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2 <html>
4 <head>
9 </head>
11 <body>
13 <hr>
14 <h1>
16 Lua 5.1 Reference Manual
17 </h1>
19 by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes
20 <p>
21 <small>
23 Freely available under the terms of the
25 </small>
26 <hr>
27 <p>
30 ·
32 ·
35 <!-- ====================================================================== -->
36 <p>
38 <!-- $Id: manual.html,v 1.1.1.2 2012/03/15 00:08:20 alnsn Exp $ -->
45 <p>
46 Lua is an extension programming language designed to support
47 general procedural programming with data description
48 facilities.
49 It also offers good support for object-oriented programming,
50 functional programming, and data-driven programming.
51 Lua is intended to be used as a powerful, light-weight
52 scripting language for any program that needs one.
54 (that is, in the common subset of ANSI C and C++).
57 <p>
58 Being an extension language, Lua has no notion of a "main" program:
61 This host program can invoke functions to execute a piece of Lua code,
62 can write and read Lua variables,
63 and can register C functions to be called by Lua code.
64 Through the use of C functions, Lua can be augmented to cope with
65 a wide range of different domains,
66 thus creating customized programming languages sharing a syntactical framework.
68 which uses the Lua library to offer a complete, stand-alone Lua interpreter.
71 <p>
72 Lua is free software,
73 and is provided as usual with no guarantees,
74 as stated in its license.
75 The implementation described in this manual is available
79 <p>
80 Like any other reference manual,
81 this document is dry in places.
82 For a discussion of the decisions behind the design of Lua,
83 see the technical papers available at Lua's web site.
84 For a detailed introduction to programming in Lua,
91 <p>
92 This section describes the lexis, the syntax, and the semantics of Lua.
93 In other words,
94 this section describes
95 which tokens are valid,
96 how they can be combined,
97 and what their combinations mean.
100 <p>
101 The language constructs will be explained using the usual extended BNF notation,
102 in which
105 Non-terminals are shown like non-terminal,
109 at the end of this manual.
115 <p>
118 in Lua can be any string of letters,
119 digits, and underscores,
120 not beginning with a digit.
121 This coincides with the definition of names in most languages.
122 (The definition of letter depends on the current locale:
123 any character considered alphabetic by the current locale
124 can be used in an identifier.)
125 Identifiers are used to name variables and table fields.
128 <p>
130 and cannot be used as names:
133 <pre>
134 and break do else elseif
135 end false for function if
136 in local nil not or
137 repeat return then true until while
138 </pre>
140 <p>
141 Lua is a case-sensitive language:
143 are two different, valid names.
144 As a convention, names starting with an underscore followed by
146 are reserved for internal global variables used by Lua.
149 <p>
150 The following strings denote other tokens:
152 <pre>
153 + - * / % ^ #
155 ( ) { } [ ]
156 ; : , . .. ...
157 </pre>
159 <p>
161 can be delimited by matching single or double quotes,
162 and can contain the following C-like escape sequences:
172 and '<code>\'</code>' (apostrophe [single quote]).
173 Moreover, a backslash followed by a real newline
174 results in a newline in the string.
175 A character in a string can also be specified by its numerical value
176 using the escape sequence <code>\<em>ddd</em></code>,
177 where <em>ddd</em> is a sequence of up to three decimal digits.
178 (Note that if a numerical escape is to be followed by a digit,
179 it must be expressed using exactly three digits.)
180 Strings in Lua can contain any 8-bit value, including embedded zeros,
181 which can be specified as '<code>\0</code>'.
184 <p>
185 Literal strings can also be defined using a long format
186 enclosed by <em>long brackets</em>.
187 We define an <em>opening long bracket of level <em>n</em></em> as an opening
188 square bracket followed by <em>n</em> equal signs followed by another
189 opening square bracket.
190 So, an opening long bracket of level 0 is written as <code>[[</code>,
191 an opening long bracket of level 1 is written as <code>[=[</code>,
192 and so on.
193 A <em>closing long bracket</em> is defined similarly;
194 for instance, a closing long bracket of level 4 is written as <code>]====]</code>.
195 A long string starts with an opening long bracket of any level and
196 ends at the first closing long bracket of the same level.
197 Literals in this bracketed form can run for several lines,
198 do not interpret any escape sequences,
199 and ignore long brackets of any other level.
200 They can contain anything except a closing bracket of the proper level.
203 <p>
204 For convenience,
205 when the opening long bracket is immediately followed by a newline,
206 the newline is not included in the string.
207 As an example, in a system using ASCII
208 (in which '<code>a</code>' is coded as 97,
209 newline is coded as 10, and '<code>1</code>' is coded as 49),
210 the five literal strings below denote the same string:
212 <pre>
213 a = 'alo\n123"'
215 a = '\97lo\10\04923"'
216 a = [[alo
218 a = [==[
219 alo
220 123"]==]
221 </pre>
223 <p>
225 and an optional decimal exponent.
226 Lua also accepts integer hexadecimal constants,
228 Examples of valid numerical constants are
230 <pre>
232 </pre>
234 <p>
236 anywhere outside a string.
239 which runs until the end of the line.
241 which runs until the corresponding closing long bracket.
