long int lrint(double x);
      long int lrintf(float x);
      long int lrintl(long double x);

[page 478]

        long long int llrint(double x);
        long long int llrintf(float x);
        long long int llrintl(long double x);
        double round(double x);
        float roundf(float x);
        long double roundl(long double x);
        long int lround(double x);
        long int lroundf(float x);
        long int lroundl(long double x);
        long long int llround(double x);
        long long int llroundf(float x);
        long long int llroundl(long double x);
        double trunc(double x);
        float truncf(float x);
        long double truncl(long double x);
        double fmod(double x, double y);
        float fmodf(float x, float y);
        long double fmodl(long double x, long double y);
        double remainder(double x, double y);
        float remainderf(float x, float y);
        long double remainderl(long double x, long double y);
        double remquo(double x, double y, int *quo);
        float remquof(float x, float y, int *quo);
        long double remquol(long double x, long double y,
             int *quo);
        double copysign(double x, double y);
        float copysignf(float x, float y);
        long double copysignl(long double x, long double y);
        double nan(const char *tagp);
        float nanf(const char *tagp);
        long double nanl(const char *tagp);
        double nextafter(double x, double y);
        float nextafterf(float x, float y);
        long double nextafterl(long double x, long double y);
        double nexttoward(double x, long double y);
        float nexttowardf(float x, long double y);
        long double nexttowardl(long double x, long double y);
        double fdim(double x, double y);
        float fdimf(float x, float y);
        long double fdiml(long double x, long double y);
        double fmax(double x, double y);

[page 479]

      float fmaxf(float x, float y);
      long double fmaxl(long double x, long double y);
      double fmin(double x, double y);
      float fminf(float x, float y);
      long double fminl(long double x, long double y);
      double fma(double x, double y, double z);
      float fmaf(float x, float y, float z);
      long double fmal(long double x, long double y,
           long double z);
      int isgreater(real-floating x, real-floating y);
      int isgreaterequal(real-floating x, real-floating y);
      int isless(real-floating x, real-floating y);
      int islessequal(real-floating x, real-floating y);
      int islessgreater(real-floating x, real-floating y);
      int isunordered(real-floating x, real-floating y);
B.12 Nonlocal jumps <setjmp.h>
      jmp_buf
      int setjmp(jmp_buf env);
      _Noreturn void longjmp(jmp_buf env, int val);
B.13 Signal handling <signal.h>
      sig_atomic_t    SIG_IGN           SIGILL           SIGTERM
      SIG_DFL         SIGABRT           SIGINT
      SIG_ERR         SIGFPE            SIGSEGV
      void (*signal(int sig, void (*func)(int)))(int);
      int raise(int sig);




[page 480]

B.14 Alignment <stdalign.h>
        alignas
        __alignas_is_defined
B.15 Variable arguments <stdarg.h>
        va_list
        type va_arg(va_list ap, type);
        void va_copy(va_list dest, va_list src);
        void va_end(va_list ap);
        void va_start(va_list ap, parmN);
B.16 Atomics <stdatomic.h>
        ATOMIC_CHAR_LOCK_FREE           atomic_uint
        ATOMIC_CHAR16_T_LOCK_FREE       atomic_long
        ATOMIC_CHAR32_T_LOCK_FREE       atomic_ulong
        ATOMIC_WCHAR_T_LOCK_FREE        atomic_llong
        ATOMIC_SHORT_LOCK_FREE          atomic_ullong
        ATOMIC_INT_LOCK_FREE            atomic_char16_t
        ATOMIC_LONG_LOCK_FREE           atomic_char32_t
        ATOMIC_LLONG_LOCK_FREE          atomic_wchar_t
        ATOMIC_ADDRESS_LOCK_FREE        atomic_int_least8_t
        ATOMIC_FLAG_INIT                atomic_uint_least8_t
        memory_order                    atomic_int_least16_t
        atomic_flag                     atomic_uint_least16_t
        atomic_bool                     atomic_int_least32_t
        atomic_address                  atomic_uint_least32_t
        memory_order_relaxed            atomic_int_least64_t
        memory_order_consume            atomic_uint_least64_t
        memory_order_acquire            atomic_int_fast8_t
        memory_order_release            atomic_uint_fast8_t
        memory_order_acq_rel            atomic_int_fast16_t
        memory_order_seq_cst            atomic_uint_fast16_t
        atomic_char                     atomic_int_fast32_t
        atomic_schar                    atomic_uint_fast32_t
        atomic_uchar                    atomic_int_fast64_t
        atomic_short                    atomic_uint_fast64_t
        atomic_ushort                   atomic_intptr_t
        atomic_int                      atomic_uintptr_t



[page 481]

      atomic_size_t                     atomic_intmax_t
      atomic_ptrdiff_t                  atomic_uintmax_t
      #define ATOMIC_VAR_INIT(C value)
      void atomic_init(volatile A *obj, C value);
      type kill_dependency(type y);
      void atomic_thread_fence(memory_order order);
      void atomic_signal_fence(memory_order order);
      _Bool atomic_is_lock_free(atomic_type const volatile *obj);
      void atomic_store(volatile A *object, C desired);
      void atomic_store_explicit(volatile A *object,
            C desired, memory_order order);
      C atomic_load(volatile A *object);
      C atomic_load_explicit(volatile A *object,
            memory_order order);
      C atomic_exchange(volatile A *object, C desired);
      C atomic_exchange_explicit(volatile A *object,
            C desired, memory_order order);
      _Bool atomic_compare_exchange_strong(volatile A *object,
            C *expected, C desired);
      _Bool atomic_compare_exchange_strong_explicit(
            volatile A *object, C *expected, C desired,
            memory_order success, memory_order failure);
      _Bool atomic_compare_exchange_weak(volatile A *object,
            C *expected, C desired);
      _Bool atomic_compare_exchange_weak_explicit(
            volatile A *object, C *expected, C desired,
            memory_order success, memory_order failure);
      C atomic_fetch_key(volatile A *object, M operand);
      C atomic_fetch_key_explicit(volatile A *object,
            M operand, memory_order order);
      bool atomic_flag_test_and_set(
            volatile atomic_flag *object);
      bool atomic_flag_test_and_set_explicit(
            volatile atomic_flag *object, memory_order order);
      void atomic_flag_clear(volatile atomic_flag *object);
      void atomic_flag_clear_explicit(
            volatile atomic_flag *object, memory_order order);




[page 482]

B.17 Boolean type and values <stdbool.h>
        bool
        true
        false
        __bool_true_false_are_defined
B.18 Common definitions <stddef.h>
        ptrdiff_t       max_align_t       NULL
        size_t          wchar_t
        offsetof(type, member-designator)
        __STDC_WANT_LIB_EXT1__
        rsize_t
B.19 Integer types <stdint.h>
        intN_t                INT_LEASTN_MIN          PTRDIFF_MAX
        uintN_t               INT_LEASTN_MAX          SIG_ATOMIC_MIN
        int_leastN_t          UINT_LEASTN_MAX         SIG_ATOMIC_MAX
        uint_leastN_t         INT_FASTN_MIN           SIZE_MAX
        int_fastN_t           INT_FASTN_MAX           WCHAR_MIN
        uint_fastN_t          UINT_FASTN_MAX          WCHAR_MAX
        intptr_t              INTPTR_MIN              WINT_MIN
        uintptr_t             INTPTR_MAX              WINT_MAX
        intmax_t              UINTPTR_MAX             INTN_C(value)
        uintmax_t             INTMAX_MIN              UINTN_C(value)
        INTN_MIN              INTMAX_MAX              INTMAX_C(value)
        INTN_MAX              UINTMAX_MAX             UINTMAX_C(value)
        UINTN_MAX             PTRDIFF_MIN
        __STDC_WANT_LIB_EXT1__
        RSIZE_MAX




[page 483]

B.20 Input/output <stdio.h>
      size_t          _IOLBF            FILENAME_MAX     TMP_MAX
      FILE            _IONBF            L_tmpnam         stderr
      fpos_t          BUFSIZ            SEEK_CUR         stdin
      NULL            EOF               SEEK_END         stdout
      _IOFBF          FOPEN_MAX         SEEK_SET
      int remove(const char *filename);
      int rename(const char *old, const char *new);
      FILE *tmpfile(void);
      char *tmpnam(char *s);
      int fclose(FILE *stream);
      int fflush(FILE *stream);
      FILE *fopen(const char * restrict filename,
           const char * restrict mode);
      FILE *freopen(const char * restrict filename,
           const char * restrict mode,
           FILE * restrict stream);
      void setbuf(FILE * restrict stream,
           char * restrict buf);
      int setvbuf(FILE * restrict stream,
           char * restrict buf,
           int mode, size_t size);
      int fprintf(FILE * restrict stream,
           const char * restrict format, ...);
      int fscanf(FILE * restrict stream,
           const char * restrict format, ...);
      int printf(const char * restrict format, ...);
      int scanf(const char * restrict format, ...);
      int snprintf(char * restrict s, size_t n,
           const char * restrict format, ...);
      int sprintf(char * restrict s,
           const char * restrict format, ...);
      int sscanf(const char * restrict s,
           const char * restrict format, ...);
      int vfprintf(FILE * restrict stream,
           const char * restrict format, va_list arg);
      int vfscanf(FILE * restrict stream,
           const char * restrict format, va_list arg);
      int vprintf(const char * restrict format, va_list arg);
      int vscanf(const char * restrict format, va_list arg);

[page 484]

        int vsnprintf(char * restrict s, size_t n,
             const char * restrict format, va_list arg);
        int vsprintf(char * restrict s,
             const char * restrict format, va_list arg);
        int vsscanf(const char * restrict s,
             const char * restrict format, va_list arg);
        int fgetc(FILE *stream);
        char *fgets(char * restrict s, int n,
             FILE * restrict stream);
        int fputc(int c, FILE *stream);
        int fputs(const char * restrict s,
             FILE * restrict stream);
        int getc(FILE *stream);
        int getchar(void);
        int putc(int c, FILE *stream);                                       *
        int putchar(int c);
        int puts(const char *s);
        int ungetc(int c, FILE *stream);
        size_t fread(void * restrict ptr,
             size_t size, size_t nmemb,
             FILE * restrict stream);
        size_t fwrite(const void * restrict ptr,
             size_t size, size_t nmemb,
             FILE * restrict stream);
        int fgetpos(FILE * restrict stream,
             fpos_t * restrict pos);
        int fseek(FILE *stream, long int offset, int whence);
        int fsetpos(FILE *stream, const fpos_t *pos);
        long int ftell(FILE *stream);
        void rewind(FILE *stream);
        void clearerr(FILE *stream);
        int feof(FILE *stream);
        int ferror(FILE *stream);
        void perror(const char *s);
        __STDC_WANT_LIB_EXT1__
        L_tmpnam_s    TMP_MAX_S         errno_t          rsize_t
        errno_t tmpfile_s(FILE * restrict * restrict streamptr);
        errno_t tmpnam_s(char *s, rsize_t maxsize);



[page 485]

      errno_t fopen_s(FILE * restrict * restrict streamptr,
           const char * restrict filename,
           const char * restrict mode);
      errno_t freopen_s(FILE * restrict * restrict newstreamptr,
           const char * restrict filename,
           const char * restrict mode,
           FILE * restrict stream);
      int fprintf_s(FILE * restrict stream,
           const char * restrict format, ...);
      int fscanf_s(FILE * restrict stream,
           const char * restrict format, ...);
      int printf_s(const char * restrict format, ...);
      int scanf_s(const char * restrict format, ...);
      int snprintf_s(char * restrict s, rsize_t n,
           const char * restrict format, ...);
      int sprintf_s(char * restrict s, rsize_t n,
           const char * restrict format, ...);
      int sscanf_s(const char * restrict s,
           const char * restrict format, ...);
      int vfprintf_s(FILE * restrict stream,
           const char * restrict format,
           va_list arg);
      int vfscanf_s(FILE * restrict stream,
           const char * restrict format,
           va_list arg);
      int vprintf_s(const char * restrict format,
           va_list arg);
      int vscanf_s(const char * restrict format,
           va_list arg);
      int vsnprintf_s(char * restrict s, rsize_t n,
           const char * restrict format,
           va_list arg);
      int vsprintf_s(char * restrict s, rsize_t n,
           const char * restrict format,
           va_list arg);
      int vsscanf_s(const char * restrict s,
           const char * restrict format,
           va_list arg);
      char *gets_s(char *s, rsize_t n);



[page 486]

B.21 General utilities <stdlib.h>
        size_t       ldiv_t            EXIT_FAILURE     MB_CUR_MAX
        wchar_t      lldiv_t           EXIT_SUCCESS
        div_t        NULL              RAND_MAX
        double atof(const char *nptr);
        int atoi(const char *nptr);
        long int atol(const char *nptr);
        long long int atoll(const char *nptr);
        double strtod(const char * restrict nptr,
             char ** restrict endptr);
        float strtof(const char * restrict nptr,
             char ** restrict endptr);
        long double strtold(const char * restrict nptr,
             char ** restrict endptr);
        long int strtol(const char * restrict nptr,
             char ** restrict endptr, int base);
        long long int strtoll(const char * restrict nptr,
             char ** restrict endptr, int base);
        unsigned long int strtoul(
             const char * restrict nptr,
             char ** restrict endptr, int base);
        unsigned long long int strtoull(
             const char * restrict nptr,
             char ** restrict endptr, int base);
        int rand(void);
        void srand(unsigned int seed);
        void *aligned_alloc(size_t alignment, size_t size);
        void *calloc(size_t nmemb, size_t size);
        void free(void *ptr);
        void *malloc(size_t size);
        void *realloc(void *ptr, size_t size);
        _Noreturn void abort(void);
        int atexit(void (*func)(void));
        int at_quick_exit(void (*func)(void));
        _Noreturn void exit(int status);
        _Noreturn void _Exit(int status);
        char *getenv(const char *name);
        _Noreturn void quick_exit(int status);
        int system(const char *string);


[page 487]

      void *bsearch(const void *key, const void *base,
           size_t nmemb, size_t size,
           int (*compar)(const void *, const void *));
      void qsort(void *base, size_t nmemb, size_t size,
           int (*compar)(const void *, const void *));
      int abs(int j);
      long int labs(long int j);
      long long int llabs(long long int j);
      div_t div(int numer, int denom);
      ldiv_t ldiv(long int numer, long int denom);
      lldiv_t lldiv(long long int numer,
           long long int denom);
      int mblen(const char *s, size_t n);
      int mbtowc(wchar_t * restrict pwc,
           const char * restrict s, size_t n);
      int wctomb(char *s, wchar_t wchar);
      size_t mbstowcs(wchar_t * restrict pwcs,
           const char * restrict s, size_t n);
      size_t wcstombs(char * restrict s,
           const wchar_t * restrict pwcs, size_t n);
      __STDC_WANT_LIB_EXT1__
      errno_t
      rsize_t
      constraint_handler_t
      constraint_handler_t set_constraint_handler_s(
           constraint_handler_t handler);
      void abort_handler_s(
           const char * restrict msg,
           void * restrict ptr,
           errno_t error);
      void ignore_handler_s(
           const char * restrict msg,
           void * restrict ptr,
           errno_t error);
      errno_t getenv_s(size_t * restrict len,
                char * restrict value, rsize_t maxsize,
                const char * restrict name);




[page 488]

        void *bsearch_s(const void *key, const void *base,
             rsize_t nmemb, rsize_t size,
             int (*compar)(const void *k, const void *y,
                             void *context),
             void *context);
        errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
             int (*compar)(const void *x, const void *y,
                             void *context),
             void *context);
        errno_t wctomb_s(int * restrict status,
             char * restrict s,
             rsize_t smax,
             wchar_t wc);
        errno_t mbstowcs_s(size_t * restrict retval,
             wchar_t * restrict dst, rsize_t dstmax,
             const char * restrict src, rsize_t len);
        errno_t wcstombs_s(size_t * restrict retval,
             char * restrict dst, rsize_t dstmax,
             const wchar_t * restrict src, rsize_t len);
B.22 String handling <string.h>
        size_t
        NULL
        void *memcpy(void * restrict s1,
             const void * restrict s2, size_t n);
        void *memmove(void *s1, const void *s2, size_t n);
        char *strcpy(char * restrict s1,
             const char * restrict s2);
        char *strncpy(char * restrict s1,
             const char * restrict s2, size_t n);
        char *strcat(char * restrict s1,
             const char * restrict s2);
        char *strncat(char * restrict s1,
             const char * restrict s2, size_t n);
        int memcmp(const void *s1, const void *s2, size_t n);
        int strcmp(const char *s1, const char *s2);
        int strcoll(const char *s1, const char *s2);
        int strncmp(const char *s1, const char *s2, size_t n);
        size_t strxfrm(char * restrict s1,
             const char * restrict s2, size_t n);
        void *memchr(const void *s, int c, size_t n);
[page 489]

      char *strchr(const char *s, int c);
      size_t strcspn(const char *s1, const char *s2);
      char *strpbrk(const char *s1, const char *s2);
      char *strrchr(const char *s, int c);
      size_t strspn(const char *s1, const char *s2);
      char *strstr(const char *s1, const char *s2);
      char *strtok(char * restrict s1,
           const char * restrict s2);
      void *memset(void *s, int c, size_t n);
      char *strerror(int errnum);
      size_t strlen(const char *s);
      __STDC_WANT_LIB_EXT1__
      errno_t
      rsize_t
      errno_t memcpy_s(void * restrict s1, rsize_t s1max,
           const void * restrict s2, rsize_t n);
      errno_t memmove_s(void *s1, rsize_t s1max,
           const void *s2, rsize_t n);
      errno_t strcpy_s(char * restrict s1,
           rsize_t s1max,
           const char * restrict s2);
      errno_t strncpy_s(char * restrict s1,
           rsize_t s1max,
           const char * restrict s2,
           rsize_t n);
      errno_t strcat_s(char * restrict s1,
           rsize_t s1max,
           const char * restrict s2);
      errno_t strncat_s(char * restrict s1,
           rsize_t s1max,
           const char * restrict s2,
           rsize_t n);
      char *strtok_s(char * restrict s1,
           rsize_t * restrict s1max,
           const char * restrict s2,
           char ** restrict ptr);
      errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
      errno_t strerror_s(char *s, rsize_t maxsize,
           errno_t errnum);
      size_t strerrorlen_s(errno_t errnum);

[page 490]

        size_t strnlen_s(const char *s, size_t maxsize);
B.23 Type-generic math <tgmath.h>
        acos         sqrt              fmod             nextafter
        asin         fabs              frexp            nexttoward
        atan         atan2             hypot            remainder
        acosh        cbrt              ilogb            remquo
        asinh        ceil              ldexp            rint
        atanh        copysign          lgamma           round
        cos          erf               llrint           scalbn
        sin          erfc              llround          scalbln
        tan          exp2              log10            tgamma
        cosh         expm1             log1p            trunc
        sinh         fdim              log2             carg
        tanh         floor             logb             cimag
        exp          fma               lrint            conj
        log          fmax              lround           cproj
        pow          fmin              nearbyint        creal
B.24 Threads <threads.h>
        ONCE_FLAG_INIT                 mtx_plain
        TSS_DTOR_ITERATIONS            mtx_recursive
        cnd_t                          mtx_timed
        thrd_t                         mtx_try
        tss_t                          thrd_timeout
        mtx_t                          thrd_success
        tss_dtor_t                     thrd_busy
        thrd_start_t                   thrd_error
        once_flag                      thrd_nomem
        xtime
      void call_once(once_flag *flag, void (*func)(void));
      int cnd_broadcast(cnd_t *cond);
      void cnd_destroy(cnd_t *cond);
      int cnd_init(cnd_t *cond);
      int cnd_signal(cnd_t *cond);
      int cnd_timedwait(cnd_t *cond, mtx_t *mtx,
           const xtime *xt);
      int cnd_wait(cnd_t *cond, mtx_t *mtx);
      void mtx_destroy(mtx_t *mtx);
      int mtx_init(mtx_t *mtx, int type);
      int mtx_lock(mtx_t *mtx);
[page 491]

      int mtx_timedlock(mtx_t *mtx, const xtime *xt);
      int mtx_trylock(mtx_t *mtx);
      int mtx_unlock(mtx_t *mtx);
      int thrd_create(thrd_t *thr, thrd_start_t func,
           void *arg);
      thrd_t thrd_current(void);
      int thrd_detach(thrd_t thr);
      int thrd_equal(thrd_t thr0, thrd_t thr1);
      void thrd_exit(int res);
      int thrd_join(thrd_t thr, int *res);
      void thrd_sleep(const xtime *xt);
      void thrd_yield(void);
      int tss_create(tss_t *key, tss_dtor_t dtor);
      void tss_delete(tss_t key);
      void *tss_get(tss_t key);
      int tss_set(tss_t key, void *val);
      int xtime_get(xtime *xt, int base);
B.25 Date and time <time.h>
      NULL                  size_t                  time_t
      CLOCKS_PER_SEC        clock_t                 struct tm
      clock_t clock(void);
      double difftime(time_t time1, time_t time0);
      time_t mktime(struct tm *timeptr);
      time_t time(time_t *timer);
      char *asctime(const struct tm *timeptr);
      char *ctime(const time_t *timer);
      struct tm *gmtime(const time_t *timer);
      struct tm *localtime(const time_t *timer);
      size_t strftime(char * restrict s,
           size_t maxsize,
           const char * restrict format,
           const struct tm * restrict timeptr);
      __STDC_WANT_LIB_EXT1__
      errno_t
      rsize_t
      errno_t asctime_s(char *s, rsize_t maxsize,
           const struct tm *timeptr);



[page 492]

        errno_t ctime_s(char *s, rsize_t maxsize,
             const time_t *timer);
        struct tm *gmtime_s(const time_t * restrict timer,
             struct tm * restrict result);
        struct tm *localtime_s(const time_t * restrict timer,
             struct tm * restrict result);
B.26 Unicode utilities <uchar.h>
        mbstate_t     size_t            char16_t         char32_t
        size_t mbrtoc16(char16_t * restrict pc16,
             const char * restrict s, size_t n,
             mbstate_t * restrict ps);
        size_t c16rtomb(char * restrict s, char16_t c16,
             mbstate_t * restrict ps);
        size_t mbrtoc32(char32_t * restrict pc32,
             const char * restrict s, size_t n,
             mbstate_t * restrict ps);
        size_t c32rtomb(char * restrict s, char32_t c32,
             mbstate_t * restrict ps);
B.27 Extended multibyte/wide character utilities <wchar.h>
        wchar_t             wint_t                  WCHAR_MAX
        size_t              struct tm               WCHAR_MIN
        mbstate_t           NULL                    WEOF
        int fwprintf(FILE * restrict stream,
             const wchar_t * restrict format, ...);
        int fwscanf(FILE * restrict stream,
             const wchar_t * restrict format, ...);
        int swprintf(wchar_t * restrict s, size_t n,
             const wchar_t * restrict format, ...);
        int swscanf(const wchar_t * restrict s,
             const wchar_t * restrict format, ...);
        int vfwprintf(FILE * restrict stream,
             const wchar_t * restrict format, va_list arg);
        int vfwscanf(FILE * restrict stream,
             const wchar_t * restrict format, va_list arg);
        int vswprintf(wchar_t * restrict s, size_t n,
             const wchar_t * restrict format, va_list arg);



[page 493]

      int vswscanf(const wchar_t * restrict s,
           const wchar_t * restrict format, va_list arg);
      int vwprintf(const wchar_t * restrict format,
           va_list arg);
      int vwscanf(const wchar_t * restrict format,
           va_list arg);
      int wprintf(const wchar_t * restrict format, ...);
      int wscanf(const wchar_t * restrict format, ...);
      wint_t fgetwc(FILE *stream);
      wchar_t *fgetws(wchar_t * restrict s, int n,
           FILE * restrict stream);
      wint_t fputwc(wchar_t c, FILE *stream);
      int fputws(const wchar_t * restrict s,
           FILE * restrict stream);
      int fwide(FILE *stream, int mode);
      wint_t getwc(FILE *stream);
      wint_t getwchar(void);
      wint_t putwc(wchar_t c, FILE *stream);
      wint_t putwchar(wchar_t c);
      wint_t ungetwc(wint_t c, FILE *stream);
      double wcstod(const wchar_t * restrict nptr,
           wchar_t ** restrict endptr);
      float wcstof(const wchar_t * restrict nptr,
           wchar_t ** restrict endptr);
      long double wcstold(const wchar_t * restrict nptr,
           wchar_t ** restrict endptr);
      long int wcstol(const wchar_t * restrict nptr,
           wchar_t ** restrict endptr, int base);
      long long int wcstoll(const wchar_t * restrict nptr,
           wchar_t ** restrict endptr, int base);
      unsigned long int wcstoul(const wchar_t * restrict nptr,
           wchar_t ** restrict endptr, int base);
      unsigned long long int wcstoull(
           const wchar_t * restrict nptr,
           wchar_t ** restrict endptr, int base);
      wchar_t *wcscpy(wchar_t * restrict s1,
           const wchar_t * restrict s2);
      wchar_t *wcsncpy(wchar_t * restrict s1,
           const wchar_t * restrict s2, size_t n);



[page 494]

        wchar_t *wmemcpy(wchar_t * restrict s1,
             const wchar_t * restrict s2, size_t n);
        wchar_t *wmemmove(wchar_t *s1, const wchar_t *s2,
             size_t n);
        wchar_t *wcscat(wchar_t * restrict s1,
             const wchar_t * restrict s2);
        wchar_t *wcsncat(wchar_t * restrict s1,
             const wchar_t * restrict s2, size_t n);
        int wcscmp(const wchar_t *s1, const wchar_t *s2);
        int wcscoll(const wchar_t *s1, const wchar_t *s2);
        int wcsncmp(const wchar_t *s1, const wchar_t *s2,
             size_t n);
        size_t wcsxfrm(wchar_t * restrict s1,
             const wchar_t * restrict s2, size_t n);
        int wmemcmp(const wchar_t *s1, const wchar_t *s2,
             size_t n);
        wchar_t *wcschr(const wchar_t *s, wchar_t c);
        size_t wcscspn(const wchar_t *s1, const wchar_t *s2);
        wchar_t *wcspbrk(const wchar_t *s1, const wchar_t *s2);
        wchar_t *wcsrchr(const wchar_t *s, wchar_t c);
        size_t wcsspn(const wchar_t *s1, const wchar_t *s2);
        wchar_t *wcsstr(const wchar_t *s1, const wchar_t *s2);
        wchar_t *wcstok(wchar_t * restrict s1,
             const wchar_t * restrict s2,
             wchar_t ** restrict ptr);
        wchar_t *wmemchr(const wchar_t *s, wchar_t c, size_t n);
        size_t wcslen(const wchar_t *s);
        wchar_t *wmemset(wchar_t *s, wchar_t c, size_t n);
        size_t wcsftime(wchar_t * restrict s, size_t maxsize,
             const wchar_t * restrict format,
             const struct tm * restrict timeptr);
        wint_t btowc(int c);
        int wctob(wint_t c);
        int mbsinit(const mbstate_t *ps);
        size_t mbrlen(const char * restrict s, size_t n,
             mbstate_t * restrict ps);
        size_t mbrtowc(wchar_t * restrict pwc,
             const char * restrict s, size_t n,
             mbstate_t * restrict ps);



[page 495]

      size_t wcrtomb(char * restrict s, wchar_t wc,
           mbstate_t * restrict ps);
      size_t mbsrtowcs(wchar_t * restrict dst,
           const char ** restrict src, size_t len,
           mbstate_t * restrict ps);
      size_t wcsrtombs(char * restrict dst,
           const wchar_t ** restrict src, size_t len,
           mbstate_t * restrict ps);
      __STDC_WANT_LIB_EXT1__
      errno_t
      rsize_t
      int fwprintf_s(FILE * restrict stream,
           const wchar_t * restrict format, ...);
      int fwscanf_s(FILE * restrict stream,
           const wchar_t * restrict format, ...);
      int snwprintf_s(wchar_t * restrict s,
           rsize_t n,
           const wchar_t * restrict format, ...);
      int swprintf_s(wchar_t * restrict s, rsize_t n,
           const wchar_t * restrict format, ...);
      int swscanf_s(const wchar_t * restrict s,
           const wchar_t * restrict format, ...);
      int vfwprintf_s(FILE * restrict stream,
           const wchar_t * restrict format,
           va_list arg);
      int vfwscanf_s(FILE * restrict stream,
           const wchar_t * restrict format, va_list arg);
      int vsnwprintf_s(wchar_t * restrict s,
           rsize_t n,
           const wchar_t * restrict format,
           va_list arg);
      int vswprintf_s(wchar_t * restrict s,
           rsize_t n,
           const wchar_t * restrict format,
           va_list arg);
      int vswscanf_s(const wchar_t * restrict s,
           const wchar_t * restrict format,
           va_list arg);



[page 496]

        int vwprintf_s(const wchar_t * restrict format,
             va_list arg);
        int vwscanf_s(const wchar_t * restrict format,
             va_list arg);
        int wprintf_s(const wchar_t * restrict format, ...);
        int wscanf_s(const wchar_t * restrict format, ...);
        errno_t wcscpy_s(wchar_t * restrict s1,
             rsize_t s1max,
             const wchar_t * restrict s2);
        errno_t wcsncpy_s(wchar_t * restrict s1,
             rsize_t s1max,
             const wchar_t * restrict s2,
             rsize_t n);
        errno_t wmemcpy_s(wchar_t * restrict s1,
             rsize_t s1max,
             const wchar_t * restrict s2,
             rsize_t n);
        errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
             const wchar_t *s2, rsize_t n);
        errno_t wcscat_s(wchar_t * restrict s1,
             rsize_t s1max,
             const wchar_t * restrict s2);
        errno_t wcsncat_s(wchar_t * restrict s1,
             rsize_t s1max,
             const wchar_t * restrict s2,
             rsize_t n);
        wchar_t *wcstok_s(wchar_t * restrict s1,
             rsize_t * restrict s1max,
             const wchar_t * restrict s2,
             wchar_t ** restrict ptr);
        size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
        errno_t wcrtomb_s(size_t * restrict retval,
             char * restrict s, rsize_t smax,
             wchar_t wc, mbstate_t * restrict ps);
        errno_t mbsrtowcs_s(size_t * restrict retval,
             wchar_t * restrict dst, rsize_t dstmax,
             const char ** restrict src, rsize_t len,
             mbstate_t * restrict ps);




[page 497]

      errno_t wcsrtombs_s(size_t * restrict retval,
           char * restrict dst, rsize_t dstmax,
           const wchar_t ** restrict src, rsize_t len,
           mbstate_t * restrict ps);
B.28 Wide character classification and mapping utilities <wctype.h>
      wint_t          wctrans_t         wctype_t         WEOF
      int iswalnum(wint_t wc);
      int iswalpha(wint_t wc);
      int iswblank(wint_t wc);
      int iswcntrl(wint_t wc);
      int iswdigit(wint_t wc);
      int iswgraph(wint_t wc);
      int iswlower(wint_t wc);
      int iswprint(wint_t wc);
      int iswpunct(wint_t wc);
      int iswspace(wint_t wc);
      int iswupper(wint_t wc);
      int iswxdigit(wint_t wc);
      int iswctype(wint_t wc, wctype_t desc);
      wctype_t wctype(const char *property);
      wint_t towlower(wint_t wc);
      wint_t towupper(wint_t wc);
      wint_t towctrans(wint_t wc, wctrans_t desc);
      wctrans_t wctrans(const char *property);




[page 498]

                                          Annex C
                                        (informative)
                                      Sequence points
1   The following are the sequence points described in 5.1.2.3:
    -- Between the evaluations of the function designator and actual arguments in a function
      call and the actual call. (6.5.2.2).
    -- Between the evaluations of the first and second operands of the following operators:
      logical AND && (6.5.13); logical OR || (6.5.14); comma , (6.5.17).                  *
    -- Between the evaluations of the first operand of the conditional ? : operator and
      whichever of the second and third operands is evaluated (6.5.15).
    -- The end of a full declarator: declarators (6.7.6);
    -- Between the evaluation of a full expression and the next full expression to be
      evaluated. The following are full expressions: an initializer that is not part of a
      compound literal (6.7.9); the expression in an expression statement (6.8.3); the
      controlling expression of a selection statement (if or switch) (6.8.4); the
      controlling expression of a while or do statement (6.8.5); each of the (optional)
      expressions of a for statement (6.8.5.3); the (optional) expression in a return
      statement (6.8.6.4).
    -- Immediately before a library function returns (7.1.4).
    -- After the actions associated with each formatted input/output function conversion
      specifier (7.21.6, 7.28.2).
    -- Immediately before and immediately after each call to a comparison function, and
      also between any call to a comparison function and any movement of the objects
      passed as arguments to that call (7.22.5).




[page 499]

                                         Annex D
                                        (normative)
                   Universal character names for identifiers
1   This clause lists the hexadecimal code values that are valid in universal character names
    in identifiers.
    D.1 Ranges of characters allowed
1   00A8, 00AA, 00AD, 00AF, 00B2-00B5, 00B7-00BA, 00BC-00BE, 00C0-00D6,
    00D8-00F6, 00F8-00FF
2   0100-167F, 1681-180D, 180F-1FFF
3   200B-200D, 202A-202E, 203F-2040, 2054, 2060-206F
4   2070-218F, 2460-24FF, 2776-2793, 2C00-2DFF, 2E80-2FFF
5   3004-3007, 3021-302F, 3031-303F
6   3040-D7FF
7   F900-FD3D, FD40-FDCF, FDF0-FE44, FE47-FFFD
8   10000-1FFFD, 20000-2FFFD, 30000-3FFFD, 40000-4FFFD, 50000-5FFFD,
    60000-6FFFD, 70000-7FFFD, 80000-8FFFD, 90000-9FFFD, A0000-AFFFD,
    B0000-BFFFD, C0000-CFFFD, D0000-DFFFD, E0000-EFFFD
    D.2 Ranges of characters disallowed initially
1   0300-036F, 1DC0-1DFF, 20D0-20FF, FE20-FE2F




[page 500]

                                         Annex E
                                       (informative)
                                Implementation limits
1   The contents of the header <limits.h> are given below, in alphabetical order. The
    minimum magnitudes shown shall be replaced by implementation-defined magnitudes
    with the same sign. The values shall all be constant expressions suitable for use in #if
    preprocessing directives. The components are described further in 5.2.4.2.1.
            #define    CHAR_BIT                               8
            #define    CHAR_MAX          UCHAR_MAX or SCHAR_MAX
            #define    CHAR_MIN                  0 or SCHAR_MIN
            #define    INT_MAX                           +32767
            #define    INT_MIN                           -32767
            #define    LONG_MAX                     +2147483647
            #define    LONG_MIN                     -2147483647
            #define    LLONG_MAX           +9223372036854775807
            #define    LLONG_MIN           -9223372036854775807
            #define    MB_LEN_MAX                             1
            #define    SCHAR_MAX                           +127
            #define    SCHAR_MIN                           -127
            #define    SHRT_MAX                          +32767
            #define    SHRT_MIN                          -32767
            #define    UCHAR_MAX                            255
            #define    USHRT_MAX                          65535
            #define    UINT_MAX                           65535
            #define    ULONG_MAX                     4294967295
            #define    ULLONG_MAX          18446744073709551615
2   The contents of the header <float.h> are given below. All integer values, except
    FLT_ROUNDS, shall be constant expressions suitable for use in #if preprocessing
    directives; all floating values shall be constant expressions. The components are
    described further in 5.2.4.2.2.
3   The values given in the following list shall be replaced by implementation-defined
    expressions:
            #define FLT_EVAL_METHOD
            #define FLT_ROUNDS
4   The values given in the following list shall be replaced by implementation-defined
    constant expressions that are greater or equal in magnitude (absolute value) to those
    shown, with the same sign:
[page 501]

           #define    DLB_DECIMAL_DIG                                10
           #define    DBL_DIG                                        10
           #define    DBL_MANT_DIG
           #define    DBL_MAX_10_EXP                               +37
           #define    DBL_MAX_EXP
           #define    DBL_MIN_10_EXP                               -37
           #define    DBL_MIN_EXP
           #define    DECIMAL_DIG                                    10
           #define    FLT_DECIMAL_DIG                                 6
           #define    FLT_DIG                                         6
           #define    FLT_MANT_DIG
           #define    FLT_MAX_10_EXP                               +37
           #define    FLT_MAX_EXP
           #define    FLT_MIN_10_EXP                               -37
           #define    FLT_MIN_EXP
           #define    FLT_RADIX                                       2
           #define    LDLB_DECIMAL_DIG                               10
           #define    LDBL_DIG                                       10
           #define    LDBL_MANT_DIG
           #define    LDBL_MAX_10_EXP                              +37
           #define    LDBL_MAX_EXP
           #define    LDBL_MIN_10_EXP                              -37
           #define    LDBL_MIN_EXP
5   The values given in the following list shall be replaced by implementation-defined
    constant expressions with values that are greater than or equal to those shown:
           #define DBL_MAX                                      1E+37
           #define FLT_MAX                                      1E+37
           #define LDBL_MAX                                     1E+37
6   The values given in the following list shall be replaced by implementation-defined
    constant expressions with (positive) values that are less than or equal to those shown:
           #define    DBL_EPSILON                                1E-9
           #define    DBL_MIN                                   1E-37
           #define    FLT_EPSILON                                1E-5
           #define    FLT_MIN                                   1E-37
           #define    LDBL_EPSILON                               1E-9
           #define    LDBL_MIN                                  1E-37




[page 502]

                                               Annex F
                                              (normative)
                          IEC 60559 floating-point arithmetic
    F.1 Introduction
1   This annex specifies C language support for the IEC 60559 floating-point standard. The
    IEC 60559 floating-point standard is specifically Binary floating-point arithmetic for
    microprocessor systems, second edition (IEC 60559:1989), previously designated
    IEC 559:1989 and as IEEE Standard for Binary Floating-Point Arithmetic
    (ANSI/IEEE 754-1985). IEEE Standard for Radix-Independent Floating-Point
    Arithmetic (ANSI/IEEE 854-1987) generalizes the binary standard to remove
    dependencies on radix and word length. IEC 60559 generally refers to the floating-point
    standard, as in IEC 60559 operation, IEC 60559 format, etc. An implementation that
    defines __STDC_IEC_559__ shall conform to the specifications in this annex.343)
    Where a binding between the C language and IEC 60559 is indicated, the
    IEC 60559-specified behavior is adopted by reference, unless stated otherwise. Since
    negative and positive infinity are representable in IEC 60559 formats, all real numbers lie
    within the range of representable values.
    F.2 Types
1   The C floating types match the IEC 60559 formats as follows:
    -- The float type matches the IEC 60559 single format.
    -- The double type matches the IEC 60559 double format.
    -- The long double type matches an IEC 60559 extended format,344) else a
      non-IEC 60559 extended format, else the IEC 60559 double format.
    Any non-IEC 60559 extended format used for the long double type shall have more
    precision than IEC 60559 double and at least the range of IEC 60559 double.345)




    343) Implementations that do not define __STDC_IEC_559__ are not required to conform to these
         specifications.
    344) ''Extended'' is IEC 60559's double-extended data format. Extended refers to both the common 80-bit
         and quadruple 128-bit IEC 60559 formats.
    345) A non-IEC 60559 long double type is required to provide infinity and NaNs, as its values include
         all double values.

[page 503]

    Recommended practice
2   The long double type should match an IEC 60559 extended format.
    F.2.1 Infinities, signed zeros, and NaNs
1   This specification does not define the behavior of signaling NaNs.346) It generally uses
    the term NaN to denote quiet NaNs. The NAN and INFINITY macros and the nan
    functions in <math.h> provide designations for IEC 60559 NaNs and infinities.
    F.3 Operators and functions
1   C operators and functions provide IEC 60559 required and recommended facilities as
    listed below.
    -- The +, -, *, and / operators provide the IEC 60559 add, subtract, multiply, and
      divide operations.
    -- The sqrt functions in <math.h> provide the IEC 60559 square root operation.
    -- The remainder functions in <math.h> provide the IEC 60559 remainder
      operation. The remquo functions in <math.h> provide the same operation but
      with additional information.
    -- The rint functions in <math.h> provide the IEC 60559 operation that rounds a
      floating-point number to an integer value (in the same precision). The nearbyint
      functions in <math.h> provide the nearbyinteger function recommended in the
      Appendix to ANSI/IEEE 854.
    -- The conversions for floating types provide the IEC 60559 conversions between
      floating-point precisions.
    -- The conversions from integer to floating types provide the IEC 60559 conversions
      from integer to floating point.
    -- The conversions from floating to integer types provide IEC 60559-like conversions
      but always round toward zero.
    -- The lrint and llrint functions in <math.h> provide the IEC 60559
      conversions, which honor the directed rounding mode, from floating point to the
      long int and long long int integer formats. The lrint and llrint
      functions can be used to implement IEC 60559 conversions from floating to other
      integer formats.
    -- The translation time conversion of floating constants and the strtod, strtof,
      strtold, fprintf, fscanf, and related library functions in <stdlib.h>,


    346) Since NaNs created by IEC 60559 operations are always quiet, quiet NaNs (along with infinities) are
         sufficient for closure of the arithmetic.

[page 504]

   <stdio.h>, and <wchar.h> provide IEC 60559 binary-decimal conversions. The
   strtold function in <stdlib.h> provides the conv function recommended in the
   Appendix to ANSI/IEEE 854.
-- The relational and equality operators provide IEC 60559 comparisons. IEC 60559
  identifies a need for additional comparison predicates to facilitate writing code that
  accounts for NaNs. The comparison macros (isgreater, isgreaterequal,
  isless, islessequal, islessgreater, and isunordered) in <math.h>
  supplement the language operators to address this need. The islessgreater and
  isunordered macros provide respectively a quiet version of the <> predicate and
  the unordered predicate recommended in the Appendix to IEC 60559.
-- The feclearexcept, feraiseexcept, and fetestexcept functions in
  <fenv.h> provide the facility to test and alter the IEC 60559 floating-point
  exception status flags. The fegetexceptflag and fesetexceptflag
  functions in <fenv.h> provide the facility to save and restore all five status flags at
  one time. These functions are used in conjunction with the type fexcept_t and the
  floating-point     exception      macros      (FE_INEXACT,         FE_DIVBYZERO,
  FE_UNDERFLOW, FE_OVERFLOW, FE_INVALID) also in <fenv.h>.
-- The fegetround and fesetround functions in <fenv.h> provide the facility
  to select among the IEC 60559 directed rounding modes represented by the rounding
  direction macros in <fenv.h> (FE_TONEAREST, FE_UPWARD, FE_DOWNWARD,
  FE_TOWARDZERO) and the values 0, 1, 2, and 3 of FLT_ROUNDS are the
  IEC 60559 directed rounding modes.
-- The fegetenv, feholdexcept, fesetenv, and feupdateenv functions in
  <fenv.h> provide a facility to manage the floating-point environment, comprising
  the IEC 60559 status flags and control modes.
-- The copysign functions in <math.h> provide the copysign function
  recommended in the Appendix to IEC 60559.
-- The fabs functions in <math.h> provide the abs function recommended in the
  Appendix to IEC 60559.
-- The unary minus (-) operator provides the unary minus (-) operation recommended
  in the Appendix to IEC 60559.
-- The scalbn and scalbln functions in <math.h> provide the scalb function
  recommended in the Appendix to IEC 60559.
-- The logb functions in <math.h> provide the logb function recommended in the
  Appendix to IEC 60559, but following the newer specifications in ANSI/IEEE 854.
-- The nextafter and nexttoward functions in <math.h> provide the nextafter
  function recommended in the Appendix to IEC 60559 (but with a minor change to

[page 505]

        better handle signed zeros).
    -- The isfinite macro in <math.h> provides the finite function recommended in
      the Appendix to IEC 60559.
    -- The isnan macro in <math.h> provides the isnan function recommended in the
      Appendix to IEC 60559.
    -- The signbit macro and the fpclassify macro in <math.h>, used in
      conjunction with the number classification macros (FP_NAN, FP_INFINITE,
      FP_NORMAL, FP_SUBNORMAL, FP_ZERO), provide the facility of the class
      function recommended in the Appendix to IEC 60559 (except that the classification
      macros defined in 7.12.3 do not distinguish signaling from quiet NaNs).
    F.4 Floating to integer conversion
1   If the integer type is _Bool, 6.3.1.2 applies and no floating-point exceptions are raised
    (even for NaN). Otherwise, if the floating value is infinite or NaN or if the integral part
    of the floating value exceeds the range of the integer type, then the ''invalid'' floating-
    point exception is raised and the resulting value is unspecified. Otherwise, the resulting
    value is determined by 6.3.1.4. Conversion of an integral floating value that does not
    exceed the range of the integer type raises no floating-point exceptions; whether
    conversion of a non-integral floating value raises the ''inexact'' floating-point exception is
    unspecified.347)
    F.5 Binary-decimal conversion
1   Conversion from the widest supported IEC 60559 format to decimal with
    DECIMAL_DIG digits and back is the identity function.348)
2   Conversions involving IEC 60559 formats follow all pertinent recommended practice. In
    particular, conversion between any supported IEC 60559 format and decimal with
    DECIMAL_DIG or fewer significant digits is correctly rounded (honoring the current
    rounding mode), which assures that conversion from the widest supported IEC 60559
    format to decimal with DECIMAL_DIG digits and back is the identity function.



    347) ANSI/IEEE 854, but not IEC 60559 (ANSI/IEEE 754), directly specifies that floating-to-integer
         conversions raise the ''inexact'' floating-point exception for non-integer in-range values. In those
         cases where it matters, library functions can be used to effect such conversions with or without raising
         the ''inexact'' floating-point exception. See rint, lrint, llrint, and nearbyint in
         <math.h>.
    348) If the minimum-width IEC 60559 extended format (64 bits of precision) is supported,
         DECIMAL_DIG shall be at least 21. If IEC 60559 double (53 bits of precision) is the widest
         IEC 60559 format supported, then DECIMAL_DIG shall be at least 17. (By contrast, LDBL_DIG and
         DBL_DIG are 18 and 15, respectively, for these formats.)

[page 506]

3   Functions such as strtod that convert character sequences to floating types honor the
    rounding direction. Hence, if the rounding direction might be upward or downward, the
    implementation cannot convert a minus-signed sequence by negating the converted
    unsigned sequence.
    F.6 The return statement
    If the return expression is evaluated in a floating-point format different from the return
    type, the expression is converted as if by assignment349) to the return type of the function
    and the resulting value is returned to the caller.
    F.7 Contracted expressions
1   A contracted expression is correctly rounded (once) and treats infinities, NaNs, signed
    zeros, subnormals, and the rounding directions in a manner consistent with the basic
    arithmetic operations covered by IEC 60559.
    Recommended practice
2   A contracted expression should raise floating-point exceptions in a manner generally
    consistent with the basic arithmetic operations.                                    *
    F.8 Floating-point environment
1   The floating-point environment defined in <fenv.h> includes the IEC 60559 floating-
    point exception status flags and directed-rounding control modes. It includes also
    IEC 60559 dynamic rounding precision and trap enablement modes, if the
    implementation supports them.350)
    F.8.1 Environment management
1   IEC 60559 requires that floating-point operations implicitly raise floating-point exception
    status flags, and that rounding control modes can be set explicitly to affect result values of
    floating-point operations. When the state for the FENV_ACCESS pragma (defined in
    <fenv.h>) is ''on'', these changes to the floating-point state are treated as side effects
    which respect sequence points.351)




    349) Assignment removes any extra range and precision.
    350) This specification does not require dynamic rounding precision nor trap enablement modes.
    351) If the state for the FENV_ACCESS pragma is ''off'', the implementation is free to assume the floating-
         point control modes will be the default ones and the floating-point status flags will not be tested,
         which allows certain optimizations (see F.9).

[page 507]

    F.8.2 Translation
1   During translation the IEC 60559 default modes are in effect:
    -- The rounding direction mode is rounding to nearest.
    -- The rounding precision mode (if supported) is set so that results are not shortened.
    -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
    Recommended practice
2   The implementation should produce a diagnostic message for each translation-time
    floating-point exception, other than ''inexact'';352) the implementation should then
    proceed with the translation of the program.
    F.8.3 Execution
1   At program startup the floating-point environment is initialized as prescribed by
    IEC 60559:
    -- All floating-point exception status flags are cleared.
    -- The rounding direction mode is rounding to nearest.
    -- The dynamic rounding precision mode (if supported) is set so that results are not
      shortened.
    -- Trapping or stopping (if supported) is disabled on all floating-point exceptions.
    F.8.4 Constant expressions
1   An arithmetic constant expression of floating type, other than one in an initializer for an
    object that has static or thread storage duration, is evaluated (as if) during execution; thus,
    it is affected by any operative floating-point control modes and raises floating-point
    exceptions as required by IEC 60559 (provided the state for the FENV_ACCESS pragma
    is ''on'').353)
2   EXAMPLE



    352) As floating constants are converted to appropriate internal representations at translation time, their
         conversion is subject to default rounding modes and raises no execution-time floating-point exceptions
         (even where the state of the FENV_ACCESS pragma is ''on''). Library functions, for example
         strtod, provide execution-time conversion of numeric strings.
    353) Where the state for the FENV_ACCESS pragma is ''on'', results of inexact expressions like 1.0/3.0
         are affected by rounding modes set at execution time, and expressions such as 0.0/0.0 and
         1.0/0.0 generate execution-time floating-point exceptions. The programmer can achieve the
         efficiency of translation-time evaluation through static initialization, such as
                  const static double one_third = 1.0/3.0;


[page 508]

             #include <fenv.h>
             #pragma STDC FENV_ACCESS ON
             void f(void)
             {
                   float w[] = { 0.0/0.0 };                  //   raises an exception
                   static float x = 0.0/0.0;                 //   does not raise an exception
                   float y = 0.0/0.0;                        //   raises an exception
                   double z = 0.0/0.0;                       //   raises an exception
                   /* ... */
             }
3   For the static initialization, the division is done at translation time, raising no (execution-time) floating-
    point exceptions. On the other hand, for the three automatic initializations the invalid division occurs at
    execution time.

    F.8.5 Initialization
1   All computation for automatic initialization is done (as if) at execution time; thus, it is
    affected by any operative modes and raises floating-point exceptions as required by
    IEC 60559 (provided the state for the FENV_ACCESS pragma is ''on''). All computation
    for initialization of objects that have static or thread storage duration is done (as if) at
    translation time.
2   EXAMPLE
             #include <fenv.h>
             #pragma STDC FENV_ACCESS ON
             void f(void)
             {
                   float u[] = { 1.1e75 };                  //   raises exceptions
                   static float v = 1.1e75;                 //   does not raise exceptions
                   float w = 1.1e75;                        //   raises exceptions
                   double x = 1.1e75;                       //   may raise exceptions
                   float y = 1.1e75f;                       //   may raise exceptions
                   long double z = 1.1e75;                  //   does not raise exceptions
                   /* ... */
             }
3   The static initialization of v raises no (execution-time) floating-point exceptions because its computation is
    done at translation time. The automatic initialization of u and w require an execution-time conversion to
    float of the wider value 1.1e75, which raises floating-point exceptions. The automatic initializations
    of x and y entail execution-time conversion; however, in some expression evaluation methods, the
    conversions is not to a narrower format, in which case no floating-point exception is raised.354) The
    automatic initialization of z entails execution-time conversion, but not to a narrower format, so no floating-
    point exception is raised. Note that the conversions of the floating constants 1.1e75 and 1.1e75f to



    354) Use of float_t and double_t variables increases the likelihood of translation-time computation.
         For example, the automatic initialization
                  double_t x = 1.1e75;
         could be done at translation time, regardless of the expression evaluation method.

[page 509]

    their internal representations occur at translation time in all cases.

    F.8.6 Changing the environment
1   Operations defined in 6.5 and functions and macros defined for the standard libraries
    change floating-point status flags and control modes just as indicated by their
    specifications (including conformance to IEC 60559). They do not change flags or modes
    (so as to be detectable by the user) in any other cases.
2   If the argument to the feraiseexcept function in <fenv.h> represents IEC 60559
    valid coincident floating-point exceptions for atomic operations (namely ''overflow'' and
    ''inexact'', or ''underflow'' and ''inexact''), then ''overflow'' or ''underflow'' is raised
    before ''inexact''.
    F.9 Optimization
1   This section identifies code transformations that might subvert IEC 60559-specified
    behavior, and others that do not.
    F.9.1 Global transformations
1   Floating-point arithmetic operations and external function calls may entail side effects
    which optimization shall honor, at least where the state of the FENV_ACCESS pragma is
    ''on''. The flags and modes in the floating-point environment may be regarded as global
    variables; floating-point operations (+, *, etc.) implicitly read the modes and write the
    flags.
2   Concern about side effects may inhibit code motion and removal of seemingly useless
    code. For example, in
             #include <fenv.h>
             #pragma STDC FENV_ACCESS ON
             void f(double x)
             {
                  /* ... */
                  for (i = 0; i < n; i++) x + 1;
                  /* ... */
             }
    x + 1 might raise floating-point exceptions, so cannot be removed. And since the loop
    body might not execute (maybe 0 >= n), x + 1 cannot be moved out of the loop. (Of
    course these optimizations are valid if the implementation can rule out the nettlesome
    cases.)
3   This specification does not require support for trap handlers that maintain information
    about the order or count of floating-point exceptions. Therefore, between function calls,
    floating-point exceptions need not be precise: the actual order and number of occurrences
    of floating-point exceptions (> 1) may vary from what the source code expresses. Thus,
[page 510]

    the preceding loop could be treated as
             if (0 < n) x + 1;
    F.9.2 Expression transformations
1   x/2 (<->) x x 0.5          Although similar transformations involving inexact constants
                           generally do not yield numerically equivalent expressions, if the
                           constants are exact then such transformations can be made on
                           IEC 60559 machines and others that round perfectly.
    1 x x and x/1 (->) x The expressions 1 x x, x/1, and x are equivalent (on IEC 60559
                      machines, among others).355)
    x/x (->) 1.0             The expressions x/x and 1.0 are not equivalent if x can be zero,
                           infinite, or NaN.
    x - y (<->) x + (-y)       The expressions x - y, x + (-y), and (-y) + x are equivalent (on
                           IEC 60559 machines, among others).
    x - y (<->) -(y - x)       The expressions x - y and -(y - x) are not equivalent because 1 - 1
                           is +0 but -(1 - 1) is -0 (in the default rounding direction).356)
    x - x (->) 0.0           The expressions x - x and 0.0 are not equivalent if x is a NaN or
                           infinite.
    0 x x (->) 0.0           The expressions 0 x x and 0.0 are not equivalent if x is a NaN,
                           infinite, or -0.
    x+0(->) x                 The expressions x + 0 and x are not equivalent if x is -0, because
                           (-0) + (+0) yields +0 (in the default rounding direction), not -0.
    x-0(->) x                 (+0) - (+0) yields -0 when rounding is downward (toward -(inf)), but
                           +0 otherwise, and (-0) - (+0) always yields -0; so, if the state of the
                           FENV_ACCESS pragma is ''off'', promising default rounding, then
                           the implementation can replace x - 0 by x, even if x might be zero.
    -x (<->) 0 - x             The expressions -x and 0 - x are not equivalent if x is +0, because
                           -(+0) yields -0, but 0 - (+0) yields +0 (unless rounding is
                           downward).

    355) Strict support for signaling NaNs -- not required by this specification -- would invalidate these and
         other transformations that remove arithmetic operators.
    356) IEC 60559 prescribes a signed zero to preserve mathematical identities across certain discontinuities.
         Examples include:
            1/(1/ (+-) (inf)) is (+-) (inf)
         and
            conj(csqrt(z)) is csqrt(conj(z)),
         for complex z.

[page 511]

    F.9.3 Relational operators
1   x != x (->) false           The expression x != x is true if x is a NaN.
    x = x (->) true            The expression x = x is false if x is a NaN.
    x < y (->) isless(x,y) (and similarly for <=, >, >=) Though numerically equal, these
                   expressions are not equivalent because of side effects when x or y is a
                   NaN and the state of the FENV_ACCESS pragma is ''on''. This
                   transformation, which would be desirable if extra code were required
                   to cause the ''invalid'' floating-point exception for unordered cases,
                   could be performed provided the state of the FENV_ACCESS pragma
                   is ''off''.
    The sense of relational operators shall be maintained. This includes handling unordered
    cases as expressed by the source code.
2   EXAMPLE
             // calls g and raises ''invalid'' if a and b are unordered
             if (a < b)
                     f();
             else
                     g();
    is not equivalent to
             // calls f and raises ''invalid'' if a and b are unordered
             if (a >= b)
                     g();
             else
                     f();
    nor to
             // calls f without raising ''invalid'' if a and b are unordered
             if (isgreaterequal(a,b))
                     g();
             else
                     f();
    nor, unless the state of the FENV_ACCESS pragma is ''off'', to
             // calls g without raising ''invalid'' if a and b are unordered
             if (isless(a,b))
                     f();
             else
                     g();
    but is equivalent to




[page 512]

            if (!(a < b))
                  g();
            else
                  f();

    F.9.4 Constant arithmetic
1   The implementation shall honor floating-point exceptions raised by execution-time
    constant arithmetic wherever the state of the FENV_ACCESS pragma is ''on''. (See F.8.4
    and F.8.5.) An operation on constants that raises no floating-point exception can be
    folded during translation, except, if the state of the FENV_ACCESS pragma is ''on'', a
    further check is required to assure that changing the rounding direction to downward does
    not alter the sign of the result,357) and implementations that support dynamic rounding
    precision modes shall assure further that the result of the operation raises no floating-
    point exception when converted to the semantic type of the operation.
    F.10 Mathematics <math.h>
1   This subclause contains specifications of <math.h> facilities that are particularly suited
    for IEC 60559 implementations.
2   The Standard C macro HUGE_VAL and its float and long double analogs,
    HUGE_VALF and HUGE_VALL, expand to expressions whose values are positive
    infinities.
3   Special cases for functions in <math.h> are covered directly or indirectly by
    IEC 60559. The functions that IEC 60559 specifies directly are identified in F.3. The
    other functions in <math.h> treat infinities, NaNs, signed zeros, subnormals, and
    (provided the state of the FENV_ACCESS pragma is ''on'') the floating-point status flags
    in a manner consistent with the basic arithmetic operations covered by IEC 60559.
4   The expression math_errhandling & MATH_ERREXCEPT shall evaluate to a
    nonzero value.
5   The ''invalid'' and ''divide-by-zero'' floating-point exceptions are raised as specified in
    subsequent subclauses of this annex.
6   The ''overflow'' floating-point exception is raised whenever an infinity -- or, because of
    rounding direction, a maximal-magnitude finite number -- is returned in lieu of a value
    whose magnitude is too large.
7   The ''underflow'' floating-point exception is raised whenever a result is tiny (essentially
    subnormal or zero) and suffers loss of accuracy.358)


    357) 0 - 0 yields -0 instead of +0 just when the rounding direction is downward.
    358) IEC 60559 allows different definitions of underflow. They all result in the same values, but differ on
         when the floating-point exception is raised.

[page 513]

8    Whether or when library functions raise the ''inexact'' floating-point exception is
     unspecified, unless explicitly specified otherwise.
9    Whether or when library functions raise an undeserved ''underflow'' floating-point
     exception is unspecified.359) Otherwise, as implied by F.8.6, the <math.h> functions do
     not raise spurious floating-point exceptions (detectable by the user), other than the
     ''inexact'' floating-point exception.
10   Whether the functions honor the rounding direction mode is implementation-defined,
     unless explicitly specified otherwise.
11   Functions with a NaN argument return a NaN result and raise no floating-point exception,
     except where stated otherwise.
12   The specifications in the following subclauses append to the definitions in <math.h>.
     For families of functions, the specifications apply to all of the functions even though only
     the principal function is shown. Unless otherwise specified, where the symbol ''(+-)''
     occurs in both an argument and the result, the result has the same sign as the argument.
     Recommended practice
13   If a function with one or more NaN arguments returns a NaN result, the result should be
     the same as one of the NaN arguments (after possible type conversion), except perhaps
     for the sign.
     F.10.1 Trigonometric functions
     F.10.1.1 The acos functions
1    -- acos(1) returns +0.
     -- acos(x) returns a NaN and raises the ''invalid'' floating-point exception for
       | x | > 1.
     F.10.1.2 The asin functions
1    -- asin((+-)0) returns (+-)0.
     -- asin(x) returns a NaN and raises the ''invalid'' floating-point exception for
       | x | > 1.




     359) It is intended that undeserved ''underflow'' and ''inexact'' floating-point exceptions are raised only if
          avoiding them would be too costly.

[page 514]

    F.10.1.3 The atan functions
1   -- atan((+-)0) returns (+-)0.
    -- atan((+-)(inf)) returns (+-)pi /2.
    F.10.1.4 The atan2 functions
1   -- atan2((+-)0, -0) returns (+-)pi .360)
    -- atan2((+-)0, +0) returns (+-)0.
    -- atan2((+-)0, x) returns (+-)pi for x < 0.
    -- atan2((+-)0, x) returns (+-)0 for x > 0.
    -- atan2(y, (+-)0) returns -pi /2 for y < 0.
    -- atan2(y, (+-)0) returns pi /2 for y > 0.
    -- atan2((+-)y, -(inf)) returns (+-)pi for finite y > 0.
    -- atan2((+-)y, +(inf)) returns (+-)0 for finite y > 0.
    -- atan2((+-)(inf), x) returns (+-)pi /2 for finite x.
    -- atan2((+-)(inf), -(inf)) returns (+-)3pi /4.
    -- atan2((+-)(inf), +(inf)) returns (+-)pi /4.
    F.10.1.5 The cos functions
1   -- cos((+-)0) returns 1.
    -- cos((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
    F.10.1.6 The sin functions
1   -- sin((+-)0) returns (+-)0.
    -- sin((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
    F.10.1.7 The tan functions
1   -- tan((+-)0) returns (+-)0.
    -- tan((+-)(inf)) returns a NaN and raises the ''invalid'' floating-point exception.




    360) atan2(0, 0) does not raise the ''invalid'' floating-point exception, nor does atan2( y , 0) raise
         the ''divide-by-zero'' floating-point exception.

[page 515]

    F.10.2 Hyperbolic functions
    F.10.2.1 The acosh functions
1   -- acosh(1) returns +0.
    -- acosh(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 1.
    -- acosh(+(inf)) returns +(inf).
    F.10.2.2 The asinh functions
1   -- asinh((+-)0) returns (+-)0.
    -- asinh((+-)(inf)) returns (+-)(inf).
    F.10.2.3 The atanh functions
1   -- atanh((+-)0) returns (+-)0.
    -- atanh((+-)1) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- atanh(x) returns a NaN and raises the ''invalid'' floating-point exception for
      | x | > 1.
    F.10.2.4 The cosh functions
1   -- cosh((+-)0) returns 1.
    -- cosh((+-)(inf)) returns +(inf).
    F.10.2.5 The sinh functions
1   -- sinh((+-)0) returns (+-)0.
    -- sinh((+-)(inf)) returns (+-)(inf).
    F.10.2.6 The tanh functions
1   -- tanh((+-)0) returns (+-)0.
    -- tanh((+-)(inf)) returns (+-)1.
    F.10.3 Exponential and logarithmic functions
    F.10.3.1 The exp functions
1   -- exp((+-)0) returns 1.
    -- exp(-(inf)) returns +0.
    -- exp(+(inf)) returns +(inf).




[page 516]

    F.10.3.2 The exp2 functions
1   -- exp2((+-)0) returns 1.
    -- exp2(-(inf)) returns +0.
    -- exp2(+(inf)) returns +(inf).
    F.10.3.3 The expm1 functions
1   -- expm1((+-)0) returns (+-)0.
    -- expm1(-(inf)) returns -1.
    -- expm1(+(inf)) returns +(inf).
    F.10.3.4 The frexp functions
1   -- frexp((+-)0, exp) returns (+-)0, and stores 0 in the object pointed to by exp.
    -- frexp((+-)(inf), exp) returns (+-)(inf), and stores an unspecified value in the object
      pointed to by exp.
    -- frexp(NaN, exp) stores an unspecified value in the object pointed to by exp
      (and returns a NaN).
2   frexp raises no floating-point exceptions.
3   When the radix of the argument is a power of 2, the returned value is exact and is
    independent of the current rounding direction mode.
4   On a binary system, the body of the frexp function might be
            {
                   *exp = (value == 0) ? 0 : (int)(1 + logb(value));
                   return scalbn(value, -(*exp));
            }
    F.10.3.5 The ilogb functions
1   When the correct result is representable in the range of the return type, the returned value
    is exact and is independent of the current rounding direction mode.
2   If the correct result is outside the range of the return type, the numeric result is
    unspecified and the ''invalid'' floating-point exception is raised.




[page 517]

    F.10.3.6 The ldexp functions
1   On a binary system, ldexp(x, exp) is equivalent to scalbn(x, exp).
    F.10.3.7 The log functions
1   -- log((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- log(1) returns +0.
    -- log(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
    -- log(+(inf)) returns +(inf).
    F.10.3.8 The log10 functions
1   -- log10((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- log10(1) returns +0.
    -- log10(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
    -- log10(+(inf)) returns +(inf).
    F.10.3.9 The log1p functions
1   -- log1p((+-)0) returns (+-)0.
    -- log1p(-1) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- log1p(x) returns a NaN and raises the ''invalid'' floating-point exception for
      x < -1.
    -- log1p(+(inf)) returns +(inf).
    F.10.3.10 The log2 functions
1   -- log2((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- log2(1) returns +0.
    -- log2(x) returns a NaN and raises the ''invalid'' floating-point exception for x < 0.
    -- log2(+(inf)) returns +(inf).
    F.10.3.11 The logb functions
1   -- logb((+-)0) returns -(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- logb((+-)(inf)) returns +(inf).
2   The returned value is exact and is independent of the current rounding direction mode.




[page 518]

    F.10.3.12 The modf functions
1   -- modf((+-)x, iptr) returns a result with the same sign as x.
    -- modf((+-)(inf), iptr) returns (+-)0 and stores (+-)(inf) in the object pointed to by iptr.
    -- modf(NaN, iptr) stores a NaN in the object pointed to by iptr (and returns a
      NaN).
2   The returned values are exact and are independent of the current rounding direction
    mode.
3   modf behaves as though implemented by
            #include <math.h>
            #include <fenv.h>
            #pragma STDC FENV_ACCESS ON
            double modf(double value, double *iptr)
            {
                 int save_round = fegetround();
                 fesetround(FE_TOWARDZERO);
                 *iptr = nearbyint(value);
                 fesetround(save_round);
                 return copysign(
                      isinf(value) ? 0.0 :
                           value - (*iptr), value);
            }
    F.10.3.13 The scalbn and scalbln functions
1   -- scalbn((+-)0, n) returns (+-)0.
    -- scalbn(x, 0) returns x.
    -- scalbn((+-)(inf), n) returns (+-)(inf).
2   If the calculation does not overflow or underflow, the returned value is exact and
    independent of the current rounding direction mode.




[page 519]

    F.10.4 Power and absolute value functions
    F.10.4.1 The cbrt functions
1   -- cbrt((+-)0) returns (+-)0.
    -- cbrt((+-)(inf)) returns (+-)(inf).
    F.10.4.2 The fabs functions
1   -- fabs((+-)0) returns +0.
    -- fabs((+-)(inf)) returns +(inf).
2   The returned value is exact and is independent of the current rounding direction mode.
    F.10.4.3 The hypot functions
1   -- hypot(x, y), hypot(y, x), and hypot(x, -y) are equivalent.
    -- hypot(x, (+-)0) is equivalent to fabs(x).
    -- hypot((+-)(inf), y) returns +(inf), even if y is a NaN.
    F.10.4.4 The pow functions
1   -- pow((+-)0, y) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception
      for y an odd integer < 0.
    -- pow((+-)0, y) returns +(inf) and raises the ''divide-by-zero'' floating-point exception
      for y < 0, finite, and not an odd integer.
    -- pow((+-)0, -(inf)) returns +(inf) and may raise the ''divide-by-zero'' floating-point
      exception.
    -- pow((+-)0, y) returns (+-)0 for y an odd integer > 0.
    -- pow((+-)0, y) returns +0 for y > 0 and not an odd integer.
    -- pow(-1, (+-)(inf)) returns 1.
    -- pow(+1, y) returns 1 for any y, even a NaN.
    -- pow(x, (+-)0) returns 1 for any x, even a NaN.
    -- pow(x, y) returns a NaN and raises the ''invalid'' floating-point exception for
      finite x < 0 and finite non-integer y.
    -- pow(x, -(inf)) returns +(inf) for | x | < 1.
    -- pow(x, -(inf)) returns +0 for | x | > 1.
    -- pow(x, +(inf)) returns +0 for | x | < 1.
    -- pow(x, +(inf)) returns +(inf) for | x | > 1.


[page 520]

    -- pow(-(inf), y) returns -0 for y an odd integer < 0.
    -- pow(-(inf), y) returns +0 for y < 0 and not an odd integer.
    -- pow(-(inf), y) returns -(inf) for y an odd integer > 0.
    -- pow(-(inf), y) returns +(inf) for y > 0 and not an odd integer.
    -- pow(+(inf), y) returns +0 for y < 0.
    -- pow(+(inf), y) returns +(inf) for y > 0.
    F.10.4.5 The sqrt functions
1   sqrt is fully specified as a basic arithmetic operation in IEC 60559. The returned value
    is dependent on the current rounding direction mode.
    F.10.5 Error and gamma functions
    F.10.5.1 The erf functions
1   -- erf((+-)0) returns (+-)0.
    -- erf((+-)(inf)) returns (+-)1.
    F.10.5.2 The erfc functions
1   -- erfc(-(inf)) returns 2.
    -- erfc(+(inf)) returns +0.
    F.10.5.3 The lgamma functions
1   -- lgamma(1) returns +0.
    -- lgamma(2) returns +0.
    -- lgamma(x) returns +(inf) and raises the ''divide-by-zero'' floating-point exception for
      x a negative integer or zero.
    -- lgamma(-(inf)) returns +(inf).
    -- lgamma(+(inf)) returns +(inf).
    F.10.5.4 The tgamma functions
1   -- tgamma((+-)0) returns (+-)(inf) and raises the ''divide-by-zero'' floating-point exception.
    -- tgamma(x) returns a NaN and raises the ''invalid'' floating-point exception for x a
      negative integer.
    -- tgamma(-(inf)) returns a NaN and raises the ''invalid'' floating-point exception.
    -- tgamma(+(inf)) returns +(inf).



[page 521]

    F.10.6 Nearest integer functions
    F.10.6.1 The ceil functions
1   -- ceil((+-)0) returns (+-)0.
    -- ceil((+-)(inf)) returns (+-)(inf).
2   The returned value is independent of the current rounding direction mode.
3   The double version of ceil behaves as though implemented by
           #include <math.h>
           #include <fenv.h>
           #pragma STDC FENV_ACCESS ON
           double ceil(double x)
           {
                double result;
                int save_round = fegetround();
                fesetround(FE_UPWARD);
                result = rint(x); // or nearbyint instead of rint
                fesetround(save_round);
                return result;
           }
4   The ceil functions may, but are not required to, raise the ''inexact'' floating-point
    exception for finite non-integer arguments, as this implementation does.
    F.10.6.2 The floor functions
1   -- floor((+-)0) returns (+-)0.
    -- floor((+-)(inf)) returns (+-)(inf).
2   The returned value and is independent of the current rounding direction mode.
3   See the sample implementation for ceil in F.10.6.1. The floor functions may, but are
    not required to, raise the ''inexact'' floating-point exception for finite non-integer
    arguments, as that implementation does.
    F.10.6.3 The nearbyint functions
1   The nearbyint functions use IEC 60559 rounding according to the current rounding
    direction. They do not raise the ''inexact'' floating-point exception if the result differs in
    value from the argument.
    -- nearbyint((+-)0) returns (+-)0 (for all rounding directions).
    -- nearbyint((+-)(inf)) returns (+-)(inf) (for all rounding directions).



[page 522]

    F.10.6.4 The rint functions
1   The rint functions differ from the nearbyint functions only in that they do raise the
    ''inexact'' floating-point exception if the result differs in value from the argument.
    F.10.6.5 The lrint and llrint functions
1   The lrint and llrint functions provide floating-to-integer conversion as prescribed
    by IEC 60559. They round according to the current rounding direction. If the rounded
    value is outside the range of the return type, the numeric result is unspecified and the
    ''invalid'' floating-point exception is raised. When they raise no other floating-point
    exception and the result differs from the argument, they raise the ''inexact'' floating-point
    exception.
    F.10.6.6 The round functions
1   -- round((+-)0) returns (+-)0.
    -- round((+-)(inf)) returns (+-)(inf).
2   The returned value is independent of the current rounding direction mode.
3   The double version of round behaves as though implemented by
            #include <math.h>
            #include <fenv.h>
            #pragma STDC FENV_ACCESS ON
            double round(double x)
            {
                 double result;
                 fenv_t save_env;
                 feholdexcept(&save_env);
                 result = rint(x);
                 if (fetestexcept(FE_INEXACT)) {
                      fesetround(FE_TOWARDZERO);
                      result = rint(copysign(0.5 + fabs(x), x));
                 }
                 feupdateenv(&save_env);
                 return result;
            }
    The round functions may, but are not required to, raise the ''inexact'' floating-point
    exception for finite non-integer numeric arguments, as this implementation does.




[page 523]

    F.10.6.7 The lround and llround functions
1   The lround and llround functions differ from the lrint and llrint functions
    with the default rounding direction just in that the lround and llround functions
    round halfway cases away from zero and need not raise the ''inexact'' floating-point
    exception for non-integer arguments that round to within the range of the return type.
    F.10.6.8 The trunc functions
1   The trunc functions use IEC 60559 rounding toward zero (regardless of the current
    rounding direction). The returned value is exact.
    -- trunc((+-)0) returns (+-)0.
    -- trunc((+-)(inf)) returns (+-)(inf).
2   The returned value is independent of the current rounding direction mode. The trunc
    functions may, but are not required to, raise the ''inexact'' floating-point exception for
    finite non-integer arguments.
    F.10.7 Remainder functions
    F.10.7.1 The fmod functions
1   -- fmod((+-)0, y) returns (+-)0 for y not zero.
    -- fmod(x, y) returns a NaN and raises the ''invalid'' floating-point exception for x
      infinite or y zero (and neither is a NaN).
    -- fmod(x, (+-)(inf)) returns x for x not infinite.
2   When subnormal results are supported, the returned value is exact and is independent of
    the current rounding direction mode.
3   The double version of fmod behaves as though implemented by
           #include <math.h>
           #include <fenv.h>
           #pragma STDC FENV_ACCESS ON
           double fmod(double x, double y)
           {
                double result;
                result = remainder(fabs(x), (y = fabs(y)));
                if (signbit(result)) result += y;
                return copysign(result, x);
           }




[page 524]

    F.10.7.2 The remainder functions
1   The remainder functions are fully specified as a basic arithmetic operation in
    IEC 60559.
2   When subnormal results are supported, the returned value is exact and is independent of
    the current rounding direction mode.
    F.10.7.3 The remquo functions
1   The remquo functions follow the specifications for the remainder functions. They
    have no further specifications special to IEC 60559 implementations.
2   When subnormal results are supported, the returned value is exact and is independent of
    the current rounding direction mode.
    F.10.8 Manipulation functions
    F.10.8.1 The copysign functions
1   copysign is specified in the Appendix to IEC 60559.
2   The returned value is exact and is independent of the current rounding direction mode.
    F.10.8.2 The nan functions
1   All IEC 60559 implementations support quiet NaNs, in all floating formats.
2   The returned value is exact and is independent of the current rounding direction mode.
    F.10.8.3 The nextafter functions
1   -- nextafter(x, y) raises the ''overflow'' and ''inexact'' floating-point exceptions
      for x finite and the function value infinite.
    -- nextafter(x, y) raises the ''underflow'' and ''inexact'' floating-point
      exceptions for the function value subnormal or zero and x != y.
2   Even though underflow or overflow can occur, the returned value is independent of the
    current rounding direction mode.
    F.10.8.4 The nexttoward functions
1   No additional requirements beyond those on nextafter.
2   Even though underflow or overflow can occur, the returned value is independent of the
    current rounding direction mode.




[page 525]

    F.10.9 Maximum, minimum, and positive difference functions
    F.10.9.1 The fdim functions
1   No additional requirements.
    F.10.9.2 The fmax functions
1   If just one argument is a NaN, the fmax functions return the other argument (if both
    arguments are NaNs, the functions return a NaN).
2   The returned value is exact and is independent of the current rounding direction mode.
3   The body of the fmax function might be361)
           { return (isgreaterequal(x, y) ||
                isnan(y)) ? x : y; }
    F.10.9.3 The fmin functions
1   The fmin functions are analogous to the fmax functions (see F.10.9.2).
2   The returned value is exact and is independent of the current rounding direction mode.
    F.10.10 Floating multiply-add
    F.10.10.1 The fma functions
1   -- fma(x, y, z) computes xy + z, correctly rounded once.
    -- fma(x, y, z) returns a NaN and optionally raises the ''invalid'' floating-point
      exception if one of x and y is infinite, the other is zero, and z is a NaN.
    -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if
      one of x and y is infinite, the other is zero, and z is not a NaN.
    -- fma(x, y, z) returns a NaN and raises the ''invalid'' floating-point exception if x
      times y is an exact infinity and z is also an infinity but with the opposite sign.




    361) Ideally, fmax would be sensitive to the sign of zero, for example fmax(-0.0, +0.0) would
         return +0; however, implementation in software might be impractical.

[page 526]

    F.10.11 Comparison macros
1   Relational operators and their corresponding comparison macros (7.12.14) produce
    equivalent result values, even if argument values are represented in wider formats. Thus,
    comparison macro arguments represented in formats wider than their semantic types are
    not converted to the semantic types, unless the wide evaluation method converts operands
    of relational operators to their semantic types. The standard wide evaluation methods
    characterized by FLT_EVAL_METHOD equal to 1 or 2 (5.2.4.2.2), do not convert
    operands of relational operators to their semantic types.




[page 527]

                                           Annex G
                                          (normative)
                   IEC 60559-compatible complex arithmetic
    G.1 Introduction
1   This annex supplements annex F to specify complex arithmetic for compatibility with
    IEC 60559 real floating-point arithmetic. An implementation that defines *
    __STDC_IEC_559_COMPLEX__ shall conform to the specifications in this annex.362)
    G.2 Types
1   There is a new keyword _Imaginary, which is used to specify imaginary types. It is
    used as a type specifier within declaration specifiers in the same way as _Complex is
    (thus, _Imaginary float is a valid type name).
2   There are three imaginary types, designated as float _Imaginary, double
    _Imaginary, and long double _Imaginary. The imaginary types (along with
    the real floating and complex types) are floating types.
3   For imaginary types, the corresponding real type is given by deleting the keyword
    _Imaginary from the type name.
4   Each imaginary type has the same representation and alignment requirements as the
    corresponding real type. The value of an object of imaginary type is the value of the real
    representation times the imaginary unit.
5   The imaginary type domain comprises the imaginary types.
    G.3 Conventions
1   A complex or imaginary value with at least one infinite part is regarded as an infinity
    (even if its other part is a NaN). A complex or imaginary value is a finite number if each
    of its parts is a finite number (neither infinite nor NaN). A complex or imaginary value is
    a zero if each of its parts is a zero.




    362) Implementations that do not define __STDC_IEC_559_COMPLEX__ are not required to conform
         to these specifications.

[page 528]

    G.4 Conversions
    G.4.1 Imaginary types
1   Conversions among imaginary types follow rules analogous to those for real floating
    types.
    G.4.2 Real and imaginary
1   When a value of imaginary type is converted to a real type other than _Bool,363) the
    result is a positive zero.
2   When a value of real type is converted to an imaginary type, the result is a positive
    imaginary zero.
    G.4.3 Imaginary and complex
1   When a value of imaginary type is converted to a complex type, the real part of the
    complex result value is a positive zero and the imaginary part of the complex result value
    is determined by the conversion rules for the corresponding real types.
2   When a value of complex type is converted to an imaginary type, the real part of the
    complex value is discarded and the value of the imaginary part is converted according to
    the conversion rules for the corresponding real types.
    G.5 Binary operators
1   The following subclauses supplement 6.5 in order to specify the type of the result for an
    operation with an imaginary operand.
2   For most operand types, the value of the result of a binary operator with an imaginary or
    complex operand is completely determined, with reference to real arithmetic, by the usual
    mathematical formula. For some operand types, the usual mathematical formula is
    problematic because of its treatment of infinities and because of undue overflow or
    underflow; in these cases the result satisfies certain properties (specified in G.5.1), but is
    not completely determined.




    363) See 6.3.1.2.

[page 529]

    G.5.1 Multiplicative operators
    Semantics
1   If one operand has real type and the other operand has imaginary type, then the result has
    imaginary type. If both operands have imaginary type, then the result has real type. (If
    either operand has complex type, then the result has complex type.)
2   If the operands are not both complex, then the result and floating-point exception
    behavior of the * operator is defined by the usual mathematical formula:
           *                  u                   iv                 u + iv

           x                  xu                i(xv)            (xu) + i(xv)

           iy               i(yu)                -yv            (-yv) + i(yu)

           x + iy       (xu) + i(yu)        (-yv) + i(xv)
3   If the second operand is not complex, then the result and floating-point exception
    behavior of the / operator is defined by the usual mathematical formula:
           /                   u                       iv

           x                  x/u                 i(-x/v)

           iy               i(y/u)                     y/v

           x + iy       (x/u) + i(y/u)        (y/v) + i(-x/v)
4   The * and / operators satisfy the following infinity properties for all real, imaginary, and
    complex operands:364)
    -- if one operand is an infinity and the other operand is a nonzero finite number or an
      infinity, then the result of the * operator is an infinity;
    -- if the first operand is an infinity and the second operand is a finite number, then the
      result of the / operator is an infinity;
    -- if the first operand is a finite number and the second operand is an infinity, then the
      result of the / operator is a zero;




    364) These properties are already implied for those cases covered in the tables, but are required for all cases
         (at least where the state for CX_LIMITED_RANGE is ''off'').

[page 530]

    -- if the first operand is a nonzero finite number or an infinity and the second operand is
      a zero, then the result of the / operator is an infinity.
5   If both operands of the * operator are complex or if the second operand of the / operator
    is complex, the operator raises floating-point exceptions if appropriate for the calculation
    of the parts of the result, and may raise spurious floating-point exceptions.
6   EXAMPLE 1 Multiplication of double _Complex operands could be implemented as follows. Note
    that the imaginary unit I has imaginary type (see G.6).
             #include <math.h>
             #include <complex.h>
             /* Multiply z * w ... */
             double complex _Cmultd(double complex z, double complex w)
             {
                    #pragma STDC FP_CONTRACT OFF
                    double a, b, c, d, ac, bd, ad, bc, x, y;
                    a = creal(z); b = cimag(z);
                    c = creal(w); d = cimag(w);
                    ac = a * c;       bd = b * d;
                    ad = a * d;       bc = b * c;
                    x = ac - bd; y = ad + bc;
                    if (isnan(x) && isnan(y)) {
                            /* Recover infinities that computed as NaN+iNaN ... */
                            int recalc = 0;
                            if ( isinf(a) || isinf(b) ) { // z is infinite
                                    /* "Box" the infinity and change NaNs in the other factor to 0 */
                                    a = copysign(isinf(a) ? 1.0 : 0.0, a);
                                    b = copysign(isinf(b) ? 1.0 : 0.0, b);
                                    if (isnan(c)) c = copysign(0.0, c);
                                    if (isnan(d)) d = copysign(0.0, d);
                                    recalc = 1;
                            }
                            if ( isinf(c) || isinf(d) ) { // w is infinite
                                    /* "Box" the infinity and change NaNs in the other factor to 0 */
                                    c = copysign(isinf(c) ? 1.0 : 0.0, c);
                                    d = copysign(isinf(d) ? 1.0 : 0.0, d);
                                    if (isnan(a)) a = copysign(0.0, a);
                                    if (isnan(b)) b = copysign(0.0, b);
                                    recalc = 1;
                            }
                            if (!recalc && (isinf(ac) || isinf(bd) ||
                                                   isinf(ad) || isinf(bc))) {
                                    /* Recover infinities from overflow by changing NaNs to 0 ... */
                                    if (isnan(a)) a = copysign(0.0, a);
                                    if (isnan(b)) b = copysign(0.0, b);
                                    if (isnan(c)) c = copysign(0.0, c);
                                    if (isnan(d)) d = copysign(0.0, d);
                                    recalc = 1;
                            }
                            if (recalc) {

[page 531]

                                      x = INFINITY * ( a * c - b * d );
                                      y = INFINITY * ( a * d + b * c );
                           }
                     }
                     return x + I * y;
            }
7   This implementation achieves the required treatment of infinities at the cost of only one isnan test in
    ordinary (finite) cases. It is less than ideal in that undue overflow and underflow may occur.

8   EXAMPLE 2      Division of two double _Complex operands could be implemented as follows.
            #include <math.h>
            #include <complex.h>
            /* Divide z / w ... */
            double complex _Cdivd(double complex z, double complex w)
            {
                   #pragma STDC FP_CONTRACT OFF
                   double a, b, c, d, logbw, denom, x, y;
                   int ilogbw = 0;
                   a = creal(z); b = cimag(z);
                   c = creal(w); d = cimag(w);
                   logbw = logb(fmax(fabs(c), fabs(d)));
                   if (logbw == INFINITY) {
                          ilogbw = (int)logbw;
                          c = scalbn(c, -ilogbw); d = scalbn(d, -ilogbw);
                   }
                   denom = c * c + d * d;
                   x = scalbn((a * c + b * d) / denom, -ilogbw);
                   y = scalbn((b * c - a * d) / denom, -ilogbw);
                     /* Recover infinities and zeros that computed as NaN+iNaN;                 */
                     /* the only cases are nonzero/zero, infinite/finite, and finite/infinite, ... */
                     if (isnan(x) && isnan(y)) {
                           if ((denom == 0.0) &&
                                 (!isnan(a) || !isnan(b))) {
                                 x = copysign(INFINITY, c) * a;
                                 y = copysign(INFINITY, c) * b;
                           }
                           else if ((isinf(a) || isinf(b)) &&
                                 isfinite(c) && isfinite(d)) {
                                 a = copysign(isinf(a) ? 1.0 : 0.0,                        a);
                                 b = copysign(isinf(b) ? 1.0 : 0.0,                        b);
                                 x = INFINITY * ( a * c + b * d );
                                 y = INFINITY * ( b * c - a * d );
                           }
                           else if (isinf(logbw) &&
                                 isfinite(a) && isfinite(b)) {
                                 c = copysign(isinf(c) ? 1.0 : 0.0,                        c);
                                 d = copysign(isinf(d) ? 1.0 : 0.0,                        d);
                                 x = 0.0 * ( a * c + b * d );
                                 y = 0.0 * ( b * c - a * d );

[page 532]

                           }
                     }
                     return x + I * y;
            }
9   Scaling the denominator alleviates the main overflow and underflow problem, which is more serious than
    for multiplication. In the spirit of the multiplication example above, this code does not defend against
    overflow and underflow in the calculation of the numerator. Scaling with the scalbn function, instead of
    with division, provides better roundoff characteristics.

    G.5.2 Additive operators
    Semantics
1   If both operands have imaginary type, then the result has imaginary type. (If one operand
    has real type and the other operand has imaginary type, or if either operand has complex
    type, then the result has complex type.)
2   In all cases the result and floating-point exception behavior of a + or - operator is defined
    by the usual mathematical formula:
           + or -              u                       iv                    u + iv

           x                 x(+-)u                     x (+-) iv              (x (+-) u) (+-) iv

           iy               (+-)u + iy                 i(y (+-) v)             (+-)u + i(y (+-) v)

           x + iy         (x (+-) u) + iy            x + i(y (+-) v)        (x (+-) u) + i(y (+-) v)
    G.6 Complex arithmetic <complex.h>
1   The macros
            imaginary
    and
            _Imaginary_I
    are defined, respectively, as _Imaginary and a constant expression of type const
    float _Imaginary with the value of the imaginary unit. The macro
            I
    is defined to be _Imaginary_I (not _Complex_I as stated in 7.3). Notwithstanding
    the provisions of 7.1.3, a program may undefine and then perhaps redefine the macro
    imaginary.
2   This subclause contains specifications for the <complex.h> functions that are
    particularly suited to IEC 60559 implementations. For families of functions, the
    specifications apply to all of the functions even though only the principal function is

[page 533]

    shown. Unless otherwise specified, where the symbol ''(+-)'' occurs in both an argument
    and the result, the result has the same sign as the argument.
3   The functions are continuous onto both sides of their branch cuts, taking into account the
    sign of zero. For example, csqrt(-2 (+-) i0) = (+-)isqrt:2.  -
4   Since complex and imaginary values are composed of real values, each function may be
    regarded as computing real values from real values. Except as noted, the functions treat
    real infinities, NaNs, signed zeros, subnormals, and the floating-point exception flags in a
    manner consistent with the specifications for real functions in F.10.365)
5   The functions cimag, conj, cproj, and creal are fully specified for all
    implementations, including IEC 60559 ones, in 7.3.9. These functions raise no floating-
    point exceptions.
6   Each of the functions cabs and carg is specified by a formula in terms of a real
    function (whose special cases are covered in annex F):
            cabs(x + iy) = hypot(x, y)
            carg(x + iy) = atan2(y, x)
7   Each of the functions casin, catan, ccos, csin, and ctan is specified implicitly by
    a formula in terms of other complex functions (whose special cases are specified below):
            casin(z)        =   -i casinh(iz)
            catan(z)        =   -i catanh(iz)
            ccos(z)         =   ccosh(iz)
            csin(z)         =   -i csinh(iz)
            ctan(z)         =   -i ctanh(iz)
8   For the other functions, the following subclauses specify behavior for special cases,
    including treatment of the ''invalid'' and ''divide-by-zero'' floating-point exceptions. For
    families of functions, the specifications apply to all of the functions even though only the
    principal function is shown. For a function f satisfying f (conj(z)) = conj( f (z)), the
    specifications for the upper half-plane imply the specifications for the lower half-plane; if
    the function f is also either even, f (-z) = f (z), or odd, f (-z) = - f (z), then the
    specifications for the first quadrant imply the specifications for the other three quadrants.
9   In the following subclauses, cis(y) is defined as cos(y) + i sin(y).




    365) As noted in G.3, a complex value with at least one infinite part is regarded as an infinity even if its
         other part is a NaN.

[page 534]

    G.6.1 Trigonometric functions
    G.6.1.1 The cacos functions
1   -- cacos(conj(z)) = conj(cacos(z)).
    -- cacos((+-)0 + i0) returns pi /2 - i0.
    -- cacos((+-)0 + iNaN) returns pi /2 + iNaN.
    -- cacos(x + i (inf)) returns pi /2 - i (inf), for finite x.
    -- cacos(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for nonzero finite x.
    -- cacos(-(inf) + iy) returns pi - i (inf), for positive-signed finite y.
    -- cacos(+(inf) + iy) returns +0 - i (inf), for positive-signed finite y.
    -- cacos(-(inf) + i (inf)) returns 3pi /4 - i (inf).
    -- cacos(+(inf) + i (inf)) returns pi /4 - i (inf).
    -- cacos((+-)(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
      result is unspecified).
    -- cacos(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite y.
    -- cacos(NaN + i (inf)) returns NaN - i (inf).
    -- cacos(NaN + iNaN) returns NaN + iNaN.
    G.6.2 Hyperbolic functions
    G.6.2.1 The cacosh functions
1   -- cacosh(conj(z)) = conj(cacosh(z)).
    -- cacosh((+-)0 + i0) returns +0 + ipi /2.
    -- cacosh(x + i (inf)) returns +(inf) + ipi /2, for finite x.
    -- cacosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
      floating-point exception, for finite x.
    -- cacosh(-(inf) + iy) returns +(inf) + ipi , for positive-signed finite y.
    -- cacosh(+(inf) + iy) returns +(inf) + i0, for positive-signed finite y.
    -- cacosh(-(inf) + i (inf)) returns +(inf) + i3pi /4.
    -- cacosh(+(inf) + i (inf)) returns +(inf) + ipi /4.
    -- cacosh((+-)(inf) + iNaN) returns +(inf) + iNaN.


[page 535]

    -- cacosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
      floating-point exception, for finite y.
    -- cacosh(NaN + i (inf)) returns +(inf) + iNaN.
    -- cacosh(NaN + iNaN) returns NaN + iNaN.
    G.6.2.2 The casinh functions
1   -- casinh(conj(z)) = conj(casinh(z)) and casinh is odd.
    -- casinh(+0 + i0) returns 0 + i0.
    -- casinh(x + i (inf)) returns +(inf) + ipi /2 for positive-signed finite x.
    -- casinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
      floating-point exception, for finite x.
    -- casinh(+(inf) + iy) returns +(inf) + i0 for positive-signed finite y.
    -- casinh(+(inf) + i (inf)) returns +(inf) + ipi /4.
    -- casinh(+(inf) + iNaN) returns +(inf) + iNaN.
    -- casinh(NaN + i0) returns NaN + i0.
    -- casinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
      floating-point exception, for finite nonzero y.
    -- casinh(NaN + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result
      is unspecified).
    -- casinh(NaN + iNaN) returns NaN + iNaN.
    G.6.2.3 The catanh functions
1   -- catanh(conj(z)) = conj(catanh(z)) and catanh is odd.
    -- catanh(+0 + i0) returns +0 + i0.
    -- catanh(+0 + iNaN) returns +0 + iNaN.
    -- catanh(+1 + i0) returns +(inf) + i0 and raises the ''divide-by-zero'' floating-point
      exception.
    -- catanh(x + i (inf)) returns +0 + ipi /2, for finite positive-signed x.
    -- catanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid''
      floating-point exception, for nonzero finite x.
    -- catanh(+(inf) + iy) returns +0 + ipi /2, for finite positive-signed y.
    -- catanh(+(inf) + i (inf)) returns +0 + ipi /2.
    -- catanh(+(inf) + iNaN) returns +0 + iNaN.

[page 536]

    -- catanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid''
      floating-point exception, for finite y.
    -- catanh(NaN + i (inf)) returns (+-)0 + ipi /2 (where the sign of the real part of the result is
      unspecified).
    -- catanh(NaN + iNaN) returns NaN + iNaN.
    G.6.2.4 The ccosh functions
1   -- ccosh(conj(z)) = conj(ccosh(z)) and ccosh is even.
    -- ccosh(+0 + i0) returns 1 + i0.
    -- ccosh(+0 + i (inf)) returns NaN (+-) i0 (where the sign of the imaginary part of the
      result is unspecified) and raises the ''invalid'' floating-point exception.
    -- ccosh(+0 + iNaN) returns NaN (+-) i0 (where the sign of the imaginary part of the
      result is unspecified).
    -- ccosh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
      exception, for finite nonzero x.
    -- ccosh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite nonzero x.
    -- ccosh(+(inf) + i0) returns +(inf) + i0.
    -- ccosh(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
    -- ccosh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
      unspecified) and raises the ''invalid'' floating-point exception.
    -- ccosh(+(inf) + iNaN) returns +(inf) + iNaN.
    -- ccosh(NaN + i0) returns NaN (+-) i0 (where the sign of the imaginary part of the
      result is unspecified).
    -- ccosh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for all nonzero numbers y.
    -- ccosh(NaN + iNaN) returns NaN + iNaN.
    G.6.2.5 The csinh functions
1   -- csinh(conj(z)) = conj(csinh(z)) and csinh is odd.
    -- csinh(+0 + i0) returns +0 + i0.
    -- csinh(+0 + i (inf)) returns (+-)0 + iNaN (where the sign of the real part of the result is
      unspecified) and raises the ''invalid'' floating-point exception.
    -- csinh(+0 + iNaN) returns (+-)0 + iNaN (where the sign of the real part of the result is
      unspecified).
[page 537]

    -- csinh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
      exception, for positive finite x.
    -- csinh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite nonzero x.
    -- csinh(+(inf) + i0) returns +(inf) + i0.
    -- csinh(+(inf) + iy) returns +(inf) cis(y), for positive finite y.
    -- csinh(+(inf) + i (inf)) returns (+-)(inf) + iNaN (where the sign of the real part of the result is
      unspecified) and raises the ''invalid'' floating-point exception.
    -- csinh(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
      is unspecified).
    -- csinh(NaN + i0) returns NaN + i0.
    -- csinh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for all nonzero numbers y.
    -- csinh(NaN + iNaN) returns NaN + iNaN.
    G.6.2.6 The ctanh functions
1   -- ctanh(conj(z)) = conj(ctanh(z))and ctanh is odd.
    -- ctanh(+0 + i0) returns +0 + i0.
    -- ctanh(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
      exception, for finite x.
    -- ctanh(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite x.
    -- ctanh(+(inf) + iy) returns 1 + i0 sin(2y), for positive-signed finite y.
    -- ctanh(+(inf) + i (inf)) returns 1 (+-) i0 (where the sign of the imaginary part of the result
      is unspecified).
    -- ctanh(+(inf) + iNaN) returns 1 (+-) i0 (where the sign of the imaginary part of the
      result is unspecified).
    -- ctanh(NaN + i0) returns NaN + i0.
    -- ctanh(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for all nonzero numbers y.
    -- ctanh(NaN + iNaN) returns NaN + iNaN.




[page 538]

    G.6.3 Exponential and logarithmic functions
    G.6.3.1 The cexp functions
1   -- cexp(conj(z)) = conj(cexp(z)).
    -- cexp((+-)0 + i0) returns 1 + i0.
    -- cexp(x + i (inf)) returns NaN + iNaN and raises the ''invalid'' floating-point
      exception, for finite x.
    -- cexp(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite x.
    -- cexp(+(inf) + i0) returns +(inf) + i0.
    -- cexp(-(inf) + iy) returns +0 cis(y), for finite y.
    -- cexp(+(inf) + iy) returns +(inf) cis(y), for finite nonzero y.
    -- cexp(-(inf) + i (inf)) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts of
      the result are unspecified).
    -- cexp(+(inf) + i (inf)) returns (+-)(inf) + iNaN and raises the ''invalid'' floating-point
      exception (where the sign of the real part of the result is unspecified).
    -- cexp(-(inf) + iNaN) returns (+-)0 (+-) i0 (where the signs of the real and imaginary parts
      of the result are unspecified).
    -- cexp(+(inf) + iNaN) returns (+-)(inf) + iNaN (where the sign of the real part of the result
      is unspecified).
    -- cexp(NaN + i0) returns NaN + i0.
    -- cexp(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for all nonzero numbers y.
    -- cexp(NaN + iNaN) returns NaN + iNaN.
    G.6.3.2 The clog functions
1   -- clog(conj(z)) = conj(clog(z)).
    -- clog(-0 + i0) returns -(inf) + ipi and raises the ''divide-by-zero'' floating-point
      exception.
    -- clog(+0 + i0) returns -(inf) + i0 and raises the ''divide-by-zero'' floating-point
      exception.
    -- clog(x + i (inf)) returns +(inf) + ipi /2, for finite x.
    -- clog(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite x.

[page 539]

    -- clog(-(inf) + iy) returns +(inf) + ipi , for finite positive-signed y.
    -- clog(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
    -- clog(-(inf) + i (inf)) returns +(inf) + i3pi /4.
    -- clog(+(inf) + i (inf)) returns +(inf) + ipi /4.
    -- clog((+-)(inf) + iNaN) returns +(inf) + iNaN.
    -- clog(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite y.
    -- clog(NaN + i (inf)) returns +(inf) + iNaN.
    -- clog(NaN + iNaN) returns NaN + iNaN.
    G.6.4 Power and absolute-value functions
    G.6.4.1 The cpow functions
1   The cpow functions raise floating-point exceptions if appropriate for the calculation of
    the parts of the result, and may also raise spurious floating-point exceptions.366)
    G.6.4.2 The csqrt functions
1   -- csqrt(conj(z)) = conj(csqrt(z)).
    -- csqrt((+-)0 + i0) returns +0 + i0.
    -- csqrt(x + i (inf)) returns +(inf) + i (inf), for all x (including NaN).
    -- csqrt(x + iNaN) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite x.
    -- csqrt(-(inf) + iy) returns +0 + i (inf), for finite positive-signed y.
    -- csqrt(+(inf) + iy) returns +(inf) + i0, for finite positive-signed y.
    -- csqrt(-(inf) + iNaN) returns NaN (+-) i (inf) (where the sign of the imaginary part of the
      result is unspecified).
    -- csqrt(+(inf) + iNaN) returns +(inf) + iNaN.
    -- csqrt(NaN + iy) returns NaN + iNaN and optionally raises the ''invalid'' floating-
      point exception, for finite y.
    -- csqrt(NaN + iNaN) returns NaN + iNaN.




    366) This allows cpow( z , c ) to be implemented as cexp(c      clog( z )) without precluding
         implementations that treat special cases more carefully.

[page 540]

    G.7 Type-generic math <tgmath.h>
1   Type-generic macros that accept complex arguments also accept imaginary arguments. If
    an argument is imaginary, the macro expands to an expression whose type is real,
    imaginary, or complex, as appropriate for the particular function: if the argument is
    imaginary, then the types of cos, cosh, fabs, carg, cimag, and creal are real; the
    types of sin, tan, sinh, tanh, asin, atan, asinh, and atanh are imaginary; and
    the types of the others are complex.
2   Given an imaginary argument, each of the type-generic macros cos, sin, tan, cosh,
    sinh, tanh, asin, atan, asinh, atanh is specified by a formula in terms of real
    functions:
            cos(iy)     =   cosh(y)
            sin(iy)     =   i sinh(y)
            tan(iy)     =   i tanh(y)
            cosh(iy)    =   cos(y)
            sinh(iy)    =   i sin(y)
            tanh(iy)    =   i tan(y)
            asin(iy)    =   i asinh(y)
            atan(iy)    =   i atanh(y)
            asinh(iy)   =   i asin(y)
            atanh(iy)   =   i atan(y)




[page 541]

                                          Annex H
                                        (informative)
                        Language independent arithmetic
    H.1 Introduction
1   This annex documents the extent to which the C language supports the ISO/IEC 10967-1
    standard for language-independent arithmetic (LIA-1). LIA-1 is more general than
    IEC 60559 (annex F) in that it covers integer and diverse floating-point arithmetics.
    H.2 Types
1   The relevant C arithmetic types meet the requirements of LIA-1 types if an
    implementation adds notification of exceptional arithmetic operations and meets the 1
    unit in the last place (ULP) accuracy requirement (LIA-1 subclause 5.2.8).
    H.2.1 Boolean type
1   The LIA-1 data type Boolean is implemented by the C data type bool with values of
    true and false, all from <stdbool.h>.
    H.2.2 Integer types
1   The signed C integer types int, long int, long long int, and the corresponding
    unsigned types are compatible with LIA-1. If an implementation adds support for the
    LIA-1 exceptional values ''integer_overflow'' and ''undefined'', then those types are
    LIA-1 conformant types. C's unsigned integer types are ''modulo'' in the LIA-1 sense
    in that overflows or out-of-bounds results silently wrap. An implementation that defines
    signed integer types as also being modulo need not detect integer overflow, in which case,
    only integer divide-by-zero need be detected.
2   The parameters for the integer data types can be accessed by the following:
    maxint        INT_MAX, LONG_MAX, LLONG_MAX, UINT_MAX, ULONG_MAX,
                  ULLONG_MAX
    minint        INT_MIN, LONG_MIN, LLONG_MIN
3   The parameter ''bounded'' is always true, and is not provided. The parameter ''minint''
    is always 0 for the unsigned types, and is not provided for those types.




[page 542]

    H.2.2.1 Integer operations
1   The integer operations on integer types are the following:
    addI           x + y
    subI           x - y
    mulI           x * y
    divI, divtI    x / y
    remI, remtI    x % y
    negI           -x
    absI           abs(x), labs(x), llabs(x)
    eqI            x == y
    neqI           x != y
    lssI           x < y
    leqI           x <= y
    gtrI           x > y
    geqI           x >= y
    where x and y are expressions of the same integer type.
    H.2.3 Floating-point types
1   The C floating-point types float, double, and long double are compatible with
    LIA-1. If an implementation adds support for the LIA-1 exceptional values
    ''underflow'', ''floating_overflow'', and ''"undefined'', then those types are conformant
    with LIA-1. An implementation that uses IEC 60559 floating-point formats and
    operations (see annex F) along with IEC 60559 status flags and traps has LIA-1
    conformant types.
    H.2.3.1 Floating-point parameters
1   The parameters for a floating point data type can be accessed by the following:
    r              FLT_RADIX
    p              FLT_MANT_DIG, DBL_MANT_DIG, LDBL_MANT_DIG
    emax           FLT_MAX_EXP, DBL_MAX_EXP, LDBL_MAX_EXP
    emin           FLT_MIN_EXP, DBL_MIN_EXP, LDBL_MIN_EXP
2   The derived constants for the floating point types are accessed by the following:


[page 543]

    fmax          FLT_MAX, DBL_MAX, LDBL_MAX
    fminN         FLT_MIN, DBL_MIN, LDBL_MIN
    epsilon       FLT_EPSILON, DBL_EPSILON, LDBL_EPSILON
    rnd_style     FLT_ROUNDS
    H.2.3.2 Floating-point operations
1   The floating-point operations on floating-point types are the following:
    addF          x + y
    subF          x - y
    mulF          x * y
    divF          x / y
    negF          -x
    absF          fabsf(x), fabs(x), fabsl(x)
    exponentF     1.f+logbf(x), 1.0+logb(x), 1.L+logbl(x)
    scaleF        scalbnf(x, n), scalbn(x, n), scalbnl(x, n),
                  scalblnf(x, li), scalbln(x, li), scalblnl(x, li)
    intpartF      modff(x, &y), modf(x, &y), modfl(x, &y)
    fractpartF    modff(x, &y), modf(x, &y), modfl(x, &y)
    eqF           x == y
    neqF          x != y
    lssF          x < y
    leqF          x <= y
    gtrF          x > y
    geqF          x >= y
    where x and y are expressions of the same floating point type, n is of type int, and li
    is of type long int.
    H.2.3.3 Rounding styles
1   The C Standard requires all floating types to use the same radix and rounding style, so
    that only one identifier for each is provided to map to LIA-1.
2   The FLT_ROUNDS parameter can be used to indicate the LIA-1 rounding styles:
    truncate      FLT_ROUNDS == 0


[page 544]

    nearest       FLT_ROUNDS == 1
    other         FLT_ROUNDS != 0 && FLT_ROUNDS != 1
    provided that an implementation extends FLT_ROUNDS to cover the rounding style used
    in all relevant LIA-1 operations, not just addition as in C.
    H.2.4 Type conversions
1   The LIA-1 type conversions are the following type casts:
    cvtI' (->) I     (int)i, (long int)i, (long long int)i,
                  (unsigned int)i, (unsigned long int)i,
                  (unsigned long long int)i
    cvtF (->) I      (int)x, (long int)x, (long long int)x,
                  (unsigned int)x, (unsigned long int)x,
                  (unsigned long long int)x
    cvtI (->) F      (float)i, (double)i, (long double)i
    cvtF' (->) F     (float)x, (double)x, (long double)x
2   In the above conversions from floating to integer, the use of (cast)x can be replaced with
    (cast)round(x), (cast)rint(x), (cast)nearbyint(x), (cast)trunc(x),
    (cast)ceil(x), or (cast)floor(x). In addition, C's floating-point to integer
    conversion functions, lrint(), llrint(), lround(), and llround(), can be
    used. They all meet LIA-1's requirements on floating to integer rounding for in-range
    values. For out-of-range values, the conversions shall silently wrap for the modulo types.
3   The fmod() function is useful for doing silent wrapping to unsigned integer types, e.g.,
    fmod( fabs(rint(x)), 65536.0 ) or (0.0 <= (y = fmod( rint(x),
    65536.0 )) ? y : 65536.0 + y) will compute an integer value in the range 0.0
    to 65535.0 which can then be cast to unsigned short int. But, the
    remainder() function is not useful for doing silent wrapping to signed integer types,
    e.g., remainder( rint(x), 65536.0 ) will compute an integer value in the
    range -32767.0 to +32768.0 which is not, in general, in the range of signed short
    int.
4   C's conversions (casts) from floating-point to floating-point can meet LIA-1
    requirements if an implementation uses round-to-nearest (IEC 60559 default).
5   C's conversions (casts) from integer to floating-point can meet LIA-1 requirements if an
    implementation uses round-to-nearest.




[page 545]

    H.3 Notification
1   Notification is the process by which a user or program is informed that an exceptional
    arithmetic operation has occurred. C's operations are compatible with LIA-1 in that C
    allows an implementation to cause a notification to occur when any arithmetic operation
    returns an exceptional value as defined in LIA-1 clause 5.
    H.3.1 Notification alternatives
1   LIA-1 requires at least the following two alternatives for handling of notifications:
    setting indicators or trap-and-terminate. LIA-1 allows a third alternative: trap-and-
    resume.
2   An implementation need only support a given notification alternative for the entire
    program. An implementation may support the ability to switch between notification
    alternatives during execution, but is not required to do so. An implementation can
    provide separate selection for each kind of notification, but this is not required.
3   C allows an implementation to provide notification. C's SIGFPE (for traps) and
    FE_INVALID, FE_DIVBYZERO, FE_OVERFLOW, FE_UNDERFLOW (for indicators)
    can provide LIA-1 notification.
4   C's signal handlers are compatible with LIA-1. Default handling of SIGFPE can
    provide trap-and-terminate behavior, except for those LIA-1 operations implemented by
    math library function calls. User-provided signal handlers for SIGFPE allow for trap-
    and-resume behavior with the same constraint.
    H.3.1.1 Indicators
1   C's <fenv.h> status flags are compatible with the LIA-1 indicators.
2   The following mapping is for floating-point types:
    undefined                FE_INVALID, FE_DIVBYZERO
    floating_overflow         FE_OVERFLOW
    underflow                FE_UNDERFLOW
3   The floating-point indicator interrogation and manipulation operations are:
    set_indicators          feraiseexcept(i)
    clear_indicators        feclearexcept(i)
    test_indicators         fetestexcept(i)
    current_indicators      fetestexcept(FE_ALL_EXCEPT)
    where i is an expression of type int representing a subset of the LIA-1 indicators.
4   C allows an implementation to provide the following LIA-1 required behavior: at
    program termination if any indicator is set the implementation shall send an unambiguous
[page 546]

    and ''hard to ignore'' message (see LIA-1 subclause 6.1.2)
5   LIA-1 does not make the distinction between floating-point and integer for ''undefined''.
    This documentation makes that distinction because <fenv.h> covers only the floating-
    point indicators.
    H.3.1.2 Traps
1   C is compatible with LIA-1's trap requirements for arithmetic operations, but not for
    math library functions (which are not permitted to invoke a user's signal handler for
    SIGFPE). An implementation can provide an alternative of notification through
    termination with a ''hard-to-ignore'' message (see LIA-1 subclause 6.1.3).
2   LIA-1 does not require that traps be precise.
3   C does require that SIGFPE be the signal corresponding to LIA-1 arithmetic exceptions,
    if there is any signal raised for them.
4   C supports signal handlers for SIGFPE and allows trapping of LIA-1 arithmetic
    exceptions. When LIA-1 arithmetic exceptions do trap, C's signal-handler mechanism
    allows trap-and-terminate (either default implementation behavior or user replacement for
    it) or trap-and-resume, at the programmer's option.




[page 547]

                                           Annex I
                                        (informative)
                                   Common warnings
1   An implementation may generate warnings in many situations, none of which are
    specified as part of this International Standard. The following are a few of the more
    common situations.
2   -- A new struct or union type appears in a function prototype (6.2.1, 6.7.2.3).
    -- A block with initialization of an object that has automatic storage duration is jumped
      into (6.2.4).
    -- An implicit narrowing conversion is encountered, such as the assignment of a long
      int or a double to an int, or a pointer to void to a pointer to any type other than
      a character type (6.3).
    -- A hexadecimal floating constant cannot be represented exactly in its evaluation format
      (6.4.4.2).
    -- An integer character constant includes more than one character or a wide character
      constant includes more than one multibyte character (6.4.4.4).
    -- The characters /* are found in a comment (6.4.7).
    -- An ''unordered'' binary operator (not comma, &&, or ||) contains a side effect to an
      lvalue in one operand, and a side effect to, or an access to the value of, the identical
      lvalue in the other operand (6.5).
    -- A function is called but no prototype has been supplied (6.5.2.2).
    -- The arguments in a function call do not agree in number and type with those of the
      parameters in a function definition that is not a prototype (6.5.2.2).
    -- An object is defined but not used (6.7).
    -- A value is given to an object of an enumerated type other than by assignment of an
      enumeration constant that is a member of that type, or an enumeration object that has
      the same type, or the value of a function that returns the same enumerated type
      (6.7.2.2).
    -- An aggregate has a partly bracketed initialization (6.7.8).
    -- A statement cannot be reached (6.8).
    -- A statement with no apparent effect is encountered (6.8).
    -- A constant expression is used as the controlling expression of a selection statement
      (6.8.4).
[page 548]

-- An incorrectly formed preprocessing group is encountered while skipping a
  preprocessing group (6.10.1).
-- An unrecognized #pragma directive is encountered (6.10.6).




[page 549]

                                            Annex J
                                         (informative)
                                      Portability issues
1   This annex collects some information about portability that appears in this International
    Standard.
    J.1 Unspecified behavior
1   The following are unspecified:
    -- The manner and timing of static initialization (5.1.2).
    -- The termination status returned to the hosted environment if the return type of main
      is not compatible with int (5.1.2.2.3).
    -- The behavior of the display device if a printing character is written when the active
      position is at the final position of a line (5.2.2).
    -- The behavior of the display device if a backspace character is written when the active
      position is at the initial position of a line (5.2.2).
    -- The behavior of the display device if a horizontal tab character is written when the
      active position is at or past the last defined horizontal tabulation position (5.2.2).
    -- The behavior of the display device if a vertical tab character is written when the active
      position is at or past the last defined vertical tabulation position (5.2.2).
    -- How an extended source character that does not correspond to a universal character
      name counts toward the significant initial characters in an external identifier (5.2.4.1).
    -- Many aspects of the representations of types (6.2.6).
    -- The value of padding bytes when storing values in structures or unions (6.2.6.1).
    -- The values of bytes that correspond to union members other than the one last stored
      into (6.2.6.1).
    -- The representation used when storing a value in an object that has more than one
      object representation for that value (6.2.6.1).
    -- The values of any padding bits in integer representations (6.2.6.2).
    -- Whether certain operators can generate negative zeros and whether a negative zero
      becomes a normal zero when stored in an object (6.2.6.2).
    -- Whether two string literals result in distinct arrays (6.4.5).
    -- The order in which subexpressions are evaluated and the order in which side effects
      take place, except as specified for the function-call (), &&, ||, ? :, and comma
[page 550]

   operators (6.5).
-- The order in which the function designator, arguments, and subexpressions within the
  arguments are evaluated in a function call (6.5.2.2).
-- The order of side effects among compound literal initialization list expressions
  (6.5.2.5).
-- The order in which the operands of an assignment operator are evaluated (6.5.16).
-- The alignment of the addressable storage unit allocated to hold a bit-field (6.7.2.1).
-- Whether a call to an inline function uses the inline definition or the external definition
  of the function (6.7.4).
-- Whether or not a size expression is evaluated when it is part of the operand of a
  sizeof operator and changing the value of the size expression would not affect the
  result of the operator (6.7.6.2).
-- The order in which any side effects occur among the initialization list expressions in
  an initializer (6.7.9).
-- The layout of storage for function parameters (6.9.1).
-- When a fully expanded macro replacement list contains a function-like macro name
  as its last preprocessing token and the next preprocessing token from the source file is
  a (, and the fully expanded replacement of that macro ends with the name of the first
  macro and the next preprocessing token from the source file is again a (, whether that
  is considered a nested replacement (6.10.3).
-- The order in which # and ## operations are evaluated during macro substitution
  (6.10.3.2, 6.10.3.3).
-- The state of the floating-point status flags when execution passes from a part of the *
  program translated with FENV_ACCESS ''off'' to a part translated with
  FENV_ACCESS ''on'' (7.6.1).
-- The order in which feraiseexcept raises floating-point exceptions, except as
  stated in F.8.6 (7.6.2.3).
-- Whether math_errhandling is a macro or an identifier with external linkage
  (7.12).
-- The results of the frexp functions when the specified value is not a floating-point
  number (7.12.6.4).
-- The numeric result of the ilogb functions when the correct value is outside the
  range of the return type (7.12.6.5, F.10.3.5).
-- The result of rounding when the value is out of range (7.12.9.5, 7.12.9.7, F.10.6.5).


[page 551]

-- The value stored by the remquo functions in the object pointed to by quo when y is
  zero (7.12.10.3).
-- Whether a comparison macro argument that is represented in a format wider than its
  semantic type is converted to the semantic type (7.12.14).
-- Whether setjmp is a macro or an identifier with external linkage (7.13).
-- Whether va_copy and va_end are macros or identifiers with external linkage
  (7.16.1).
-- The hexadecimal digit before the decimal point when a non-normalized floating-point
  number is printed with an a or A conversion specifier (7.21.6.1, 7.28.2.1).
-- The value of the file position indicator after a successful call to the ungetc function
  for a text stream, or the ungetwc function for any stream, until all pushed-back
  characters are read or discarded (7.21.7.10, 7.28.3.10).
-- The details of the value stored by the fgetpos function (7.21.9.1).
-- The details of the value returned by the ftell function for a text stream (7.21.9.4).
-- Whether the strtod, strtof, strtold, wcstod, wcstof, and wcstold
  functions convert a minus-signed sequence to a negative number directly or by
  negating the value resulting from converting the corresponding unsigned sequence
  (7.22.1.3, 7.28.4.1.1).
-- The order and contiguity of storage allocated by successive calls to the calloc,
  malloc, and realloc functions (7.22.3).
-- The amount of storage allocated by a successful call to the calloc, malloc, or
  realloc function when 0 bytes was requested (7.22.3).
-- Which of two elements that compare as equal is matched by the bsearch function
  (7.22.5.1).
-- The order of two elements that compare as equal in an array sorted by the qsort
  function (7.22.5.2).
-- The encoding of the calendar time returned by the time function (7.26.2.4).
-- The characters stored by the strftime or wcsftime function if any of the time
  values being converted is outside the normal range (7.26.3.5, 7.28.5.1).
-- The conversion state after an encoding error occurs (7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1,
  7.28.6.4.2,
-- The resulting value when the ''invalid'' floating-point exception is raised during
  IEC 60559 floating to integer conversion (F.4).



[page 552]

    -- Whether conversion of non-integer IEC 60559 floating values to integer raises the
      ''inexact'' floating-point exception (F.4).
    -- Whether or when library functions in <math.h> raise the ''inexact'' floating-point
      exception in an IEC 60559 conformant implementation (F.10).
    -- Whether or when library functions in <math.h> raise an undeserved ''underflow''
      floating-point exception in an IEC 60559 conformant implementation (F.10).
    -- The exponent value stored by frexp for a NaN or infinity (F.10.3.4).
    -- The numeric result returned by the lrint, llrint, lround, and llround
      functions if the rounded value is outside the range of the return type (F.10.6.5,
      F.10.6.7).
    -- The sign of one part of the complex result of several math functions for certain
      special cases in IEC 60559 compatible implementations (G.6.1.1, G.6.2.2, G.6.2.3,
      G.6.2.4, G.6.2.5, G.6.2.6, G.6.3.1, G.6.4.2).
    J.2 Undefined behavior
1   The behavior is undefined in the following circumstances:
    -- A ''shall'' or ''shall not'' requirement that appears outside of a constraint is violated
      (clause 4).
    -- A nonempty source file does not end in a new-line character which is not immediately
      preceded by a backslash character or ends in a partial preprocessing token or
      comment (5.1.1.2).
    -- Token concatenation produces a character sequence matching the syntax of a
      universal character name (5.1.1.2).
    -- A program in a hosted environment does not define a function named main using one
      of the specified forms (5.1.2.2.1).
    -- The execution of a program contains a data race (5.1.2.4).
    -- A character not in the basic source character set is encountered in a source file, except
      in an identifier, a character constant, a string literal, a header name, a comment, or a
      preprocessing token that is never converted to a token (5.2.1).
    -- An identifier, comment, string literal, character constant, or header name contains an
      invalid multibyte character or does not begin and end in the initial shift state (5.2.1.2).
    -- The same identifier has both internal and external linkage in the same translation unit
      (6.2.2).
    -- An object is referred to outside of its lifetime (6.2.4).



[page 553]

-- The value of a pointer to an object whose lifetime has ended is used (6.2.4).
-- The value of an object with automatic storage duration is used while it is
  indeterminate (6.2.4, 6.7.9, 6.8).
-- A trap representation is read by an lvalue expression that does not have character type
  (6.2.6.1).
-- A trap representation is produced by a side effect that modifies any part of the object
  using an lvalue expression that does not have character type (6.2.6.1).
-- The operands to certain operators are such that they could produce a negative zero
  result, but the implementation does not support negative zeros (6.2.6.2).
-- Two declarations of the same object or function specify types that are not compatible
  (6.2.7).
-- A program requires the formation of a composite type from a variable length array
  type whose size is specified by an expression that is not evaluated (6.2.7).
-- Conversion to or from an integer type produces a value outside the range that can be
  represented (6.3.1.4).
-- Demotion of one real floating type to another produces a value outside the range that
  can be represented (6.3.1.5).
-- An lvalue does not designate an object when evaluated (6.3.2.1).
-- A non-array lvalue with an incomplete type is used in a context that requires the value
  of the designated object (6.3.2.1).
-- An lvalue designating an object of automatic storage duration that could have been
  declared with the register storage class is used in a context that requires the value
  of the designated object, but the object is uninitialized. (6.3.2.1).
-- An lvalue having array type is converted to a pointer to the initial element of the
  array, and the array object has register storage class (6.3.2.1).
-- An attempt is made to use the value of a void expression, or an implicit or explicit
  conversion (except to void) is applied to a void expression (6.3.2.2).
-- Conversion of a pointer to an integer type produces a value outside the range that can
  be represented (6.3.2.3).
-- Conversion between two pointer types produces a result that is incorrectly aligned
  (6.3.2.3).
-- A pointer is used to call a function whose type is not compatible with the referenced
  type (6.3.2.3).



[page 554]

-- An unmatched ' or " character is encountered on a logical source line during
  tokenization (6.4).
-- A reserved keyword token is used in translation phase 7 or 8 for some purpose other
  than as a keyword (6.4.1).
-- A universal character name in an identifier does not designate a character whose
  encoding falls into one of the specified ranges (6.4.2.1).
-- The initial character of an identifier is a universal character name designating a digit
  (6.4.2.1).
-- Two identifiers differ only in nonsignificant characters (6.4.2.1).
-- The identifier __func__ is explicitly declared (6.4.2.2).
-- The program attempts to modify a string literal (6.4.5).
-- The characters ', \, ", //, or /* occur in the sequence between the < and >
  delimiters, or the characters ', \, //, or /* occur in the sequence between the "
  delimiters, in a header name preprocessing token (6.4.7).
-- A side effect on a scalar object is unsequenced relative to either a different side effect
  on the same scalar object or a value computation using the value of the same scalar
  object (6.5).
-- An exceptional condition occurs during the evaluation of an expression (6.5).
-- An object has its stored value accessed other than by an lvalue of an allowable type
  (6.5).
-- For a call to a function without a function prototype in scope, the number of *
  arguments does not equal the number of parameters (6.5.2.2).
-- For call to a function without a function prototype in scope where the function is
  defined with a function prototype, either the prototype ends with an ellipsis or the
  types of the arguments after promotion are not compatible with the types of the
  parameters (6.5.2.2).
-- For a call to a function without a function prototype in scope where the function is not
  defined with a function prototype, the types of the arguments after promotion are not
  compatible with those of the parameters after promotion (with certain exceptions)
  (6.5.2.2).
-- A function is defined with a type that is not compatible with the type (of the
  expression) pointed to by the expression that denotes the called function (6.5.2.2).
-- A member of an atomic structure or union is accessed (6.5.2.3).
-- The operand of the unary * operator has an invalid value (6.5.3.2).


[page 555]

-- A pointer is converted to other than an integer or pointer type (6.5.4).
-- The value of the second operand of the / or % operator is zero (6.5.5).
-- Addition or subtraction of a pointer into, or just beyond, an array object and an
  integer type produces a result that does not point into, or just beyond, the same array
  object (6.5.6).
-- Addition or subtraction of a pointer into, or just beyond, an array object and an
  integer type produces a result that points just beyond the array object and is used as
  the operand of a unary * operator that is evaluated (6.5.6).
-- Pointers that do not point into, or just beyond, the same array object are subtracted
  (6.5.6).
-- An array subscript is out of range, even if an object is apparently accessible with the
  given subscript (as in the lvalue expression a[1][7] given the declaration int
  a[4][5]) (6.5.6).
-- The result of subtracting two pointers is not representable in an object of type
  ptrdiff_t (6.5.6).
-- An expression is shifted by a negative number or by an amount greater than or equal
  to the width of the promoted expression (6.5.7).
-- An expression having signed promoted type is left-shifted and either the value of the
  expression is negative or the result of shifting would be not be representable in the
  promoted type (6.5.7).
-- Pointers that do not point to the same aggregate or union (nor just beyond the same
  array object) are compared using relational operators (6.5.8).
-- An object is assigned to an inexactly overlapping object or to an exactly overlapping
  object with incompatible type (6.5.16.1).
-- An expression that is required to be an integer constant expression does not have an
  integer type; has operands that are not integer constants, enumeration constants,
  character constants, sizeof expressions whose results are integer constants, or
  immediately-cast floating constants; or contains casts (outside operands to sizeof
  operators) other than conversions of arithmetic types to integer types (6.6).
-- A constant expression in an initializer is not, or does not evaluate to, one of the
  following: an arithmetic constant expression, a null pointer constant, an address
  constant, or an address constant for a complete object type plus or minus an integer
  constant expression (6.6).
-- An arithmetic constant expression does not have arithmetic type; has operands that
  are not integer constants, floating constants, enumeration constants, character
  constants, or sizeof expressions; or contains casts (outside operands to sizeof

[page 556]

   operators) other than conversions of arithmetic types to arithmetic types (6.6).
-- The value of an object is accessed by an array-subscript [], member-access . or ->,
  address &, or indirection * operator or a pointer cast in creating an address constant
  (6.6).
-- An identifier for an object is declared with no linkage and the type of the object is
  incomplete after its declarator, or after its init-declarator if it has an initializer (6.7).
-- A function is declared at block scope with an explicit storage-class specifier other
  than extern (6.7.1).
-- A structure or union is defined as containing no named members, no anonymous
  structures, and no anonymous unions (6.7.2.1).
-- An attempt is made to access, or generate a pointer to just past, a flexible array
  member of a structure when the referenced object provides no elements for that array
  (6.7.2.1).
-- When the complete type is needed, an incomplete structure or union type is not
  completed in the same scope by another declaration of the tag that defines the content
  (6.7.2.3).
-- An attempt is made to modify an object defined with a const-qualified type through
  use of an lvalue with non-const-qualified type (6.7.3).
-- An attempt is made to refer to an object defined with a volatile-qualified type through
  use of an lvalue with non-volatile-qualified type (6.7.3).
-- The specification of a function type includes any type qualifiers (6.7.3).                        *
-- Two qualified types that are required to be compatible do not have the identically
  qualified version of a compatible type (6.7.3).
-- An object which has been modified is accessed through a restrict-qualified pointer to
  a const-qualified type, or through a restrict-qualified pointer and another pointer that
  are not both based on the same object (6.7.3.1).
-- A restrict-qualified pointer is assigned a value based on another restricted pointer
  whose associated block neither began execution before the block associated with this
  pointer, nor ended before the assignment (6.7.3.1).
-- A function with external linkage is declared with an inline function specifier, but is
  not also defined in the same translation unit (6.7.4).
-- A function declared with a _Noreturn function specifier returns to its caller (6.7.4).
-- The definition of an object has an alignment specifier and another declaration of that
  object has a different alignment specifier (6.7.5).


[page 557]

-- Declarations of an object in different translation units have different alignment
  specifiers (6.7.5).
-- Two pointer types that are required to be compatible are not identically qualified, or
  are not pointers to compatible types (6.7.6.1).
-- The size expression in an array declaration is not a constant expression and evaluates
  at program execution time to a nonpositive value (6.7.6.2).
-- In a context requiring two array types to be compatible, they do not have compatible
  element types, or their size specifiers evaluate to unequal values (6.7.6.2).
-- A declaration of an array parameter includes the keyword static within the [ and
  ] and the corresponding argument does not provide access to the first element of an
  array with at least the specified number of elements (6.7.6.3).
-- A storage-class specifier or type qualifier modifies the keyword void as a function
  parameter type list (6.7.6.3).
-- In a context requiring two function types to be compatible, they do not have
  compatible return types, or their parameters disagree in use of the ellipsis terminator
  or the number and type of parameters (after default argument promotion, when there
  is no parameter type list or when one type is specified by a function definition with an
  identifier list) (6.7.6.3).
-- The value of an unnamed member of a structure or union is used (6.7.9).
-- The initializer for a scalar is neither a single expression nor a single expression
  enclosed in braces (6.7.9).
-- The initializer for a structure or union object that has automatic storage duration is
  neither an initializer list nor a single expression that has compatible structure or union
  type (6.7.9).
-- The initializer for an aggregate or union, other than an array initialized by a string
  literal, is not a brace-enclosed list of initializers for its elements or members (6.7.9).
-- An identifier with external linkage is used, but in the program there does not exist
  exactly one external definition for the identifier, or the identifier is not used and there
  exist multiple external definitions for the identifier (6.9).
-- A function definition includes an identifier list, but the types of the parameters are not
  declared in a following declaration list (6.9.1).
-- An adjusted parameter type in a function definition is not a complete object type
  (6.9.1).
-- A function that accepts a variable number of arguments is defined without a
  parameter type list that ends with the ellipsis notation (6.9.1).

[page 558]

-- The } that terminates a function is reached, and the value of the function call is used
  by the caller (6.9.1).
-- An identifier for an object with internal linkage and an incomplete type is declared
  with a tentative definition (6.9.2).
-- The token defined is generated during the expansion of a #if or #elif
  preprocessing directive, or the use of the defined unary operator does not match
  one of the two specified forms prior to macro replacement (6.10.1).
-- The #include preprocessing directive that results after expansion does not match
  one of the two header name forms (6.10.2).
-- The character sequence in an #include preprocessing directive does not start with a
  letter (6.10.2).
-- There are sequences of preprocessing tokens within the list of macro arguments that
  would otherwise act as preprocessing directives (6.10.3).
-- The result of the preprocessing operator # is not a valid character string literal
  (6.10.3.2).
-- The result of the preprocessing operator ## is not a valid preprocessing token
  (6.10.3.3).
-- The #line preprocessing directive that results after expansion does not match one of
  the two well-defined forms, or its digit sequence specifies zero or a number greater
  than 2147483647 (6.10.4).
-- A non-STDC #pragma preprocessing directive that is documented as causing
  translation failure or some other form of undefined behavior is encountered (6.10.6).
-- A #pragma STDC preprocessing directive does not match one of the well-defined
  forms (6.10.6).
-- The name of a predefined macro, or the identifier defined, is the subject of a
  #define or #undef preprocessing directive (6.10.8).
-- An attempt is made to copy an object to an overlapping object by use of a library
  function, other than as explicitly allowed (e.g., memmove) (clause 7).
-- A file with the same name as one of the standard headers, not provided as part of the
  implementation, is placed in any of the standard places that are searched for included
  source files (7.1.2).
-- A header is included within an external declaration or definition (7.1.2).
-- A function, object, type, or macro that is specified as being declared or defined by
  some standard header is used before any header that declares or defines it is included
  (7.1.2).

[page 559]

-- A standard header is included while a macro is defined with the same name as a
  keyword (7.1.2).
-- The program attempts to declare a library function itself, rather than via a standard
  header, but the declaration does not have external linkage (7.1.2).
-- The program declares or defines a reserved identifier, other than as allowed by 7.1.4
  (7.1.3).
-- The program removes the definition of a macro whose name begins with an
  underscore and either an uppercase letter or another underscore (7.1.3).
-- An argument to a library function has an invalid value or a type not expected by a
  function with variable number of arguments (7.1.4).
-- The pointer passed to a library function array parameter does not have a value such
  that all address computations and object accesses are valid (7.1.4).
-- The macro definition of assert is suppressed in order to access an actual function
  (7.2).
-- The argument to the assert macro does not have a scalar type (7.2).
-- The CX_LIMITED_RANGE, FENV_ACCESS, or FP_CONTRACT pragma is used in
  any context other than outside all external declarations or preceding all explicit
  declarations and statements inside a compound statement (7.3.4, 7.6.1, 7.12.2).
-- The value of an argument to a character handling function is neither equal to the value
  of EOF nor representable as an unsigned char (7.4).
-- A macro definition of errno is suppressed in order to access an actual object, or the
  program defines an identifier with the name errno (7.5).
-- Part of the program tests floating-point status flags, sets floating-point control modes,
  or runs under non-default mode settings, but was translated with the state for the
  FENV_ACCESS pragma ''off'' (7.6.1).
-- The exception-mask argument for one of the functions that provide access to the
  floating-point status flags has a nonzero value not obtained by bitwise OR of the
  floating-point exception macros (7.6.2).
-- The fesetexceptflag function is used to set floating-point status flags that were
  not specified in the call to the fegetexceptflag function that provided the value
  of the corresponding fexcept_t object (7.6.2.4).
-- The argument to fesetenv or feupdateenv is neither an object set by a call to
  fegetenv or feholdexcept, nor is it an environment macro (7.6.4.3, 7.6.4.4).
-- The value of the result of an integer arithmetic or conversion function cannot be
  represented (7.8.2.1, 7.8.2.2, 7.8.2.3, 7.8.2.4, 7.22.6.1, 7.22.6.2, 7.22.1).

[page 560]

-- The program modifies the string pointed to by the value returned by the setlocale
  function (7.11.1.1).
-- The program modifies the structure pointed to by the value returned by the
  localeconv function (7.11.2.1).
-- A macro definition of math_errhandling is suppressed or the program defines
  an identifier with the name math_errhandling (7.12).
-- An argument to a floating-point classification or comparison macro is not of real
  floating type (7.12.3, 7.12.14).
-- A macro definition of setjmp is suppressed in order to access an actual function, or
  the program defines an external identifier with the name setjmp (7.13).
-- An invocation of the setjmp macro occurs other than in an allowed context
  (7.13.2.1).
-- The longjmp function is invoked to restore a nonexistent environment (7.13.2.1).
-- After a longjmp, there is an attempt to access the value of an object of automatic
  storage duration that does not have volatile-qualified type, local to the function
  containing the invocation of the corresponding setjmp macro, that was changed
  between the setjmp invocation and longjmp call (7.13.2.1).
-- The program specifies an invalid pointer to a signal handler function (7.14.1.1).
-- A signal handler returns when the signal corresponded to a computational exception
  (7.14.1.1).
-- A signal occurs as the result of calling the abort or raise function, and the signal
  handler calls the raise function (7.14.1.1).
-- A signal occurs other than as the result of calling the abort or raise function, and
  the signal handler refers to an object with static or thread storage duration that is not a
  lock-free atomic object other than by assigning a value to an object declared as
  volatile sig_atomic_t, or calls any function in the standard library other
  than the abort function, the _Exit function, the quick_exit function, or the
  signal function (for the same signal number) (7.14.1.1).
-- The value of errno is referred to after a signal occurred other than as the result of
  calling the abort or raise function and the corresponding signal handler obtained
  a SIG_ERR return from a call to the signal function (7.14.1.1).
-- A signal is generated by an asynchronous signal handler (7.14.1.1).
-- A function with a variable number of arguments attempts to access its varying
  arguments other than through a properly declared and initialized va_list object, or
  before the va_start macro is invoked (7.16, 7.16.1.1, 7.16.1.4).

[page 561]

-- The macro va_arg is invoked using the parameter ap that was passed to a function
  that invoked the macro va_arg with the same parameter (7.16).
-- A macro definition of va_start, va_arg, va_copy, or va_end is suppressed in
  order to access an actual function, or the program defines an external identifier with
  the name va_copy or va_end (7.16.1).
-- The va_start or va_copy macro is invoked without a corresponding invocation
  of the va_end macro in the same function, or vice versa (7.16.1, 7.16.1.2, 7.16.1.3,
  7.16.1.4).
-- The type parameter to the va_arg macro is not such that a pointer to an object of
  that type can be obtained simply by postfixing a * (7.16.1.1).
-- The va_arg macro is invoked when there is no actual next argument, or with a
  specified type that is not compatible with the promoted type of the actual next
  argument, with certain exceptions (7.16.1.1).
-- The va_copy or va_start macro is called to initialize a va_list that was
  previously initialized by either macro without an intervening invocation of the
  va_end macro for the same va_list (7.16.1.2, 7.16.1.4).
-- The parameter parmN of a va_start macro is declared with the register
  storage class, with a function or array type, or with a type that is not compatible with
  the type that results after application of the default argument promotions (7.16.1.4).
-- The member designator parameter of an offsetof macro is an invalid right
  operand of the . operator for the type parameter, or designates a bit-field (7.19).
-- The argument in an instance of one of the integer-constant macros is not a decimal,
  octal, or hexadecimal constant, or it has a value that exceeds the limits for the
  corresponding type (7.20.4).
-- A byte input/output function is applied to a wide-oriented stream, or a wide character
  input/output function is applied to a byte-oriented stream (7.21.2).
-- Use is made of any portion of a file beyond the most recent wide character written to
  a wide-oriented stream (7.21.2).
-- The value of a pointer to a FILE object is used after the associated file is closed
  (7.21.3).
-- The stream for the fflush function points to an input stream or to an update stream
  in which the most recent operation was input (7.21.5.2).
-- The string pointed to by the mode argument in a call to the fopen function does not
  exactly match one of the specified character sequences (7.21.5.3).
-- An output operation on an update stream is followed by an input operation without an
    intervening call to the fflush function or a file positioning function, or an input
[page 562]

   operation on an update stream is followed by an output operation with an intervening
   call to a file positioning function (7.21.5.3).
-- An attempt is made to use the contents of the array that was supplied in a call to the
  setvbuf function (7.21.5.6).
-- There are insufficient arguments for the format in a call to one of the formatted
  input/output functions, or an argument does not have an appropriate type (7.21.6.1,
  7.21.6.2, 7.28.2.1, 7.28.2.2).
-- The format in a call to one of the formatted input/output functions or to the
  strftime or wcsftime function is not a valid multibyte character sequence that
  begins and ends in its initial shift state (7.21.6.1, 7.21.6.2, 7.26.3.5, 7.28.2.1, 7.28.2.2,
  7.28.5.1).
-- In a call to one of the formatted output functions, a precision appears with a
  conversion specifier other than those described (7.21.6.1, 7.28.2.1).
-- A conversion specification for a formatted output function uses an asterisk to denote
  an argument-supplied field width or precision, but the corresponding argument is not
  provided (7.21.6.1, 7.28.2.1).
-- A conversion specification for a formatted output function uses a # or 0 flag with a
  conversion specifier other than those described (7.21.6.1, 7.28.2.1).
-- A conversion specification for one of the formatted input/output functions uses a
  length modifier with a conversion specifier other than those described (7.21.6.1,
  7.21.6.2, 7.28.2.1, 7.28.2.2).
-- An s conversion specifier is encountered by one of the formatted output functions,
  and the argument is missing the null terminator (unless a precision is specified that
  does not require null termination) (7.21.6.1, 7.28.2.1).
-- An n conversion specification for one of the formatted input/output functions includes
  any flags, an assignment-suppressing character, a field width, or a precision (7.21.6.1,
  7.21.6.2, 7.28.2.1, 7.28.2.2).
-- A % conversion specifier is encountered by one of the formatted input/output
  functions, but the complete conversion specification is not exactly %% (7.21.6.1,
  7.21.6.2, 7.28.2.1, 7.28.2.2).
-- An invalid conversion specification is found in the format for one of the formatted
  input/output functions, or the strftime or wcsftime function (7.21.6.1, 7.21.6.2,
  7.26.3.5, 7.28.2.1, 7.28.2.2, 7.28.5.1).
-- The number of characters transmitted by a formatted output function is greater than
  INT_MAX (7.21.6.1, 7.21.6.3, 7.21.6.8, 7.21.6.10).


[page 563]

-- The result of a conversion by one of the formatted input functions cannot be
  represented in the corresponding object, or the receiving object does not have an
  appropriate type (7.21.6.2, 7.28.2.2).
-- A c, s, or [ conversion specifier is encountered by one of the formatted input
  functions, and the array pointed to by the corresponding argument is not large enough
  to accept the input sequence (and a null terminator if the conversion specifier is s or
  [) (7.21.6.2, 7.28.2.2).
-- A c, s, or [ conversion specifier with an l qualifier is encountered by one of the
  formatted input functions, but the input is not a valid multibyte character sequence
  that begins in the initial shift state (7.21.6.2, 7.28.2.2).
-- The input item for a %p conversion by one of the formatted input functions is not a
  value converted earlier during the same program execution (7.21.6.2, 7.28.2.2).
-- The vfprintf, vfscanf, vprintf, vscanf, vsnprintf, vsprintf,
  vsscanf, vfwprintf, vfwscanf, vswprintf, vswscanf, vwprintf, or
  vwscanf function is called with an improperly initialized va_list argument, or
  the argument is used (other than in an invocation of va_end) after the function
  returns (7.21.6.8, 7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
  7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10).
-- The contents of the array supplied in a call to the fgets or fgetws function are
  used after a read error occurred (7.21.7.2, 7.28.3.2).
-- The file position indicator for a binary stream is used after a call to the ungetc
  function where its value was zero before the call (7.21.7.10).
-- The file position indicator for a stream is used after an error occurred during a call to
  the fread or fwrite function (7.21.8.1, 7.21.8.2).
-- A partial element read by a call to the fread function is used (7.21.8.1).
-- The fseek function is called for a text stream with a nonzero offset and either the
  offset was not returned by a previous successful call to the ftell function on a
  stream associated with the same file or whence is not SEEK_SET (7.21.9.2).
-- The fsetpos function is called to set a position that was not returned by a previous
  successful call to the fgetpos function on a stream associated with the same file
  (7.21.9.3).
-- A non-null pointer returned by a call to the calloc, malloc, or realloc function
  with a zero requested size is used to access an object (7.22.3).
-- The value of a pointer that refers to space deallocated by a call to the free or
  realloc function is used (7.22.3).


[page 564]

-- The alignment requested of the aligned_alloc function is not valid or not
  supported by the implementation, or the size requested is not an integral multiple of
  the alignment (7.22.3.1).
-- The pointer argument to the free or realloc function does not match a pointer
  earlier returned by a memory management function, or the space has been deallocated
  by a call to free or realloc (7.22.3.3, 7.22.3.5).
-- The value of the object allocated by the malloc function is used (7.22.3.4).
-- The value of any bytes in a new object allocated by the realloc function beyond
  the size of the old object are used (7.22.3.5).
-- The program calls the exit or quick_exit function more than once, or calls both
  functions (7.22.4.4, 7.22.4.7).
-- During the call to a function registered with the atexit or at_quick_exit
  function, a call is made to the longjmp function that would terminate the call to the
  registered function (7.22.4.4, 7.22.4.7).
-- The string set up by the getenv or strerror function is modified by the program
  (7.22.4.6, 7.23.6.2).
-- A command is executed through the system function in a way that is documented as
  causing termination or some other form of undefined behavior (7.22.4.8).
-- A searching or sorting utility function is called with an invalid pointer argument, even
  if the number of elements is zero (7.22.5).
-- The comparison function called by a searching or sorting utility function alters the
  contents of the array being searched or sorted, or returns ordering values
  inconsistently (7.22.5).
-- The array being searched by the bsearch function does not have its elements in
  proper order (7.22.5.1).
-- The current conversion state is used by a multibyte/wide character conversion
  function after changing the LC_CTYPE category (7.22.7).
-- A string or wide string utility function is instructed to access an array beyond the end
  of an object (7.23.1, 7.28.4).
-- A string or wide string utility function is called with an invalid pointer argument, even
  if the length is zero (7.23.1, 7.28.4).
-- The contents of the destination array are used after a call to the strxfrm,
  strftime, wcsxfrm, or wcsftime function in which the specified length was
  too small to hold the entire null-terminated result (7.23.4.5, 7.26.3.5, 7.28.4.4.4,
  7.28.5.1).

[page 565]

    -- The first argument in the very first call to the strtok or wcstok is a null pointer
      (7.23.5.8, 7.28.4.5.7).
    -- The type of an argument to a type-generic macro is not compatible with the type of
      the corresponding parameter of the selected function (7.24).
    -- A complex argument is supplied for a generic parameter of a type-generic macro that
      has no corresponding complex function (7.24).
    -- At least one field of the broken-down time passed to asctime contains a value
      outside its normal range, or the calculated year exceeds four digits or is less than the
      year 1000 (7.26.3.1).
    -- The argument corresponding to an s specifier without an l qualifier in a call to the
      fwprintf function does not point to a valid multibyte character sequence that
      begins in the initial shift state (7.28.2.11).
    -- In a call to the wcstok function, the object pointed to by ptr does not have the
      value stored by the previous call for the same wide string (7.28.4.5.7).
    -- An mbstate_t object is used inappropriately (7.28.6).
    -- The value of an argument of type wint_t to a wide character classification or case
      mapping function is neither equal to the value of WEOF nor representable as a
      wchar_t (7.29.1).
    -- The iswctype function is called using a different LC_CTYPE category from the
      one in effect for the call to the wctype function that returned the description
      (7.29.2.2.1).
    -- The towctrans function is called using a different LC_CTYPE category from the
      one in effect for the call to the wctrans function that returned the description
      (7.29.3.2.1).
    J.3 Implementation-defined behavior
1   A conforming implementation is required to document its choice of behavior in each of
    the areas listed in this subclause. The following are implementation-defined:




[page 566]

    J.3.1 Translation
1   -- How a diagnostic is identified (3.10, 5.1.1.3).
    -- Whether each nonempty sequence of white-space characters other than new-line is
      retained or replaced by one space character in translation phase 3 (5.1.1.2).
    J.3.2 Environment
1   -- The mapping between physical source file multibyte characters and the source
      character set in translation phase 1 (5.1.1.2).
    -- The name and type of the function called at program startup in a freestanding
      environment (5.1.2.1).
    -- The effect of program termination in a freestanding environment (5.1.2.1).
    -- An alternative manner in which the main function may be defined (5.1.2.2.1).
    -- The values given to the strings pointed to by the argv argument to main (5.1.2.2.1).
    -- What constitutes an interactive device (5.1.2.3).
    -- Whether a program can have more than one thread of execution in a freestanding
      environment (5.1.2.4).
    -- The set of signals, their semantics, and their default handling (7.14).
    -- Signal values other than SIGFPE, SIGILL, and SIGSEGV that correspond to a
      computational exception (7.14.1.1).
    -- Signals for which the equivalent of signal(sig, SIG_IGN); is executed at
      program startup (7.14.1.1).
    -- The set of environment names and the method for altering the environment list used
      by the getenv function (7.22.4.6).
    -- The manner of execution of the string by the system function (7.22.4.8).
    J.3.3 Identifiers
1   -- Which additional multibyte characters may appear in identifiers and their
      correspondence to universal character names (6.4.2).
    -- The number of significant initial characters in an identifier (5.2.4.1, 6.4.2).




[page 567]

    J.3.4 Characters
1   -- The number of bits in a byte (3.6).
    -- The values of the members of the execution character set (5.2.1).
    -- The unique value of the member of the execution character set produced for each of
      the standard alphabetic escape sequences (5.2.2).
    -- The value of a char object into which has been stored any character other than a
      member of the basic execution character set (6.2.5).
    -- Which of signed char or unsigned char has the same range, representation,
      and behavior as ''plain'' char (6.2.5, 6.3.1.1).
    -- The mapping of members of the source character set (in character constants and string
      literals) to members of the execution character set (6.4.4.4, 5.1.1.2).
    -- The value of an integer character constant containing more than one character or
      containing a character or escape sequence that does not map to a single-byte
      execution character (6.4.4.4).
    -- The value of a wide character constant containing more than one multibyte character
      or a single multibyte character that maps to multiple members of the extended
      execution character set, or containing a multibyte character or escape sequence not
      represented in the extended execution character set (6.4.4.4).
    -- The current locale used to convert a wide character constant consisting of a single
      multibyte character that maps to a member of the extended execution character set
      into a corresponding wide character code (6.4.4.4).
    -- Whether differently-prefixed wide string literal tokens can be concatenated and, if so,
      the treatment of the resulting multibyte character sequence (6.4.5).
    -- The current locale used to convert a wide string literal into corresponding wide
      character codes (6.4.5).
    -- The value of a string literal containing a multibyte character or escape sequence not
      represented in the execution character set (6.4.5).
    -- The encoding of any of wchar_t, char16_t, and char32_t where the
      corresponding  standard   encoding macro      (__STDC_ISO_10646__,
      __STDC_UTF_16__, or __STDC_UTF_32__) is not defined (6.10.8.2).




[page 568]

    J.3.5 Integers
1   -- Any extended integer types that exist in the implementation (6.2.5).
    -- Whether signed integer types are represented using sign and magnitude, two's
      complement, or ones' complement, and whether the extraordinary value is a trap
      representation or an ordinary value (6.2.6.2).
    -- The rank of any extended integer type relative to another extended integer type with
      the same precision (6.3.1.1).
    -- The result of, or the signal raised by, converting an integer to a signed integer type
      when the value cannot be represented in an object of that type (6.3.1.3).
    -- The results of some bitwise operations on signed integers (6.5).
    J.3.6 Floating point
1   -- The accuracy of the floating-point operations and of the library functions in
      <math.h> and <complex.h> that return floating-point results (5.2.4.2.2).
    -- The accuracy of the conversions between floating-point internal representations and
      string representations performed by the library functions in <stdio.h>,
      <stdlib.h>, and <wchar.h> (5.2.4.2.2).
    -- The rounding behaviors characterized by non-standard values of FLT_ROUNDS
      (5.2.4.2.2).
    -- The evaluation methods characterized by non-standard negative values of
      FLT_EVAL_METHOD (5.2.4.2.2).
    -- The direction of rounding when an integer is converted to a floating-point number that
      cannot exactly represent the original value (6.3.1.4).
    -- The direction of rounding when a floating-point number is converted to a narrower
      floating-point number (6.3.1.5).
    -- How the nearest representable value or the larger or smaller representable value
      immediately adjacent to the nearest representable value is chosen for certain floating
      constants (6.4.4.2).
    -- Whether and how floating expressions are contracted when not disallowed by the
      FP_CONTRACT pragma (6.5).
    -- The default state for the FENV_ACCESS pragma (7.6.1).
    -- Additional floating-point exceptions, rounding           modes,     environments,   and
      classifications, and their macro names (7.6, 7.12).
    -- The default state for the FP_CONTRACT pragma (7.12.2).


[page 569]

    J.3.7 Arrays and pointers
1   -- The result of converting a pointer to an integer or vice versa (6.3.2.3).
    -- The size of the result of subtracting two pointers to elements of the same array
      (6.5.6).
    J.3.8 Hints
1   -- The extent to which suggestions made by using the register storage-class
      specifier are effective (6.7.1).
    -- The extent to which suggestions made by using the inline function specifier are
      effective (6.7.4).
    J.3.9 Structures, unions, enumerations, and bit-fields
1   -- Whether a ''plain'' int bit-field is treated as a signed int bit-field or as an
      unsigned int bit-field (6.7.2, 6.7.2.1).
    -- Allowable bit-field types other than _Bool, signed int, and unsigned int
      (6.7.2.1).
    -- Whether atomic types are permitted for bit-fields (6.7.2.1).
    -- Whether a bit-field can straddle a storage-unit boundary (6.7.2.1).
    -- The order of allocation of bit-fields within a unit (6.7.2.1).
    -- The alignment of non-bit-field members of structures (6.7.2.1). This should present
      no problem unless binary data written by one implementation is read by another.
    -- The integer type compatible with each enumerated type (6.7.2.2).
    J.3.10 Qualifiers
1   -- What constitutes an access to an object that has volatile-qualified type (6.7.3).
    J.3.11 Preprocessing directives
1   -- The locations within #pragma directives where header name preprocessing tokens
      are recognized (6.4, 6.4.7).
    -- How sequences in both forms of header names are mapped to headers or external
      source file names (6.4.7).
    -- Whether the value of a character constant in a constant expression that controls
      conditional inclusion matches the value of the same character constant in the
      execution character set (6.10.1).
    -- Whether the value of a single-character character constant in a constant expression
      that controls conditional inclusion may have a negative value (6.10.1).


[page 570]

    -- The places that are searched for an included < > delimited header, and how the places
      are specified or the header is identified (6.10.2).
    -- How the named source file is searched for in an included " " delimited header
      (6.10.2).
    -- The method by which preprocessing tokens (possibly resulting from macro
      expansion) in a #include directive are combined into a header name (6.10.2).
    -- The nesting limit for #include processing (6.10.2).
    -- Whether the # operator inserts a \ character before the \ character that begins a
      universal character name in a character constant or string literal (6.10.3.2).
    -- The behavior on each recognized non-STDC #pragma directive (6.10.6).
    -- The definitions for __DATE__ and __TIME__ when respectively, the date and
      time of translation are not available (6.10.8.1).
    J.3.12 Library functions
1   -- Any library facilities available to a freestanding program, other than the minimal set
      required by clause 4 (5.1.2.1).
    -- The format of the diagnostic printed by the assert macro (7.2.1.1).
    -- The representation of the floating-point               status   flags   stored   by   the
      fegetexceptflag function (7.6.2.2).
    -- Whether the feraiseexcept function raises the ''inexact'' floating-point
      exception in addition to the ''overflow'' or ''underflow'' floating-point exception
      (7.6.2.3).
    -- Strings other than "C" and "" that may be passed as the second argument to the
      setlocale function (7.11.1.1).
    -- The types defined for float_t and double_t when the value of the
      FLT_EVAL_METHOD macro is less than 0 (7.12).
    -- Domain errors for the mathematics functions, other than those required by this
      International Standard (7.12.1).
    -- The values returned by the mathematics functions on domain errors or pole errors
      (7.12.1).
    -- The values returned by the mathematics functions on underflow range errors, whether
      errno is set to the value of the macro ERANGE when the integer expression
      math_errhandling & MATH_ERRNO is nonzero, and whether the ''underflow''
      floating-point exception is raised when the integer expression math_errhandling
      & MATH_ERREXCEPT is nonzero. (7.12.1).

[page 571]

-- Whether a domain error occurs or zero is returned when an fmod function has a
  second argument of zero (7.12.10.1).
-- Whether a domain error occurs or zero is returned when a remainder function has
  a second argument of zero (7.12.10.2).
-- The base-2 logarithm of the modulus used by the remquo functions in reducing the
  quotient (7.12.10.3).
-- Whether a domain error occurs or zero is returned when a remquo function has a
  second argument of zero (7.12.10.3).
-- Whether the equivalent of signal(sig, SIG_DFL); is executed prior to the call
  of a signal handler, and, if not, the blocking of signals that is performed (7.14.1.1).
-- The null pointer constant to which the macro NULL expands (7.19).
-- Whether the last line of a text stream requires a terminating new-line character
  (7.21.2).
-- Whether space characters that are written out to a text stream immediately before a
  new-line character appear when read in (7.21.2).
-- The number of null characters that may be appended to data written to a binary
  stream (7.21.2).
-- Whether the file position indicator of an append-mode stream is initially positioned at
  the beginning or end of the file (7.21.3).
-- Whether a write on a text stream causes the associated file to be truncated beyond that
  point (7.21.3).
-- The characteristics of file buffering (7.21.3).
-- Whether a zero-length file actually exists (7.21.3).
-- The rules for composing valid file names (7.21.3).
-- Whether the same file can be simultaneously open multiple times (7.21.3).
-- The nature and choice of encodings used for multibyte characters in files (7.21.3).
-- The effect of the remove function on an open file (7.21.4.1).
-- The effect if a file with the new name exists prior to a call to the rename function
  (7.21.4.2).
-- Whether an open temporary file is removed upon abnormal program termination
  (7.21.4.3).
-- Which changes of mode are permitted (if any), and under what circumstances
  (7.21.5.4).

[page 572]

-- The style used to print an infinity or NaN, and the meaning of any n-char or n-wchar
  sequence printed for a NaN (7.21.6.1, 7.28.2.1).
-- The output for %p conversion in the fprintf or fwprintf function (7.21.6.1,
  7.28.2.1).
-- The interpretation of a - character that is neither the first nor the last character, nor
  the second where a ^ character is the first, in the scanlist for %[ conversion in the
  fscanf or fwscanf function (7.21.6.2, 7.28.2.1).
-- The set of sequences matched by a %p conversion and the interpretation of the
  corresponding input item in the fscanf or fwscanf function (7.21.6.2, 7.28.2.2).
-- The value to which the macro errno is set by the fgetpos, fsetpos, or ftell
  functions on failure (7.21.9.1, 7.21.9.3, 7.21.9.4).
-- The meaning of any n-char or n-wchar sequence in a string representing a NaN that is
  converted by the strtod, strtof, strtold, wcstod, wcstof, or wcstold
  function (7.22.1.3, 7.28.4.1.1).
-- Whether or not the strtod, strtof, strtold, wcstod, wcstof, or wcstold
  function sets errno to ERANGE when underflow occurs (7.22.1.3, 7.28.4.1.1).
-- Whether the calloc, malloc, and realloc functions return a null pointer or a
  pointer to an allocated object when the size requested is zero (7.22.3).
-- Whether open streams with unwritten buffered data are flushed, open streams are
  closed, or temporary files are removed when the abort or _Exit function is called
  (7.22.4.1, 7.22.4.5).
-- The termination status returned to the host environment by the abort, exit,
  _Exit, or quick_exit function (7.22.4.1, 7.22.4.4, 7.22.4.5, 7.22.4.7).
-- The value returned by the system function when its argument is not a null pointer
  (7.22.4.8).
-- The local time zone and Daylight Saving Time (7.26.1).
-- The range and precision of times representable in clock_t and time_t (7.26).
-- The era for the clock function (7.26.2.1).
-- The replacement string for the %Z specifier to the strftime, and wcsftime
  functions in the "C" locale (7.26.3.5, 7.28.5.1).
-- Whether the functions in <math.h> honor the rounding direction mode in an
  IEC 60559 conformant implementation, unless explicitly specified otherwise (F.10).




[page 573]

    J.3.13 Architecture
1   -- The values or expressions assigned to the macros specified in the headers
      <float.h>, <limits.h>, and <stdint.h> (5.2.4.2, 7.20.2, 7.20.3).
    -- The result of attempting to indirectly access an object with automatic or thread
      storage duration from a thread other than the one with which it is associated (6.2.4).
    -- The number, order, and encoding of bytes in any object (when not explicitly specified
      in this International Standard) (6.2.6.1).
    -- Whether any extended alignments are supported and the contexts in which they are
      supported (6.2.8).
    -- Valid alignment values other than those returned by an alignof expression for
      fundamental types, if any (6.2.8).
    -- The value of the result of the sizeof and alignof operators (6.5.3.4).
    J.4 Locale-specific behavior
1   The following characteristics of a hosted environment are locale-specific and are required
    to be documented by the implementation:
    -- Additional members of the source and execution character sets beyond the basic
      character set (5.2.1).
    -- The presence, meaning, and representation of additional multibyte characters in the
      execution character set beyond the basic character set (5.2.1.2).
    -- The shift states used for the encoding of multibyte characters (5.2.1.2).
    -- The direction of writing of successive printing characters (5.2.2).
    -- The decimal-point character (7.1.1).
    -- The set of printing characters (7.4, 7.29.2).
    -- The set of control characters (7.4, 7.29.2).
    -- The sets of characters tested for by the isalpha, isblank, islower, ispunct,
      isspace, isupper, iswalpha, iswblank, iswlower, iswpunct,
      iswspace, or iswupper functions (7.4.1.2, 7.4.1.3, 7.4.1.7, 7.4.1.9, 7.4.1.10,
      7.4.1.11, 7.29.2.1.2, 7.29.2.1.3, 7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10, 7.29.2.1.11).
    -- The native environment (7.11.1.1).
    -- Additional subject sequences accepted by the numeric conversion functions (7.22.1,
      7.28.4.1).
    -- The collation sequence of the execution character set (7.23.4.3, 7.28.4.4.2).


[page 574]

    -- The contents of the error message strings set up by the strerror function
      (7.23.6.2).
    -- The formats for time and date (7.26.3.5, 7.28.5.1).
    -- Character mappings that are supported by the towctrans function (7.29.1).
    -- Character classifications that are supported by the iswctype function (7.29.1).
    J.5 Common extensions
1   The following extensions are widely used in many systems, but are not portable to all
    implementations. The inclusion of any extension that may cause a strictly conforming
    program to become invalid renders an implementation nonconforming. Examples of such
    extensions are new keywords, extra library functions declared in standard headers, or
    predefined macros with names that do not begin with an underscore.
    J.5.1 Environment arguments
1   In a hosted environment, the main function receives a third argument, char *envp[],
    that points to a null-terminated array of pointers to char, each of which points to a string
    that provides information about the environment for this execution of the program
    (5.1.2.2.1).
    J.5.2 Specialized identifiers
1   Characters other than the underscore _, letters, and digits, that are not part of the basic
    source character set (such as the dollar sign $, or characters in national character sets)
    may appear in an identifier (6.4.2).
    J.5.3 Lengths and cases of identifiers
1   All characters in identifiers (with or without external linkage) are significant (6.4.2).
    J.5.4 Scopes of identifiers
1   A function identifier, or the identifier of an object the declaration of which contains the
    keyword extern, has file scope (6.2.1).
    J.5.5 Writable string literals
1   String literals are modifiable (in which case, identical string literals should denote distinct
    objects) (6.4.5).




[page 575]

    J.5.6 Other arithmetic types
1   Additional arithmetic types, such as __int128 or double double, and their
    appropriate conversions are defined (6.2.5, 6.3.1). Additional floating types may have
    more range or precision than long double, may be used for evaluating expressions of
    other floating types, and may be used to define float_t or double_t.
    J.5.7 Function pointer casts
1   A pointer to an object or to void may be cast to a pointer to a function, allowing data to
    be invoked as a function (6.5.4).
2   A pointer to a function may be cast to a pointer to an object or to void, allowing a
    function to be inspected or modified (for example, by a debugger) (6.5.4).
    J.5.8 Extended bit-field types
1   A bit-field may be declared with a type other than _Bool, unsigned int, or
    signed int, with an appropriate maximum width (6.7.2.1).
    J.5.9 The fortran keyword
1   The fortran function specifier may be used in a function declaration to indicate that
    calls suitable for FORTRAN should be generated, or that a different representation for the
    external name is to be generated (6.7.4).
    J.5.10 The asm keyword
1   The asm keyword may be used to insert assembly language directly into the translator
    output (6.8). The most common implementation is via a statement of the form:
           asm ( character-string-literal );
    J.5.11 Multiple external definitions
1   There may be more than one external definition for the identifier of an object, with or
    without the explicit use of the keyword extern; if the definitions disagree, or more than
    one is initialized, the behavior is undefined (6.9.2).
    J.5.12 Predefined macro names
1   Macro names that do not begin with an underscore, describing the translation and
    execution environments, are defined by the implementation before translation begins
    (6.10.8).




[page 576]

    J.5.13 Floating-point status flags
1   If any floating-point status flags are set on normal termination after all calls to functions
    registered by the atexit function have been made (see 7.22.4.4), the implementation
    writes some diagnostics indicating the fact to the stderr stream, if it is still open,
    J.5.14 Extra arguments for signal handlers
1   Handlers for specific signals are called with extra arguments in addition to the signal
    number (7.14.1.1).
    J.5.15 Additional stream types and file-opening modes
1   Additional mappings from files to streams are supported (7.21.2).
2   Additional file-opening modes may be specified by characters appended to the mode
    argument of the fopen function (7.21.5.3).
    J.5.16 Defined file position indicator
1   The file position indicator is decremented by each successful call to the ungetc or
    ungetwc function for a text stream, except if its value was zero before a call (7.21.7.10,
    7.28.3.10).
    J.5.17 Math error reporting
1   Functions declared in <complex.h> and <math.h> raise SIGFPE to report errors
    instead of, or in addition to, setting errno or raising floating-point exceptions (7.3,
    7.12).




[page 577]

                                           Annex K
                                          (normative)
                              Bounds-checking interfaces
    K.1 Background
1   Traditionally, the C Library has contained many functions that trust the programmer to
    provide output character arrays big enough to hold the result being produced. Not only
    do these functions not check that the arrays are big enough, they frequently lack the
    information needed to perform such checks. While it is possible to write safe, robust, and
    error-free code using the existing library, the library tends to promote programming styles
    that lead to mysterious failures if a result is too big for the provided array.
2   A common programming style is to declare character arrays large enough to handle most
    practical cases. However, if these arrays are not large enough to handle the resulting
    strings, data can be written past the end of the array overwriting other data and program
    structures. The program never gets any indication that a problem exists, and so never has
    a chance to recover or to fail gracefully.
3   Worse, this style of programming has compromised the security of computers and
    networks. Buffer overflows can often be exploited to run arbitrary code with the
    permissions of the vulnerable (defective) program.
4   If the programmer writes runtime checks to verify lengths before calling library
    functions, then those runtime checks frequently duplicate work done inside the library
    functions, which discover string lengths as a side effect of doing their job.
5   This annex provides alternative library functions that promote safer, more secure
    programming. The alternative functions verify that output buffers are large enough for
    the intended result and return a failure indicator if they are not. Data is never written past
    the end of an array. All string results are null terminated.
6   This annex also addresses another problem that complicates writing robust code:
    functions that are not reentrant because they return pointers to static objects owned by the
    function. Such functions can be troublesome since a previously returned result can
    change if the function is called again, perhaps by another thread.




[page 578]

    K.2 Scope
1   This annex specifies a series of optional extensions that can be useful in the mitigation of
    security vulnerabilities in programs, and comprise new functions, macros, and types
    declared or defined in existing standard headers.
2   An implementation that defines __STDC_LIB_EXT1__ shall conform to the
    specifications in this annex.367)
3   Subclause K.3 should be read as if it were merged into the parallel structure of named
    subclauses of clause 7.
    K.3 Library
    K.3.1 Introduction
    K.3.1.1 Standard headers
1   The functions, macros, and types declared or defined in K.3 and its subclauses are not
    declared or defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
    defined as a macro which expands to the integer constant 0 at the point in the source file
    where the appropriate header is first included.
2   The functions, macros, and types declared or defined in K.3 and its subclauses are
    declared and defined by their respective headers if __STDC_WANT_LIB_EXT1__ is
    defined as a macro which expands to the integer constant 1 at the point in the source file
    where the appropriate header is first included.368)
3   It is implementation-defined whether the functions, macros, and types declared or defined
    in K.3 and its subclauses are declared or defined by their respective headers if
    __STDC_WANT_LIB_EXT1__ is not defined as a macro at the point in the source file
    where the appropriate header is first included.369)
4   Within a preprocessing translation unit, __STDC_WANT_LIB_EXT1__ shall be
    defined identically for all inclusions of any headers from subclause K.3. If
    __STDC_WANT_LIB_EXT1__ is defined differently for any such inclusion, the
    implementation shall issue a diagnostic as if a preprocessor error directive were used.


    367) Implementations that do not define __STDC_LIB_EXT1__ are not required to conform to these
         specifications.
    368) Future revisions of this International Standard may define meanings for other values of
         __STDC_WANT_LIB_EXT1__.
    369) Subclause 7.1.3 reserves certain names and patterns of names that an implementation may use in
         headers. All other names are not reserved, and a conforming implementation is not permitted to use
         them. While some of the names defined in K.3 and its subclauses are reserved, others are not. If an
         unreserved name is defined in a header when __STDC_WANT_LIB_EXT1__ is defined as 0, the
         implementation is not conforming.

[page 579]

    K.3.1.2 Reserved identifiers
1   Each macro name in any of the following subclauses is reserved for use as specified if it
    is defined by any of its associated headers when included; unless explicitly stated
    otherwise (see 7.1.4).
2   All identifiers with external linkage in any of the following subclauses are reserved for
    use as identifiers with external linkage if any of them are used by the program. None of
    them are reserved if none of them are used.
3   Each identifier with file scope listed in any of the following subclauses is reserved for use
    as a macro name and as an identifier with file scope in the same name space if it is
    defined by any of its associated headers when included.
    K.3.1.3 Use of errno
1   An implementation may set errno for the functions defined in this annex, but is not
    required to.
    K.3.1.4 Runtime-constraint violations
1   Most functions in this annex include as part of their specification a list of runtime-
    constraints. These runtime-constraints are requirements on the program using the
    library.370)
2   Implementations shall verify that the runtime-constraints for a function are not violated
    by the program. If a runtime-constraint is violated, the implementation shall call the
    currently registered runtime-constraint handler (see set_constraint_handler_s
    in <stdlib.h>). Multiple runtime-constraint violations in the same call to a library
    function result in only one call to the runtime-constraint handler. It is unspecified which
    one of the multiple runtime-constraint violations cause the handler to be called.
3   If the runtime-constraints section for a function states an action to be performed when a
    runtime-constraint violation occurs, the function shall perform the action before calling
    the runtime-constraint handler. If the runtime-constraints section lists actions that are
    prohibited when a runtime-constraint violation occurs, then such actions are prohibited to
    the function both before calling the handler and after the handler returns.
4   The runtime-constraint handler might not return. If the handler does return, the library
    function whose runtime-constraint was violated shall return some indication of failure as
    given by the returns section in the function's specification.



    370) Although runtime-constraints replace many cases of undefined behavior, undefined behavior still
         exists in this annex. Implementations are free to detect any case of undefined behavior and treat it as a
         runtime-constraint violation by calling the runtime-constraint handler. This license comes directly
         from the definition of undefined behavior.

[page 580]

    K.3.2 Errors <errno.h>
1   The header <errno.h> defines a type.
2   The type is
             errno_t
    which is type int.371)
    K.3.3 Common definitions <stddef.h>
1   The header <stddef.h> defines a type.
2   The type is
             rsize_t
    which is the type size_t.372)
    K.3.4 Integer types <stdint.h>
1   The header <stdint.h> defines a macro.
2   The macro is
             RSIZE_MAX
    which expands to a value373) of type size_t. Functions that have parameters of type
    rsize_t consider it a runtime-constraint violation if the values of those parameters are
    greater than RSIZE_MAX.
    Recommended practice
3   Extremely large object sizes are frequently a sign that an object's size was calculated
    incorrectly. For example, negative numbers appear as very large positive numbers when
    converted to an unsigned type like size_t. Also, some implementations do not support
    objects as large as the maximum value that can be represented by type size_t.
4   For those reasons, it is sometimes beneficial to restrict the range of object sizes to detect
    programming errors. For implementations targeting machines with large address spaces,
    it is recommended that RSIZE_MAX be defined as the smaller of the size of the largest
    object supported or (SIZE_MAX >> 1), even if this limit is smaller than the size of
    some legitimate, but very large, objects. Implementations targeting machines with small
    address spaces may wish to define RSIZE_MAX as SIZE_MAX, which means that there

    371) As a matter of programming style, errno_t may be used as the type of something that deals only
         with the values that might be found in errno. For example, a function which returns the value of
         errno might be declared as having the return type errno_t.
    372) See the description of the RSIZE_MAX macro in <stdint.h>.
    373) The macro RSIZE_MAX need not expand to a constant expression.

[page 581]

    is no object size that is considered a runtime-constraint violation.
    K.3.5 Input/output <stdio.h>
1   The header <stdio.h> defines several macros and two types.
2   The macros are
           L_tmpnam_s
    which expands to an integer constant expression that is the size needed for an array of
    char large enough to hold a temporary file name string generated by the tmpnam_s
    function;
           TMP_MAX_S
    which expands to an integer constant expression that is the maximum number of unique
    file names that can be generated by the tmpnam_s function.
3   The types are
           errno_t
    which is type int; and
           rsize_t
    which is the type size_t.
    K.3.5.1 Operations on files
    K.3.5.1.1 The tmpfile_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdio.h>
           errno_t tmpfile_s(FILE * restrict * restrict streamptr);
    Runtime-constraints
2   streamptr shall not be a null pointer.
3   If there is a runtime-constraint violation, tmpfile_s does not attempt to create a file.
    Description
4   The tmpfile_s function creates a temporary binary file that is different from any other
    existing file and that will automatically be removed when it is closed or at program
    termination. If the program terminates abnormally, whether an open temporary file is
    removed is implementation-defined. The file is opened for update with "wb+" mode
    with the meaning that mode has in the fopen_s function (including the mode's effect
    on exclusive access and file permissions).


[page 582]

5   If the file was created successfully, then the pointer to FILE pointed to by streamptr
    will be set to the pointer to the object controlling the opened file. Otherwise, the pointer
    to FILE pointed to by streamptr will be set to a null pointer.
    Recommended practice
    It should be possible to open at least TMP_MAX_S temporary files during the lifetime of
    the program (this limit may be shared with tmpnam_s) and there should be no limit on
    the number simultaneously open other than this limit and any limit on the number of open
    files (FOPEN_MAX).
    Returns
6   The tmpfile_s function returns zero if it created the file. If it did not create the file or
    there was a runtime-constraint violation, tmpfile_s returns a nonzero value.
    K.3.5.1.2 The tmpnam_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdio.h>
            errno_t tmpnam_s(char *s, rsize_t maxsize);
    Runtime-constraints
2   s shall not be a null pointer. maxsize shall be less than or equal to RSIZE_MAX.
    maxsize shall be greater than the length of the generated file name string.
    Description
3   The tmpnam_s function generates a string that is a valid file name and that is not the
    same as the name of an existing file.374) The function is potentially capable of generating
    TMP_MAX_S different strings, but any or all of them may already be in use by existing
    files and thus not be suitable return values. The lengths of these strings shall be less than
    the value of the L_tmpnam_s macro.
4   The tmpnam_s function generates a different string each time it is called.
5   It is assumed that s points to an array of at least maxsize characters. This array will be
    set to generated string, as specified below.



    374) Files created using strings generated by the tmpnam_s function are temporary only in the sense that
         their names should not collide with those generated by conventional naming rules for the
         implementation. It is still necessary to use the remove function to remove such files when their use
         is ended, and before program termination. Implementations should take care in choosing the patterns
         used for names returned by tmpnam_s. For example, making a thread id part of the names avoids the
         race condition and possible conflict when multiple programs run simultaneously by the same user
         generate the same temporary file names.

[page 583]

6    The implementation shall behave as if no library function except tmpnam calls the
     tmpnam_s function.375)
     Recommended practice
7    After a program obtains a file name using the tmpnam_s function and before the
     program creates a file with that name, the possibility exists that someone else may create
     a file with that same name. To avoid this race condition, the tmpfile_s function
     should be used instead of tmpnam_s when possible. One situation that requires the use
     of the tmpnam_s function is when the program needs to create a temporary directory
     rather than a temporary file.
     Returns
8    If no suitable string can be generated, or if there is a runtime-constraint violation, the
     tmpnam_s function writes a null character to s[0] (only if s is not null and maxsize
     is greater than zero) and returns a nonzero value.
9    Otherwise, the tmpnam_s function writes the string in the array pointed to by s and
     returns zero.
     Environmental limits
10   The value of the macro TMP_MAX_S shall be at least 25.
     K.3.5.2 File access functions
     K.3.5.2.1 The fopen_s function
     Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdio.h>
            errno_t fopen_s(FILE * restrict * restrict streamptr,
                 const char * restrict filename,
                 const char * restrict mode);
     Runtime-constraints
2    None of streamptr, filename, or mode shall be a null pointer.
3    If there is a runtime-constraint violation, fopen_s does not attempt to open a file.
     Furthermore, if streamptr is not a null pointer, fopen_s sets *streamptr to the
     null pointer.




     375) An implementation may have tmpnam call tmpnam_s (perhaps so there is only one naming
          convention for temporary files), but this is not required.

[page 584]

    Description
4   The fopen_s function opens the file whose name is the string pointed to by
    filename, and associates a stream with it.
5   The mode string shall be as described for fopen, with the addition that modes starting
    with the character 'w' or 'a' may be preceded by the character 'u', see below:
    uw             truncate to zero length or create text file for writing, default
                   permissions
    uwx            create text file for writing, default permissions
    ua             append; open or create text file for writing at end-of-file, default
                   permissions
    uwb            truncate to zero length or create binary file for writing, default
                   permissions
    uwbx           create binary file for writing, default permissions
    uab            append; open or create binary file for writing at end-of-file, default
                   permissions
    uw+            truncate to zero length or create text file for update, default
                   permissions
    uw+x           create text file for update, default permissions
    ua+            append; open or create text file for update, writing at end-of-file,
                   default permissions
    uw+b or uwb+   truncate to zero length or create binary file for update, default
                   permissions
    uw+bx or uwb+x create binary file for update, default permissions
    ua+b or uab+   append; open or create binary file for update, writing at end-of-file,
                   default permissions
6   Opening a file with exclusive mode ('x' as the last character in the mode argument)
    fails if the file already exists or cannot be created.
7   To the extent that the underlying system supports the concepts, files opened for writing
    shall be opened with exclusive (also known as non-shared) access. If the file is being
    created, and the first character of the mode string is not 'u', to the extent that the
    underlying system supports it, the file shall have a file permission that prevents other
    users on the system from accessing the file. If the file is being created and first character
    of the mode string is 'u', then by the time the file has been closed, it shall have the
    system default file access permissions.376)
8   If the file was opened successfully, then the pointer to FILE pointed to by streamptr
    will be set to the pointer to the object controlling the opened file. Otherwise, the pointer


    376) These are the same permissions that the file would have been created with by fopen.

[page 585]

    to FILE pointed to by streamptr will be set to a null pointer.
    Returns
9   The fopen_s function returns zero if it opened the file. If it did not open the file or if
    there was a runtime-constraint violation, fopen_s returns a nonzero value.
    K.3.5.2.2 The freopen_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdio.h>
           errno_t freopen_s(FILE * restrict * restrict newstreamptr,
                const char * restrict filename,
                const char * restrict mode,
                FILE * restrict stream);
    Runtime-constraints
2   None of newstreamptr, mode, and stream shall be a null pointer.
3   If there is a runtime-constraint violation, freopen_s neither attempts to close any file
    associated with stream nor attempts to open a file. Furthermore, if newstreamptr is
    not a null pointer, fopen_s sets *newstreamptr to the null pointer.
    Description
4   The freopen_s function opens the file whose name is the string pointed to by
    filename and associates the stream pointed to by stream with it. The mode
    argument has the same meaning as in the fopen_s function (including the mode's effect
    on exclusive access and file permissions).
5   If filename is a null pointer, the freopen_s function attempts to change the mode of
    the stream to that specified by mode, as if the name of the file currently associated with
    the stream had been used. It is implementation-defined which changes of mode are
    permitted (if any), and under what circumstances.
6   The freopen_s function first attempts to close any file that is associated with stream.
    Failure to close the file is ignored. The error and end-of-file indicators for the stream are
    cleared.
7   If the file was opened successfully, then the pointer to FILE pointed to by
    newstreamptr will be set to the value of stream. Otherwise, the pointer to FILE
    pointed to by newstreamptr will be set to a null pointer.
    Returns
8   The freopen_s function returns zero if it opened the file. If it did not open the file or
    there was a runtime-constraint violation, freopen_s returns a nonzero value.

[page 586]

    K.3.5.3 Formatted input/output functions
1   Unless explicitly stated otherwise, if the execution of a function described in this
    subclause causes copying to take place between objects that overlap, the objects take on
    unspecified values.
    K.3.5.3.1 The fprintf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdio.h>
             int fprintf_s(FILE * restrict stream,
                  const char * restrict format, ...);
    Runtime-constraints
2   Neither stream nor format shall be a null pointer. The %n specifier377) (modified or
    not by flags, field width, or precision) shall not appear in the string pointed to by
    format. Any argument to fprintf_s corresponding to a %s specifier shall not be a
    null pointer.
3   If there is a runtime-constraint violation,378) the fprintf_s function does not attempt
    to produce further output, and it is unspecified to what extent fprintf_s produced
    output before discovering the runtime-constraint violation.
    Description
4   The fprintf_s function is equivalent to the fprintf function except for the explicit
    runtime-constraints listed above.
    Returns
5   The fprintf_s function returns the number of characters transmitted, or a negative
    value if an output error, encoding error, or runtime-constraint violation occurred.




    377) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.
    378) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
         implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
         constraint violation.

[page 587]

    K.3.5.3.2 The fscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdio.h>
            int fscanf_s(FILE * restrict stream,
                 const char * restrict format, ...);
    Runtime-constraints
2   Neither stream nor format shall be a null pointer. Any argument indirected though in
    order to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation,379) the fscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent fscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion
    specifiers apply to a pair of arguments (unless assignment suppression is indicated by a
    *). The first of these arguments is the same as for fscanf. That argument is
    immediately followed in the argument list by the second argument, which has type
    rsize_t and gives the number of elements in the array pointed to by the first argument
    of the pair. If the first argument points to a scalar object, it is considered to be an array of
    one element.380)
5   A matching failure occurs if the number of elements in a receiving object is insufficient to
    hold the converted input (including any trailing null character).
    Returns
6   The fscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the

    379) Because an implementation may treat any undefined behavior as a runtime-constraint violation, an
         implementation may treat any unsupported specifiers in the string pointed to by format as a runtime-
         constraint violation.
    380) If the format is known at translation time, an implementation may issue a diagnostic for any argument
         used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
         argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
         the format is not known at translation time. For example, an implementation may issue a diagnostic
         for each argument after format that has of type pointer to one of char, signed char,
         unsigned char, or void that is not followed by an argument of a type compatible with
         rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
         using the hh length modifier, a length argument must follow the pointer argument. Another useful
         diagnostic could flag any non-pointer argument following format that did not have a type
         compatible with rsize_t.

[page 588]

    fscanf_s function returns the number of input items assigned, which can be fewer than
    provided for, or even zero, in the event of an early matching failure.
7   EXAMPLE 1        The call:
             #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdio.h>
             /* ... */
             int n, i; float x; char name[50];
             n = fscanf_s(stdin, "%d%f%s", &i, &x, name, (rsize_t) 50);
    with the input line:
             25 54.32E-1 thompson
    will assign to n the value 3, to i the value 25, to x the value 5.432, and to name the sequence
    thompson\0.

8   EXAMPLE 2        The call:
             #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdio.h>
             /* ... */
             int n; char s[5];
             n = fscanf_s(stdin, "%s", s, sizeof s);
    with the input line:
             hello
    will assign to n the value 0 since a matching failure occurred because the sequence hello\0 requires an
    array of six characters to store it.

    K.3.5.3.3 The printf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdio.h>
             int printf_s(const char * restrict format, ...);
    Runtime-constraints
2   format shall not be a null pointer. The %n specifier381) (modified or not by flags, field
    width, or precision) shall not appear in the string pointed to by format. Any argument
    to printf_s corresponding to a %s specifier shall not be a null pointer.
3   If there is a runtime-constraint violation, the printf_s function does not attempt to
    produce further output, and it is unspecified to what extent printf_s produced output
    before discovering the runtime-constraint violation.


    381) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.

[page 589]

    Description
4   The printf_s function is equivalent to the printf function except for the explicit
    runtime-constraints listed above.
    Returns
5   The printf_s function returns the number of characters transmitted, or a negative
    value if an output error, encoding error, or runtime-constraint violation occurred.
    K.3.5.3.4 The scanf_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdio.h>
           int scanf_s(const char * restrict format, ...);
    Runtime-constraints
2   format shall not be a null pointer. Any argument indirected though in order to store
    converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the scanf_s function does not attempt to
    perform further input, and it is unspecified to what extent scanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The scanf_s function is equivalent to fscanf_s with the argument stdin
    interposed before the arguments to scanf_s.
    Returns
5   The scanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    scanf_s function returns the number of input items assigned, which can be fewer than
    provided for, or even zero, in the event of an early matching failure.
    K.3.5.3.5 The snprintf_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdio.h>
           int snprintf_s(char * restrict s, rsize_t n,
                const char * restrict format, ...);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The %n specifier382) (modified or not by flags, field width, or
    precision) shall not appear in the string pointed to by format. Any argument to
[page 590]

    snprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
    error shall occur.
3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the snprintf_s function sets s[0] to the
    null character.
    Description
4   The snprintf_s function is equivalent to the snprintf function except for the
    explicit runtime-constraints listed above.
5   The snprintf_s function, unlike sprintf_s, will truncate the result to fit within the
    array pointed to by s.
    Returns
6   The snprintf_s function returns the number of characters that would have been
    written had n been sufficiently large, not counting the terminating null character, or a
    negative value if a runtime-constraint violation occurred. Thus, the null-terminated
    output has been completely written if and only if the returned value is nonnegative and
    less than n.
    K.3.5.3.6 The sprintf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdio.h>
             int sprintf_s(char * restrict s, rsize_t n,
                  const char * restrict format, ...);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The number of characters (including the trailing null) required for the
    result to be written to the array pointed to by s shall not be greater than n. The %n
    specifier383) (modified or not by flags, field width, or precision) shall not appear in the
    string pointed to by format. Any argument to sprintf_s corresponding to a %s
    specifier shall not be a null pointer. No encoding error shall occur.



    382) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.
    383) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.

[page 591]

3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the sprintf_s function sets s[0] to the
    null character.
    Description
4   The sprintf_s function is equivalent to the sprintf function except for the
    parameter n and the explicit runtime-constraints listed above.
5   The sprintf_s function, unlike snprintf_s, treats a result too big for the array
    pointed to by s as a runtime-constraint violation.
    Returns
6   If no runtime-constraint violation occurred, the sprintf_s function returns the number
    of characters written in the array, not counting the terminating null character. If an
    encoding error occurred, sprintf_s returns a negative value. If any other runtime-
    constraint violation occurred, sprintf_s returns zero.
    K.3.5.3.7 The sscanf_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdio.h>
           int sscanf_s(const char * restrict s,
                const char * restrict format, ...);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. Any argument indirected though in order
    to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the sscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent sscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The sscanf_s function is equivalent to fscanf_s, except that input is obtained from
    a string (specified by the argument s) rather than from a stream. Reaching the end of the
    string is equivalent to encountering end-of-file for the fscanf_s function. If copying
    takes place between objects that overlap, the objects take on unspecified values.
    Returns
5   The sscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    sscanf_s function returns the number of input items assigned, which can be fewer than
    provided for, or even zero, in the event of an early matching failure.

[page 592]

    K.3.5.3.8 The vfprintf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdarg.h>
             #include <stdio.h>
             int vfprintf_s(FILE * restrict stream,
                  const char * restrict format,
                  va_list arg);
    Runtime-constraints
2   Neither stream nor format shall be a null pointer. The %n specifier384) (modified or
    not by flags, field width, or precision) shall not appear in the string pointed to by
    format. Any argument to vfprintf_s corresponding to a %s specifier shall not be a
    null pointer.
3   If there is a runtime-constraint violation, the vfprintf_s function does not attempt to
    produce further output, and it is unspecified to what extent vfprintf_s produced
    output before discovering the runtime-constraint violation.
    Description
4   The vfprintf_s function is equivalent to the vfprintf function except for the
    explicit runtime-constraints listed above.
    Returns
5   The vfprintf_s function returns the number of characters transmitted, or a negative
    value if an output error, encoding error, or runtime-constraint violation occurred.
    K.3.5.3.9 The vfscanf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdarg.h>
             #include <stdio.h>
             int vfscanf_s(FILE * restrict stream,
                  const char * restrict format,
                  va_list arg);




    384) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.

[page 593]

    Runtime-constraints
2   Neither stream nor format shall be a null pointer. Any argument indirected though in
    order to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the vfscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent vfscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The vfscanf_s function is equivalent to fscanf_s, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfscanf_s function does not invoke the
    va_end macro.385)
    Returns
5   The vfscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    vfscanf_s function returns the number of input items assigned, which can be fewer
    than provided for, or even zero, in the event of an early matching failure.
    K.3.5.3.10 The vprintf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdarg.h>
             #include <stdio.h>
             int vprintf_s(const char * restrict format,
                  va_list arg);
    Runtime-constraints
2   format shall not be a null pointer. The %n specifier386) (modified or not by flags, field
    width, or precision) shall not appear in the string pointed to by format. Any argument
    to vprintf_s corresponding to a %s specifier shall not be a null pointer.
3   If there is a runtime-constraint violation, the vprintf_s function does not attempt to
    produce further output, and it is unspecified to what extent vprintf_s produced output
    before discovering the runtime-constraint violation.

    385) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
         vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
         indeterminate.
    386) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.

[page 594]

    Description
4   The vprintf_s function is equivalent to the vprintf function except for the explicit
    runtime-constraints listed above.
    Returns
5   The vprintf_s function returns the number of characters transmitted, or a negative
    value if an output error, encoding error, or runtime-constraint violation occurred.
    K.3.5.3.11 The vscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <stdio.h>
            int vscanf_s(const char * restrict format,
                 va_list arg);
    Runtime-constraints
2   format shall not be a null pointer. Any argument indirected though in order to store
    converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the vscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent vscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The vscanf_s function is equivalent to scanf_s, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vscanf_s function does not invoke the
    va_end macro.387)
    Returns
5   The vscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    vscanf_s function returns the number of input items assigned, which can be fewer than
    provided for, or even zero, in the event of an early matching failure.




    387) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
         vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
         indeterminate.

[page 595]

    K.3.5.3.12 The vsnprintf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdarg.h>
             #include <stdio.h>
             int vsnprintf_s(char * restrict s, rsize_t n,
                  const char * restrict format,
                  va_list arg);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The %n specifier388) (modified or not by flags, field width, or
    precision) shall not appear in the string pointed to by format. Any argument to
    vsnprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
    error shall occur.
3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the vsnprintf_s function sets s[0] to the
    null character.
    Description
4   The vsnprintf_s function is equivalent to the vsnprintf function except for the
    explicit runtime-constraints listed above.
5   The vsnprintf_s function, unlike vsprintf_s, will truncate the result to fit within
    the array pointed to by s.
    Returns
6   The vsnprintf_s function returns the number of characters that would have been
    written had n been sufficiently large, not counting the terminating null character, or a
    negative value if a runtime-constraint violation occurred. Thus, the null-terminated
    output has been completely written if and only if the returned value is nonnegative and
    less than n.




    388) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.

[page 596]

    K.3.5.3.13 The vsprintf_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdarg.h>
             #include <stdio.h>
             int vsprintf_s(char * restrict s, rsize_t n,
                  const char * restrict format,
                  va_list arg);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The number of characters (including the trailing null) required for the
    result to be written to the array pointed to by s shall not be greater than n. The %n
    specifier389) (modified or not by flags, field width, or precision) shall not appear in the
    string pointed to by format. Any argument to vsprintf_s corresponding to a %s
    specifier shall not be a null pointer. No encoding error shall occur.
3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the vsprintf_s function sets s[0] to the
    null character.
    Description
4   The vsprintf_s function is equivalent to the vsprintf function except for the
    parameter n and the explicit runtime-constraints listed above.
5   The vsprintf_s function, unlike vsnprintf_s, treats a result too big for the array
    pointed to by s as a runtime-constraint violation.
    Returns
6   If no runtime-constraint violation occurred, the vsprintf_s function returns the
    number of characters written in the array, not counting the terminating null character. If
    an encoding error occurred, vsprintf_s returns a negative value. If any other
    runtime-constraint violation occurred, vsprintf_s returns zero.




    389) It is not a runtime-constraint violation for the characters %n to appear in sequence in the string pointed
         at by format when those characters are not a interpreted as a %n specifier. For example, if the entire
         format string was %%n.

[page 597]

    K.3.5.3.14 The vsscanf_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdarg.h>
           #include <stdio.h>
           int vsscanf_s(const char * restrict s,
                const char * restrict format,
                va_list arg);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. Any argument indirected though in order
    to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the vsscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent vsscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The vsscanf_s function is equivalent to sscanf_s, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vsscanf_s function does not invoke the
    va_end macro.390)
    Returns
5   The vsscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    vscanf_s function returns the number of input items assigned, which can be fewer than
    provided for, or even zero, in the event of an early matching failure.
    K.3.5.4 Character input/output functions
    K.3.5.4.1 The gets_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <stdio.h>
           char *gets_s(char *s, rsize_t n);




    390) As the functions vfprintf_s, vfscanf_s, vprintf_s, vscanf_s, vsnprintf_s,
         vsprintf_s, and vsscanf_s invoke the va_arg macro, the value of arg after the return is
         indeterminate.

[page 598]

    Runtime-constraints
2   s shall not be a null pointer. n shall neither be equal to zero nor be greater than
    RSIZE_MAX. A new-line character, end-of-file, or read error shall occur within reading
    n-1 characters from stdin.391)
3   If there is a runtime-constraint violation, s[0] is set to the null character, and characters
    are read and discarded from stdin until a new-line character is read, or end-of-file or a
    read error occurs.
    Description
4   The gets_s function reads at most one less than the number of characters specified by n
    from the stream pointed to by stdin, into the array pointed to by s. No additional
    characters are read after a new-line character (which is discarded) or after end-of-file.
    The discarded new-line character does not count towards number of characters read. A
    null character is written immediately after the last character read into the array.
5   If end-of-file is encountered and no characters have been read into the array, or if a read
    error occurs during the operation, then s[0] is set to the null character, and the other
    elements of s take unspecified values.
    Recommended practice
6   The fgets function allows properly-written programs to safely process input lines too
    long to store in the result array. In general this requires that callers of fgets pay
    attention to the presence or absence of a new-line character in the result array. Consider
    using fgets (along with any needed processing based on new-line characters) instead of
    gets_s.
    Returns
7   The gets_s function returns s if successful. If there was a runtime-constraint violation,
    or if end-of-file is encountered and no characters have been read into the array, or if a
    read error occurs during the operation, then a null pointer is returned.




    391) The gets_s function, unlike the historical gets function, makes it a runtime-constraint violation for
         a line of input to overflow the buffer to store it. Unlike the fgets function, gets_s maintains a
         one-to-one relationship between input lines and successful calls to gets_s. Programs that use gets
         expect such a relationship.

[page 599]

    K.3.6 General utilities <stdlib.h>
1   The header <stdlib.h> defines three types.
2   The types are
            errno_t
    which is type int; and
            rsize_t
    which is the type size_t; and
            constraint_handler_t
    which has the following definition
            typedef void (*constraint_handler_t)(
                 const char * restrict msg,
                 void * restrict ptr,
                 errno_t error);
    K.3.6.1 Runtime-constraint handling
    K.3.6.1.1 The set_constraint_handler_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdlib.h>
            constraint_handler_t set_constraint_handler_s(
                 constraint_handler_t handler);
    Description
2   The set_constraint_handler_s function sets the runtime-constraint handler to
    be handler. The runtime-constraint handler is the function to be called when a library
    function detects a runtime-constraint violation. Only the most recent handler registered
    with set_constraint_handler_s is called when a runtime-constraint violation
    occurs.
3   When the handler is called, it is passed the following arguments in the following order:
       1.   A pointer to a character string describing the runtime-constraint violation.
       2.   A null pointer or a pointer to an implementation defined object.
       3.   If the function calling the handler has a return type declared as errno_t, the
            return value of the function is passed. Otherwise, a positive value of type
            errno_t is passed.



[page 600]

4   The implementation has a default constraint handler that is used if no calls to the
    set_constraint_handler_s function have been made. The behavior of the
    default handler is implementation-defined, and it may cause the program to exit or abort.
5   If the handler argument to set_constraint_handler_s is a null pointer, the
    implementation default handler becomes the current constraint handler.
    Returns
6   The set_constraint_handler_s function returns a pointer to the previously
    registered handler.392)
    K.3.6.1.2 The abort_handler_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdlib.h>
            void abort_handler_s(
                 const char * restrict msg,
                 void * restrict ptr,
                 errno_t error);
    Description
2   A pointer to the abort_handler_s function shall be a suitable argument to the
    set_constraint_handler_s function.
3   The abort_handler_s function writes a message on the standard error stream in an
    implementation-defined format. The message shall include the string pointed to by msg.
    The abort_handler_s function then calls the abort function.393)
    Returns
4   The abort_handler_s function does not return to its caller.




    392) If the previous handler was registered by calling set_constraint_handler_s with a null
         pointer argument, a pointer to the implementation default handler is returned (not NULL).
    393) Many implementations invoke a debugger when the abort function is called.

[page 601]

    K.3.6.1.3 The ignore_handler_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdlib.h>
            void ignore_handler_s(
                 const char * restrict msg,
                 void * restrict ptr,
                 errno_t error);
    Description
2   A pointer to the ignore_handler_s function shall be a suitable argument to the
    set_constraint_handler_s function.
3   The ignore_handler_s function simply returns to its caller.394)
    Returns
4   The ignore_handler_s function returns no value.
    K.3.6.2 Communication with the environment
    K.3.6.2.1 The getenv_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdlib.h>
            errno_t getenv_s(size_t * restrict len,
                       char * restrict value, rsize_t maxsize,
                       const char * restrict name);
    Runtime-constraints
2   name shall not be a null pointer. maxsize shall neither equal zero nor be greater than
    RSIZE_MAX. If maxsize is not equal to zero, then value shall not be a null pointer.
3   If there is a runtime-constraint violation, the integer pointed to by len is set to 0 (if len
    is not null), and the environment list is not searched.
    Description
4   The getenv_s function searches an environment list, provided by the host environment,
    for a string that matches the string pointed to by name.


    394) If the runtime-constraint handler is set to the ignore_handler_s function, any library function in
         which a runtime-constraint violation occurs will return to its caller. The caller can determine whether
         a runtime-constraint violation occurred based on the library function's specification (usually, the
         library function returns a nonzero errno_t).

[page 602]

5   If that name is found then getenv_s performs the following actions. If len is not a
    null pointer, the length of the string associated with the matched list member is stored in
    the integer pointed to by len. If the length of the associated string is less than maxsize,
    then the associated string is copied to the array pointed to by value.
6   If that name is not found then getenv_s performs the following actions. If len is not
    a null pointer, zero is stored in the integer pointed to by len. If maxsize is greater than
    zero, then value[0] is set to the null character.
7   The set of environment names and the method for altering the environment list are
    implementation-defined.
    Returns
8   The getenv_s function returns zero if the specified name is found and the associated
    string was successfully stored in value. Otherwise, a nonzero value is returned.
    K.3.6.3 Searching and sorting utilities
1   These utilities make use of a comparison function to search or sort arrays of unspecified
    type. Where an argument declared as size_t nmemb specifies the length of the array
    for a function, if nmemb has the value zero on a call to that function, then the comparison
    function is not called, a search finds no matching element, sorting performs no
    rearrangement, and the pointer to the array may be null.
2   The implementation shall ensure that the second argument of the comparison function
    (when called from bsearch_s), or both arguments (when called from qsort_s), are
    pointers to elements of the array.395) The first argument when called from bsearch_s
    shall equal key.
3   The comparison function shall not alter the contents of either the array or search key. The
    implementation may reorder elements of the array between calls to the comparison
    function, but shall not otherwise alter the contents of any individual element.
4   When the same objects (consisting of size bytes, irrespective of their current positions
    in the array) are passed more than once to the comparison function, the results shall be
    consistent with one another. That is, for qsort_s they shall define a total ordering on
    the array, and for bsearch_s the same object shall always compare the same way with
    the key.




    395) That is, if the value passed is p, then the following expressions are always valid and nonzero:
                  ((char *)p - (char *)base) % size == 0
                  (char *)p >= (char *)base
                  (char *)p < (char *)base + nmemb * size


[page 603]

5   A sequence point occurs immediately before and immediately after each call to the
    comparison function, and also between any call to the comparison function and any
    movement of the objects passed as arguments to that call.
    K.3.6.3.1 The bsearch_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <stdlib.h>
             void *bsearch_s(const void *key, const void *base,
                  rsize_t nmemb, rsize_t size,
                  int (*compar)(const void *k, const void *y,
                                  void *context),
                  void *context);
    Runtime-constraints
2   Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
    zero, then none of key, base, or compar shall be a null pointer.
3   If there is a runtime-constraint violation, the bsearch_s function does not search the
    array.
    Description
4   The bsearch_s function searches an array of nmemb objects, the initial element of
    which is pointed to by base, for an element that matches the object pointed to by key.
    The size of each element of the array is specified by size.
5   The comparison function pointed to by compar is called with three arguments. The first
    two point to the key object and to an array element, in that order. The function shall
    return an integer less than, equal to, or greater than zero if the key object is considered,
    respectively, to be less than, to match, or to be greater than the array element. The array
    shall consist of: all the elements that compare less than, all the elements that compare
    equal to, and all the elements that compare greater than the key object, in that order.396)
    The third argument to the comparison function is the context argument passed to
    bsearch_s. The sole use of context by bsearch_s is to pass it to the comparison
    function.397)




    396) In practice, this means that the entire array has been sorted according to the comparison function.
    397) The context argument is for the use of the comparison function in performing its duties. For
         example, it might specify a collating sequence used by the comparison function.

[page 604]

    Returns
6   The bsearch_s function returns a pointer to a matching element of the array, or a null
    pointer if no match is found or there is a runtime-constraint violation. If two elements
    compare as equal, which element is matched is unspecified.
    K.3.6.3.2 The qsort_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdlib.h>
            errno_t qsort_s(void *base, rsize_t nmemb, rsize_t size,
                 int (*compar)(const void *x, const void *y,
                                 void *context),
                 void *context);
    Runtime-constraints
2   Neither nmemb nor size shall be greater than RSIZE_MAX. If nmemb is not equal to
    zero, then neither base nor compar shall be a null pointer.
3   If there is a runtime-constraint violation, the qsort_s function does not sort the array.
    Description
4   The qsort_s function sorts an array of nmemb objects, the initial element of which is
    pointed to by base. The size of each object is specified by size.
5   The contents of the array are sorted into ascending order according to a comparison
    function pointed to by compar, which is called with three arguments. The first two
    point to the objects being compared. The function shall return an integer less than, equal
    to, or greater than zero if the first argument is considered to be respectively less than,
    equal to, or greater than the second. The third argument to the comparison function is the
    context argument passed to qsort_s. The sole use of context by qsort_s is to
    pass it to the comparison function.398)
6   If two elements compare as equal, their relative order in the resulting sorted array is
    unspecified.
    Returns
7   The qsort_s function returns zero if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.




    398) The context argument is for the use of the comparison function in performing its duties. For
         example, it might specify a collating sequence used by the comparison function.

[page 605]

    K.3.6.4 Multibyte/wide character conversion functions
1   The behavior of the multibyte character functions is affected by the LC_CTYPE category
    of the current locale. For a state-dependent encoding, each function is placed into its
    initial conversion state by a call for which its character pointer argument, s, is a null
    pointer. Subsequent calls with s as other than a null pointer cause the internal conversion
    state of the function to be altered as necessary. A call with s as a null pointer causes
    these functions to set the int pointed to by their status argument to a nonzero value if
    encodings have state dependency, and zero otherwise.399) Changing the LC_CTYPE
    category causes the conversion state of these functions to be indeterminate.
    K.3.6.4.1 The wctomb_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdlib.h>
            errno_t wctomb_s(int * restrict status,
                 char * restrict s,
                 rsize_t smax,
                 wchar_t wc);
    Runtime-constraints
2   Let n denote the number of bytes needed to represent the multibyte character
    corresponding to the wide character given by wc (including any shift sequences).
3   If s is not a null pointer, then smax shall not be less than n, and smax shall not be
    greater than RSIZE_MAX. If s is a null pointer, then smax shall equal zero.
4   If there is a runtime-constraint violation, wctomb_s does not modify the int pointed to
    by status, and if s is not a null pointer, no more than smax elements in the array
    pointed to by s will be accessed.
    Description
5   The wctomb_s function determines n and stores the multibyte character representation
    of wc in the array whose first element is pointed to by s (if s is not a null pointer). The
    number of characters stored never exceeds MB_CUR_MAX or smax. If wc is a null wide
    character, a null byte is stored, preceded by any shift sequence needed to restore the
    initial shift state, and the function is left in the initial conversion state.
6   The implementation shall behave as if no library function calls the wctomb_s function.




    399) If the locale employs special bytes to change the shift state, these bytes do not produce separate wide
         character codes, but are grouped with an adjacent multibyte character.

[page 606]

7    If s is a null pointer, the wctomb_s function stores into the int pointed to by status a
     nonzero or zero value, if multibyte character encodings, respectively, do or do not have
     state-dependent encodings.
8    If s is not a null pointer, the wctomb_s function stores into the int pointed to by
     status either n or -1 if wc, respectively, does or does not correspond to a valid
     multibyte character.
9    In no case will the int pointed to by status be set to a value greater than the
     MB_CUR_MAX macro.
     Returns
10   The wctomb_s function returns zero if successful, and a nonzero value if there was a
     runtime-constraint violation or wc did not correspond to a valid multibyte character.
     K.3.6.5 Multibyte/wide string conversion functions
1    The behavior of the multibyte string functions is affected by the LC_CTYPE category of
     the current locale.
     K.3.6.5.1 The mbstowcs_s function
     Synopsis
1            #include <stdlib.h>
             errno_t mbstowcs_s(size_t * restrict retval,
                  wchar_t * restrict dst, rsize_t dstmax,
                  const char * restrict src, rsize_t len);
     Runtime-constraints
2    Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
     neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
     then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
     zero. If dst is not a null pointer and len is not less than dstmax, then a null character
     shall occur within the first dstmax multibyte characters of the array pointed to by src.
3    If there is a runtime-constraint violation, then mbstowcs_s does the following. If
     retval is not a null pointer, then mbstowcs_s sets *retval to (size_t)(-1). If
     dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
     then mbstowcs_s sets dst[0] to the null wide character.
     Description
4    The mbstowcs_s function converts a sequence of multibyte characters that begins in
     the initial shift state from the array pointed to by src into a sequence of corresponding
     wide characters. If dst is not a null pointer, the converted characters are stored into the
     array pointed to by dst. Conversion continues up to and including a terminating null
     character, which is also stored. Conversion stops earlier in two cases: when a sequence of
[page 607]

    bytes is encountered that does not form a valid multibyte character, or (if dst is not a
    null pointer) when len wide characters have been stored into the array pointed to by
    dst.400) If dst is not a null pointer and no null wide character was stored into the array
    pointed to by dst, then dst[len] is set to the null wide character. Each conversion
    takes place as if by a call to the mbrtowc function.
5   Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
    sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
    the mbstowcs_s function stores the value (size_t)(-1) into *retval.
    Otherwise, the mbstowcs_s function stores into *retval the number of multibyte
    characters successfully converted, not including the terminating null character (if any).
6   All elements following the terminating null wide character (if any) written by
    mbstowcs_s in the array of dstmax wide characters pointed to by dst take
    unspecified values when mbstowcs_s returns.401)
7   If copying takes place between objects that overlap, the objects take on unspecified
    values.
    Returns
8   The mbstowcs_s function returns zero if no runtime-constraint violation and no
    encoding error occurred. Otherwise, a nonzero value is returned.
    K.3.6.5.2 The wcstombs_s function
    Synopsis
1            #include <stdlib.h>
             errno_t wcstombs_s(size_t * restrict retval,
                  char * restrict dst, rsize_t dstmax,
                  const wchar_t * restrict src, rsize_t len);
    Runtime-constraints
2   Neither retval nor src shall be a null pointer. If dst is not a null pointer, then
    neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null pointer,
    then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall not equal
    zero. If dst is not a null pointer and len is not less than dstmax, then the conversion
    shall have been stopped (see below) because a terminating null wide character was
    reached or because an encoding error occurred.




    400) Thus, the value of len is ignored if dst is a null pointer.
    401) This allows an implementation to attempt converting the multibyte string before discovering a
         terminating null character did not occur where required.

[page 608]

3   If there is a runtime-constraint violation, then wcstombs_s does the following. If
    retval is not a null pointer, then wcstombs_s sets *retval to (size_t)(-1). If
    dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
    then wcstombs_s sets dst[0] to the null character.
    Description
4   The wcstombs_s function converts a sequence of wide characters from the array
    pointed to by src into a sequence of corresponding multibyte characters that begins in
    the initial shift state. If dst is not a null pointer, the converted characters are then stored
    into the array pointed to by dst. Conversion continues up to and including a terminating
    null wide character, which is also stored. Conversion stops earlier in two cases:
    -- when a wide character is reached that does not correspond to a valid multibyte
      character;
    -- (if dst is not a null pointer) when the next multibyte character would exceed the
        limit of n total bytes to be stored into the array pointed to by dst. If the wide
        character being converted is the null wide character, then n is the lesser of len or
        dstmax. Otherwise, n is the lesser of len or dstmax-1.
    If the conversion stops without converting a null wide character and dst is not a null
    pointer, then a null character is stored into the array pointed to by dst immediately
    following any multibyte characters already stored. Each conversion takes place as if by a
    call to the wcrtomb function.402)
5   Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
    wide character that does not correspond to a valid multibyte character, an encoding error
    occurs: the wcstombs_s function stores the value (size_t)(-1) into *retval.
    Otherwise, the wcstombs_s function stores into *retval the number of bytes in the
    resulting multibyte character sequence, not including the terminating null character (if
    any).
6   All elements following the terminating null character (if any) written by wcstombs_s
    in the array of dstmax elements pointed to by dst take unspecified values when
    wcstombs_s returns.403)
7   If copying takes place between objects that overlap, the objects take on unspecified
    values.


    402) If conversion stops because a terminating null wide character has been reached, the bytes stored
         include those necessary to reach the initial shift state immediately before the null byte. However, if
         the conversion stops before a terminating null wide character has been reached, the result will be null
         terminated, but might not end in the initial shift state.
    403) When len is not less than dstmax, the implementation might fill the array before discovering a
         runtime-constraint violation.

[page 609]

    Returns
8   The wcstombs_s function returns zero if no runtime-constraint violation and no
    encoding error occurred. Otherwise, a nonzero value is returned.
    K.3.7 String handling <string.h>
1   The header <string.h> defines two types.
2   The types are
           errno_t
    which is type int; and
           rsize_t
    which is the type size_t.
    K.3.7.1 Copying functions
    K.3.7.1.1 The memcpy_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <string.h>
           errno_t memcpy_s(void * restrict s1, rsize_t s1max,
                const void * restrict s2, rsize_t n);
    Runtime-constraints
2   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
    RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
    objects that overlap.
3   If there is a runtime-constraint violation, the memcpy_s function stores zeros in the first
    s1max characters of the object pointed to by s1 if s1 is not a null pointer and s1max is
    not greater than RSIZE_MAX.
    Description
4   The memcpy_s function copies n characters from the object pointed to by s2 into the
    object pointed to by s1.
    Returns
5   The memcpy_s function returns zero if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.




[page 610]

    K.3.7.1.2 The memmove_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            errno_t memmove_s(void *s1, rsize_t s1max,
                 const void *s2, rsize_t n);
    Runtime-constraints
2   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
    RSIZE_MAX. n shall not be greater than s1max.
3   If there is a runtime-constraint violation, the memmove_s function stores zeros in the
    first s1max characters of the object pointed to by s1 if s1 is not a null pointer and
    s1max is not greater than RSIZE_MAX.
    Description
4   The memmove_s function copies n characters from the object pointed to by s2 into the
    object pointed to by s1. This copying takes place as if the n characters from the object
    pointed to by s2 are first copied into a temporary array of n characters that does not
    overlap the objects pointed to by s1 or s2, and then the n characters from the temporary
    array are copied into the object pointed to by s1.
    Returns
5   The memmove_s function returns zero if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.
    K.3.7.1.3 The strcpy_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            errno_t strcpy_s(char * restrict s1,
                 rsize_t s1max,
                 const char * restrict s2);
    Runtime-constraints
2   Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
    s1max shall not equal zero. s1max shall be greater than strnlen_s(s2, s1max).
    Copying shall not take place between objects that overlap.
3   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
    greater than zero and not greater than RSIZE_MAX, then strcpy_s sets s1[0] to the
    null character.

[page 611]

    Description
4   The strcpy_s function copies the string pointed to by s2 (including the terminating
    null character) into the array pointed to by s1.
5   All elements following the terminating null character (if any) written by strcpy_s in
    the array of s1max characters pointed to by s1 take unspecified values when
    strcpy_s returns.404)
    Returns
6   The strcpy_s function returns zero405) if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.
    K.3.7.1.4 The strncpy_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            errno_t strncpy_s(char * restrict s1,
                 rsize_t s1max,
                 const char * restrict s2,
                 rsize_t n);
    Runtime-constraints
2   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
    RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
    shall be greater than strnlen_s(s2, s1max). Copying shall not take place between
    objects that overlap.
3   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
    greater than zero and not greater than RSIZE_MAX, then strncpy_s sets s1[0] to the
    null character.
    Description
4   The strncpy_s function copies not more than n successive characters (characters that
    follow a null character are not copied) from the array pointed to by s2 to the array
    pointed to by s1. If no null character was copied from s2, then s1[n] is set to a null
    character.


    404) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
         any of those characters are null. Such an approach might write a character to every element of s1
         before discovering that the first element should be set to the null character.
    405) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
         within the array pointed to by s1 and that the result in s1 is null terminated.

[page 612]

5   All elements following the terminating null character (if any) written by strncpy_s in
    the array of s1max characters pointed to by s1 take unspecified values when
    strncpy_s returns.406)
    Returns
6   The strncpy_s function returns zero407) if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.
7   EXAMPLE 1 The strncpy_s function can be used to copy a string without the danger that the result
    will not be null terminated or that characters will be written past the end of the destination array.
            #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            /* ... */
            char src1[100] = "hello";
            char src2[7] = {'g', 'o', 'o', 'd', 'b', 'y', 'e'};
            char dst1[6], dst2[5], dst3[5];
            int r1, r2, r3;
            r1 = strncpy_s(dst1, 6, src1, 100);
            r2 = strncpy_s(dst2, 5, src2, 7);
            r3 = strncpy_s(dst3, 5, src2, 4);
    The first call will assign to r1 the value zero and to dst1 the sequence hello\0.
    The second call will assign to r2 a nonzero value and to dst2 the sequence \0.
    The third call will assign to r3 the value zero and to dst3 the sequence good\0.

    K.3.7.2 Concatenation functions
    K.3.7.2.1 The strcat_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            errno_t strcat_s(char * restrict s1,
                 rsize_t s1max,
                 const char * restrict s2);
    Runtime-constraints
2   Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
    strcat_s.




    406) This allows an implementation to copy characters from s2 to s1 while simultaneously checking if
         any of those characters are null. Such an approach might write a character to every element of s1
         before discovering that the first element should be set to the null character.
    407) A zero return value implies that all of the requested characters from the string pointed to by s2 fit
         within the array pointed to by s1 and that the result in s1 is null terminated.

[page 613]

3   Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
    s1max shall not equal zero. m shall not equal zero.408) m shall be greater than
    strnlen_s(s2, m). Copying shall not take place between objects that overlap.
4   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
    greater than zero and not greater than RSIZE_MAX, then strcat_s sets s1[0] to the
    null character.
    Description
5   The strcat_s function appends a copy of the string pointed to by s2 (including the
    terminating null character) to the end of the string pointed to by s1. The initial character
    from s2 overwrites the null character at the end of s1.
6   All elements following the terminating null character (if any) written by strcat_s in
    the array of s1max characters pointed to by s1 take unspecified values when
    strcat_s returns.409)
    Returns
7   The strcat_s function returns zero410) if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.
    K.3.7.2.2 The strncat_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            errno_t strncat_s(char * restrict s1,
                 rsize_t s1max,
                 const char * restrict s2,
                 rsize_t n);
    Runtime-constraints
2   Let m denote the value s1max - strnlen_s(s1, s1max) upon entry to
    strncat_s.
3   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
    RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.411) If n is not less


    408) Zero means that s1 was not null terminated upon entry to strcat_s.
    409) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
         any of those characters are null. Such an approach might write a character to every element of s1
         before discovering that the first element should be set to the null character.
    410) A zero return value implies that all of the requested characters from the string pointed to by s2 were
         appended to the string pointed to by s1 and that the result in s1 is null terminated.

[page 614]

    than m, then m shall be greater than strnlen_s(s2, m). Copying shall not take
    place between objects that overlap.
4   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
    greater than zero and not greater than RSIZE_MAX, then strncat_s sets s1[0] to the
    null character.
    Description
5   The strncat_s function appends not more than n successive characters (characters
    that follow a null character are not copied) from the array pointed to by s2 to the end of
    the string pointed to by s1. The initial character from s2 overwrites the null character at
    the end of s1. If no null character was copied from s2, then s1[s1max-m+n] is set to
    a null character.
6   All elements following the terminating null character (if any) written by strncat_s in
    the array of s1max characters pointed to by s1 take unspecified values when
    strncat_s returns.412)
    Returns
7   The strncat_s function returns zero413) if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.
8   EXAMPLE 1 The strncat_s function can be used to copy a string without the danger that the result
    will not be null terminated or that characters will be written past the end of the destination array.
            #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            /* ... */
            char s1[100] = "good";
            char s2[6] = "hello";
            char s3[6] = "hello";
            char s4[7] = "abc";
            char s5[1000] = "bye";
            int r1, r2, r3, r4;
            r1 = strncat_s(s1, 100, s5, 1000);
            r2 = strncat_s(s2, 6, "", 1);
            r3 = strncat_s(s3, 6, "X", 2);
            r4 = strncat_s(s4, 7, "defghijklmn", 3);
    After the first call r1 will have the value zero and s1 will contain the sequence goodbye\0.



    411) Zero means that s1 was not null terminated upon entry to strncat_s.
    412) This allows an implementation to append characters from s2 to s1 while simultaneously checking if
         any of those characters are null. Such an approach might write a character to every element of s1
         before discovering that the first element should be set to the null character.
    413) A zero return value implies that all of the requested characters from the string pointed to by s2 were
         appended to the string pointed to by s1 and that the result in s1 is null terminated.

[page 615]

    After the second call r2 will have the value zero and s2 will contain the sequence hello\0.
    After the third call r3 will have a nonzero value and s3 will contain the sequence \0.
    After the fourth call r4 will have the value zero and s4 will contain the sequence abcdef\0.

    K.3.7.3 Search functions
    K.3.7.3.1 The strtok_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            char *strtok_s(char * restrict s1,
                 rsize_t * restrict s1max,
                 const char * restrict s2,
                 char ** restrict ptr);
    Runtime-constraints
2   None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
    shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
    The end of the token found shall occur within the first *s1max characters of s1 for the
    first call, and shall occur within the first *s1max characters of where searching resumes
    on subsequent calls.
3   If there is a runtime-constraint violation, the strtok_s function does not indirect
    through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
    Description
4   A sequence of calls to the strtok_s function breaks the string pointed to by s1 into a
    sequence of tokens, each of which is delimited by a character from the string pointed to
    by s2. The fourth argument points to a caller-provided char pointer into which the
    strtok_s function stores information necessary for it to continue scanning the same
    string.
5   The first call in a sequence has a non-null first argument and s1max points to an object
    whose value is the number of elements in the character array pointed to by the first
    argument. The first call stores an initial value in the object pointed to by ptr and
    updates the value pointed to by s1max to reflect the number of elements that remain in
    relation to ptr. Subsequent calls in the sequence have a null first argument and the
    objects pointed to by s1max and ptr are required to have the values stored by the
    previous call in the sequence, which are then updated. The separator string pointed to by
    s2 may be different from call to call.
6   The first call in the sequence searches the string pointed to by s1 for the first character
    that is not contained in the current separator string pointed to by s2. If no such character
    is found, then there are no tokens in the string pointed to by s1 and the strtok_s
    function returns a null pointer. If such a character is found, it is the start of the first token.
[page 616]

7    The strtok_s function then searches from there for the first character in s1 that is
     contained in the current separator string. If no such character is found, the current token
     extends to the end of the string pointed to by s1, and subsequent searches in the same
     string for a token return a null pointer. If such a character is found, it is overwritten by a
     null character, which terminates the current token.
8    In all cases, the strtok_s function stores sufficient information in the pointer pointed
     to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
     value for ptr, shall start searching just past the element overwritten by a null character
     (if any).
     Returns
9    The strtok_s function returns a pointer to the first character of a token, or a null
     pointer if there is no token or there is a runtime-constraint violation.
10   EXAMPLE
             #define __STDC_WANT_LIB_EXT1__ 1
             #include <string.h>
             static char str1[] = "?a???b,,,#c";
             static char str2[] = "\t \t";
             char *t, *ptr1, *ptr2;
             rsize_t max1 = sizeof(str1);
             rsize_t max2 = sizeof(str2);
             t   =   strtok_s(str1,   &max1,   "?", &ptr1);        //   t   points to the token "a"
             t   =   strtok_s(NULL,   &max1,   ",", &ptr1);        //   t   points to the token "??b"
             t   =   strtok_s(str2,   &max2,   " \t", &ptr2);      //   t   is a null pointer
             t   =   strtok_s(NULL,   &max1,   "#,", &ptr1);       //   t   points to the token "c"
             t   =   strtok_s(NULL,   &max1,   "?", &ptr1);        //   t   is a null pointer

     K.3.7.4 Miscellaneous functions
     K.3.7.4.1 The memset_s function
     Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <string.h>
             errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n)
     Runtime-constraints
2    s shall not be a null pointer. Neither smax nor n shall be greater than RSIZE_MAX. n
     shall not be greater than smax.
3    If there is a runtime-constraint violation, then if s is not a null pointer and smax is not
     greater than RSIZE_MAX, the memset_s function stores the value of c (converted to an
     unsigned char) into each of the first smax characters of the object pointed to by s.



[page 617]

    Description
4   The memset_s function copies the value of c (converted to an unsigned char) into
    each of the first n characters of the object pointed to by s. Unlike memset, any call to
    the memset_s function shall be evaluated strictly according to the rules of the abstract
    machine as described in (5.1.2.3). That is, any call to the memset_s function shall
    assume that the memory indicated by s and n may be accessible in the future and thus
    must contain the values indicated by c.
    Returns
5   The memset_s function returns zero if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.
    K.3.7.4.2 The strerror_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <string.h>
           errno_t strerror_s(char *s, rsize_t maxsize,
                errno_t errnum);
    Runtime-constraints
2   s shall not be a null pointer. maxsize shall not be greater than RSIZE_MAX.
    maxsize shall not equal zero.
3   If there is a runtime-constraint violation, then the array (if any) pointed to by s is not
    modified.
    Description
4   The strerror_s function maps the number in errnum to a locale-specific message
    string. Typically, the values for errnum come from errno, but strerror_s shall
    map any value of type int to a message.
5   If the length of the desired string is less than maxsize, then the string is copied to the
    array pointed to by s.
6   Otherwise, if maxsize is greater than zero, then maxsize-1 characters are copied
    from the string to the array pointed to by s and then s[maxsize-1] is set to the null
    character. Then, if maxsize is greater than 3, then s[maxsize-2],
    s[maxsize-3], and s[maxsize-4] are set to the character period (.).
    Returns
7   The strerror_s function returns zero if the length of the desired string was less than
    maxsize and there was no runtime-constraint violation. Otherwise, the strerror_s
    function returns a nonzero value.

[page 618]

    K.3.7.4.3 The strerrorlen_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            size_t strerrorlen_s(errno_t errnum);
    Description
2   The strerrorlen_s function calculates the length of the (untruncated) locale-specific
    message string that the strerror_s function maps to errnum.
    Returns
3   The strerrorlen_s function returns the number of characters (not including the null
    character) in the full message string.
    K.3.7.4.4 The strnlen_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <string.h>
            size_t strnlen_s(const char *s, size_t maxsize);
    Description
2   The strnlen_s function computes the length of the string pointed to by s.
    Returns
3   If s is a null pointer,414) then the strnlen_s function returns zero.
4   Otherwise, the strnlen_s function returns the number of characters that precede the
    terminating null character. If there is no null character in the first maxsize characters of
    s then strnlen_s returns maxsize. At most the first maxsize characters of s shall
    be accessed by strnlen_s.




    414) Note that the strnlen_s function has no runtime-constraints. This lack of runtime-constraints
         along with the values returned for a null pointer or an unterminated string argument make
         strnlen_s useful in algorithms that gracefully handle such exceptional data.

[page 619]

    K.3.8 Date and time <time.h>
1   The header <time.h> defines two types.
2   The types are
            errno_t
    which is type int; and
            rsize_t
    which is the type size_t.
    K.3.8.1 Components of time
1   A broken-down time is normalized if the values of the members of the tm structure are in
    their normal rages.415)
    K.3.8.2 Time conversion functions
1   Like the strftime function, the asctime_s and ctime_s functions do not return a
    pointer to a static object, and other library functions are permitted to call them.
    K.3.8.2.1 The asctime_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <time.h>
            errno_t asctime_s(char *s, rsize_t maxsize,
                 const struct tm *timeptr);
    Runtime-constraints
2   Neither s nor timeptr shall be a null pointer. maxsize shall not be less than 26 and
    shall not be greater than RSIZE_MAX. The broken-down time pointed to by timeptr
    shall be normalized. The calendar year represented by the broken-down time pointed to
    by timeptr shall not be less than calendar year 0 and shall not be greater than calendar
    year 9999.
3   If there is a runtime-constraint violation, there is no attempt to convert the time, and
    s[0] is set to a null character if s is not a null pointer and maxsize is not zero and is
    not greater than RSIZE_MAX.
    Description
4   The asctime_s function converts the normalized broken-down time in the structure
    pointed to by timeptr into a 26 character (including the null character) string in the


    415) The normal ranges are defined in 7.26.1.

[page 620]

    form
            Sun Sep 16 01:03:52 1973\n\0
    The fields making up this string are (in order):
       1.   The name of the day of the week represented by timeptr->tm_wday using the
            following three character weekday names: Sun, Mon, Tue, Wed, Thu, Fri, and Sat.
       2.   The character space.
       3. The name of the month represented by timeptr->tm_mon using the following
          three character month names: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct,
          Nov, and Dec.
       4.   The character space.
       5.   The value of timeptr->tm_mday as if printed using the fprintf format
            "%2d".
       6.   The character space.
       7.   The value of timeptr->tm_hour as if printed using the fprintf format
            "%.2d".
       8.   The character colon.
       9.   The value of timeptr->tm_min as if printed using the fprintf format
            "%.2d".
     10.    The character colon.
     11.    The value of timeptr->tm_sec as if printed using the fprintf format
            "%.2d".
     12.    The character space.
     13.    The value of timeptr->tm_year + 1900 as if printed using the fprintf
            format "%4d".
     14.    The character new line.
     15.    The null character.
    Recommended practice
    The strftime function allows more flexible formatting and supports locale-specific
    behavior. If you do not require the exact form of the result string produced by the
    asctime_s function, consider using the strftime function instead.
    Returns
5   The asctime_s function returns zero if the time was successfully converted and stored
    into the array pointed to by s. Otherwise, it returns a nonzero value.
[page 621]

    K.3.8.2.2 The ctime_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <time.h>
           errno_t ctime_s(char *s, rsize_t maxsize,
                const time_t *timer);
    Runtime-constraints
2   Neither s nor timer shall be a null pointer. maxsize shall not be less than 26 and
    shall not be greater than RSIZE_MAX.
3   If there is a runtime-constraint violation, s[0] is set to a null character if s is not a null
    pointer and maxsize is not equal zero and is not greater than RSIZE_MAX.
    Description
4   The ctime_s function converts the calendar time pointed to by timer to local time in
    the form of a string. It is equivalent to
           asctime_s(s, maxsize, localtime_s(timer))
    Recommended practice
    The strftime function allows more flexible formatting and supports locale-specific
    behavior. If you do not require the exact form of the result string produced by the
    ctime_s function, consider using the strftime function instead.
    Returns
5   The ctime_s function returns zero if the time was successfully converted and stored
    into the array pointed to by s. Otherwise, it returns a nonzero value.
    K.3.8.2.3 The gmtime_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <time.h>
           struct tm *gmtime_s(const time_t * restrict timer,
                struct tm * restrict result);
    Runtime-constraints
2   Neither timer nor result shall be a null pointer.
3   If there is a runtime-constraint violation, there is no attempt to convert the time.
    Description
4   The gmtime_s function converts the calendar time pointed to by timer into a broken-
    down time, expressed as UTC. The broken-down time is stored in the structure pointed
[page 622]

    to by result.
    Returns
5   The gmtime_s function returns result, or a null pointer if the specified time cannot
    be converted to UTC or there is a runtime-constraint violation.
    K.3.8.2.4 The localtime_s function
    Synopsis
1            #define __STDC_WANT_LIB_EXT1__ 1
             #include <time.h>
             struct tm *localtime_s(const time_t * restrict timer,
                  struct tm * restrict result);
    Runtime-constraints
2   Neither timer nor result shall be a null pointer.
3   If there is a runtime-constraint violation, there is no attempt to convert the time.
    Description
4   The localtime_s function converts the calendar time pointed to by timer into a
    broken-down time, expressed as local time. The broken-down time is stored in the
    structure pointed to by result.
    Returns
5   The localtime_s function returns result, or a null pointer if the specified time
    cannot be converted to local time or there is a runtime-constraint violation.
    K.3.9 Extended multibyte and wide character utilities <wchar.h>
1   The header <wchar.h> defines two types.
2   The types are
             errno_t
    which is type int; and
             rsize_t
    which is the type size_t.
3   Unless explicitly stated otherwise, if the execution of a function described in this
    subclause causes copying to take place between objects that overlap, the objects take on
    unspecified values.




[page 623]

    K.3.9.1 Formatted wide character input/output functions
    K.3.9.1.1 The fwprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            int fwprintf_s(FILE * restrict stream,
                 const wchar_t * restrict format, ...);
    Runtime-constraints
2   Neither stream nor format shall be a null pointer. The %n specifier416) (modified or
    not by flags, field width, or precision) shall not appear in the wide string pointed to by
    format. Any argument to fwprintf_s corresponding to a %s specifier shall not be a
    null pointer.
3   If there is a runtime-constraint violation, the fwprintf_s function does not attempt to
    produce further output, and it is unspecified to what extent fwprintf_s produced
    output before discovering the runtime-constraint violation.
    Description
4   The fwprintf_s function is equivalent to the fwprintf function except for the
    explicit runtime-constraints listed above.
    Returns
5   The fwprintf_s function returns the number of wide characters transmitted, or a
    negative value if an output error, encoding error, or runtime-constraint violation occurred.
    K.3.9.1.2 The fwscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdio.h>
            #include <wchar.h>
            int fwscanf_s(FILE * restrict stream,
                 const wchar_t * restrict format, ...);
    Runtime-constraints
2   Neither stream nor format shall be a null pointer. Any argument indirected though in
    order to store converted input shall not be a null pointer.


    416) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 624]

3   If there is a runtime-constraint violation, the fwscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent fwscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The fwscanf_s function is equivalent to fwscanf except that the c, s, and [
    conversion specifiers apply to a pair of arguments (unless assignment suppression is
    indicated by a *). The first of these arguments is the same as for fwscanf. That
    argument is immediately followed in the argument list by the second argument, which has
    type size_t and gives the number of elements in the array pointed to by the first
    argument of the pair. If the first argument points to a scalar object, it is considered to be
    an array of one element.417)
5   A matching failure occurs if the number of elements in a receiving object is insufficient to
    hold the converted input (including any trailing null character).
    Returns
6   The fwscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    fwscanf_s function returns the number of input items assigned, which can be fewer
    than provided for, or even zero, in the event of an early matching failure.
    K.3.9.1.3 The snwprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            int snwprintf_s(wchar_t * restrict s,
                 rsize_t n,
                 const wchar_t * restrict format, ...);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The %n specifier418) (modified or not by flags, field width, or

    417) If the format is known at translation time, an implementation may issue a diagnostic for any argument
         used to store the result from a c, s, or [ conversion specifier if that argument is not followed by an
         argument of a type compatible with rsize_t. A limited amount of checking may be done if even if
         the format is not known at translation time. For example, an implementation may issue a diagnostic
         for each argument after format that has of type pointer to one of char, signed char,
         unsigned char, or void that is not followed by an argument of a type compatible with
         rsize_t. The diagnostic could warn that unless the pointer is being used with a conversion specifier
         using the hh length modifier, a length argument must follow the pointer argument. Another useful
         diagnostic could flag any non-pointer argument following format that did not have a type
         compatible with rsize_t.

[page 625]

    precision) shall not appear in the wide string pointed to by format. Any argument to
    snwprintf_s corresponding to a %s specifier shall not be a null pointer. No encoding
    error shall occur.
3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the snwprintf_s function sets s[0] to the
    null wide character.
    Description
4   The snwprintf_s function is equivalent to the swprintf function except for the
    explicit runtime-constraints listed above.
5   The snwprintf_s function, unlike swprintf_s, will truncate the result to fit within
    the array pointed to by s.
    Returns
6   The snwprintf_s function returns the number of wide characters that would have
    been written had n been sufficiently large, not counting the terminating wide null
    character, or a negative value if a runtime-constraint violation occurred. Thus, the null-
    terminated output has been completely written if and only if the returned value is
    nonnegative and less than n.
    K.3.9.1.4 The swprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            int swprintf_s(wchar_t * restrict s, rsize_t n,
                 const wchar_t * restrict format, ...);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The number of wide characters (including the trailing null) required
    for the result to be written to the array pointed to by s shall not be greater than n. The %n
    specifier419) (modified or not by flags, field width, or precision) shall not appear in the
    wide string pointed to by format. Any argument to swprintf_s corresponding to a
    %s specifier shall not be a null pointer. No encoding error shall occur.


    418) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".
    419) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 626]

3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the swprintf_s function sets s[0] to the
    null wide character.
    Description
4   The swprintf_s function is equivalent to the swprintf function except for the
    explicit runtime-constraints listed above.
5   The swprintf_s function, unlike snwprintf_s, treats a result too big for the array
    pointed to by s as a runtime-constraint violation.
    Returns
6   If no runtime-constraint violation occurred, the swprintf_s function returns the
    number of wide characters written in the array, not counting the terminating null wide
    character. If an encoding error occurred or if n or more wide characters are requested to
    be written, swprintf_s returns a negative value. If any other runtime-constraint
    violation occurred, swprintf_s returns zero.
    K.3.9.1.5 The swscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            int swscanf_s(const wchar_t * restrict s,
                 const wchar_t * restrict format, ...);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. Any argument indirected though in order
    to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the swscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent swscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The swscanf_s function is equivalent to fwscanf_s, except that the argument s
    specifies a wide string from which the input is to be obtained, rather than from a stream.
    Reaching the end of the wide string is equivalent to encountering end-of-file for the
    fwscanf_s function.
    Returns
5   The swscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    swscanf_s function returns the number of input items assigned, which can be fewer
    than provided for, or even zero, in the event of an early matching failure.
[page 627]

    K.3.9.1.6 The vfwprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <stdio.h>
            #include <wchar.h>
            int vfwprintf_s(FILE * restrict stream,
                 const wchar_t * restrict format,
                 va_list arg);
    Runtime-constraints
2   Neither stream nor format shall be a null pointer. The %n specifier420) (modified or
    not by flags, field width, or precision) shall not appear in the wide string pointed to by
    format. Any argument to vfwprintf_s corresponding to a %s specifier shall not be
    a null pointer.
3   If there is a runtime-constraint violation, the vfwprintf_s function does not attempt
    to produce further output, and it is unspecified to what extent vfwprintf_s produced
    output before discovering the runtime-constraint violation.
    Description
4   The vfwprintf_s function is equivalent to the vfwprintf function except for the
    explicit runtime-constraints listed above.
    Returns
5   The vfwprintf_s function returns the number of wide characters transmitted, or a
    negative value if an output error, encoding error, or runtime-constraint violation occurred.
    K.3.9.1.7 The vfwscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <stdio.h>
            #include <wchar.h>
            int vfwscanf_s(FILE * restrict stream,
                 const wchar_t * restrict format, va_list arg);



    420) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 628]

    Runtime-constraints
2   Neither stream nor format shall be a null pointer. Any argument indirected though in
    order to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the vfwscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent vfwscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The vfwscanf_s function is equivalent to fwscanf_s, with the variable argument
    list replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vfwscanf_s function does not invoke the
    va_end macro.421)
    Returns
5   The vfwscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    vfwscanf_s function returns the number of input items assigned, which can be fewer
    than provided for, or even zero, in the event of an early matching failure.
    K.3.9.1.8 The vsnwprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <wchar.h>
            int vsnwprintf_s(wchar_t * restrict s,
                 rsize_t n,
                 const wchar_t * restrict format,
                 va_list arg);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The %n specifier422) (modified or not by flags, field width, or
    precision) shall not appear in the wide string pointed to by format. Any argument to
    vsnwprintf_s corresponding to a %s specifier shall not be a null pointer. No
    encoding error shall occur.

    421) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
         value of arg after the return is indeterminate.
    422) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 629]

3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the vsnwprintf_s function sets s[0] to
    the null wide character.
    Description
4   The vsnwprintf_s function is equivalent to the vswprintf function except for the
    explicit runtime-constraints listed above.
5   The vsnwprintf_s function, unlike vswprintf_s, will truncate the result to fit
    within the array pointed to by s.
    Returns
6   The vsnwprintf_s function returns the number of wide characters that would have
    been written had n been sufficiently large, not counting the terminating null character, or
    a negative value if a runtime-constraint violation occurred. Thus, the null-terminated
    output has been completely written if and only if the returned value is nonnegative and
    less than n.
    K.3.9.1.9 The vswprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <wchar.h>
            int vswprintf_s(wchar_t * restrict s,
                 rsize_t n,
                 const wchar_t * restrict format,
                 va_list arg);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. n shall neither equal zero nor be greater
    than RSIZE_MAX. The number of wide characters (including the trailing null) required
    for the result to be written to the array pointed to by s shall not be greater than n. The %n
    specifier423) (modified or not by flags, field width, or precision) shall not appear in the
    wide string pointed to by format. Any argument to vswprintf_s corresponding to a
    %s specifier shall not be a null pointer. No encoding error shall occur.
3   If there is a runtime-constraint violation, then if s is not a null pointer and n is greater
    than zero and less than RSIZE_MAX, then the vswprintf_s function sets s[0] to the
    null wide character.

    423) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 630]

    Description
4   The vswprintf_s function is equivalent to the vswprintf function except for the
    explicit runtime-constraints listed above.
5   The vswprintf_s function, unlike vsnwprintf_s, treats a result too big for the
    array pointed to by s as a runtime-constraint violation.
    Returns
6   If no runtime-constraint violation occurred, the vswprintf_s function returns the
    number of wide characters written in the array, not counting the terminating null wide
    character. If an encoding error occurred or if n or more wide characters are requested to
    be written, vswprintf_s returns a negative value. If any other runtime-constraint
    violation occurred, vswprintf_s returns zero.
    K.3.9.1.10 The vswscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <wchar.h>
            int vswscanf_s(const wchar_t * restrict s,
                 const wchar_t * restrict format,
                 va_list arg);
    Runtime-constraints
2   Neither s nor format shall be a null pointer. Any argument indirected though in order
    to store converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the vswscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent vswscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The vswscanf_s function is equivalent to swscanf_s, with the variable argument
    list replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vswscanf_s function does not invoke the
    va_end macro.424)




    424) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
         value of arg after the return is indeterminate.

[page 631]

    Returns
5   The vswscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    vswscanf_s function returns the number of input items assigned, which can be fewer
    than provided for, or even zero, in the event of an early matching failure.
    K.3.9.1.11 The vwprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <wchar.h>
            int vwprintf_s(const wchar_t * restrict format,
                 va_list arg);
    Runtime-constraints
2   format shall not be a null pointer. The %n specifier425) (modified or not by flags, field
    width, or precision) shall not appear in the wide string pointed to by format. Any
    argument to vwprintf_s corresponding to a %s specifier shall not be a null pointer.
3   If there is a runtime-constraint violation, the vwprintf_s function does not attempt to
    produce further output, and it is unspecified to what extent vwprintf_s produced
    output before discovering the runtime-constraint violation.
    Description
4   The vwprintf_s function is equivalent to the vwprintf function except for the
    explicit runtime-constraints listed above.
    Returns
5   The vwprintf_s function returns the number of wide characters transmitted, or a
    negative value if an output error, encoding error, or runtime-constraint violation occurred.




    425) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 632]

    K.3.9.1.12 The vwscanf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <stdarg.h>
            #include <wchar.h>
            int vwscanf_s(const wchar_t * restrict format,
                 va_list arg);
    Runtime-constraints
2   format shall not be a null pointer. Any argument indirected though in order to store
    converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the vwscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent vwscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The vwscanf_s function is equivalent to wscanf_s, with the variable argument list
    replaced by arg, which shall have been initialized by the va_start macro (and
    possibly subsequent va_arg calls). The vwscanf_s function does not invoke the
    va_end macro.426)
    Returns
5   The vwscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    vwscanf_s function returns the number of input items assigned, which can be fewer
    than provided for, or even zero, in the event of an early matching failure.
    K.3.9.1.13 The wprintf_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            int wprintf_s(const wchar_t * restrict format, ...);
    Runtime-constraints
2   format shall not be a null pointer. The %n specifier427) (modified or not by flags, field

    426) As the functions vfwscanf_s, vwscanf_s, and vswscanf_s invoke the va_arg macro, the
         value of arg after the return is indeterminate.
    427) It is not a runtime-constraint violation for the wide characters %n to appear in sequence in the wide
         string pointed at by format when those wide characters are not a interpreted as a %n specifier. For
         example, if the entire format string was L"%%n".

[page 633]

    width, or precision) shall not appear in the wide string pointed to by format. Any
    argument to wprintf_s corresponding to a %s specifier shall not be a null pointer.
3   If there is a runtime-constraint violation, the wprintf_s function does not attempt to
    produce further output, and it is unspecified to what extent wprintf_s produced output
    before discovering the runtime-constraint violation.
    Description
4   The wprintf_s function is equivalent to the wprintf function except for the explicit
    runtime-constraints listed above.
    Returns
5   The wprintf_s function returns the number of wide characters transmitted, or a
    negative value if an output error, encoding error, or runtime-constraint violation occurred.
    K.3.9.1.14 The wscanf_s function
    Synopsis
1          #define __STDC_WANT_LIB_EXT1__ 1
           #include <wchar.h>
           int wscanf_s(const wchar_t * restrict format, ...);
    Runtime-constraints
2   format shall not be a null pointer. Any argument indirected though in order to store
    converted input shall not be a null pointer.
3   If there is a runtime-constraint violation, the wscanf_s function does not attempt to
    perform further input, and it is unspecified to what extent wscanf_s performed input
    before discovering the runtime-constraint violation.
    Description
4   The wscanf_s function is equivalent to fwscanf_s with the argument stdin
    interposed before the arguments to wscanf_s.
    Returns
5   The wscanf_s function returns the value of the macro EOF if an input failure occurs
    before any conversion or if there is a runtime-constraint violation. Otherwise, the
    wscanf_s function returns the number of input items assigned, which can be fewer than
    provided for, or even zero, in the event of an early matching failure.




[page 634]

    K.3.9.2 General wide string utilities
    K.3.9.2.1 Wide string copying functions
    K.3.9.2.1.1 The wcscpy_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            errno_t wcscpy_s(wchar_t * restrict s1,
                 rsize_t s1max,
                 const wchar_t * restrict s2);
    Runtime-constraints
2   Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
    s1max shall not equal zero. s1max shall be greater than wcsnlen_s(s2, s1max).
    Copying shall not take place between objects that overlap.
3   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
    greater than zero and not greater than RSIZE_MAX, then wcscpy_s sets s1[0] to the
    null wide character.
    Description
4   The wcscpy_s function copies the wide string pointed to by s2 (including the
    terminating null wide character) into the array pointed to by s1.
5   All elements following the terminating null wide character (if any) written by
    wcscpy_s in the array of s1max wide characters pointed to by s1 take unspecified
    values when wcscpy_s returns.428)
    Returns
6   The wcscpy_s function returns zero429) if there was no runtime-constraint violation.
    Otherwise, a nonzero value is returned.




    428) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
         if any of those wide characters are null. Such an approach might write a wide character to every
         element of s1 before discovering that the first element should be set to the null wide character.
    429) A zero return value implies that all of the requested wide characters from the string pointed to by s2
         fit within the array pointed to by s1 and that the result in s1 is null terminated.

[page 635]

     K.3.9.2.1.2 The wcsncpy_s function
     Synopsis
7            #define __STDC_WANT_LIB_EXT1__ 1
             #include <wchar.h>
             errno_t wcsncpy_s(wchar_t * restrict s1,
                  rsize_t s1max,
                  const wchar_t * restrict s2,
                  rsize_t n);
     Runtime-constraints
8    Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
     RSIZE_MAX. s1max shall not equal zero. If n is not less than s1max, then s1max
     shall be greater than wcsnlen_s(s2, s1max). Copying shall not take place between
     objects that overlap.
9    If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
     greater than zero and not greater than RSIZE_MAX, then wcsncpy_s sets s1[0] to the
     null wide character.
     Description
10   The wcsncpy_s function copies not more than n successive wide characters (wide
     characters that follow a null wide character are not copied) from the array pointed to by
     s2 to the array pointed to by s1. If no null wide character was copied from s2, then
     s1[n] is set to a null wide character.
11   All elements following the terminating null wide character (if any) written by
     wcsncpy_s in the array of s1max wide characters pointed to by s1 take unspecified
     values when wcsncpy_s returns.430)
     Returns
12   The wcsncpy_s function returns zero431) if there was no runtime-constraint violation.
     Otherwise, a nonzero value is returned.
13   EXAMPLE 1 The wcsncpy_s function can be used to copy a wide string without the danger that the
     result will not be null terminated or that wide characters will be written past the end of the destination
     array.




     430) This allows an implementation to copy wide characters from s2 to s1 while simultaneously checking
          if any of those wide characters are null. Such an approach might write a wide character to every
          element of s1 before discovering that the first element should be set to the null wide character.
     431) A zero return value implies that all of the requested wide characters from the string pointed to by s2
          fit within the array pointed to by s1 and that the result in s1 is null terminated.

[page 636]

             #define __STDC_WANT_LIB_EXT1__ 1
             #include <wchar.h>
             /* ... */
             wchar_t src1[100] = L"hello";
             wchar_t src2[7] = {L'g', L'o', L'o', L'd', L'b', L'y', L'e'};
             wchar_t dst1[6], dst2[5], dst3[5];
             int r1, r2, r3;
             r1 = wcsncpy_s(dst1, 6, src1, 100);
             r2 = wcsncpy_s(dst2, 5, src2, 7);
             r3 = wcsncpy_s(dst3, 5, src2, 4);
     The first call will assign to r1 the value zero and to dst1 the sequence of wide characters hello\0.
     The second call will assign to r2 a nonzero value and to dst2 the sequence of wide characters \0.
     The third call will assign to r3 the value zero and to dst3 the sequence of wide characters good\0.

     K.3.9.2.1.3 The wmemcpy_s function
     Synopsis
14           #define __STDC_WANT_LIB_EXT1__ 1
             #include <wchar.h>
             errno_t wmemcpy_s(wchar_t * restrict s1,
                  rsize_t s1max,
                  const wchar_t * restrict s2,
                  rsize_t n);
     Runtime-constraints
15   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
     RSIZE_MAX. n shall not be greater than s1max. Copying shall not take place between
     objects that overlap.
16   If there is a runtime-constraint violation, the wmemcpy_s function stores zeros in the
     first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
     s1max is not greater than RSIZE_MAX.
     Description
17   The wmemcpy_s function copies n successive wide characters from the object pointed
     to by s2 into the object pointed to by s1.
     Returns
18   The wmemcpy_s function returns zero if there was no runtime-constraint violation.
     Otherwise, a nonzero value is returned.




[page 637]

     K.3.9.2.1.4 The wmemmove_s function
     Synopsis
19          #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            errno_t wmemmove_s(wchar_t *s1, rsize_t s1max,
                 const wchar_t *s2, rsize_t n);
     Runtime-constraints
20   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
     RSIZE_MAX. n shall not be greater than s1max.
21   If there is a runtime-constraint violation, the wmemmove_s function stores zeros in the
     first s1max wide characters of the object pointed to by s1 if s1 is not a null pointer and
     s1max is not greater than RSIZE_MAX.
     Description
22   The wmemmove_s function copies n successive wide characters from the object pointed
     to by s2 into the object pointed to by s1. This copying takes place as if the n wide
     characters from the object pointed to by s2 are first copied into a temporary array of n
     wide characters that does not overlap the objects pointed to by s1 or s2, and then the n
     wide characters from the temporary array are copied into the object pointed to by s1.
     Returns
23   The wmemmove_s function returns zero if there was no runtime-constraint violation.
     Otherwise, a nonzero value is returned.
     K.3.9.2.2 Wide string concatenation functions
     K.3.9.2.2.1 The wcscat_s function
     Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            errno_t wcscat_s(wchar_t * restrict s1,
                 rsize_t s1max,
                 const wchar_t * restrict s2);
     Runtime-constraints
2    Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
     wcscat_s.
3    Neither s1 nor s2 shall be a null pointer. s1max shall not be greater than RSIZE_MAX.
     s1max shall not equal zero. m shall not equal zero.432) m shall be greater than
     wcsnlen_s(s2, m). Copying shall not take place between objects that overlap.

[page 638]

4    If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
     greater than zero and not greater than RSIZE_MAX, then wcscat_s sets s1[0] to the
     null wide character.
     Description
5    The wcscat_s function appends a copy of the wide string pointed to by s2 (including
     the terminating null wide character) to the end of the wide string pointed to by s1. The
     initial wide character from s2 overwrites the null wide character at the end of s1.
6    All elements following the terminating null wide character (if any) written by
     wcscat_s in the array of s1max wide characters pointed to by s1 take unspecified
     values when wcscat_s returns.433)
     Returns
7    The wcscat_s function returns zero434) if there was no runtime-constraint violation.
     Otherwise, a nonzero value is returned.
     K.3.9.2.2.2 The wcsncat_s function
     Synopsis
8             #define __STDC_WANT_LIB_EXT1__ 1
              #include <wchar.h>
              errno_t wcsncat_s(wchar_t * restrict s1,
                   rsize_t s1max,
                   const wchar_t * restrict s2,
                   rsize_t n);
     Runtime-constraints
9    Let m denote the value s1max - wcsnlen_s(s1, s1max) upon entry to
     wcsncat_s.
10   Neither s1 nor s2 shall be a null pointer. Neither s1max nor n shall be greater than
     RSIZE_MAX. s1max shall not equal zero. m shall not equal zero.435) If n is not less
     than m, then m shall be greater than wcsnlen_s(s2, m). Copying shall not take
     place between objects that overlap.


     432) Zero means that s1 was not null terminated upon entry to wcscat_s.
     433) This allows an implementation to append wide characters from s2 to s1 while simultaneously
          checking if any of those wide characters are null. Such an approach might write a wide character to
          every element of s1 before discovering that the first element should be set to the null wide character.
     434) A zero return value implies that all of the requested wide characters from the wide string pointed to by
          s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.
     435) Zero means that s1 was not null terminated upon entry to wcsncat_s.

[page 639]

11   If there is a runtime-constraint violation, then if s1 is not a null pointer and s1max is
     greater than zero and not greater than RSIZE_MAX, then wcsncat_s sets s1[0] to the
     null wide character.
     Description
12   The wcsncat_s function appends not more than n successive wide characters (wide
     characters that follow a null wide character are not copied) from the array pointed to by
     s2 to the end of the wide string pointed to by s1. The initial wide character from s2
     overwrites the null wide character at the end of s1. If no null wide character was copied
     from s2, then s1[s1max-m+n] is set to a null wide character.
13   All elements following the terminating null wide character (if any) written by
     wcsncat_s in the array of s1max wide characters pointed to by s1 take unspecified
     values when wcsncat_s returns.436)
     Returns
14   The wcsncat_s function returns zero437) if there was no runtime-constraint violation.
     Otherwise, a nonzero value is returned.
15   EXAMPLE 1 The wcsncat_s function can be used to copy a wide string without the danger that the
     result will not be null terminated or that wide characters will be written past the end of the destination
     array.
              #define __STDC_WANT_LIB_EXT1__ 1
              #include <wchar.h>
              /* ... */
              wchar_t s1[100] = L"good";
              wchar_t s2[6] = L"hello";
              wchar_t s3[6] = L"hello";
              wchar_t s4[7] = L"abc";
              wchar_t s5[1000] = L"bye";
              int r1, r2, r3, r4;
              r1 = wcsncat_s(s1, 100, s5, 1000);
              r2 = wcsncat_s(s2, 6, L"", 1);
              r3 = wcsncat_s(s3, 6, L"X", 2);
              r4 = wcsncat_s(s4, 7, L"defghijklmn", 3);
     After the first call r1 will have the value zero and s1 will be the wide character sequence goodbye\0.
     After the second call r2 will have the value zero and s2 will be the wide character sequence hello\0.
     After the third call r3 will have a nonzero value and s3 will be the wide character sequence \0.
     After the fourth call r4 will have the value zero and s4 will be the wide character sequence abcdef\0.




     436) This allows an implementation to append wide characters from s2 to s1 while simultaneously
          checking if any of those wide characters are null. Such an approach might write a wide character to
          every element of s1 before discovering that the first element should be set to the null wide character.
     437) A zero return value implies that all of the requested wide characters from the wide string pointed to by
          s2 were appended to the wide string pointed to by s1 and that the result in s1 is null terminated.

[page 640]

    K.3.9.2.3 Wide string search functions
    K.3.9.2.3.1 The wcstok_s function
    Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            wchar_t *wcstok_s(wchar_t * restrict s1,
                 rsize_t * restrict s1max,
                 const wchar_t * restrict s2,
                 wchar_t ** restrict ptr);
    Runtime-constraints
2   None of s1max, s2, or ptr shall be a null pointer. If s1 is a null pointer, then *ptr
    shall not be a null pointer. The value of *s1max shall not be greater than RSIZE_MAX.
    The end of the token found shall occur within the first *s1max wide characters of s1 for
    the first call, and shall occur within the first *s1max wide characters of where searching
    resumes on subsequent calls.
3   If there is a runtime-constraint violation, the wcstok_s function does not indirect
    through the s1 or s2 pointers, and does not store a value in the object pointed to by ptr.
    Description
4   A sequence of calls to the wcstok_s function breaks the wide string pointed to by s1
    into a sequence of tokens, each of which is delimited by a wide character from the wide
    string pointed to by s2. The fourth argument points to a caller-provided wchar_t
    pointer into which the wcstok_s function stores information necessary for it to
    continue scanning the same wide string.
5   The first call in a sequence has a non-null first argument and s1max points to an object
    whose value is the number of elements in the wide character array pointed to by the first
    argument. The first call stores an initial value in the object pointed to by ptr and
    updates the value pointed to by s1max to reflect the number of elements that remain in
    relation to ptr. Subsequent calls in the sequence have a null first argument and the
    objects pointed to by s1max and ptr are required to have the values stored by the
    previous call in the sequence, which are then updated. The separator wide string pointed
    to by s2 may be different from call to call.
6   The first call in the sequence searches the wide string pointed to by s1 for the first wide
    character that is not contained in the current separator wide string pointed to by s2. If no
    such wide character is found, then there are no tokens in the wide string pointed to by s1
    and the wcstok_s function returns a null pointer. If such a wide character is found, it is
    the start of the first token.


[page 641]

7    The wcstok_s function then searches from there for the first wide character in s1 that
     is contained in the current separator wide string. If no such wide character is found, the
     current token extends to the end of the wide string pointed to by s1, and subsequent
     searches in the same wide string for a token return a null pointer. If such a wide character
     is found, it is overwritten by a null wide character, which terminates the current token.
8    In all cases, the wcstok_s function stores sufficient information in the pointer pointed
     to by ptr so that subsequent calls, with a null pointer for s1 and the unmodified pointer
     value for ptr, shall start searching just past the element overwritten by a null wide
     character (if any).
     Returns
9    The wcstok_s function returns a pointer to the first wide character of a token, or a null
     pointer if there is no token or there is a runtime-constraint violation.
10   EXAMPLE
            #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            static wchar_t str1[] = L"?a???b,,,#c";
            static wchar_t str2[] = L"\t \t";
            wchar_t *t, *ptr1, *ptr2;
            rsize_t max1 = wcslen(str1)+1;
            rsize_t max2 = wcslen(str2)+1;
            t   =   wcstok_s(str1,   &max1,   "?", &ptr1);        //   t   points to the token "a"
            t   =   wcstok_s(NULL,   &max1,   ",", &ptr1);        //   t   points to the token "??b"
            t   =   wcstok_s(str2,   &max2,   " \t", &ptr2);      //   t   is a null pointer
            t   =   wcstok_s(NULL,   &max1,   "#,", &ptr1);       //   t   points to the token "c"
            t   =   wcstok_s(NULL,   &max1,   "?", &ptr1);        //   t   is a null pointer

     K.3.9.2.4 Miscellaneous functions
     K.3.9.2.4.1 The wcsnlen_s function
     Synopsis
1           #define __STDC_WANT_LIB_EXT1__ 1
            #include <wchar.h>
            size_t wcsnlen_s(const wchar_t *s, size_t maxsize);
     Description
2    The wcsnlen_s function computes the length of the wide string pointed to by s.
     Returns
3    If s is a null pointer,438) then the wcsnlen_s function returns zero.
4    Otherwise, the wcsnlen_s function returns the number of wide characters that precede
     the terminating null wide character. If there is no null wide character in the first
     maxsize wide characters of s then wcsnlen_s returns maxsize. At most the first

[page 642]

    maxsize wide characters of s shall be accessed by wcsnlen_s.
    K.3.9.3 Extended multibyte/wide character conversion utilities
    K.3.9.3.1 Restartable multibyte/wide character conversion functions
1   Unlike wcrtomb, wcrtomb_s does not permit the ps parameter (the pointer to the
    conversion state) to be a null pointer.
    K.3.9.3.1.1 The wcrtomb_s function
    Synopsis
2           #include <wchar.h>
            errno_t wcrtomb_s(size_t * restrict retval,
                 char * restrict s, rsize_t smax,
                 wchar_t wc, mbstate_t * restrict ps);
    Runtime-constraints
3   Neither retval nor ps shall be a null pointer. If s is not a null pointer, then smax
    shall not equal zero and shall not be greater than RSIZE_MAX. If s is not a null pointer,
    then smax shall be not be less than the number of bytes to be stored in the array pointed
    to by s. If s is a null pointer, then smax shall equal zero.
4   If there is a runtime-constraint violation, then wcrtomb_s does the following. If s is
    not a null pointer and smax is greater than zero and not greater than RSIZE_MAX, then
    wcrtomb_s sets s[0] to the null character. If retval is not a null pointer, then
    wcrtomb_s sets *retval to (size_t)(-1).
    Description
5   If s is a null pointer, the wcrtomb_s function is equivalent to the call
                    wcrtomb_s(&retval, buf, sizeof buf, L'\0', ps)
    where retval and buf are internal variables of the appropriate types, and the size of
    buf is greater than MB_CUR_MAX.
6   If s is not a null pointer, the wcrtomb_s function determines the number of bytes
    needed to represent the multibyte character that corresponds to the wide character given
    by wc (including any shift sequences), and stores the multibyte character representation
    in the array whose first element is pointed to by s. At most MB_CUR_MAX bytes are
    stored. If wc is a null wide character, a null byte is stored, preceded by any shift
    sequence needed to restore the initial shift state; the resulting state described is the initial
    conversion state.

    438) Note that the wcsnlen_s function has no runtime-constraints. This lack of runtime-constraints
         along with the values returned for a null pointer or an unterminated wide string argument make
         wcsnlen_s useful in algorithms that gracefully handle such exceptional data.

[page 643]

7   If wc does not correspond to a valid multibyte character, an encoding error occurs: the
    wcrtomb_s function stores the value (size_t)(-1) into *retval and the
    conversion state is unspecified. Otherwise, the wcrtomb_s function stores into
    *retval the number of bytes (including any shift sequences) stored in the array pointed
    to by s.
    Returns
8   The wcrtomb_s function returns zero if no runtime-constraint violation and no
    encoding error occurred. Otherwise, a nonzero value is returned.
    K.3.9.3.2 Restartable multibyte/wide string conversion functions
1   Unlike mbsrtowcs and wcsrtombs, mbsrtowcs_s and wcsrtombs_s do not
    permit the ps parameter (the pointer to the conversion state) to be a null pointer.
    K.3.9.3.2.1 The mbsrtowcs_s function
    Synopsis
2          #include <wchar.h>
           errno_t mbsrtowcs_s(size_t * restrict retval,
                wchar_t * restrict dst, rsize_t dstmax,
                const char ** restrict src, rsize_t len,
                mbstate_t * restrict ps);
    Runtime-constraints
3   None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
    then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
    pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
    not equal zero. If dst is not a null pointer and len is not less than dstmax, then a null
    character shall occur within the first dstmax multibyte characters of the array pointed to
    by *src.
4   If there is a runtime-constraint violation, then mbsrtowcs_s does the following. If
    retval is not a null pointer, then mbsrtowcs_s sets *retval to (size_t)(-1).
    If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
    then mbsrtowcs_s sets dst[0] to the null wide character.
    Description
5   The mbsrtowcs_s function converts a sequence of multibyte characters that begins in
    the conversion state described by the object pointed to by ps, from the array indirectly
    pointed to by src into a sequence of corresponding wide characters. If dst is not a null
    pointer, the converted characters are stored into the array pointed to by dst. Conversion
    continues up to and including a terminating null character, which is also stored.
    Conversion stops earlier in two cases: when a sequence of bytes is encountered that does
    not form a valid multibyte character, or (if dst is not a null pointer) when len wide
[page 644]

     characters have been stored into the array pointed to by dst.439) If dst is not a null
     pointer and no null wide character was stored into the array pointed to by dst, then
     dst[len] is set to the null wide character. Each conversion takes place as if by a call
     to the mbrtowc function.
6    If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
     pointer (if conversion stopped due to reaching a terminating null character) or the address
     just past the last multibyte character converted (if any). If conversion stopped due to
     reaching a terminating null character and if dst is not a null pointer, the resulting state
     described is the initial conversion state.
7    Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
     sequence of bytes that do not form a valid multibyte character, an encoding error occurs:
     the mbsrtowcs_s function stores the value (size_t)(-1) into *retval and the
     conversion state is unspecified. Otherwise, the mbsrtowcs_s function stores into
     *retval the number of multibyte characters successfully converted, not including the
     terminating null character (if any).
8    All elements following the terminating null wide character (if any) written by
     mbsrtowcs_s in the array of dstmax wide characters pointed to by dst take
     unspecified values when mbsrtowcs_s returns.440)
9    If copying takes place between objects that overlap, the objects take on unspecified
     values.
     Returns
10   The mbsrtowcs_s function returns zero if no runtime-constraint violation and no
     encoding error occurred. Otherwise, a nonzero value is returned.
     K.3.9.3.2.2 The wcsrtombs_s function
     Synopsis
11            #include <wchar.h>
              errno_t wcsrtombs_s(size_t * restrict retval,
                   char * restrict dst, rsize_t dstmax,
                   const wchar_t ** restrict src, rsize_t len,
                   mbstate_t * restrict ps);




     439) Thus, the value of len is ignored if dst is a null pointer.
     440) This allows an implementation to attempt converting the multibyte string before discovering a
          terminating null character did not occur where required.

[page 645]

     Runtime-constraints
12   None of retval, src, *src, or ps shall be null pointers. If dst is not a null pointer,
     then neither len nor dstmax shall be greater than RSIZE_MAX. If dst is a null
     pointer, then dstmax shall equal zero. If dst is not a null pointer, then dstmax shall
     not equal zero. If dst is not a null pointer and len is not less than dstmax, then the
     conversion shall have been stopped (see below) because a terminating null wide character
     was reached or because an encoding error occurred.
13   If there is a runtime-constraint violation, then wcsrtombs_s does the following. If
     retval is not a null pointer, then wcsrtombs_s sets *retval to (size_t)(-1).
     If dst is not a null pointer and dstmax is greater than zero and less than RSIZE_MAX,
     then wcsrtombs_s sets dst[0] to the null character.
     Description
14   The wcsrtombs_s function converts a sequence of wide characters from the array
     indirectly pointed to by src into a sequence of corresponding multibyte characters that
     begins in the conversion state described by the object pointed to by ps. If dst is not a
     null pointer, the converted characters are then stored into the array pointed to by dst.
     Conversion continues up to and including a terminating null wide character, which is also
     stored. Conversion stops earlier in two cases:
     -- when a wide character is reached that does not correspond to a valid multibyte
       character;
     -- (if dst is not a null pointer) when the next multibyte character would exceed the
         limit of n total bytes to be stored into the array pointed to by dst. If the wide
         character being converted is the null wide character, then n is the lesser of len or
         dstmax. Otherwise, n is the lesser of len or dstmax-1.
     If the conversion stops without converting a null wide character and dst is not a null
     pointer, then a null character is stored into the array pointed to by dst immediately
     following any multibyte characters already stored. Each conversion takes place as if by a
     call to the wcrtomb function.441)
15   If dst is not a null pointer, the pointer object pointed to by src is assigned either a null
     pointer (if conversion stopped due to reaching a terminating null wide character) or the
     address just past the last wide character converted (if any). If conversion stopped due to
     reaching a terminating null wide character, the resulting state described is the initial
     conversion state.


     441) If conversion stops because a terminating null wide character has been reached, the bytes stored
          include those necessary to reach the initial shift state immediately before the null byte. However, if
          the conversion stops before a terminating null wide character has been reached, the result will be null
          terminated, but might not end in the initial shift state.

[page 646]

16   Regardless of whether dst is or is not a null pointer, if the input conversion encounters a
     wide character that does not correspond to a valid multibyte character, an encoding error
     occurs: the wcsrtombs_s function stores the value (size_t)(-1) into *retval
     and the conversion state is unspecified. Otherwise, the wcsrtombs_s function stores
     into *retval the number of bytes in the resulting multibyte character sequence, not
     including the terminating null character (if any).
17   All elements following the terminating null character (if any) written by wcsrtombs_s
     in the array of dstmax elements pointed to by dst take unspecified values when
     wcsrtombs_s returns.442)
18   If copying takes place between objects that overlap, the objects take on unspecified
     values.
     Returns
19   The wcsrtombs_s function returns zero if no runtime-constraint violation and no
     encoding error occurred. Otherwise, a nonzero value is returned.




     442) When len is not less than dstmax, the implementation might fill the array before discovering a
          runtime-constraint violation.

[page 647]

                                                Annex L
                                               (normative)
                                            Analyzability
    L.1 Scope
1   This annex specifies optional behavior that can aid in the analyzability of C programs.
2   An implementation that defines __STDC_ANALYZABLE__ shall conform to the
    specifications in this annex.443)
    L.2 Definitions
    L.2.1
1   out-of-bounds store
    an (attempted) access (3.1) that, at run time, for a given computational state, would
    modify (or, for an object declared volatile, fetch) one or more bytes that lie outside
    the bounds permitted by this Standard.
    L.2.2
1   bounded undefined behavior
    undefined behavior (3.4.3) that does not perform an out-of-bounds store.
2   NOTE 1    The behavior might perform a trap.

3   NOTE 2    Any values produced or stored might be indeterminate values.

    L.2.3
1   critical undefined behavior
    undefined behavior that is not bounded undefined behavior.
2   NOTE     The behavior might perform an out-of-bounds store or perform a trap.




    443) Implementations that do not define __STDC_ANALYZABLE__ are not required to conform to these
         specifications.

[page 648]

    L.3 Requirements
1   If the program performs a trap (3.19.5), the implementation is permitted to invoke a
    runtime-constraint handler. Any such semantics are implementation-defined.
2   All undefined behavior shall be limited to bounded undefined behavior, except for the
    following which are permitted to result in critical undefined behavior:
    -- An object is referred to outside of its lifetime (6.2.4).
    -- An lvalue does not designate an object when evaluated (6.3.2.1).
    -- A pointer is used to call a function whose type is not compatible with the referenced
      type (6.3.2.3).
    -- The operand of the unary * operator has an invalid value (6.5.3.2).
    -- Addition or subtraction of a pointer into, or just beyond, an array object and an
      integer type produces a result that points just beyond the array object and is used as
      the operand of a unary * operator that is evaluated (6.5.6).
    -- An argument to a library function has an invalid value or a type not expected by a
      function with variable number of arguments (7.1.4).
    -- The value of a pointer that refers to space deallocated by a call to the free or realloc
      function is used (7.22.3).
    -- A string or wide string utility function is instructed to access an array beyond the end
      of an object (7.23.1, 7.28.4).




[page 649]


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[page 650]

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        arithmetic -- Part 1: Integer and floating point arithmetic.


[page 651]

 38.   ISO/IEC TR 19769:2004, Information technology -- Programming languages,
       their environments and system software interfaces -- Extensions for the
       programming language C to support new character data types.
 39.   ISO/IEC TR 24731-1:2007, Information technology -- Programming languages,
       their environments and system software interfaces -- Extensions to the C library
       -- Part 1: Bounds-checking interfaces.




[page 652]


Index
[^ x ^], 3.20                                                    , (comma operator), 5.1.2.4, 6.5.17
                                                               , (comma punctuator), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,
[_ x _], 3.21                                                         6.7.2.3, 6.7.9
! (logical negation operator), 6.5.3.3                         - (subtraction operator), 6.2.6.2, 6.5.6, F.3, G.5.2
!= (inequality operator), 6.5.9                                - (unary minus operator), 6.5.3.3, F.3
# operator, 6.10.3.2                                           -- (postfix decrement operator), 6.3.2.1, 6.5.2.4
# preprocessing directive, 6.10.7                              -- (prefix decrement operator), 6.3.2.1, 6.5.3.1
# punctuator, 6.10                                             -= (subtraction assignment operator), 6.5.16.2
## operator, 6.10.3.3                                          -> (structure/union pointer operator), 6.5.2.3
#define preprocessing directive, 6.10.3                        . (structure/union member operator), 6.3.2.1,
#elif preprocessing directive, 6.10.1                               6.5.2.3
#else preprocessing directive, 6.10.1                          . punctuator, 6.7.9
#endif preprocessing directive, 6.10.1                         ... (ellipsis punctuator), 6.5.2.2, 6.7.6.3, 6.10.3
#error preprocessing directive, 4, 6.10.5                      / (division operator), 6.2.6.2, 6.5.5, F.3, G.5.1
#if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,             /* */ (comment delimiters), 6.4.9
     6.10.1, 7.1.4                                             // (comment delimiter), 6.4.9
#ifdef preprocessing directive, 6.10.1                         /= (division assignment operator), 6.5.16.2
#ifndef preprocessing directive, 6.10.1                        : (colon punctuator), 6.7.2.1
#include preprocessing directive, 5.1.1.2,                     :> (alternative spelling of ]), 6.4.6
     6.10.2                                                    ; (semicolon punctuator), 6.7, 6.7.2.1, 6.8.3,
#line preprocessing directive, 6.10.4                               6.8.5, 6.8.6
#pragma preprocessing directive, 6.10.6                        < (less-than operator), 6.5.8
#undef preprocessing directive, 6.10.3.5, 7.1.3,               <% (alternative spelling of {), 6.4.6
     7.1.4                                                     <: (alternative spelling of [), 6.4.6
% (remainder operator), 6.2.6.2, 6.5.5                         << (left-shift operator), 6.2.6.2, 6.5.7
%: (alternative spelling of #), 6.4.6                          <<= (left-shift assignment operator), 6.5.16.2
%:%: (alternative spelling of ##), 6.4.6                       <= (less-than-or-equal-to operator), 6.5.8
%= (remainder assignment operator), 6.5.16.2                   <assert.h> header, 7.2
%> (alternative spelling of }), 6.4.6                          <complex.h> header, 5.2.4.2.2, 6.10.8.3, 7.1.2,
& (address operator), 6.3.2.1, 6.5.3.2                              7.3, 7.24, 7.30.1, G.6, J.5.17
& (bitwise AND operator), 6.2.6.2, 6.5.10                      <ctype.h> header, 7.4, 7.30.2
&& (logical AND operator), 5.1.2.4, 6.5.13                     <errno.h> header, 7.5, 7.30.3, K.3.2
&= (bitwise AND assignment operator), 6.5.16.2                 <fenv.h> header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F,
' ' (space character), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,                H
     7.4.1.10, 7.29.2.1.3                                      <float.h> header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
( ) (cast operator), 6.5.4                                          7.28.4.1.1
( ) (function-call operator), 6.5.2.2                          <inttypes.h> header, 7.8, 7.30.4
( ) (parentheses punctuator), 6.7.6.3, 6.8.4, 6.8.5            <iso646.h> header, 4, 7.9
( ){ } (compound-literal operator), 6.5.2.5                    <limits.h> header, 4, 5.2.4.2.1, 6.2.5, 7.10
* (asterisk punctuator), 6.7.6.1, 6.7.6.2                      <locale.h> header, 7.11, 7.30.5
* (indirection operator), 6.5.2.1, 6.5.3.2                     <math.h> header, 5.2.4.2.2, 6.5, 7.12, 7.24, F,
* (multiplication operator), 6.2.6.2, 6.5.5, F.3,                   F.10, J.5.17
     G.5.1                                                     <setjmp.h> header, 7.13
*= (multiplication assignment operator), 6.5.16.2              <signal.h> header, 7.14, 7.30.6
+ (addition operator), 6.2.6.2, 6.5.2.1, 6.5.3.2,              <stdalign.h> header, 4, 7.15
     6.5.6, F.3, G.5.2                                         <stdarg.h> header, 4, 6.7.6.3, 7.16
+ (unary plus operator), 6.5.3.3                               <stdatomic.h> header, 6.10.8.3, 7.1.2, 7.17
++ (postfix increment operator), 6.3.2.1, 6.5.2.4               <stdbool.h> header, 4, 7.18, 7.30.7, H
++ (prefix increment operator), 6.3.2.1, 6.5.3.1                <stddef.h> header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
+= (addition assignment operator), 6.5.16.2
[page 653]

     6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3                      \x hexadecimal digits (hexadecimal-character
<stdint.h> header, 4, 5.2.4.2, 6.10.1, 7.8,                       escape sequence), 6.4.4.4
     7.20, 7.30.8, K.3.3, K.3.4                              ^ (bitwise exclusive OR operator), 6.2.6.2, 6.5.11
<stdio.h> header, 5.2.4.2.2, 7.21, 7.30.9, F,                ^= (bitwise exclusive OR assignment operator),
     K.3.5                                                        6.5.16.2
<stdlib.h> header, 5.2.4.2.2, 7.22, 7.30.10, F,              __alignas_is_defined macro, 7.15
     K.3.1.4, K.3.6                                          __bool_true_false_are_defined
<string.h> header, 7.23, 7.30.11, K.3.7                           macro, 7.18
<tgmath.h> header, 7.24, G.7                                 __cplusplus macro, 6.10.8
<threads.h> header, 6.10.8.3, 7.1.2, 7.25                    __DATE__ macro, 6.10.8.1
<time.h> header, 7.26, K.3.8                                 __FILE__ macro, 6.10.8.1, 7.2.1.1
<uchar.h> header, 6.4.4.4, 6.4.5, 7.27                       __func__ identifier, 6.4.2.2, 7.2.1.1
<wchar.h> header, 5.2.4.2.2, 7.21.1, 7.28,                   __LINE__ macro, 6.10.8.1, 7.2.1.1
     7.30.12, F, K.3.9                                       __STDC_, 6.11.9
<wctype.h> header, 7.29, 7.30.13                             __STDC__ macro, 6.10.8.1
= (equal-sign punctuator), 6.7, 6.7.2.2, 6.7.9               __STDC_ANALYZABLE__ macro, 6.10.8.3, L.1
= (simple assignment operator), 6.5.16.1                     __STDC_HOSTED__ macro, 6.10.8.1
== (equality operator), 6.5.9                                __STDC_IEC_559__ macro, 6.10.8.3, F.1
> (greater-than operator), 6.5.8                             __STDC_IEC_559_COMPLEX__ macro,
>= (greater-than-or-equal-to operator), 6.5.8                     6.10.8.3, G.1
>> (right-shift operator), 6.2.6.2, 6.5.7                    __STDC_ISO_10646__ macro, 6.10.8.2
>>= (right-shift assignment operator), 6.5.16.2              __STDC_LIB_EXT1__ macro, 6.10.8.3, K.2
? : (conditional operator), 5.1.2.4, 6.5.15                  __STDC_MB_MIGHT_NEQ_WC__ macro,
?? (trigraph sequences), 5.2.1.1                                  6.10.8.2, 7.19
[ ] (array subscript operator), 6.5.2.1, 6.5.3.2             __STDC_NO_COMPLEX__ macro, 6.10.8.3,
[ ] (brackets punctuator), 6.7.6.2, 6.7.9                         7.3.1
\ (backslash character), 5.1.1.2, 5.2.1, 6.4.4.4             __STDC_NO_THREADS__ macro, 6.10.8.3,
\ (escape character), 6.4.4.4                                     7.17.1, 7.25.1
\" (double-quote escape sequence), 6.4.4.4,                  __STDC_NO_VLA__ macro, 6.10.8.3
     6.4.5, 6.10.9                                           __STDC_UTF_16__ macro, 6.10.8.2
\\ (backslash escape sequence), 6.4.4.4, 6.10.9              __STDC_UTF_32__ macro, 6.10.8.2
\' (single-quote escape sequence), 6.4.4.4, 6.4.5            __STDC_VERSION__ macro, 6.10.8.1
\0 (null character), 5.2.1, 6.4.4.4, 6.4.5                   __STDC_WANT_LIB_EXT1__ macro, K.3.1.1
  padding of binary stream, 7.21.2                           __TIME__ macro, 6.10.8.1
\? (question-mark escape sequence), 6.4.4.4                  __VA_ARGS__ identifier, 6.10.3, 6.10.3.1
\a (alert escape sequence), 5.2.2, 6.4.4.4                   _Alignas, 6.7.5
\b (backspace escape sequence), 5.2.2, 6.4.4.4               _Atomic type qualifier, 6.7.3
\f (form-feed escape sequence), 5.2.2, 6.4.4.4,              _Bool type, 6.2.5, 6.3.1.1, 6.3.1.2, 6.7.2, 7.17.1,
     7.4.1.10                                                     F.4
\n (new-line escape sequence), 5.2.2, 6.4.4.4,               _Bool type conversions, 6.3.1.2
     7.4.1.10                                                _Complex types, 6.2.5, 6.7.2, 7.3.1, G
\octal digits (octal-character escape sequence),             _Complex_I macro, 7.3.1
     6.4.4.4                                                 _Exit function, 7.22.4.5, 7.22.4.7
\r (carriage-return escape sequence), 5.2.2,                 _Imaginary keyword, G.2
     6.4.4.4, 7.4.1.10                                       _Imaginary types, 7.3.1, G
\t (horizontal-tab escape sequence), 5.2.2,                  _Imaginary_I macro, 7.3.1, G.6
     6.4.4.4, 7.4.1.3, 7.4.1.10, 7.29.2.1.3                  _IOFBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
\U (universal character names), 6.4.3                        _IOLBF macro, 7.21.1, 7.21.5.6
\u (universal character names), 6.4.3                        _IONBF macro, 7.21.1, 7.21.5.5, 7.21.5.6
\v (vertical-tab escape sequence), 5.2.2, 6.4.4.4,           _Noreturn, 6.7.4
     7.4.1.10                                                _Pragma operator, 5.1.1.2, 6.10.9

[page 654]

_Static_assert, 6.7.10, 7.2                                  allocated storage, order and contiguity, 7.22.3
_Thread_local storage-class specifier, 6.2.4,                 and macro, 7.9
     6.7.1                                                   AND operators
{ } (braces punctuator), 6.7.2.2, 6.7.2.3, 6.7.9,               bitwise (&), 6.2.6.2, 6.5.10
     6.8.2                                                      bitwise assignment (&=), 6.5.16.2
{ } (compound-literal operator), 6.5.2.5                        logical (&&), 5.1.2.4, 6.5.13
| (bitwise inclusive OR operator), 6.2.6.2, 6.5.12           and_eq macro, 7.9
|= (bitwise inclusive OR assignment operator),               anonymous structure, 6.7.2.1
     6.5.16.2                                                anonymous union, 6.7.2.1
|| (logical OR operator), 5.1.2.4, 6.5.14                    ANSI/IEEE 754, F.1
~ (bitwise complement operator), 6.2.6.2, 6.5.3.3            ANSI/IEEE 854, F.1
                                                             argc (main function parameter), 5.1.2.2.1
abort function, 7.2.1.1, 7.14.1.1, 7.21.3,                   argument, 3.3
      7.22.4.1, 7.25.3.6, K.3.6.1.2                             array, 6.9.1
abort_handler_s function, K.3.6.1.2                             default promotions, 6.5.2.2
abs function, 7.22.6.1                                          function, 6.5.2.2, 6.9.1
absolute-value functions                                        macro, substitution, 6.10.3.1
   complex, 7.3.8, G.6.4                                     argument, complex, 7.3.9.1
   integer, 7.8.2.1, 7.22.6.1                                argv (main function parameter), 5.1.2.2.1
   real, 7.12.7, F.10.4                                      arithmetic constant expression, 6.6
abstract declarator, 6.7.7                                   arithmetic conversions, usual, see usual arithmetic
abstract machine, 5.1.2.3                                          conversions
access, 3.1, 6.7.3, L.2.1                                    arithmetic operators
accuracy, see floating-point accuracy                            additive, 6.2.6.2, 6.5.6, G.5.2
acos functions, 7.12.4.1, F.10.1.1                              bitwise, 6.2.6.2, 6.5.3.3, 6.5.10, 6.5.11, 6.5.12
acos type-generic macro, 7.24                                   increment and decrement, 6.5.2.4, 6.5.3.1
acosh functions, 7.12.5.1, F.10.2.1                             multiplicative, 6.2.6.2, 6.5.5, G.5.1
acosh type-generic macro, 7.24                                  shift, 6.2.6.2, 6.5.7
acquire fence, 7.17.4                                           unary, 6.5.3.3
acquire operation, 5.1.2.4                                   arithmetic types, 6.2.5
active position, 5.2.2                                       arithmetic, pointer, 6.5.6
actual argument, 3.3                                         array
actual parameter (deprecated), 3.3                              argument, 6.9.1
addition assignment operator (+=), 6.5.16.2                     declarator, 6.7.6.2
addition operator (+), 6.2.6.2, 6.5.2.1, 6.5.3.2,               initialization, 6.7.9
      6.5.6, F.3, G.5.2                                         multidimensional, 6.5.2.1
additive expressions, 6.5.6, G.5.2                              parameter, 6.9.1
address constant, 6.6                                           storage order, 6.5.2.1
address operator (&), 6.3.2.1, 6.5.3.2                          subscript operator ([ ]), 6.5.2.1, 6.5.3.2
address-free, 7.17.5                                            subscripting, 6.5.2.1
aggregate initialization, 6.7.9                                 type, 6.2.5
aggregate types, 6.2.5                                          type conversion, 6.3.2.1
alert escape sequence (\a), 5.2.2, 6.4.4.4                      variable length, 6.7.6, 6.7.6.2, 6.10.8.3
aliasing, 6.5                                                arrow operator (->), 6.5.2.3
alignas macro, 7.15                                          as-if rule, 5.1.2.3
aligned_alloc function, 7.22.3, 7.22.3.1                     ASCII code set, 5.2.1.1
alignment, 3.2, 6.2.8, 7.22.3.1                              asctime function, 7.26.3.1
   pointer, 6.2.5, 6.3.2.3                                   asctime_s function, K.3.8.2, K.3.8.2.1
   structure/union member, 6.7.2.1                           asin functions, 7.12.4.2, F.10.1.2
alignment specifier, 6.7.5                                    asin type-generic macro, 7.24, G.7
alignof operator, 6.5.3, 6.5.3.4                             asinh functions, 7.12.5.2, F.10.2.2

[page 655]

asinh type-generic macro, 7.24, G.7                           atomic_is_lock_free generic function,
asm keyword, J.5.10                                               7.17.5.1
assert macro, 7.2.1.1                                         ATOMIC_LLONG_LOCK_FREE macro, 7.17.1
assert.h header, 7.2                                          atomic_load generic functions, 7.17.7.2
assignment                                                    ATOMIC_LONG_LOCK_FREE macro, 7.17.1
   compound, 6.5.16.2                                         ATOMIC_SHORT_LOCK_FREE macro, 7.17.1
   conversion, 6.5.16.1                                       atomic_signal_fence function, 7.17.4.2
   expression, 6.5.16                                         atomic_store generic functions, 7.17.7.1
   operators, 6.3.2.1, 6.5.16                                 atomic_thread_fence function, 7.17.4.1
   simple, 6.5.16.1                                           ATOMIC_VAR_INIT macro, 7.17.2.1
associativity of operators, 6.5                               ATOMIC_WCHAR_T_LOCK_FREE macro, 7.17.1
asterisk punctuator (*), 6.7.6.1, 6.7.6.2                     atomics header, 7.17
at_quick_exit function, 7.22.4.2, 7.22.4.3,                   auto storage-class specifier, 6.7.1, 6.9
     7.22.4.4, 7.22.4.5, 7.22.4.7                             automatic storage duration, 5.2.3, 6.2.4
atan functions, 7.12.4.3, F.10.1.3
atan type-generic macro, 7.24, G.7                            backslash character (\), 5.1.1.2, 5.2.1, 6.4.4.4
atan2 functions, 7.12.4.4, F.10.1.4                           backslash escape sequence (\\), 6.4.4.4, 6.10.9
atan2 type-generic macro, 7.24                                backspace escape sequence (\b), 5.2.2, 6.4.4.4
atanh functions, 7.12.5.3, F.10.2.3                           basic character set, 3.6, 3.7.2, 5.2.1
atanh type-generic macro, 7.24, G.7                           basic types, 6.2.5
atexit function, 7.22.4.2, 7.22.4.3, 7.22.4.4,                behavior, 3.4
     7.22.4.5, 7.22.4.7, J.5.13                               binary streams, 7.21.2, 7.21.7.10, 7.21.9.2,
atof function, 7.22.1, 7.22.1.1                                     7.21.9.4
atoi function, 7.22.1, 7.22.1.2                               bit, 3.5
atol function, 7.22.1, 7.22.1.2                                  high order, 3.6
atoll function, 7.22.1, 7.22.1.2                                 low order, 3.6
atomic lock-free macros, 7.17.1, 7.17.5                       bit-field, 6.7.2.1
atomic operations, 5.1.2.4                                    bitand macro, 7.9
atomic types, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1,               bitor macro, 7.9
     6.5.2.3, 6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3,           bitwise operators, 6.5
     7.17.6                                                      AND, 6.2.6.2, 6.5.10
atomic_address type, 7.17.1, 7.17.6                              AND assignment (&=), 6.5.16.2
ATOMIC_ADDRESS_LOCK_FREE macro, 7.17.1                           complement (~), 6.2.6.2, 6.5.3.3
atomic_bool type, 7.17.1, 7.17.6                                 exclusive OR, 6.2.6.2, 6.5.11
ATOMIC_CHAR16_T_LOCK_FREE macro,                                 exclusive OR assignment (^=), 6.5.16.2
     7.17.1                                                      inclusive OR, 6.2.6.2, 6.5.12
ATOMIC_CHAR32_T_LOCK_FREE macro,                                 inclusive OR assignment (|=), 6.5.16.2
     7.17.1                                                      shift, 6.2.6.2, 6.5.7
ATOMIC_CHAR_LOCK_FREE macro, 7.17.1                           blank character, 7.4.1.3
atomic_compare_exchange generic                               block, 6.8, 6.8.2, 6.8.4, 6.8.5
     functions, 7.17.7.4                                      block scope, 6.2.1
atomic_exchange generic functions, 7.17.7.3                   block structure, 6.2.1
atomic_fetch and modify generic functions,                    bold type convention, 6.1
     7.17.7.5                                                 bool macro, 7.18
atomic_flag type, 7.17.1, 7.17.8                              boolean type, 6.3.1.2
atomic_flag_clear functions, 7.17.8.2                         boolean type conversion, 6.3.1.1, 6.3.1.2
ATOMIC_FLAG_INIT macro, 7.17.1, 7.17.8                        bounded undefined behavior, L.2.2
atomic_flag_test_and_set functions,                           braces punctuator ({ }), 6.7.2.2, 6.7.2.3, 6.7.9,
     7.17.8.1                                                       6.8.2
atomic_init generic function, 7.17.2.2                        brackets operator ([ ]), 6.5.2.1, 6.5.3.2
ATOMIC_INT_LOCK_FREE macro, 7.17.1                            brackets punctuator ([ ]), 6.7.6.2, 6.7.9

[page 656]

branch cuts, 7.3.3                                                type-generic macro for, 7.24
break statement, 6.8.6.3                                       ccosh functions, 7.3.6.4, G.6.2.4
broken-down time, 7.26.1, 7.26.2.3, 7.26.3,                       type-generic macro for, 7.24
     7.26.3.1, 7.26.3.3, 7.26.3.4, 7.26.3.5,                   ceil functions, 7.12.9.1, F.10.6.1
     K.3.8.2.1, K.3.8.2.3, K.3.8.2.4                           ceil type-generic macro, 7.24
bsearch function, 7.22.5, 7.22.5.1                             cerf function, 7.30.1
bsearch_s function, K.3.6.3, K.3.6.3.1                         cerfc function, 7.30.1
btowc function, 7.28.6.1.1                                     cexp functions, 7.3.7.1, G.6.3.1
BUFSIZ macro, 7.21.1, 7.21.2, 7.21.5.5                            type-generic macro for, 7.24
byte, 3.6, 6.5.3.4                                             cexp2 function, 7.30.1
byte input/output functions, 7.21.1                            cexpm1 function, 7.30.1
byte-oriented stream, 7.21.2                                   char type, 6.2.5, 6.3.1.1, 6.7.2, K.3.5.3.2,
                                                                     K.3.9.1.2
C program, 5.1.1.1                                             char type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
c16rtomb function, 7.27.1.2                                          6.3.1.8
c32rtomb function, 7.27.1.4                                    char16_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
cabs functions, 7.3.8.1, G.6                                   char32_t type, 6.4.4.4, 6.4.5, 6.10.8.2, 7.27
  type-generic macro for, 7.24                                 CHAR_BIT macro, 5.2.4.2.1, 6.7.2.1
cacos functions, 7.3.5.1, G.6.1.1                              CHAR_MAX macro, 5.2.4.2.1, 7.11.2.1
  type-generic macro for, 7.24                                 CHAR_MIN macro, 5.2.4.2.1
cacosh functions, 7.3.6.1, G.6.2.1                             character, 3.7, 3.7.1
  type-generic macro for, 7.24                                 character array initialization, 6.7.9
calendar time, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4,           character case mapping functions, 7.4.2
      7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2,                    wide character, 7.29.3.1
      K.3.8.2.3, K.3.8.2.4                                           extensible, 7.29.3.2
call by value, 6.5.2.2                                         character classification functions, 7.4.1
call_once function, 7.25.1, 7.25.2.1                              wide character, 7.29.2.1
calloc function, 7.22.3, 7.22.3.2                                    extensible, 7.29.2.2
carg functions, 7.3.9.1, G.6                                   character constant, 5.1.1.2, 5.2.1, 6.4.4.4
carg type-generic macro, 7.24, G.7                             character display semantics, 5.2.2
carriage-return escape sequence (\r), 5.2.2,                   character handling header, 7.4, 7.11.1.1
      6.4.4.4, 7.4.1.10                                        character input/output functions, 7.21.7, K.3.5.4
carries a dependency, 5.1.2.4                                     wide character, 7.28.3
case label, 6.8.1, 6.8.4.2                                     character sets, 5.2.1
case mapping functions                                         character string literal, see string literal
  character, 7.4.2                                             character type conversion, 6.3.1.1
  wide character, 7.29.3.1                                     character types, 6.2.5, 6.7.9
      extensible, 7.29.3.2                                     cimag functions, 7.3.9.2, 7.3.9.5, G.6
casin functions, 7.3.5.2, G.6                                  cimag type-generic macro, 7.24, G.7
  type-generic macro for, 7.24                                 cis function, G.6
casinh functions, 7.3.6.2, G.6.2.2                             classification functions
  type-generic macro for, 7.24                                    character, 7.4.1
cast expression, 6.5.4                                            floating-point, 7.12.3
cast operator (( )), 6.5.4                                        wide character, 7.29.2.1
catan functions, 7.3.5.3, G.6                                        extensible, 7.29.2.2
  type-generic macro for, 7.24                                 clearerr function, 7.21.10.1
catanh functions, 7.3.6.3, G.6.2.3                             clgamma function, 7.30.1
  type-generic macro for, 7.24                                 clock function, 7.26.2.1
cbrt functions, 7.12.7.1, F.10.4.1                             clock_t type, 7.26.1, 7.26.2.1
cbrt type-generic macro, 7.24                                  CLOCKS_PER_SEC macro, 7.26.1, 7.26.2.1
ccos functions, 7.3.5.4, G.6                                   clog functions, 7.3.7.2, G.6.3.2

[page 657]

  type-generic macro for, 7.24                                  string, 7.23.3, K.3.7.2
clog10 function, 7.30.1                                         wide string, 7.28.4.3, K.3.9.2.2
clog1p function, 7.30.1                                       concatenation, preprocessing, see preprocessing
clog2 function, 7.30.1                                             concatenation
CMPLX macros, 7.3.9.3                                         conceptual models, 5.1
cnd_broadcast function, 7.25.3.1, 7.25.3.5,                   conditional features, 4, 6.2.5, 6.7.6.2, 6.10.8.3,
     7.25.3.6                                                      7.1.2, F.1, G.1, K.2, L.1
cnd_destroy function, 7.25.3.2                                conditional inclusion, 6.10.1
cnd_init function, 7.25.3.3                                   conditional operator (? :), 5.1.2.4, 6.5.15
cnd_signal function, 7.25.3.4, 7.25.3.5,                      conflict, 5.1.2.4
     7.25.3.6                                                 conformance, 4
cnd_t type, 7.25.1                                            conj functions, 7.3.9.4, G.6
cnd_timedwait function, 7.25.3.5                              conj type-generic macro, 7.24
cnd_wait function, 7.25.3.3, 7.25.3.6                         const type qualifier, 6.7.3
collating sequences, 5.2.1                                    const-qualified type, 6.2.5, 6.3.2.1, 6.7.3
colon punctuator (:), 6.7.2.1                                 constant expression, 6.6, F.8.4
comma operator (,), 5.1.2.4, 6.5.17                           constants, 6.4.4
comma punctuator (,), 6.5.2, 6.7, 6.7.2.1, 6.7.2.2,             as primary expression, 6.5.1
     6.7.2.3, 6.7.9                                             character, 6.4.4.4
command processor, 7.22.4.8                                     enumeration, 6.2.1, 6.4.4.3
comment delimiters (/* */ and //), 6.4.9                        floating, 6.4.4.2
comments, 5.1.1.2, 6.4, 6.4.9                                   hexadecimal, 6.4.4.1
common extensions, J.5                                          integer, 6.4.4.1
common initial sequence, 6.5.2.3                                octal, 6.4.4.1
common real type, 6.3.1.8                                     constraint, 3.8, 4
common warnings, I                                            constraint_handler_t type, K.3.6
comparison functions, 7.22.5, 7.22.5.1, 7.22.5.2,             consume operation, 5.1.2.4
     K.3.6.3, K.3.6.3.1, K.3.6.3.2                            content of structure/union/enumeration, 6.7.2.3
  string, 7.23.4                                              contiguity of allocated storage, 7.22.3
  wide string, 7.28.4.4                                       continue statement, 6.8.6.2
comparison macros, 7.12.14                                    contracted expression, 6.5, 7.12.2, F.7
comparison, pointer, 6.5.8                                    control character, 5.2.1, 7.4
compatible type, 6.2.7, 6.7.2, 6.7.3, 6.7.6                   control wide character, 7.29.2
compl macro, 7.9                                              conversion, 6.3
complement operator (~), 6.2.6.2, 6.5.3.3                       arithmetic operands, 6.3.1
complete type, 6.2.5                                            array argument, 6.9.1
complex macro, 7.3.1                                            array parameter, 6.9.1
complex numbers, 6.2.5, G                                       arrays, 6.3.2.1
complex type conversion, 6.3.1.6, 6.3.1.7                       boolean, 6.3.1.2
complex type domain, 6.2.5                                      boolean, characters, and integers, 6.3.1.1
complex types, 6.2.5, 6.7.2, 6.10.8.3, G                        by assignment, 6.5.16.1
complex.h header, 5.2.4.2.2, 6.10.8.3, 7.1.2,                   by return statement, 6.8.6.4
     7.3, 7.24, 7.30.1, G.6, J.5.17                             complex types, 6.3.1.6
compliance, see conformance                                     explicit, 6.3
components of time, 7.26.1, K.3.8.1                             function, 6.3.2.1
composite type, 6.2.7                                           function argument, 6.5.2.2, 6.9.1
compound assignment, 6.5.16.2                                   function designators, 6.3.2.1
compound literals, 6.5.2.5                                      function parameter, 6.9.1
compound statement, 6.8.2                                       imaginary, G.4.1
compound-literal operator (( ){ }), 6.5.2.5                     imaginary and complex, G.4.3
concatenation functions                                         implicit, 6.3

[page 658]

   lvalues, 6.3.2.1                                             csinh functions, 7.3.6.5, G.6.2.5
   pointer, 6.3.2.1, 6.3.2.3                                      type-generic macro for, 7.24
   real and complex, 6.3.1.7                                    csqrt functions, 7.3.8.3, G.6.4.2
   real and imaginary, G.4.2                                      type-generic macro for, 7.24
   real floating and integer, 6.3.1.4, F.3, F.4                  ctan functions, 7.3.5.6, G.6
   real floating types, 6.3.1.5, F.3                               type-generic macro for, 7.24
   signed and unsigned integers, 6.3.1.3                        ctanh functions, 7.3.6.6, G.6.2.6
   usual arithmetic, see usual arithmetic                         type-generic macro for, 7.24
         conversions                                            ctgamma function, 7.30.1
   void type, 6.3.2.2                                           ctime function, 7.26.3.2
conversion functions                                            ctime_s function, K.3.8.2, K.3.8.2.2
   multibyte/wide character, 7.22.7, K.3.6.4                    ctype.h header, 7.4, 7.30.2
      extended, 7.28.6, K.3.9.3                                 current object, 6.7.9
      restartable, 7.27.1, 7.28.6.3, K.3.9.3.1                  CX_LIMITED_RANGE pragma, 6.10.6, 7.3.4
   multibyte/wide string, 7.22.8, K.3.6.5
      restartable, 7.28.6.4, K.3.9.3.2                          data race, 5.1.2.4, 7.1.4, 7.22.2.1, 7.22.4.6,
   numeric, 7.8.2.3, 7.22.1                                          7.23.5.8, 7.23.6.2, 7.26.3, 7.27.1, 7.28.6.3,
      wide string, 7.8.2.4, 7.28.4.1                                 7.28.6.4
   single byte/wide character, 7.28.6.1                         data stream, see streams
   time, 7.26.3, K.3.8.2                                        date and time header, 7.26, K.3.8
      wide character, 7.28.5                                    Daylight Saving Time, 7.26.1
conversion specifier, 7.21.6.1, 7.21.6.2, 7.28.2.1,              DBL_DECIMAL_DIG macro, 5.2.4.2.2
      7.28.2.2                                                  DBL_DIG macro, 5.2.4.2.2
conversion state, 7.22.7, 7.27.1, 7.27.1.1,                     DBL_EPSILON macro, 5.2.4.2.2
      7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.6,                     DBL_HAS_SUBNORM macro, 5.2.4.2.2
      7.28.6.2.1, 7.28.6.3, 7.28.6.3.2, 7.28.6.3.3,             DBL_MANT_DIG macro, 5.2.4.2.2
      7.28.6.4, 7.28.6.4.1, 7.28.6.4.2, K.3.6.4,                DBL_MAX macro, 5.2.4.2.2
      K.3.9.3.1, K.3.9.3.1.1, K.3.9.3.2, K.3.9.3.2.1,           DBL_MAX_10_EXP macro, 5.2.4.2.2
      K.3.9.3.2.2                                               DBL_MAX_EXP macro, 5.2.4.2.2
conversion state functions, 7.28.6.2                            DBL_MIN macro, 5.2.4.2.2
copying functions                                               DBL_MIN_10_EXP macro, 5.2.4.2.2
   string, 7.23.2, K.3.7.1                                      DBL_MIN_EXP macro, 5.2.4.2.2
   wide string, 7.28.4.2, K.3.9.2.1                             DBL_TRUE_MIN macro, 5.2.4.2.2
copysign functions, 7.3.9.5, 7.12.11.1, F.3,                    decimal constant, 6.4.4.1
      F.10.8.1                                                  decimal digit, 5.2.1
copysign type-generic macro, 7.24                               decimal-point character, 7.1.1, 7.11.2.1
correctly rounded result, 3.9                                   DECIMAL_DIG macro, 5.2.4.2.2, 7.21.6.1,
corresponding real type, 6.2.5                                       7.22.1.3, 7.28.2.1, 7.28.4.1.1, F.5
cos functions, 7.12.4.5, F.10.1.5                               declaration specifiers, 6.7
cos type-generic macro, 7.24, G.7                               declarations, 6.7
cosh functions, 7.12.5.4, F.10.2.4                                function, 6.7.6.3
cosh type-generic macro, 7.24, G.7                                pointer, 6.7.6.1
cpow functions, 7.3.8.2, G.6.4.1                                  structure/union, 6.7.2.1
   type-generic macro for, 7.24                                   typedef, 6.7.8
cproj functions, 7.3.9.5, G.6                                   declarator, 6.7.6
cproj type-generic macro, 7.24                                    abstract, 6.7.7
creal functions, 7.3.9.6, G.6                                   declarator type derivation, 6.2.5, 6.7.6
creal type-generic macro, 7.24, G.7                             decrement operators, see arithmetic operators,
critical undefined behavior, L.2.3                                    increment and decrement
csin functions, 7.3.5.5, G.6                                    default argument promotions, 6.5.2.2
   type-generic macro for, 7.24                                 default initialization, 6.7.9

[page 659]

default label, 6.8.1, 6.8.4.2                                  elif preprocessing directive, 6.10.1
define preprocessing directive, 6.10.3                         ellipsis punctuator (...), 6.5.2.2, 6.7.6.3, 6.10.3
defined operator, 6.10.1, 6.10.8                               else preprocessing directive, 6.10.1
definition, 6.7                                                 else statement, 6.8.4.1
   function, 6.9.1                                             empty statement, 6.8.3
dependency-ordered before, 5.1.2.4                             encoding error, 7.21.3, 7.27.1.1, 7.27.1.2,
derived declarator types, 6.2.5                                      7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3,
derived types, 6.2.5                                                 7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2,
designated initializer, 6.7.9                                        K.3.6.5.1, K.3.6.5.2, K.3.9.3.1.1, K.3.9.3.2.1,
destringizing, 6.10.9                                                K.3.9.3.2.2
device input/output, 5.1.2.3                                   end-of-file, 7.28.1
diagnostic message, 3.10, 5.1.1.3                              end-of-file indicator, 7.21.1, 7.21.5.3, 7.21.7.1,
diagnostics, 5.1.1.3                                                 7.21.7.5, 7.21.7.6, 7.21.7.10, 7.21.9.2,
diagnostics header, 7.2                                              7.21.9.3, 7.21.10.1, 7.21.10.2, 7.28.3.1,
difftime function, 7.26.2.2                                          7.28.3.10
digit, 5.2.1, 7.4                                              end-of-file macro, see EOF macro
digraphs, 6.4.6                                                end-of-line indicator, 5.2.1
direct input/output functions, 7.21.8                          endif preprocessing directive, 6.10.1
display device, 5.2.2                                          enum type, 6.2.5, 6.7.2, 6.7.2.2
div function, 7.22.6.2                                         enumerated type, 6.2.5
div_t type, 7.22                                               enumeration, 6.2.5, 6.7.2.2
division assignment operator (/=), 6.5.16.2                    enumeration constant, 6.2.1, 6.4.4.3
division operator (/), 6.2.6.2, 6.5.5, F.3, G.5.1              enumeration content, 6.7.2.3
do statement, 6.8.5.2                                          enumeration members, 6.7.2.2
documentation of implementation, 4                             enumeration specifiers, 6.7.2.2
domain error, 7.12.1, 7.12.4.1, 7.12.4.2, 7.12.4.4,            enumeration tag, 6.2.3, 6.7.2.3
      7.12.5.1, 7.12.5.3, 7.12.6.5, 7.12.6.7,                  enumerator, 6.7.2.2
      7.12.6.8, 7.12.6.9, 7.12.6.10, 7.12.6.11,                environment, 5
      7.12.7.4, 7.12.7.5, 7.12.8.4, 7.12.9.5,                  environment functions, 7.22.4, K.3.6.2
      7.12.9.7, 7.12.10.1, 7.12.10.2, 7.12.10.3                environment list, 7.22.4.6, K.3.6.2.1
dot operator (.), 6.5.2.3                                      environmental considerations, 5.2
double _Complex type, 6.2.5                                    environmental limits, 5.2.4, 7.13.1.1, 7.21.2,
double _Complex type conversion, 6.3.1.6,                            7.21.3, 7.21.4.4, 7.21.6.1, 7.22.2.1, 7.22.4.2,
      6.3.1.7, 6.3.1.8                                               7.22.4.3, 7.28.2.1, K.3.5.1.2
double _Imaginary type, G.2                                    EOF macro, 7.4, 7.21.1, 7.21.5.1, 7.21.5.2,
double type, 6.2.5, 6.4.4.2, 6.7.2, 7.21.6.2,                        7.21.6.2, 7.21.6.7, 7.21.6.9, 7.21.6.11,
      7.28.2.2, F.2                                                  7.21.6.14, 7.21.7.1, 7.21.7.3, 7.21.7.4,
double type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,                   7.21.7.5, 7.21.7.6, 7.21.7.8, 7.21.7.9,
      6.3.1.8                                                        7.21.7.10, 7.28.1, 7.28.2.2, 7.28.2.4,
double-precision arithmetic, 5.1.2.3                                 7.28.2.6, 7.28.2.8, 7.28.2.10, 7.28.2.12,
double-quote escape sequence (\"), 6.4.4.4,                          7.28.3.4, 7.28.6.1.1, 7.28.6.1.2, K.3.5.3.7,
      6.4.5, 6.10.9                                                  K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.2,
double_t type, 7.12, J.5.6                                           K.3.9.1.5, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12,
                                                                     K.3.9.1.14
EDOM macro, 7.5, 7.12.1, see also domain error                 equal-sign punctuator (=), 6.7, 6.7.2.2, 6.7.9
effective type, 6.5                                            equal-to operator, see equality operator
EILSEQ macro, 7.5, 7.21.3, 7.27.1.1, 7.27.1.2,                 equality expressions, 6.5.9
     7.27.1.3, 7.27.1.4, 7.28.3.1, 7.28.3.3,                   equality operator (==), 6.5.9
     7.28.6.3.2, 7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2,           ERANGE macro, 7.5, 7.8.2.3, 7.8.2.4, 7.12.1,
     see also encoding error                                         7.22.1.3, 7.22.1.4, 7.28.4.1.1, 7.28.4.1.2, see
element type, 6.2.5                                                  also range error, pole error

[page 660]

erf functions, 7.12.8.1, F.10.5.1                               exp2 functions, 7.12.6.2, F.10.3.2
erf type-generic macro, 7.24                                    exp2 type-generic macro, 7.24
erfc functions, 7.12.8.2, F.10.5.2                              explicit conversion, 6.3
erfc type-generic macro, 7.24                                   expm1 functions, 7.12.6.3, F.10.3.3
errno macro, 7.1.3, 7.3.2, 7.5, 7.8.2.3, 7.8.2.4,               expm1 type-generic macro, 7.24
      7.12.1, 7.14.1.1, 7.21.3, 7.21.9.3, 7.21.10.4,            exponent part, 6.4.4.2
      7.22.1, 7.22.1.3, 7.22.1.4, 7.23.6.2, 7.27.1.1,           exponential functions
      7.27.1.2, 7.27.1.3, 7.27.1.4, 7.28.3.1,                     complex, 7.3.7, G.6.3
      7.28.3.3, 7.28.4.1.1, 7.28.4.1.2, 7.28.6.3.2,               real, 7.12.6, F.10.3
      7.28.6.3.3, 7.28.6.4.1, 7.28.6.4.2, J.5.17,               expression, 6.5
      K.3.1.3, K.3.7.4.2                                          assignment, 6.5.16
errno.h header, 7.5, 7.30.3, K.3.2                                cast, 6.5.4
errno_t type, K.3.2, K.3.5, K.3.6, K.3.6.1.1,                     constant, 6.6
      K.3.7, K.3.8, K.3.9                                         evaluation, 5.1.2.3
error                                                             full, 6.8
   domain, see domain error                                       order of evaluation, see order of evaluation
   encoding, see encoding error                                   parenthesized, 6.5.1
   pole, see pole error                                           primary, 6.5.1
   range, see range error                                         unary, 6.5.3
error conditions, 7.12.1                                        expression statement, 6.8.3
error functions, 7.12.8, F.10.5                                 extended alignment, 6.2.8
error indicator, 7.21.1, 7.21.5.3, 7.21.7.1,                    extended character set, 3.7.2, 5.2.1, 5.2.1.2
      7.21.7.3, 7.21.7.5, 7.21.7.6, 7.21.7.7,                   extended characters, 5.2.1
      7.21.7.8, 7.21.9.2, 7.21.10.1, 7.21.10.3,                 extended integer types, 6.2.5, 6.3.1.1, 6.4.4.1,
      7.28.3.1, 7.28.3.3                                             7.20
error preprocessing directive, 4, 6.10.5                        extended multibyte/wide character conversion
error-handling functions, 7.21.10, 7.23.6.2,                         utilities, 7.28.6, K.3.9.3
      K.3.7.4.2, K.3.7.4.3                                      extensible wide character case mapping functions,
escape character (\), 6.4.4.4                                        7.29.3.2
escape sequences, 5.2.1, 5.2.2, 6.4.4.4, 6.11.4                 extensible wide character classification functions,
evaluation format, 5.2.4.2.2, 6.4.4.2, 7.12                          7.29.2.2
evaluation method, 5.2.4.2.2, 6.5, F.8.5                        extern storage-class specifier, 6.2.2, 6.7.1
evaluation of expression, 5.1.2.3                               external definition, 6.9
evaluation order, see order of evaluation                       external identifiers, underscore, 7.1.3
exceptional condition, 6.5                                      external linkage, 6.2.2
excess precision, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                   external name, 6.4.2.1
excess range, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                       external object definitions, 6.9.2
exclusive OR operators
   bitwise (^), 6.2.6.2, 6.5.11                                 fabs functions, 7.12.7.2, F.3, F.10.4.2
   bitwise assignment (^=), 6.5.16.2                            fabs type-generic macro, 7.24, G.7
executable program, 5.1.1.1                                     false macro, 7.18
execution character set, 5.2.1                                  fclose function, 7.21.5.1
execution environment, 5, 5.1.2, see also                       fdim functions, 7.12.12.1, F.10.9.1
      environmental limits                                      fdim type-generic macro, 7.24
execution sequence, 5.1.2.3, 6.8                                FE_ALL_EXCEPT macro, 7.6
exit function, 5.1.2.2.3, 7.21.3, 7.22, 7.22.4.4,               FE_DFL_ENV macro, 7.6
      7.22.4.5, 7.22.4.7                                        FE_DIVBYZERO macro, 7.6, 7.12, F.3
EXIT_FAILURE macro, 7.22, 7.22.4.4                              FE_DOWNWARD macro, 7.6, F.3
EXIT_SUCCESS macro, 7.22, 7.22.4.4                              FE_INEXACT macro, 7.6, F.3
exp functions, 7.12.6.1, F.10.3.1                               FE_INVALID macro, 7.6, 7.12, F.3
exp type-generic macro, 7.24                                    FE_OVERFLOW macro, 7.6, 7.12, F.3

[page 661]

FE_TONEAREST macro, 7.6, F.3                                 float _Complex type conversion, 6.3.1.6,
FE_TOWARDZERO macro, 7.6, F.3                                     6.3.1.7, 6.3.1.8
FE_UNDERFLOW macro, 7.6, F.3                                 float _Imaginary type, G.2
FE_UPWARD macro, 7.6, F.3                                    float type, 6.2.5, 6.4.4.2, 6.7.2, F.2
feclearexcept function, 7.6.2, 7.6.2.1, F.3                  float type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
fegetenv function, 7.6.4.1, 7.6.4.3, 7.6.4.4, F.3                 6.3.1.8
fegetexceptflag function, 7.6.2, 7.6.2.2, F.3                float.h header, 4, 5.2.4.2.2, 7.7, 7.22.1.3,
fegetround function, 7.6, 7.6.3.1, F.3                            7.28.4.1.1
feholdexcept function, 7.6.4.2, 7.6.4.3,                     float_t type, 7.12, J.5.6
     7.6.4.4, F.3                                            floating constant, 6.4.4.2
fence, 5.1.2.4                                               floating suffix, f or F, 6.4.4.2
fences, 7.17.4                                               floating type conversion, 6.3.1.4, 6.3.1.5, 6.3.1.7,
fenv.h header, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H                F.3, F.4
FENV_ACCESS pragma, 6.10.6, 7.6.1, F.8, F.9,                 floating types, 6.2.5, 6.11.1
     F.10                                                    floating-point accuracy, 5.2.4.2.2, 6.4.4.2, 6.5,
fenv_t type, 7.6                                                  7.22.1.3, F.5, see also contracted expression
feof function, 7.21.10.2                                     floating-point arithmetic functions, 7.12, F.10
feraiseexcept function, 7.6.2, 7.6.2.3, F.3                  floating-point classification functions, 7.12.3
ferror function, 7.21.10.3                                   floating-point control mode, 7.6, F.8.6
fesetenv function, 7.6.4.3, F.3                              floating-point environment, 7.6, F.8, F.8.6
fesetexceptflag function, 7.6.2, 7.6.2.4, F.3                floating-point exception, 7.6, 7.6.2, F.10
fesetround function, 7.6, 7.6.3.2, F.3                       floating-point number, 5.2.4.2.2, 6.2.5
fetestexcept function, 7.6.2, 7.6.2.5, F.3                   floating-point rounding mode, 5.2.4.2.2
feupdateenv function, 7.6.4.2, 7.6.4.4, F.3                  floating-point status flag, 7.6, F.8.6
fexcept_t type, 7.6, F.3                                     floor functions, 7.12.9.2, F.10.6.2
fflush function, 7.21.5.2, 7.21.5.3                          floor type-generic macro, 7.24
fgetc function, 7.21.1, 7.21.3, 7.21.7.1,                    FLT_DECIMAL_DIG macro, 5.2.4.2.2
     7.21.7.5, 7.21.8.1                                      FLT_DIG macro, 5.2.4.2.2
fgetpos function, 7.21.2, 7.21.9.1, 7.21.9.3                 FLT_EPSILON macro, 5.2.4.2.2
fgets function, 7.21.1, 7.21.7.2, K.3.5.4.1                  FLT_EVAL_METHOD macro, 5.2.4.2.2, 6.6, 7.12,
fgetwc function, 7.21.1, 7.21.3, 7.28.3.1,                        F.10.11
     7.28.3.6                                                FLT_HAS_SUBNORM macro, 5.2.4.2.2
fgetws function, 7.21.1, 7.28.3.2                            FLT_MANT_DIG macro, 5.2.4.2.2
field width, 7.21.6.1, 7.28.2.1                               FLT_MAX macro, 5.2.4.2.2
file, 7.21.3                                                  FLT_MAX_10_EXP macro, 5.2.4.2.2
  access functions, 7.21.5, K.3.5.2                          FLT_MAX_EXP macro, 5.2.4.2.2
  name, 7.21.3                                               FLT_MIN macro, 5.2.4.2.2
  operations, 7.21.4, K.3.5.1                                FLT_MIN_10_EXP macro, 5.2.4.2.2
  position indicator, 7.21.1, 7.21.2, 7.21.3,                FLT_MIN_EXP macro, 5.2.4.2.2
        7.21.5.3, 7.21.7.1, 7.21.7.3, 7.21.7.10,             FLT_RADIX macro, 5.2.4.2.2, 7.21.6.1, 7.22.1.3,
        7.21.8.1, 7.21.8.2, 7.21.9.1, 7.21.9.2,                   7.28.2.1, 7.28.4.1.1
        7.21.9.3, 7.21.9.4, 7.21.9.5, 7.28.3.1,              FLT_ROUNDS macro, 5.2.4.2.2, 7.6, F.3
        7.28.3.3, 7.28.3.10                                  FLT_TRUE_MIN macro, 5.2.4.2.2
  positioning functions, 7.21.9                              fma functions, 7.12, 7.12.13.1, F.10.10.1
file scope, 6.2.1, 6.9                                        fma type-generic macro, 7.24
FILE type, 7.21.1, 7.21.3                                    fmax functions, 7.12.12.2, F.10.9.2
FILENAME_MAX macro, 7.21.1                                   fmax type-generic macro, 7.24
flags, 7.21.6.1, 7.28.2.1, see also floating-point             fmin functions, 7.12.12.3, F.10.9.3
     status flag                                              fmin type-generic macro, 7.24
flexible array member, 6.7.2.1                                fmod functions, 7.12.10.1, F.10.7.1
float _Complex type, 6.2.5                                   fmod type-generic macro, 7.24

[page 662]

fopen function, 7.21.5.3, 7.21.5.4, K.3.5.2.1                       K.3.5.3.7, K.3.5.3.9
FOPEN_MAX macro, 7.21.1, 7.21.3, 7.21.4.3,                    fseek function, 7.21.1, 7.21.5.3, 7.21.7.10,
     K.3.5.1.1                                                      7.21.9.2, 7.21.9.4, 7.21.9.5, 7.28.3.10
fopen_s function, K.3.5.1.1, K.3.5.2.1,                       fsetpos function, 7.21.2, 7.21.5.3, 7.21.7.10,
     K.3.5.2.2                                                      7.21.9.1, 7.21.9.3, 7.28.3.10
for statement, 6.8.5, 6.8.5.3                                 ftell function, 7.21.9.2, 7.21.9.4
form-feed character, 5.2.1, 6.4                               full declarator, 6.7.6
form-feed escape sequence (\f), 5.2.2, 6.4.4.4,               full expression, 6.8
     7.4.1.10                                                 fully buffered stream, 7.21.3
formal argument (deprecated), 3.16                            function
formal parameter, 3.16                                           argument, 6.5.2.2, 6.9.1
formatted input/output functions, 7.11.1.1, 7.21.6,              body, 6.9.1
     K.3.5.3                                                     call, 6.5.2.2
   wide character, 7.28.2, K.3.9.1                                  library, 7.1.4
fortran keyword, J.5.9                                           declarator, 6.7.6.3, 6.11.6
forward reference, 3.11                                          definition, 6.7.6.3, 6.9.1, 6.11.7
FP_CONTRACT pragma, 6.5, 6.10.6, 7.12.2, see                     designator, 6.3.2.1
     also contracted expression                                  image, 5.2.3
FP_FAST_FMA macro, 7.12                                          inline, 6.7.4
FP_FAST_FMAF macro, 7.12                                         library, 5.1.1.1, 7.1.4
FP_FAST_FMAL macro, 7.12                                         name length, 5.2.4.1, 6.4.2.1, 6.11.3
FP_ILOGB0 macro, 7.12, 7.12.6.5                                  no-return, 6.7.4
FP_ILOGBNAN macro, 7.12, 7.12.6.5                                parameter, 5.1.2.2.1, 6.5.2.2, 6.7, 6.9.1
FP_INFINITE macro, 7.12, F.3                                     prototype, 5.1.2.2.1, 6.2.1, 6.2.7, 6.5.2.2, 6.7,
FP_NAN macro, 7.12, F.3                                                6.7.6.3, 6.9.1, 6.11.6, 6.11.7, 7.1.2, 7.12
FP_NORMAL macro, 7.12, F.3                                       prototype scope, 6.2.1, 6.7.6.2
FP_SUBNORMAL macro, 7.12, F.3                                    recursive call, 6.5.2.2
FP_ZERO macro, 7.12, F.3                                         return, 6.8.6.4, F.6
fpclassify macro, 7.12.3.1, F.3                                  scope, 6.2.1
fpos_t type, 7.21.1, 7.21.2                                      type, 6.2.5
fprintf function, 7.8.1, 7.21.1, 7.21.6.1,                       type conversion, 6.3.2.1
     7.21.6.2, 7.21.6.3, 7.21.6.5, 7.21.6.6,                  function specifiers, 6.7.4
     7.21.6.8, 7.28.2.2, F.3, K.3.5.3.1                       function type, 6.2.5
fprintf_s function, K.3.5.3.1                                 function-call operator (( )), 6.5.2.2
fputc function, 5.2.2, 7.21.1, 7.21.3, 7.21.7.3,              function-like macro, 6.10.3
     7.21.7.7, 7.21.8.2                                       fundamental alignment, 6.2.8
fputs function, 7.21.1, 7.21.7.4                              future directions
fputwc function, 7.21.1, 7.21.3, 7.28.3.3,                       language, 6.11
     7.28.3.8                                                    library, 7.30
fputws function, 7.21.1, 7.28.3.4                             fwide function, 7.21.2, 7.28.3.5
fread function, 7.21.1, 7.21.8.1                              fwprintf function, 7.8.1, 7.21.1, 7.21.6.2,
free function, 7.22.3.3, 7.22.3.5                                   7.28.2.1, 7.28.2.2, 7.28.2.3, 7.28.2.5,
freestanding execution environment, 4, 5.1.2,                       7.28.2.11, K.3.9.1.1
     5.1.2.1                                                  fwprintf_s function, K.3.9.1.1
freopen function, 7.21.2, 7.21.5.4                            fwrite function, 7.21.1, 7.21.8.2
freopen_s function, K.3.5.2.2                                 fwscanf function, 7.8.1, 7.21.1, 7.28.2.2,
frexp functions, 7.12.6.4, F.10.3.4                                 7.28.2.4, 7.28.2.6, 7.28.2.12, 7.28.3.10,
frexp type-generic macro, 7.24                                      K.3.9.1.2
fscanf function, 7.8.1, 7.21.1, 7.21.6.2,                     fwscanf_s function, K.3.9.1.2, K.3.9.1.5,
     7.21.6.4, 7.21.6.7, 7.21.6.9, F.3, K.3.5.3.2                   K.3.9.1.7, K.3.9.1.14
fscanf_s function, K.3.5.3.2, K.3.5.3.4,

[page 663]

gamma functions, 7.12.8, F.10.5                               name spaces, 6.2.3
general utilities, 7.22, K.3.6                                reserved, 6.4.1, 7.1.3, K.3.1.2
  wide string, 7.28.4, K.3.9.2                                 scope, 6.2.1
general wide string utilities, 7.28.4, K.3.9.2                 type, 6.2.5
generic parameters, 7.24                                    identifier list, 6.7.6
generic selection, 6.5.1.1                                  identifier nondigit, 6.4.2.1
getc function, 7.21.1, 7.21.7.5, 7.21.7.6                   IEC 559, F.1
getchar function, 7.21.1, 7.21.7.6                          IEC 60559, 2, 5.1.2.3, 5.2.4.2.2, 6.10.8.3, 7.3.3,
getenv function, 7.22.4.6                                         7.6, 7.6.4.2, 7.12.1, 7.12.10.2, 7.12.14, F, G,
getenv_s function, K.3.6.2.1                                      H.1
gets function, K.3.5.4.1                                    IEEE 754, F.1
gets_s function, K.3.5.4.1                                  IEEE 854, F.1
getwc function, 7.21.1, 7.28.3.6, 7.28.3.7                  IEEE floating-point arithmetic standard, see
getwchar function, 7.21.1, 7.28.3.7                               IEC 60559, ANSI/IEEE 754,
gmtime function, 7.26.3.3                                         ANSI/IEEE 854
gmtime_s function, K.3.8.2.3                                if preprocessing directive, 5.2.4.2.1, 5.2.4.2.2,
goto statement, 6.2.1, 6.8.1, 6.8.6.1                             6.10.1, 7.1.4
graphic characters, 5.2.1                                   if statement, 6.8.4.1
greater-than operator (>), 6.5.8                            ifdef preprocessing directive, 6.10.1
greater-than-or-equal-to operator (>=), 6.5.8               ifndef preprocessing directive, 6.10.1
                                                            ignore_handler_s function, K.3.6.1.3
happens before, 5.1.2.4                                     ilogb functions, 7.12, 7.12.6.5, F.10.3.5
header, 5.1.1.1, 7.1.2, see also standard headers           ilogb type-generic macro, 7.24
header names, 6.4, 6.4.7, 6.10.2                            imaginary macro, 7.3.1, G.6
hexadecimal constant, 6.4.4.1                               imaginary numbers, G
hexadecimal digit, 6.4.4.1, 6.4.4.2, 6.4.4.4                imaginary type domain, G.2
hexadecimal prefix, 6.4.4.1                                  imaginary types, G
hexadecimal-character escape sequence                       imaxabs function, 7.8.2.1
     (\x hexadecimal digits), 6.4.4.4                       imaxdiv function, 7.8, 7.8.2.2
high-order bit, 3.6                                         imaxdiv_t type, 7.8
horizontal-tab character, 5.2.1, 6.4                        implementation, 3.12
horizontal-tab escape sequence (\r), 7.29.2.1.3             implementation limit, 3.13, 4, 5.2.4.2, 6.4.2.1,
horizontal-tab escape sequence (\t), 5.2.2,                       6.7.6, 6.8.4.2, E, see also environmental
     6.4.4.4, 7.4.1.3, 7.4.1.10                                   limits
hosted execution environment, 4, 5.1.2, 5.1.2.2             implementation-defined behavior, 3.4.1, 4, J.3
HUGE_VAL macro, 7.12, 7.12.1, 7.22.1.3,                     implementation-defined value, 3.19.1
     7.28.4.1.1, F.10                                       implicit conversion, 6.3
HUGE_VALF macro, 7.12, 7.12.1, 7.22.1.3,                    implicit initialization, 6.7.9
     7.28.4.1.1, F.10                                       include preprocessing directive, 5.1.1.2, 6.10.2
HUGE_VALL macro, 7.12, 7.12.1, 7.22.1.3,                    inclusive OR operators
     7.28.4.1.1, F.10                                         bitwise (|), 6.2.6.2, 6.5.12
hyperbolic functions                                           bitwise assignment (|=), 6.5.16.2
  complex, 7.3.6, G.6.2                                     incomplete type, 6.2.5
  real, 7.12.5, F.10.2                                      increment operators, see arithmetic operators,
hypot functions, 7.12.7.3, F.10.4.3                               increment and decrement
hypot type-generic macro, 7.24                              indeterminate value, 3.19.2
                                                            indeterminately sequenced, 5.1.2.3, 6.5.2.2,
I macro, 7.3.1, 7.3.9.5, G.6                                      6.5.2.4, 6.5.16.2, see also sequenced before,
identifier, 6.4.2.1, 6.5.1                                         unsequenced
   linkage, see linkage                                     indirection operator (*), 6.5.2.1, 6.5.3.2
   maximum length, 6.4.2.1                                  inequality operator (!=), 6.5.9

[page 664]

infinitary, 7.12.1                                                    extended, 6.2.5, 6.3.1.1, 6.4.4.1, 7.20
INFINITY macro, 7.3.9.5, 7.12, F.2.1                              inter-thread happens before, 5.1.2.4
initial position, 5.2.2                                           interactive device, 5.1.2.3, 7.21.3, 7.21.5.3
initial shift state, 5.2.1.2                                      internal linkage, 6.2.2
initialization, 5.1.2, 6.2.4, 6.3.2.1, 6.5.2.5, 6.7.9,            internal name, 6.4.2.1
      F.8.5                                                       interrupt, 5.2.3
   in blocks, 6.8                                                 INTMAX_C macro, 7.20.4.2
initializer, 6.7.9                                                INTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
   permitted form, 6.6                                            INTMAX_MIN macro, 7.8.2.3, 7.8.2.4, 7.20.2.5
   string literal, 6.3.2.1                                        intmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,
inline, 6.7.4                                                           7.28.2.1, 7.28.2.2
inner scope, 6.2.1                                                INTN_C macros, 7.20.4.1
input failure, 7.28.2.6, 7.28.2.8, 7.28.2.10,                     INTN_MAX macros, 7.20.2.1
      K.3.5.3.2, K.3.5.3.4, K.3.5.3.7, K.3.5.3.9,                 INTN_MIN macros, 7.20.2.1
      K.3.5.3.11, K.3.5.3.14, K.3.9.1.2, K.3.9.1.5,               intN_t types, 7.20.1.1
      K.3.9.1.7, K.3.9.1.10, K.3.9.1.12, K.3.9.1.14               INTPTR_MAX macro, 7.20.2.4
input/output functions                                            INTPTR_MIN macro, 7.20.2.4
   character, 7.21.7, K.3.5.4                                     intptr_t type, 7.20.1.4
   direct, 7.21.8                                                 inttypes.h header, 7.8, 7.30.4
   formatted, 7.21.6, K.3.5.3                                     isalnum function, 7.4.1.1, 7.4.1.9, 7.4.1.10
      wide character, 7.28.2, K.3.9.1                             isalpha function, 7.4.1.1, 7.4.1.2
   wide character, 7.28.3                                         isblank function, 7.4.1.3
      formatted, 7.28.2, K.3.9.1                                  iscntrl function, 7.4.1.2, 7.4.1.4, 7.4.1.7,
input/output header, 7.21, K.3.5                                        7.4.1.11
input/output, device, 5.1.2.3                                     isdigit function, 7.4.1.1, 7.4.1.2, 7.4.1.5,
int type, 6.2.5, 6.3.1.1, 6.3.1.3, 6.4.4.1, 6.7.2                       7.4.1.7, 7.4.1.11, 7.11.1.1
int type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,                   isfinite macro, 7.12.3.2, F.3
      6.3.1.8                                                     isgraph function, 7.4.1.6
INT_FASTN_MAX macros, 7.20.2.3                                    isgreater macro, 7.12.14.1, F.3
INT_FASTN_MIN macros, 7.20.2.3                                    isgreaterequal macro, 7.12.14.2, F.3
int_fastN_t types, 7.20.1.3                                       isinf macro, 7.12.3.3
INT_LEASTN_MAX macros, 7.20.2.2                                   isless macro, 7.12.14.3, F.3
INT_LEASTN_MIN macros, 7.20.2.2                                   islessequal macro, 7.12.14.4, F.3
int_leastN_t types, 7.20.1.2                                      islessgreater macro, 7.12.14.5, F.3
INT_MAX macro, 5.2.4.2.1, 7.12, 7.12.6.5                          islower function, 7.4.1.2, 7.4.1.7, 7.4.2.1,
INT_MIN macro, 5.2.4.2.1, 7.12                                          7.4.2.2
integer arithmetic functions, 7.8.2.1, 7.8.2.2,                   isnan macro, 7.12.3.4, F.3
      7.22.6                                                      isnormal macro, 7.12.3.5
integer character constant, 6.4.4.4                               ISO 31-11, 2, 3
integer constant, 6.4.4.1                                         ISO 4217, 2, 7.11.2.1
integer constant expression, 6.3.2.3, 6.6, 6.7.2.1,               ISO 8601, 2, 7.26.3.5
      6.7.2.2, 6.7.6.2, 6.7.9, 6.7.10, 6.8.4.2, 6.10.1,           ISO/IEC 10646, 2, 6.4.2.1, 6.4.3, 6.10.8.2
      7.1.4                                                       ISO/IEC 10976-1, H.1
integer conversion rank, 6.3.1.1                                  ISO/IEC 2382-1, 2, 3
integer promotions, 5.1.2.3, 5.2.4.2.1, 6.3.1.1,                  ISO/IEC 646, 2, 5.2.1.1
      6.5.2.2, 6.5.3.3, 6.5.7, 6.8.4.2, 7.20.2, 7.20.3,           ISO/IEC 9945-2, 7.11
      7.21.6.1, 7.28.2.1                                          iso646.h header, 4, 7.9                          *
integer suffix, 6.4.4.1                                            isprint function, 5.2.2, 7.4.1.8
integer type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,               ispunct function, 7.4.1.2, 7.4.1.7, 7.4.1.9,
      F.3, F.4                                                          7.4.1.11
integer types, 6.2.5, 7.20                                        isspace function, 7.4.1.2, 7.4.1.7, 7.4.1.9,

[page 665]

      7.4.1.10, 7.4.1.11, 7.21.6.2, 7.22.1.3,                   LC_ALL macro, 7.11, 7.11.1.1, 7.11.2.1
      7.22.1.4, 7.28.2.2                                        LC_COLLATE macro, 7.11, 7.11.1.1, 7.23.4.3,
isunordered macro, 7.12.14.6, F.3                                     7.28.4.4.2
isupper function, 7.4.1.2, 7.4.1.11, 7.4.2.1,                   LC_CTYPE macro, 7.11, 7.11.1.1, 7.22, 7.22.7,
      7.4.2.2                                                         7.22.8, 7.28.6, 7.29.1, 7.29.2.2.1, 7.29.2.2.2,
iswalnum function, 7.29.2.1.1, 7.29.2.1.9,                            7.29.3.2.1, 7.29.3.2.2, K.3.6.4, K.3.6.5
      7.29.2.1.10, 7.29.2.2.1                                   LC_MONETARY macro, 7.11, 7.11.1.1, 7.11.2.1
iswalpha function, 7.29.2.1.1, 7.29.2.1.2,                      LC_NUMERIC macro, 7.11, 7.11.1.1, 7.11.2.1
      7.29.2.2.1                                                LC_TIME macro, 7.11, 7.11.1.1, 7.26.3.5
iswblank function, 7.29.2.1.3, 7.29.2.2.1                       lconv structure type, 7.11
iswcntrl function, 7.29.2.1.2, 7.29.2.1.4,                      LDBL_DECIMAL_DIG macro, 5.2.4.2.2
      7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1                       LDBL_DIG macro, 5.2.4.2.2
iswctype function, 7.29.2.2.1, 7.29.2.2.2                       LDBL_EPSILON macro, 5.2.4.2.2
iswdigit function, 7.29.2.1.1, 7.29.2.1.2,                      LDBL_HAS_SUBNORM macro, 5.2.4.2.2
      7.29.2.1.5, 7.29.2.1.7, 7.29.2.1.11, 7.29.2.2.1           LDBL_MANT_DIG macro, 5.2.4.2.2
iswgraph function, 7.29.2.1, 7.29.2.1.6,                        LDBL_MAX macro, 5.2.4.2.2
      7.29.2.1.10, 7.29.2.2.1                                   LDBL_MAX_10_EXP macro, 5.2.4.2.2
iswlower function, 7.29.2.1.2, 7.29.2.1.7,                      LDBL_MAX_EXP macro, 5.2.4.2.2
      7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2                        LDBL_MIN macro, 5.2.4.2.2
iswprint function, 7.29.2.1.6, 7.29.2.1.8,                      LDBL_MIN_10_EXP macro, 5.2.4.2.2
      7.29.2.2.1                                                LDBL_MIN_EXP macro, 5.2.4.2.2
iswpunct function, 7.29.2.1, 7.29.2.1.2,                        LDBL_TRUE_MIN macro, 5.2.4.2.2
      7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10,                      ldexp functions, 7.12.6.6, F.10.3.6
      7.29.2.1.11, 7.29.2.2.1                                   ldexp type-generic macro, 7.24
iswspace function, 7.21.6.2, 7.28.2.2,                          ldiv function, 7.22.6.2
      7.28.4.1.1, 7.28.4.1.2, 7.29.2.1.2, 7.29.2.1.6,           ldiv_t type, 7.22
      7.29.2.1.7, 7.29.2.1.9, 7.29.2.1.10,                      leading underscore in identifiers, 7.1.3
      7.29.2.1.11, 7.29.2.2.1                                   left-shift assignment operator (<<=), 6.5.16.2
iswupper function, 7.29.2.1.2, 7.29.2.1.11,                     left-shift operator (<<), 6.2.6.2, 6.5.7
      7.29.2.2.1, 7.29.3.1.1, 7.29.3.1.2                        length
iswxdigit function, 7.29.2.1.12, 7.29.2.2.1                        external name, 5.2.4.1, 6.4.2.1, 6.11.3
isxdigit function, 7.4.1.12, 7.11.1.1                              function name, 5.2.4.1, 6.4.2.1, 6.11.3
italic type convention, 3, 6.1                                     identifier, 6.4.2.1
iteration statements, 6.8.5                                        internal name, 5.2.4.1, 6.4.2.1
                                                                length function, 7.22.7.1, 7.23.6.3, 7.28.4.6.1,
jmp_buf type, 7.13                                                    7.28.6.3.1, K.3.7.4.4, K.3.9.2.4.1
jump statements, 6.8.6                                          length modifier, 7.21.6.1, 7.21.6.2, 7.28.2.1,
                                                                      7.28.2.2
keywords, 6.4.1, G.2, J.5.9, J.5.10                             less-than operator (<), 6.5.8
kill_dependency macro, 5.1.2.4, 7.17.3.1                        less-than-or-equal-to operator (<=), 6.5.8
known constant size, 6.2.5                                      letter, 5.2.1, 7.4
                                                                lexical elements, 5.1.1.2, 6.4
L_tmpnam macro, 7.21.1, 7.21.4.4                                lgamma functions, 7.12.8.3, F.10.5.3
L_tmpnam_s macro, K.3.5, K.3.5.1.2                              lgamma type-generic macro, 7.24
label name, 6.2.1, 6.2.3                                        library, 5.1.1.1, 7, K.3
labeled statement, 6.8.1                                           future directions, 7.30
labs function, 7.22.6.1                                            summary, B
language, 6                                                        terms, 7.1.1
   future directions, 6.11                                         use of functions, 7.1.4
   syntax summary, A                                            lifetime, 6.2.4
Latin alphabet, 5.2.1, 6.4.2.1                                  limits

[page 666]

   environmental, see environmental limits                      6.3.1.6, 6.3.1.7, 6.3.1.8
   implementation, see implementation limits               long double _Imaginary type, G.2
   numerical, see numerical limits                         long double suffix, l or L, 6.4.4.2
   translation, see translation limits                     long double type, 6.2.5, 6.4.4.2, 6.7.2,
limits.h header, 4, 5.2.4.2.1, 6.2.5, 7.10                      7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2, F.2
line buffered stream, 7.21.3                               long double type conversion, 6.3.1.4, 6.3.1.5,
line number, 6.10.4, 6.10.8.1                                   6.3.1.7, 6.3.1.8
line preprocessing directive, 6.10.4                       long int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,
lines, 5.1.1.2, 7.21.2                                          7.21.6.2, 7.28.2.1, 7.28.2.2
   preprocessing directive, 6.10                           long int type conversion, 6.3.1.1, 6.3.1.3,
linkage, 6.2.2, 6.7, 6.7.4, 6.7.6.2, 6.9, 6.9.2,                6.3.1.4, 6.3.1.8
      6.11.2                                               long integer suffix, l or L, 6.4.4.1
llabs function, 7.22.6.1                                   long long int type, 6.2.5, 6.3.1.1, 6.7.2,
lldiv function, 7.22.6.2                                        7.21.6.1, 7.21.6.2, 7.28.2.1, 7.28.2.2
lldiv_t type, 7.22                                         long long int type conversion, 6.3.1.1,
LLONG_MAX macro, 5.2.4.2.1, 7.22.1.4,                           6.3.1.3, 6.3.1.4, 6.3.1.8
      7.28.4.1.2                                           long long integer suffix, ll or LL, 6.4.4.1
LLONG_MIN macro, 5.2.4.2.1, 7.22.1.4,                      LONG_MAX macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
      7.28.4.1.2                                           LONG_MIN macro, 5.2.4.2.1, 7.22.1.4, 7.28.4.1.2
llrint functions, 7.12.9.5, F.3, F.10.6.5                  longjmp function, 7.13.1.1, 7.13.2.1, 7.22.4.4,
llrint type-generic macro, 7.24                                 7.22.4.7
llround functions, 7.12.9.7, F.10.6.7                      loop body, 6.8.5
llround type-generic macro, 7.24                           low-order bit, 3.6
local time, 7.26.1                                         lowercase letter, 5.2.1
locale, 3.4.2                                              lrint functions, 7.12.9.5, F.3, F.10.6.5
locale-specific behavior, 3.4.2, J.4                        lrint type-generic macro, 7.24
locale.h header, 7.11, 7.30.5                              lround functions, 7.12.9.7, F.10.6.7
localeconv function, 7.11.1.1, 7.11.2.1                    lround type-generic macro, 7.24
localization, 7.11                                         lvalue, 6.3.2.1, 6.5.1, 6.5.2.4, 6.5.3.1, 6.5.16,
localtime function, 7.26.3.4                                    6.7.2.4
localtime_s function, K.3.8.2.4                            lvalue conversion, 6.3.2.1, 6.5.16, 6.5.16.1,
log functions, 7.12.6.7, F.10.3.7                               6.5.16.2
log type-generic macro, 7.24
log10 functions, 7.12.6.8, F.10.3.8                        macro argument substitution, 6.10.3.1
log10 type-generic macro, 7.24                             macro definition
log1p functions, 7.12.6.9, F.10.3.9                          library function, 7.1.4
log1p type-generic macro, 7.24                             macro invocation, 6.10.3
log2 functions, 7.12.6.10, F.10.3.10                       macro name, 6.10.3
log2 type-generic macro, 7.24                                length, 5.2.4.1
logarithmic functions                                        predefined, 6.10.8, 6.11.9
   complex, 7.3.7, G.6.3                                     redefinition, 6.10.3
   real, 7.12.6, F.10.3                                      scope, 6.10.3.5
logb functions, 7.12.6.11, F.3, F.10.3.11                  macro parameter, 6.10.3
logb type-generic macro, 7.24                              macro preprocessor, 6.10
logical operators                                          macro replacement, 6.10.3
   AND (&&), 5.1.2.4, 6.5.13                               magnitude, complex, 7.3.8.1
   negation (!), 6.5.3.3                                   main function, 5.1.2.2.1, 5.1.2.2.3, 6.7.3.1, 6.7.4,
   OR (||), 5.1.2.4, 6.5.14                                     7.21.3
logical source lines, 5.1.1.2                              malloc function, 7.22.3, 7.22.3.4, 7.22.3.5
long double _Complex type, 6.2.5                           manipulation functions
long double _Complex type conversion,                        complex, 7.3.9

[page 667]

  real, 7.12.11, F.10.8                                    modf functions, 7.12.6.12, F.10.3.12
matching failure, 7.28.2.6, 7.28.2.8, 7.28.2.10,           modifiable lvalue, 6.3.2.1
     K.3.9.1.7, K.3.9.1.10, K.3.9.1.12                     modification order, 5.1.2.4
math.h header, 5.2.4.2.2, 6.5, 7.12, 7.24, F,              modulus functions, 7.12.6.12
     F.10, J.5.17                                          modulus, complex, 7.3.8.1
MATH_ERREXCEPT macro, 7.12, F.10                           mtx_destroy function, 7.25.4.1
math_errhandling macro, 7.1.3, 7.12, F.10                  mtx_init function, 7.25.1, 7.25.4.2
MATH_ERRNO macro, 7.12                                     mtx_lock function, 7.25.4.3
max_align_t type, 7.19                                     mtx_t type, 7.25.1
maximum functions, 7.12.12, F.10.9                         mtx_timedlock function, 7.25.4.4
MB_CUR_MAX macro, 7.1.1, 7.22, 7.22.7.2,                   mtx_trylock function, 7.25.4.5
     7.22.7.3, 7.27.1.2, 7.27.1.4, 7.28.6.3.3,             mtx_unlock function, 7.25.4.3, 7.25.4.4,
     K.3.6.4.1, K.3.9.3.1.1                                     7.25.4.5, 7.25.4.6
MB_LEN_MAX macro, 5.2.4.2.1, 7.1.1, 7.22                   multibyte character, 3.7.2, 5.2.1.2, 6.4.4.4
mblen function, 7.22.7.1, 7.28.6.3                         multibyte conversion functions
mbrlen function, 7.28.6.3.1                                  wide character, 7.22.7, K.3.6.4
mbrtoc16 function, 6.4.4.4, 6.4.5, 7.27.1.1                     extended, 7.28.6, K.3.9.3
mbrtoc32 function, 6.4.4.4, 6.4.5, 7.27.1.3                     restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
mbrtowc function, 7.21.3, 7.21.6.1, 7.21.6.2,                wide string, 7.22.8, K.3.6.5
     7.28.2.1, 7.28.2.2, 7.28.6.3.1, 7.28.6.3.2,                restartable, 7.28.6.4, K.3.9.3.2
     7.28.6.4.1, K.3.6.5.1, K.3.9.3.2.1                    multibyte string, 7.1.1
mbsinit function, 7.28.6.2.1                               multibyte/wide character conversion functions,
mbsrtowcs function, 7.28.6.4.1, K.3.9.3.2                       7.22.7, K.3.6.4
mbsrtowcs_s function, K.3.9.3.2, K.3.9.3.2.1                 extended, 7.28.6, K.3.9.3
mbstate_t type, 7.21.2, 7.21.3, 7.21.6.1,                    restartable, 7.27.1, 7.28.6.3, K.3.9.3.1
     7.21.6.2, 7.27, 7.27.1, 7.28.1, 7.28.2.1,             multibyte/wide string conversion functions,
     7.28.2.2, 7.28.6, 7.28.6.2.1, 7.28.6.3,                    7.22.8, K.3.6.5
     7.28.6.3.1, 7.28.6.4                                    restartable, 7.28.6.4, K.3.9.3.2
mbstowcs function, 6.4.5, 7.22.8.1, 7.28.6.4               multidimensional array, 6.5.2.1
mbstowcs_s function, K.3.6.5.1                             multiplication assignment operator (*=), 6.5.16.2
mbtowc function, 6.4.4.4, 7.22.7.1, 7.22.7.2,              multiplication operator (*), 6.2.6.2, 6.5.5, F.3,
     7.22.8.1, 7.28.6.3                                         G.5.1
member access operators (. and ->), 6.5.2.3                multiplicative expressions, 6.5.5, G.5.1
member alignment, 6.7.2.1
memchr function, 7.23.5.1                                  n-char sequence, 7.22.1.3
memcmp function, 7.23.4, 7.23.4.1                          n-wchar sequence, 7.28.4.1.1
memcpy function, 7.23.2.1                                  name
memcpy_s function, K.3.7.1.1                                 external, 5.2.4.1, 6.4.2.1, 6.11.3
memmove function, 7.23.2.2                                   file, 7.21.3
memmove_s function, K.3.7.1.2                                internal, 5.2.4.1, 6.4.2.1
memory location, 3.14                                        label, 6.2.3
memory management functions, 7.22.3                          structure/union member, 6.2.3
memory_order type, 7.17.1, 7.17.3                          name spaces, 6.2.3
memset function, 7.23.6.1, K.3.7.4.1                       named label, 6.8.1
memset_s function, K.3.7.4.1                               NaN, 5.2.4.2.2
minimum functions, 7.12.12, F.10.9                         nan functions, 7.12.11.2, F.2.1, F.10.8.2
minus operator, unary, 6.5.3.3                             NAN macro, 7.12, F.2.1
miscellaneous functions                                    NDEBUG macro, 7.2
  string, 7.23.6, K.3.7.4                                  nearbyint functions, 7.12.9.3, 7.12.9.4, F.3,
  wide string, 7.28.4.6, K.3.9.2.4                              F.10.6.3
mktime function, 7.26.2.3                                  nearbyint type-generic macro, 7.24

[page 668]

nearest integer functions, 7.12.9, F.10.6                       operating system, 5.1.2.1, 7.22.4.8
negation operator (!), 6.5.3.3                                  operations on files, 7.21.4, K.3.5.1
negative zero, 6.2.6.2, 7.12.11.1                               operator, 6.4.6
new-line character, 5.1.1.2, 5.2.1, 6.4, 6.10, 6.10.4           operators, 6.5
new-line escape sequence (\n), 5.2.2, 6.4.4.4,                     additive, 6.2.6.2, 6.5.6
     7.4.1.10                                                      alignof, 6.5.3.4
nextafter functions, 7.12.11.3, 7.12.11.4, F.3,                    assignment, 6.5.16
     F.10.8.3                                                      associativity, 6.5
nextafter type-generic macro, 7.24                                 equality, 6.5.9
nexttoward functions, 7.12.11.4, F.3, F.10.8.4                     multiplicative, 6.2.6.2, 6.5.5, G.5.1
nexttoward type-generic macro, 7.24                                postfix, 6.5.2
no linkage, 6.2.2                                                  precedence, 6.5
no-return function, 6.7.4                                          preprocessing, 6.10.1, 6.10.3.2, 6.10.3.3, 6.10.9
non-stop floating-point control mode, 7.6.4.2                       relational, 6.5.8
nongraphic characters, 5.2.2, 6.4.4.4                              shift, 6.5.7
nonlocal jumps header, 7.13                                        sizeof, 6.5.3.4
norm, complex, 7.3.8.1                                             unary, 6.5.3
normalized broken-down time, K.3.8.1, K.3.8.2.1                    unary arithmetic, 6.5.3.3
not macro, 7.9                                                  optional features, see conditional features
not-equal-to operator, see inequality operator                  or macro, 7.9
not_eq macro, 7.9                                               OR operators
null character (\0), 5.2.1, 6.4.4.4, 6.4.5                         bitwise exclusive (^), 6.2.6.2, 6.5.11
  padding of binary stream, 7.21.2                                 bitwise exclusive assignment (^=), 6.5.16.2
NULL macro, 7.11, 7.19, 7.21.1, 7.22, 7.23.1,                      bitwise inclusive (|), 6.2.6.2, 6.5.12
     7.26.1, 7.28.1                                                bitwise inclusive assignment (|=), 6.5.16.2
null pointer, 6.3.2.3                                              logical (||), 5.1.2.4, 6.5.14
null pointer constant, 6.3.2.3                                  or_eq macro, 7.9
null preprocessing directive, 6.10.7                            order of allocated storage, 7.22.3
null statement, 6.8.3                                           order of evaluation, 6.5, 6.5.16, 6.10.3.2, 6.10.3.3,
null wide character, 7.1.1                                            see also sequence points
number classification macros, 7.12, 7.12.3.1                     ordinary identifier name space, 6.2.3
numeric conversion functions, 7.8.2.3, 7.22.1                   orientation of stream, 7.21.2, 7.28.3.5
  wide string, 7.8.2.4, 7.28.4.1                                out-of-bounds store, L.2.1
numerical limits, 5.2.4.2                                       outer scope, 6.2.1
                                                                over-aligned, 6.2.8
object, 3.15
object representation, 6.2.6.1                                  padding
object type, 6.2.5                                                binary stream, 7.21.2
object-like macro, 6.10.3                                         bits, 6.2.6.2, 7.20.1.1
observable behavior, 5.1.2.3                                      structure/union, 6.2.6.1, 6.7.2.1
obsolescence, 6.11, 7.30                                        parameter, 3.16
octal constant, 6.4.4.1                                           array, 6.9.1
octal digit, 6.4.4.1, 6.4.4.4                                     ellipsis, 6.7.6.3, 6.10.3
octal-character escape sequence (\octal digits),                  function, 6.5.2.2, 6.7, 6.9.1
     6.4.4.4                                                      macro, 6.10.3
offsetof macro, 7.19                                              main function, 5.1.2.2.1
on-off switch, 6.10.6                                             program, 5.1.2.2.1
once_flag type, 7.25.1                                          parameter type list, 6.7.6.3
ONCE_FLAG_INIT macro, 7.25.1                                    parentheses punctuator (( )), 6.7.6.3, 6.8.4, 6.8.5
ones' complement, 6.2.6.2                                       parenthesized expression, 6.5.1
operand, 6.4.6, 6.5                                             parse state, 7.21.2

[page 669]

perform a trap, 3.19.5                                        preprocessor, 6.10
permitted form of initializer, 6.6                            PRIcFASTN macros, 7.8.1
perror function, 7.21.10.4                                    PRIcLEASTN macros, 7.8.1
phase angle, complex, 7.3.9.1                                 PRIcMAX macros, 7.8.1
physical source lines, 5.1.1.2                                PRIcN macros, 7.8.1
placemarker, 6.10.3.3                                         PRIcPTR macros, 7.8.1
plus operator, unary, 6.5.3.3                                 primary expression, 6.5.1
pointer arithmetic, 6.5.6                                     printf function, 7.21.1, 7.21.6.3, 7.21.6.10,
pointer comparison, 6.5.8                                           K.3.5.3.3
pointer declarator, 6.7.6.1                                   printf_s function, K.3.5.3.3
pointer operator (->), 6.5.2.3                                printing character, 5.2.2, 7.4, 7.4.1.8
pointer to function, 6.5.2.2                                  printing wide character, 7.29.2
pointer type, 6.2.5                                           program diagnostics, 7.2.1
pointer type conversion, 6.3.2.1, 6.3.2.3                     program execution, 5.1.2.2.2, 5.1.2.3
pointer, null, 6.3.2.3                                        program file, 5.1.1.1
pole error, 7.12.1, 7.12.5.3, 7.12.6.7, 7.12.6.8,             program image, 5.1.1.2
     7.12.6.9, 7.12.6.10, 7.12.6.11, 7.12.7.4,                program name (argv[0]), 5.1.2.2.1
     7.12.8.3, 7.12.8.4                                       program parameters, 5.1.2.2.1
portability, 4, J                                             program startup, 5.1.2, 5.1.2.1, 5.1.2.2.1
position indicator, file, see file position indicator           program structure, 5.1.1.1
positive difference, 7.12.12.1                                program termination, 5.1.2, 5.1.2.1, 5.1.2.2.3,
positive difference functions, 7.12.12, F.10.9                      5.1.2.3
postfix decrement operator (--), 6.3.2.1, 6.5.2.4              program, conforming, 4
postfix expressions, 6.5.2                                     program, strictly conforming, 4
postfix increment operator (++), 6.3.2.1, 6.5.2.4              promotions
pow functions, 7.12.7.4, F.10.4.4                                default argument, 6.5.2.2
pow type-generic macro, 7.24                                     integer, 5.1.2.3, 6.3.1.1
power functions                                               prototype, see function prototype
  complex, 7.3.8, G.6.4                                       pseudo-random sequence functions, 7.22.2
  real, 7.12.7, F.10.4                                        PTRDIFF_MAX macro, 7.20.3
pp-number, 6.4.8                                              PTRDIFF_MIN macro, 7.20.3
pragma operator, 6.10.9                                       ptrdiff_t type, 7.17.1, 7.19, 7.20.3, 7.21.6.1,
pragma preprocessing directive, 6.10.6, 6.11.8                      7.21.6.2, 7.28.2.1, 7.28.2.2
precedence of operators, 6.5                                  punctuators, 6.4.6
precedence of syntax rules, 5.1.1.2                           putc function, 7.21.1, 7.21.7.7, 7.21.7.8
precision, 6.2.6.2, 6.3.1.1, 7.21.6.1, 7.28.2.1               putchar function, 7.21.1, 7.21.7.8
  excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                         puts function, 7.21.1, 7.21.7.9
predefined macro names, 6.10.8, 6.11.9                         putwc function, 7.21.1, 7.28.3.8, 7.28.3.9
prefix decrement operator (--), 6.3.2.1, 6.5.3.1               putwchar function, 7.21.1, 7.28.3.9
prefix increment operator (++), 6.3.2.1, 6.5.3.1
preprocessing concatenation, 6.10.3.3                         qsort function, 7.22.5, 7.22.5.2
preprocessing directives, 5.1.1.2, 6.10                       qsort_s function, K.3.6.3, K.3.6.3.2
preprocessing file, 5.1.1.1, 6.10                              qualified types, 6.2.5
preprocessing numbers, 6.4, 6.4.8                             qualified version of type, 6.2.5
preprocessing operators                                       question-mark escape sequence (\?), 6.4.4.4
  #, 6.10.3.2                                                 quick_exit function, 7.22.4.3, 7.22.4.4,
  ##, 6.10.3.3                                                     7.22.4.7
  _Pragma, 5.1.1.2, 6.10.9                                    quiet NaN, 5.2.4.2.2
  defined, 6.10.1
preprocessing tokens, 5.1.1.2, 6.4, 6.10                      raise function, 7.14, 7.14.1.1, 7.14.2.1, 7.22.4.1
preprocessing translation unit, 5.1.1.1                       rand function, 7.22, 7.22.2.1, 7.22.2.2

[page 670]

RAND_MAX macro, 7.22, 7.22.2.1                               restrict-qualified type, 6.2.5, 6.7.3
range                                                        return statement, 6.8.6.4, F.6
   excess, 5.2.4.2.2, 6.3.1.8, 6.8.6.4                       rewind function, 7.21.5.3, 7.21.7.10, 7.21.9.5,
range error, 7.12.1, 7.12.5.4, 7.12.5.5, 7.12.6.1,                 7.28.3.10
      7.12.6.2, 7.12.6.3, 7.12.6.5, 7.12.6.6,                right-shift assignment operator (>>=), 6.5.16.2
      7.12.6.13, 7.12.7.3, 7.12.7.4, 7.12.8.2,               right-shift operator (>>), 6.2.6.2, 6.5.7
      7.12.8.3, 7.12.8.4, 7.12.9.5, 7.12.9.7,                rint functions, 7.12.9.4, F.3, F.10.6.4
      7.12.11.3, 7.12.12.1, 7.12.13.1                        rint type-generic macro, 7.24
rank, see integer conversion rank                            round functions, 7.12.9.6, F.10.6.6
read-modify-write operations, 5.1.2.4                        round type-generic macro, 7.24
real floating type conversion, 6.3.1.4, 6.3.1.5,              rounding mode, floating point, 5.2.4.2.2
      6.3.1.7, F.3, F.4                                      RSIZE_MAX macro, K.3.3, K.3.4, K.3.5.1.2,
real floating types, 6.2.5                                          K.3.5.3.5, K.3.5.3.6, K.3.5.3.12, K.3.5.3.13,
real type domain, 6.2.5                                            K.3.5.4.1, K.3.6.2.1, K.3.6.3.1, K.3.6.3.2,
real types, 6.2.5                                                  K.3.6.4.1, K.3.6.5.1, K.3.6.5.2, K.3.7.1.1,
real-floating, 7.12.3                                               K.3.7.1.2, K.3.7.1.3, K.3.7.1.4, K.3.7.2.1,
realloc function, 7.22.3, 7.22.3.5                                 K.3.7.2.2, K.3.7.3.1, K.3.7.4.1, K.3.7.4.2,
recommended practice, 3.17                                         K.3.8.2.1, K.3.8.2.2, K.3.9.1.3, K.3.9.1.4,
recursion, 6.5.2.2                                                 K.3.9.1.8, K.3.9.1.9, K.3.9.2.1.1, K.3.9.2.1.2,
recursive function call, 6.5.2.2                                   K.3.9.2.1.3, K.3.9.2.1.4, K.3.9.2.2.1,
redefinition of macro, 6.10.3                                       K.3.9.2.2.2, K.3.9.2.3.1, K.3.9.3.1.1,
reentrancy, 5.1.2.3, 5.2.3                                         K.3.9.3.2.1, K.3.9.3.2.2
   library functions, 7.1.4                                  rsize_t type, K.3.3, K.3.4, K.3.5, K.3.5.3.2,
referenced type, 6.2.5                                             K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
register storage-class specifier, 6.7.1, 6.9                  runtime-constraint, 3.18
relational expressions, 6.5.8                                Runtime-constraint handling functions, K.3.6.1
relaxed atomic operations, 5.1.2.4                           rvalue, 6.3.2.1
release fence, 7.17.4
release operation, 5.1.2.4                                   same scope, 6.2.1
release sequence, 5.1.2.4                                    save calling environment function, 7.13.1
reliability of data, interrupted, 5.1.2.3                    scalar types, 6.2.5
remainder assignment operator (%=), 6.5.16.2                 scalbln function, 7.12.6.13, F.3, F.10.3.13
remainder functions, 7.12.10, F.10.7                         scalbln type-generic macro, 7.24
remainder functions, 7.12.10.2, 7.12.10.3, F.3,              scalbn function, 7.12.6.13, F.3, F.10.3.13
      F.10.7.2                                               scalbn type-generic macro, 7.24
remainder operator (%), 6.2.6.2, 6.5.5                       scanf function, 7.21.1, 7.21.6.4, 7.21.6.11
remainder type-generic macro, 7.24                           scanf_s function, K.3.5.3.4, K.3.5.3.11
remove function, 7.21.4.1, 7.21.4.4, K.3.5.1.2               scanlist, 7.21.6.2, 7.28.2.2
remquo functions, 7.12.10.3, F.3, F.10.7.3                   scanset, 7.21.6.2, 7.28.2.2
remquo type-generic macro, 7.24                              SCHAR_MAX macro, 5.2.4.2.1
rename function, 7.21.4.2                                    SCHAR_MIN macro, 5.2.4.2.1
representations of types, 6.2.6                              SCNcFASTN macros, 7.8.1
   pointer, 6.2.5                                            SCNcLEASTN macros, 7.8.1
rescanning and replacement, 6.10.3.4                         SCNcMAX macros, 7.8.1
reserved identifiers, 6.4.1, 7.1.3, K.3.1.2                   SCNcN macros, 7.8.1
restartable multibyte/wide character conversion              SCNcPTR macros, 7.8.1
      functions, 7.27.1, 7.28.6.3, K.3.9.3.1                 scope of identifier, 6.2.1, 6.9.2
restartable multibyte/wide string conversion                 search functions
      functions, 7.28.6.4, K.3.9.3.2                           string, 7.23.5, K.3.7.3
restore calling environment function, 7.13.2                   utility, 7.22.5, K.3.6.3
restrict type qualifier, 6.7.3, 6.7.3.1                         wide string, 7.28.4.5, K.3.9.2.3

[page 671]

SEEK_CUR macro, 7.21.1, 7.21.9.2                                 sign and magnitude, 6.2.6.2
SEEK_END macro, 7.21.1, 7.21.9.2                                 sign bit, 6.2.6.2
SEEK_SET macro, 7.21.1, 7.21.9.2                                 signal function, 7.14.1.1, 7.22.4.5, 7.22.4.7
selection statements, 6.8.4                                      signal handler, 5.1.2.3, 5.2.3, 7.14.1.1, 7.14.2.1
self-referential structure, 6.7.2.3                              signal handling functions, 7.14.1
semicolon punctuator (;), 6.7, 6.7.2.1, 6.8.3,                   signal.h header, 7.14, 7.30.6
      6.8.5, 6.8.6                                               signaling NaN, 5.2.4.2.2, F.2.1
separate compilation, 5.1.1.1                                    signals, 5.1.2.3, 5.2.3, 7.14.1
separate translation, 5.1.1.1                                    signbit macro, 7.12.3.6, F.3
sequence points, 5.1.2.3, 6.5.2.2, 6.5.13, 6.5.14,               signed char type, 6.2.5, 7.21.6.1, 7.21.6.2,
      6.5.15, 6.5.17, 6.7.3, 6.7.3.1, 6.7.6, 6.8,                     7.28.2.1, 7.28.2.2, K.3.5.3.2, K.3.9.1.2
      7.1.4, 7.21.6, 7.22.5, 7.28.2, C, K.3.6.3                  signed character, 6.3.1.1
sequenced after, see sequenced before                            signed integer types, 6.2.5, 6.3.1.3, 6.4.4.1
sequenced before, 5.1.2.3, 6.5, 6.5.2.2, 6.5.2.4,                signed type conversion, 6.3.1.1, 6.3.1.3, 6.3.1.4,
      6.5.16, see also indeterminately sequenced,                     6.3.1.8
      unsequenced                                                signed types, 6.2.5, 6.7.2
sequencing of statements, 6.8                                    significand part, 6.4.4.2
set_constraint_handler_s function,                               SIGSEGV macro, 7.14, 7.14.1.1
      K.3.1.4, K.3.6.1.1, K.3.6.1.2, K.3.6.1.3                   SIGTERM macro, 7.14
setbuf function, 7.21.3, 7.21.5.1, 7.21.5.5                      simple assignment operator (=), 6.5.16.1
setjmp macro, 7.1.3, 7.13.1.1, 7.13.2.1                          sin functions, 7.12.4.6, F.10.1.6
setjmp.h header, 7.13                                            sin type-generic macro, 7.24, G.7
setlocale function, 7.11.1.1, 7.11.2.1                           single-byte character, 3.7.1, 5.2.1.2
setvbuf function, 7.21.1, 7.21.3, 7.21.5.1,                      single-byte/wide character conversion functions,
      7.21.5.5, 7.21.5.6                                              7.28.6.1
shall, 4                                                         single-precision arithmetic, 5.1.2.3
shift expressions, 6.5.7                                         single-quote escape sequence (\'), 6.4.4.4, 6.4.5
shift sequence, 7.1.1                                            singularity, 7.12.1
shift states, 5.2.1.2                                            sinh functions, 7.12.5.5, F.10.2.5
short identifier, character, 5.2.4.1, 6.4.3                       sinh type-generic macro, 7.24, G.7
short int type, 6.2.5, 6.3.1.1, 6.7.2, 7.21.6.1,                 SIZE_MAX macro, 7.20.3
      7.21.6.2, 7.28.2.1, 7.28.2.2                               size_t type, 6.2.8, 6.5.3.4, 7.19, 7.20.3, 7.21.1,
short int type conversion, 6.3.1.1, 6.3.1.3,                          7.21.6.1, 7.21.6.2, 7.22, 7.23.1, 7.26.1, 7.27,
      6.3.1.4, 6.3.1.8                                                7.28.1, 7.28.2.1, 7.28.2.2, K.3.3, K.3.4,
SHRT_MAX macro, 5.2.4.2.1                                             K.3.5, K.3.6, K.3.7, K.3.8, K.3.9, K.3.9.1.2
SHRT_MIN macro, 5.2.4.2.1                                        sizeof operator, 6.3.2.1, 6.5.3, 6.5.3.4
side effects, 5.1.2.3, 6.2.6.1, 6.3.2.2, 6.5, 6.5.2.4,           snprintf function, 7.21.6.5, 7.21.6.12,
      6.5.16, 6.7.9, 6.8.3, 7.6, 7.6.1, 7.21.7.5,                     K.3.5.3.5
      7.21.7.7, 7.28.3.6, 7.28.3.8, F.8.1, F.9.1,                snprintf_s function, K.3.5.3.5, K.3.5.3.6
      F.9.3                                                      snwprintf_s function, K.3.9.1.3, K.3.9.1.4
SIG_ATOMIC_MAX macro, 7.20.3                                     sorting utility functions, 7.22.5, K.3.6.3
SIG_ATOMIC_MIN macro, 7.20.3                                     source character set, 5.1.1.2, 5.2.1
sig_atomic_t type, 5.1.2.3, 7.14, 7.14.1.1,                      source file, 5.1.1.1
      7.20.3                                                        name, 6.10.4, 6.10.8.1
SIG_DFL macro, 7.14, 7.14.1.1                                    source file inclusion, 6.10.2
SIG_ERR macro, 7.14, 7.14.1.1                                    source lines, 5.1.1.2
SIG_IGN macro, 7.14, 7.14.1.1                                    source text, 5.1.1.2
SIGABRT macro, 7.14, 7.22.4.1                                    space character (' '), 5.1.1.2, 5.2.1, 6.4, 7.4.1.3,
SIGFPE macro, 7.12.1, 7.14, 7.14.1.1, J.5.17                          7.4.1.10, 7.29.2.1.3
SIGILL macro, 7.14, 7.14.1.1                                     sprintf function, 7.21.6.6, 7.21.6.13, K.3.5.3.6
SIGINT macro, 7.14                                               sprintf_s function, K.3.5.3.5, K.3.5.3.6

[page 672]

sqrt functions, 7.12.7.5, F.3, F.10.4.5                         do, 6.8.5.2
sqrt type-generic macro, 7.24                                   else, 6.8.4.1
srand function, 7.22.2.2                                        expression, 6.8.3
sscanf function, 7.21.6.7, 7.21.6.14                            for, 6.8.5.3
sscanf_s function, K.3.5.3.7, K.3.5.3.14                        goto, 6.8.6.1
standard error stream, 7.21.1, 7.21.3, 7.21.10.4                if, 6.8.4.1
standard headers, 4, 7.1.2                                      iteration, 6.8.5
   <assert.h>, 7.2                                              jump, 6.8.6
   <complex.h>, 5.2.4.2.2, 6.10.8.3, 7.1.2, 7.3,                labeled, 6.8.1
        7.24, 7.30.1, G.6, J.5.17                               null, 6.8.3
   <ctype.h>, 7.4, 7.30.2                                       return, 6.8.6.4, F.6
   <errno.h>, 7.5, 7.30.3, K.3.2                                selection, 6.8.4
   <fenv.h>, 5.1.2.3, 5.2.4.2.2, 7.6, 7.12, F, H                sequencing, 6.8
   <float.h>, 4, 5.2.4.2.2, 7.7, 7.22.1.3,                      switch, 6.8.4.2
        7.28.4.1.1                                              while, 6.8.5.1
   <inttypes.h>, 7.8, 7.30.4                                 static assertions, 6.7.10
   <iso646.h>, 4, 7.9                                        static storage duration, 6.2.4
   <limits.h>, 4, 5.2.4.2.1, 6.2.5, 7.10                     static storage-class specifier, 6.2.2, 6.2.4, 6.7.1
   <locale.h>, 7.11, 7.30.5                                  static, in array declarators, 6.7.6.2, 6.7.6.3
   <math.h>, 5.2.4.2.2, 6.5, 7.12, 7.24, F, F.10,            static_assert declaration, 6.7.10
        J.5.17                                               static_assert macro, 7.2
   <setjmp.h>, 7.13                                          stdalign.h header, 4, 7.15
   <signal.h>, 7.14, 7.30.6                                  stdarg.h header, 4, 6.7.6.3, 7.16
   <stdalign.h>, 4, 7.15                                     stdatomic.h header, 6.10.8.3, 7.1.2, 7.17
   <stdarg.h>, 4, 6.7.6.3, 7.16                              stdbool.h header, 4, 7.18, 7.30.7, H
   <stdatomic.h>, 6.10.8.3, 7.1.2, 7.17                      STDC, 6.10.6, 6.11.8
   <stdbool.h>, 4, 7.18, 7.30.7, H                           stddef.h header, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,
   <stddef.h>, 4, 6.3.2.1, 6.3.2.3, 6.4.4.4,                       6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3
        6.4.5, 6.5.3.4, 6.5.6, 7.19, K.3.3                   stderr macro, 7.21.1, 7.21.2, 7.21.3
   <stdint.h>, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,                stdin macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.4,
        7.30.8, K.3.3, K.3.4                                       7.21.7.6, 7.28.2.12, 7.28.3.7, K.3.5.3.4,
   <stdio.h>, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5                    K.3.5.4.1, K.3.9.1.14
   <stdlib.h>, 5.2.4.2.2, 7.22, 7.30.10, F,                  stdint.h header, 4, 5.2.4.2, 6.10.1, 7.8, 7.20,
        K.3.1.4, K.3.6                                             7.30.8, K.3.3, K.3.4
   <string.h>, 7.23, 7.30.11, K.3.7                          stdio.h header, 5.2.4.2.2, 7.21, 7.30.9, F, K.3.5
   <tgmath.h>, 7.24, G.7                                     stdlib.h header, 5.2.4.2.2, 7.22, 7.30.10, F,
   <threads.h>, 6.10.8.3, 7.1.2, 7.25                              K.3.1.4, K.3.6
   <time.h>, 7.26, K.3.8                                     stdout macro, 7.21.1, 7.21.2, 7.21.3, 7.21.6.3,
   <uchar.h>, 6.4.4.4, 6.4.5, 7.27                                 7.21.7.8, 7.21.7.9, 7.28.2.11, 7.28.3.9
   <wchar.h>, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12,              storage duration, 6.2.4
        F, K.3.9                                             storage order of array, 6.5.2.1
   <wctype.h>, 7.29, 7.30.13                                 storage unit (bit-field), 6.2.6.1, 6.7.2.1
standard input stream, 7.21.1, 7.21.3                        storage-class specifiers, 6.7.1, 6.11.5
standard integer types, 6.2.5                                strcat function, 7.23.3.1
standard output stream, 7.21.1, 7.21.3                       strcat_s function, K.3.7.2.1
standard signed integer types, 6.2.5                         strchr function, 7.23.5.2
state-dependent encoding, 5.2.1.2, 7.22.7, K.3.6.4           strcmp function, 7.23.4, 7.23.4.2
statements, 6.8                                              strcoll function, 7.11.1.1, 7.23.4.3, 7.23.4.5
   break, 6.8.6.3                                            strcpy function, 7.23.2.3
   compound, 6.8.2                                           strcpy_s function, K.3.7.1.3
   continue, 6.8.6.2                                         strcspn function, 7.23.5.3

[page 673]

streams, 7.21.2, 7.22.4.4                                                7.22.1.4, 7.28.2.2
   fully buffered, 7.21.3                                          strtoull function, 7.8.2.3, 7.22.1.2, 7.22.1.4
   line buffered, 7.21.3                                           strtoumax function, 7.8.2.3
   orientation, 7.21.2                                             struct hack, see flexible array member
   standard error, 7.21.1, 7.21.3                                  struct lconv, 7.11
   standard input, 7.21.1, 7.21.3                                  struct tm, 7.26.1
   standard output, 7.21.1, 7.21.3                                 structure
   unbuffered, 7.21.3                                                 arrow operator (->), 6.5.2.3
strerror function, 7.21.10.4, 7.23.6.2                                content, 6.7.2.3
strerror_s function, K.3.7.4.2, K.3.7.4.3                             dot operator (.), 6.5.2.3
strerrorlen_s function, K.3.7.4.3                                     initialization, 6.7.9
strftime function, 7.11.1.1, 7.26.3, 7.26.3.5,                        member alignment, 6.7.2.1
      7.28.5.1, K.3.8.2, K.3.8.2.1, K.3.8.2.2                         member name space, 6.2.3
stricter, 6.2.8                                                       member operator (.), 6.3.2.1, 6.5.2.3
strictly conforming program, 4                                        pointer operator (->), 6.5.2.3
string, 7.1.1                                                         specifier, 6.7.2.1
   comparison functions, 7.23.4                                       tag, 6.2.3, 6.7.2.3
   concatenation functions, 7.23.3, K.3.7.2                           type, 6.2.5, 6.7.2.1
   conversion functions, 7.11.1.1                                  strxfrm function, 7.11.1.1, 7.23.4.5
   copying functions, 7.23.2, K.3.7.1                              subnormal floating-point numbers, 5.2.4.2.2
   library function conventions, 7.23.1                            subscripting, 6.5.2.1
   literal, 5.1.1.2, 5.2.1, 6.3.2.1, 6.4.5, 6.5.1, 6.7.9           subtraction assignment operator (-=), 6.5.16.2
   miscellaneous functions, 7.23.6, K.3.7.4                        subtraction operator (-), 6.2.6.2, 6.5.6, F.3, G.5.2
   numeric conversion functions, 7.8.2.3, 7.22.1                   suffix
   search functions, 7.23.5, K.3.7.3                                  floating constant, 6.4.4.2
string handling header, 7.23, K.3.7                                   integer constant, 6.4.4.1
string.h header, 7.23, 7.30.11, K.3.7                              switch body, 6.8.4.2
stringizing, 6.10.3.2, 6.10.9                                      switch case label, 6.8.1, 6.8.4.2
strlen function, 7.23.6.3                                          switch default label, 6.8.1, 6.8.4.2
strncat function, 7.23.3.2                                         switch statement, 6.8.1, 6.8.4.2
strncat_s function, K.3.7.2.2                                      swprintf function, 7.28.2.3, 7.28.2.7,
strncmp function, 7.23.4, 7.23.4.4                                       K.3.9.1.3, K.3.9.1.4
strncpy function, 7.23.2.4                                         swprintf_s function, K.3.9.1.3, K.3.9.1.4
strncpy_s function, K.3.7.1.4                                      swscanf function, 7.28.2.4, 7.28.2.8
strnlen_s function, K.3.7.4.4                                      swscanf_s function, K.3.9.1.5, K.3.9.1.10
stronger, 6.2.8                                                    symbols, 3
strpbrk function, 7.23.5.4                                         synchronization operation, 5.1.2.4
strrchr function, 7.23.5.5                                         synchronize with, 5.1.2.4
strspn function, 7.23.5.6                                          syntactic categories, 6.1
strstr function, 7.23.5.7                                          syntax notation, 6.1
strtod function, 7.12.11.2, 7.21.6.2, 7.22.1.3,                    syntax rule precedence, 5.1.1.2
      7.28.2.2, F.3                                                syntax summary, language, A
strtof function, 7.12.11.2, 7.22.1.3, F.3                          system function, 7.22.4.8
strtoimax function, 7.8.2.3
strtok function, 7.23.5.8                                          tab characters, 5.2.1, 6.4
strtok_s function, K.3.7.3.1                                       tag compatibility, 6.2.7
strtol function, 7.8.2.3, 7.21.6.2, 7.22.1.2,                      tag name space, 6.2.3
      7.22.1.4, 7.28.2.2                                           tags, 6.7.2.3
strtold function, 7.12.11.2, 7.22.1.3, F.3                         tan functions, 7.12.4.7, F.10.1.7
strtoll function, 7.8.2.3, 7.22.1.2, 7.22.1.4                      tan type-generic macro, 7.24, G.7
strtoul function, 7.8.2.3, 7.21.6.2, 7.22.1.2,                     tanh functions, 7.12.5.6, F.10.2.6

[page 674]

tanh type-generic macro, 7.24, G.7                            toupper function, 7.4.2.2
temporary lifetime, 6.2.4                                     towctrans function, 7.29.3.2.1, 7.29.3.2.2
tentative definition, 6.9.2                                    towlower function, 7.29.3.1.1, 7.29.3.2.1
terms, 3                                                      towupper function, 7.29.3.1.2, 7.29.3.2.1
text streams, 7.21.2, 7.21.7.10, 7.21.9.2, 7.21.9.4           translation environment, 5, 5.1.1
tgamma functions, 7.12.8.4, F.10.5.4                          translation limits, 5.2.4.1
tgamma type-generic macro, 7.24                               translation phases, 5.1.1.2
tgmath.h header, 7.24, G.7                                    translation unit, 5.1.1.1, 6.9
thrd_create function, 7.25.1, 7.25.5.1                        trap, see perform a trap
thrd_current function, 7.25.5.2                               trap representation, 3.19.4, 6.2.6.1, 6.2.6.2,
thrd_detach function, 7.25.5.3                                      6.3.2.3, 6.5.2.3
thrd_equal function, 7.25.5.4                                 trigonometric functions
thrd_exit function, 7.25.5.5                                     complex, 7.3.5, G.6.1
thrd_join function, 7.25.5.6                                     real, 7.12.4, F.10.1
thrd_sleep function, 7.25.5.7                                 trigraph sequences, 5.1.1.2, 5.2.1.1
thrd_start_t type, 7.25.1                                     true macro, 7.18
thrd_t type, 7.25.1                                           trunc functions, 7.12.9.8, F.10.6.8
thrd_yield function, 7.25.5.8                                 trunc type-generic macro, 7.24
thread of execution, 5.1.2.4, 7.1.4, 7.6, 7.22.4.6            truncation, 6.3.1.4, 7.12.9.8, 7.21.3, 7.21.5.3
thread storage duration, 6.2.4, 7.6                           truncation toward zero, 6.5.5
threads header, 7.25                                          tss_create function, 7.25.6.1
threads.h header, 6.10.8.3, 7.1.2, 7.25                       tss_delete function, 7.25.6.2
time                                                          TSS_DTOR_ITERATIONS macro, 7.25.1
   broken down, 7.26.1, 7.26.2.3, 7.26.3, 7.26.3.1,           tss_dtor_t type, 7.25.1
         7.26.3.3, 7.26.3.4, 7.26.3.5, K.3.8.2.1,             tss_get function, 7.25.6.3
         K.3.8.2.3, K.3.8.2.4                                 tss_set function, 7.25.6.4
   calendar, 7.26.1, 7.26.2.2, 7.26.2.3, 7.26.2.4,            tss_t type, 7.25.1
         7.26.3.2, 7.26.3.3, 7.26.3.4, K.3.8.2.2,             two's complement, 6.2.6.2, 7.20.1.1
         K.3.8.2.3, K.3.8.2.4                                 type category, 6.2.5
   components, 7.26.1, K.3.8.1                                type conversion, 6.3
   conversion functions, 7.26.3, K.3.8.2                      type definitions, 6.7.8
      wide character, 7.28.5                                  type domain, 6.2.5, G.2
   local, 7.26.1                                              type names, 6.7.7
   manipulation functions, 7.26.2                             type punning, 6.5.2.3
   normalized broken down, K.3.8.1, K.3.8.2.1                 type qualifiers, 6.7.3
time function, 7.26.2.4                                       type specifiers, 6.7.2
time.h header, 7.26, K.3.8                                    type-generic macro, 7.24, G.7
time_t type, 7.26.1                                           typedef declaration, 6.7.8
TIME_UTC macro, 7.25.7.1                                      typedef storage-class specifier, 6.7.1, 6.7.8
tm structure type, 7.26.1, 7.28.1, K.3.8.1                    types, 6.2.5
TMP_MAX macro, 7.21.1, 7.21.4.3, 7.21.4.4                        atomic, 5.1.2.3, 6.2.5, 6.2.6.1, 6.3.2.1, 6.5.2.3,
TMP_MAX_S macro, K.3.5, K.3.5.1.1, K.3.5.1.2                           6.5.2.4, 6.5.16.2, 6.7.2.4, 6.10.8.3, 7.17.6
tmpfile function, 7.21.4.3, 7.22.4.4                             character, 6.7.9
tmpfile_s function, K.3.5.1.1, K.3.5.1.2                         compatible, 6.2.7, 6.7.2, 6.7.3, 6.7.6
tmpnam function, 7.21.1, 7.21.4.3, 7.21.4.4,                     complex, 6.2.5, G
      K.3.5.1.2                                                  composite, 6.2.7
tmpnam_s function, K.3.5, K.3.5.1.1, K.3.5.1.2                   const qualified, 6.7.3
token, 5.1.1.2, 6.4, see also preprocessing tokens               conversions, 6.3
token concatenation, 6.10.3.3                                    imaginary, G
token pasting, 6.10.3.3                                          restrict qualified, 6.7.3
tolower function, 7.4.2.1                                        volatile qualified, 6.7.3

[page 675]

uchar.h header, 6.4.4.4, 6.4.5, 7.27                      universal character name, 6.4.3
UCHAR_MAX macro, 5.2.4.2.1                                unnormalized floating-point numbers, 5.2.4.2.2
UINT_FASTN_MAX macros, 7.20.2.3                           unqualified type, 6.2.5
uint_fastN_t types, 7.20.1.3                              unqualified version of type, 6.2.5
uint_least16_t type, 7.27                                 unsequenced, 5.1.2.3, 6.5, 6.5.16, see also
uint_least32_t type, 7.27                                       indeterminately sequenced, sequenced
UINT_LEASTN_MAX macros, 7.20.2.2                                before
uint_leastN_t types, 7.20.1.2                             unsigned char type, K.3.5.3.2, K.3.9.1.2
UINT_MAX macro, 5.2.4.2.1                                 unsigned integer suffix, u or U, 6.4.4.1
UINTMAX_C macro, 7.20.4.2                                 unsigned integer types, 6.2.5, 6.3.1.3, 6.4.4.1
UINTMAX_MAX macro, 7.8.2.3, 7.8.2.4, 7.20.2.5             unsigned type conversion, 6.3.1.1, 6.3.1.3,
uintmax_t type, 7.20.1.5, 7.21.6.1, 7.21.6.2,                   6.3.1.4, 6.3.1.8
     7.28.2.1, 7.28.2.2                                   unsigned types, 6.2.5, 6.7.2, 7.21.6.1, 7.21.6.2,
UINTN_C macros, 7.20.4.1                                        7.28.2.1, 7.28.2.2
UINTN_MAX macros, 7.20.2.1                                unspecified behavior, 3.4.4, 4, J.1
uintN_t types, 7.20.1.1                                   unspecified value, 3.19.3
UINTPTR_MAX macro, 7.20.2.4                               uppercase letter, 5.2.1
uintptr_t type, 7.20.1.4                                  use of library functions, 7.1.4
ULLONG_MAX macro, 5.2.4.2.1, 7.22.1.4,                    USHRT_MAX macro, 5.2.4.2.1
     7.28.4.1.2                                           usual arithmetic conversions, 6.3.1.8, 6.5.5, 6.5.6,
ULONG_MAX macro, 5.2.4.2.1, 7.22.1.4,                           6.5.8, 6.5.9, 6.5.10, 6.5.11, 6.5.12, 6.5.15
     7.28.4.1.2                                           UTF-16, 6.10.8.2
unary arithmetic operators, 6.5.3.3                       UTF-32, 6.10.8.2
unary expression, 6.5.3                                   UTF-8 string literal, see string literal
unary minus operator (-), 6.5.3.3, F.3                    utilities, general, 7.22, K.3.6
unary operators, 6.5.3                                       wide string, 7.28.4, K.3.9.2
unary plus operator (+), 6.5.3.3
unbuffered stream, 7.21.3                                 va_arg macro, 7.16, 7.16.1, 7.16.1.1, 7.16.1.2,
undef preprocessing directive, 6.10.3.5, 7.1.3,                7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
     7.1.4                                                     7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
undefined behavior, 3.4.3, 4, J.2                               7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
underscore character, 6.4.2.1                                  7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
underscore, leading, in identifier, 7.1.3                       K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
ungetc function, 7.21.1, 7.21.7.10, 7.21.9.2,             va_copy macro, 7.1.3, 7.16, 7.16.1, 7.16.1.1,
     7.21.9.3                                                  7.16.1.2, 7.16.1.3
ungetwc function, 7.21.1, 7.28.3.10                       va_end macro, 7.1.3, 7.16, 7.16.1, 7.16.1.3,
Unicode, 7.27, see also char16_t type,                         7.16.1.4, 7.21.6.8, 7.21.6.9, 7.21.6.10,
     char32_t type, wchar_t type                               7.21.6.11, 7.21.6.12, 7.21.6.13, 7.21.6.14,
Unicode required set, 6.10.8.2                                 7.28.2.5, 7.28.2.6, 7.28.2.7, 7.28.2.8,
union                                                          7.28.2.9, 7.28.2.10, K.3.5.3.9, K.3.5.3.11,
  arrow operator (->), 6.5.2.3                                 K.3.5.3.14, K.3.9.1.7, K.3.9.1.10, K.3.9.1.12
  content, 6.7.2.3                                        va_list type, 7.16, 7.16.1.3
  dot operator (.), 6.5.2.3                               va_start macro, 7.16, 7.16.1, 7.16.1.1,
  initialization, 6.7.9                                        7.16.1.2, 7.16.1.3, 7.16.1.4, 7.21.6.8,
  member alignment, 6.7.2.1                                    7.21.6.9, 7.21.6.10, 7.21.6.11, 7.21.6.12,
  member name space, 6.2.3                                     7.21.6.13, 7.21.6.14, 7.28.2.5, 7.28.2.6,
  member operator (.), 6.3.2.1, 6.5.2.3                        7.28.2.7, 7.28.2.8, 7.28.2.9, 7.28.2.10,
  pointer operator (->), 6.5.2.3                               K.3.5.3.9, K.3.5.3.11, K.3.5.3.14, K.3.9.1.7,
  specifier, 6.7.2.1                                            K.3.9.1.10, K.3.9.1.12
  tag, 6.2.3, 6.7.2.3                                     value, 3.19
  type, 6.2.5, 6.7.2.1                                    value bits, 6.2.6.2

[page 676]

variable arguments, 6.10.3, 7.16                             vswscanf function, 7.28.2.8
variable arguments header, 7.16                              vswscanf_s function, K.3.9.1.10
variable length array, 6.7.6, 6.7.6.2, 6.10.8.3              vwprintf function, 7.21.1, 7.28.2.9, K.3.9.1.11
variably modified type, 6.7.6, 6.7.6.2, 6.10.8.3              vwprintf_s function, K.3.9.1.11
vertical-tab character, 5.2.1, 6.4                           vwscanf function, 7.21.1, 7.28.2.10, 7.28.3.10
vertical-tab escape sequence (\v), 5.2.2, 6.4.4.4,           vwscanf_s function, K.3.9.1.12
     7.4.1.10
vfprintf function, 7.21.1, 7.21.6.8, K.3.5.3.8               warnings, I
vfprintf_s function, K.3.5.3.8, K.3.5.3.9,                   wchar.h header, 5.2.4.2.2, 7.21.1, 7.28, 7.30.12,
     K.3.5.3.11, K.3.5.3.14                                      F, K.3.9
vfscanf function, 7.21.1, 7.21.6.8, 7.21.6.9                 WCHAR_MAX macro, 7.20.3, 7.28.1
vfscanf_s function, K.3.5.3.9, K.3.5.3.11,                   WCHAR_MIN macro, 7.20.3, 7.28.1
     K.3.5.3.14                                              wchar_t type, 3.7.3, 6.4.5, 6.7.9, 6.10.8.2, 7.19,
vfwprintf function, 7.21.1, 7.28.2.5, K.3.9.1.6                  7.20.3, 7.21.6.1, 7.21.6.2, 7.22, 7.28.1,
vfwprintf_s function, K.3.9.1.6                                  7.28.2.1, 7.28.2.2
vfwscanf function, 7.21.1, 7.28.2.6, 7.28.3.10               wcrtomb function, 7.21.3, 7.21.6.2, 7.28.2.2,
vfwscanf_s function, K.3.9.1.7                                   7.28.6.3.3, 7.28.6.4.2, K.3.6.5.2, K.3.9.3.1,
visibility of identifier, 6.2.1                                   K.3.9.3.2.2
visible sequence of side effects, 5.1.2.4                    wcrtomb_s function, K.3.9.3.1, K.3.9.3.1.1
visible side effect, 5.1.2.4                                 wcscat function, 7.28.4.3.1
VLA, see variable length array                               wcscat_s function, K.3.9.2.2.1
void expression, 6.3.2.2                                     wcschr function, 7.28.4.5.1
void function parameter, 6.7.6.3                             wcscmp function, 7.28.4.4.1, 7.28.4.4.4
void type, 6.2.5, 6.3.2.2, 6.7.2, K.3.5.3.2,                 wcscoll function, 7.28.4.4.2, 7.28.4.4.4
     K.3.9.1.2                                               wcscpy function, 7.28.4.2.1
void type conversion, 6.3.2.2                                wcscpy_s function, K.3.9.2.1.1
volatile storage, 5.1.2.3                                    wcscspn function, 7.28.4.5.2
volatile type qualifier, 6.7.3                                wcsftime function, 7.11.1.1, 7.28.5.1
volatile-qualified type, 6.2.5, 6.7.3                         wcslen function, 7.28.4.6.1
vprintf function, 7.21.1, 7.21.6.8, 7.21.6.10,               wcsncat function, 7.28.4.3.2
     K.3.5.3.10                                              wcsncat_s function, K.3.9.2.2.2
vprintf_s function, K.3.5.3.9, K.3.5.3.10,                   wcsncmp function, 7.28.4.4.3
     K.3.5.3.11, K.3.5.3.14                                  wcsncpy function, 7.28.4.2.2
vscanf function, 7.21.1, 7.21.6.8, 7.21.6.11                 wcsncpy_s function, K.3.9.2.1.2
vscanf_s function, K.3.5.3.9, K.3.5.3.11,                    wcsnlen_s function, K.3.9.2.4.1
     K.3.5.3.14                                              wcspbrk function, 7.28.4.5.3
vsnprintf function, 7.21.6.8, 7.21.6.12,                     wcsrchr function, 7.28.4.5.4
     K.3.5.3.12                                              wcsrtombs function, 7.28.6.4.2, K.3.9.3.2
vsnprintf_s function, K.3.5.3.9, K.3.5.3.11,                 wcsrtombs_s function, K.3.9.3.2, K.3.9.3.2.2
     K.3.5.3.12, K.3.5.3.13, K.3.5.3.14                      wcsspn function, 7.28.4.5.5
vsnwprintf_s function, K.3.9.1.8, K.3.9.1.9                  wcsstr function, 7.28.4.5.6
vsprintf function, 7.21.6.8, 7.21.6.13,                      wcstod function, 7.21.6.2, 7.28.2.2
     K.3.5.3.13                                              wcstod function, 7.28.4.1.1
vsprintf_s function, K.3.5.3.9, K.3.5.3.11,                  wcstof function, 7.28.4.1.1
     K.3.5.3.12, K.3.5.3.13, K.3.5.3.14                      wcstoimax function, 7.8.2.4
vsscanf function, 7.21.6.8, 7.21.6.14                        wcstok function, 7.28.4.5.7
vsscanf_s function, K.3.5.3.9, K.3.5.3.11,                   wcstok_s function, K.3.9.2.3.1
     K.3.5.3.14                                              wcstol function, 7.8.2.4, 7.21.6.2, 7.28.2.2,
vswprintf function, 7.28.2.7, K.3.9.1.8,                         7.28.4.1.2
     K.3.9.1.9                                               wcstold function, 7.28.4.1.1
vswprintf_s function, K.3.9.1.8, K.3.9.1.9                   wcstoll function, 7.8.2.4, 7.28.4.1.2

[page 677]

wcstombs function, 7.22.8.2, 7.28.6.4                           7.29.1
wcstombs_s function, K.3.6.5.2                               wmemchr function, 7.28.4.5.8
wcstoul function, 7.8.2.4, 7.21.6.2, 7.28.2.2,               wmemcmp function, 7.28.4.4.5
     7.28.4.1.2                                              wmemcpy function, 7.28.4.2.3
wcstoull function, 7.8.2.4, 7.28.4.1.2                       wmemcpy_s function, K.3.9.2.1.3
wcstoumax function, 7.8.2.4                                  wmemmove function, 7.28.4.2.4
wcsxfrm function, 7.28.4.4.4                                 wmemmove_s function, K.3.9.2.1.4
wctob function, 7.28.6.1.2, 7.29.2.1                         wmemset function, 7.28.4.6.2
wctomb function, 7.22.7.3, 7.22.8.2, 7.28.6.3                wprintf function, 7.21.1, 7.28.2.9, 7.28.2.11,
wctomb_s function, K.3.6.4.1                                    K.3.9.1.13
wctrans function, 7.29.3.2.1, 7.29.3.2.2                     wprintf_s function, K.3.9.1.13
wctrans_t type, 7.29.1, 7.29.3.2.2                           wscanf function, 7.21.1, 7.28.2.10, 7.28.2.12,
wctype function, 7.29.2.2.1, 7.29.2.2.2                         7.28.3.10
wctype.h header, 7.29, 7.30.13                               wscanf_s function, K.3.9.1.12, K.3.9.1.14
wctype_t type, 7.29.1, 7.29.2.2.2
weaker, 6.2.8                                                xor macro, 7.9
WEOF macro, 7.28.1, 7.28.3.1, 7.28.3.3, 7.28.3.6,            xor_eq macro, 7.9
     7.28.3.7, 7.28.3.8, 7.28.3.9, 7.28.3.10,                xtime type, 7.25.1, 7.25.3.5, 7.25.4.4, 7.25.5.7,
     7.28.6.1.1, 7.29.1                                          7.25.7.1
while statement, 6.8.5.1                                     xtime_get function, 7.25.7.1
white space, 5.1.1.2, 6.4, 6.10, 7.4.1.10,
     7.29.2.1.10
white-space characters, 6.4
wide character, 3.7.3
  case mapping functions, 7.29.3.1
     extensible, 7.29.3.2
  classification functions, 7.29.2.1
     extensible, 7.29.2.2
  constant, 6.4.4.4
  formatted input/output functions, 7.28.2,
        K.3.9.1
  input functions, 7.21.1
  input/output functions, 7.21.1, 7.28.3
  output functions, 7.21.1
  single-byte conversion functions, 7.28.6.1
wide string, 7.1.1
wide string comparison functions, 7.28.4.4
wide string concatenation functions, 7.28.4.3,
     K.3.9.2.2
wide string copying functions, 7.28.4.2, K.3.9.2.1
wide string literal, see string literal
wide string miscellaneous functions, 7.28.4.6,
     K.3.9.2.4
wide string numeric conversion functions, 7.8.2.4,
     7.28.4.1
wide string search functions, 7.28.4.5, K.3.9.2.3
wide-oriented stream, 7.21.2
width, 6.2.6.2
WINT_MAX macro, 7.20.3
WINT_MIN macro, 7.20.3
wint_t type, 7.20.3, 7.21.6.1, 7.28.1, 7.28.2.1,

[page 678]