242 Long comments are frequently used to disable code temporarily.
250 <p>
252 This means that
253 variables do not have types; only values do.
254 There are no type definitions in the language.
255 All values carry their own type.
258 <p>
260 This means that all values can be stored in variables,
261 passed as arguments to other functions, and returned as results.
264 <p>
265 There are eight basic types in Lua:
270 whose main property is to be different from any other value;
271 it usually represents the absence of a useful value.
274 any other value makes it true.
276 (It is easy to build Lua interpreters that use other
277 internal representations for numbers,
278 such as single-precision float or long integers;
282 Lua is 8-bit clean:
283 strings can contain any 8-bit character,
287 <p>
288 Lua can call (and manipulate) functions written in Lua and
289 functions written in C
293 <p>
295 be stored in Lua variables.
296 This type corresponds to a block of raw memory
297 and has no pre-defined operations in Lua,
298 except assignment and identity test.
300 the programmer can define operations for userdata values
302 Userdata values cannot be created or modified in Lua,
303 only through the C API.
304 This guarantees the integrity of data owned by the host program.
307 <p>
310 Do not confuse Lua threads with operating-system threads.
311 Lua supports coroutines on all systems,
312 even those that do not support threads.
315 <p>
317 that is, arrays that can be indexed not only with numbers,
321 Tables are the sole data structuring mechanism in Lua;
322 they can be used to represent ordinary arrays,
323 symbol tables, sets, records, graphs, trees, etc.
324 To represent records, Lua uses the field name as an index.
325 The language supports this representation by
327 There are several convenient ways to create tables in Lua
331 <p>
332 Like indices,
334 In particular,
335 because functions are first-class values,
336 table fields can contain functions.
340 <p>
344 Assignment, parameter passing, and function returns
345 always manipulate references to such values;
346 these operations do not imply any kind of copy.
349 <p>
350 The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type
351 of a given value.
357 <p>
358 Lua provides automatic conversion between
359 string and number values at run time.
360 Any arithmetic operation applied to a string tries to convert
361 this string to a number, following the usual conversion rules.
362 Conversely, whenever a number is used where a string is expected,
363 the number is converted to a string, in a reasonable format.
364 For complete control over how numbers are converted to strings,
376 <p>
377 Variables are places that store values.
379 There are three kinds of variables in Lua:
380 global variables, local variables, and table fields.
383 <p>
384 A single name can denote a global variable or a local variable
385 (or a function's formal parameter,
386 which is a particular kind of local variable):
388 <pre>
389 var ::= Name
390 </pre><p>
394 <p>
395 Any variable is assumed to be global unless explicitly declared
398 local variables can be freely accessed by functions
402 <p>
406 <p>
407 Square brackets are used to index a table:
409 <pre>
411 </pre><p>
412 The meaning of accesses to global variables
413 and table fields can be changed via metatables.
418 This function is not defined or callable in Lua.
419 We use it here only for explanatory purposes.)
422 <p>
426 <pre>
428 </pre>
430 <p>
431 All global variables live as fields in ordinary Lua tables,
434 Each function has its own reference to an environment,
435 so that all global variables in this function
436 will refer to this environment table.
437 When a function is created,
438 it inherits the environment from the function that created it.
439 To get the environment table of a Lua function,
441 To replace it,
443 (You can only manipulate the environment of C functions
447 <p>
450 which in turn is equivalent to
452 <pre>
453 gettable_event(_env, "x")
454 </pre><p>
458 This function is not defined or callable in Lua.
460 We use them here only for explanatory purposes.)
468 <p>
469 Lua supports an almost conventional set of statements,
470 similar to those in Pascal or C.
471 This set includes
472 assignments, control structures, function calls,
473 and variable declarations.
479 <p>
481 A chunk is simply a sequence of statements,
482 which are executed sequentially.
483 Each statement can be optionally followed by a semicolon:
485 <pre>
487 </pre><p>
491 <p>
492 Lua handles a chunk as the body of an anonymous function
493 with a variable number of arguments
495 As such, chunks can define local variables,
496 receive arguments, and return values.
499 <p>
500 A chunk can be stored in a file or in a string inside the host program.
501 To execute a chunk,
502 Lua first pre-compiles the chunk into instructions for a virtual machine,
503 and then it executes the compiled code
504 with an interpreter for the virtual machine.
507 <p>
508 Chunks can also be pre-compiled into binary form;
510 Programs in source and compiled forms are interchangeable;
511 Lua automatically detects the file type and acts accordingly.
519 A block is a list of statements;
520 syntactically, a block is the same as a chunk:
522 <pre>
523 block ::= chunk
524 </pre>
526 <p>
527 A block can be explicitly delimited to produce a single statement:
529 <pre>
531 </pre><p>
532 Explicit blocks are useful
533 to control the scope of variable declarations.
534 Explicit blocks are also sometimes used to
544 <p>
545 Lua allows multiple assignments.
546 Therefore, the syntax for assignment
547 defines a list of variables on the left side
548 and a list of expressions on the right side.
549 The elements in both lists are separated by commas:
551 <pre>
555 </pre><p>
559 <p>
560 Before the assignment,
562 the list of variables.
563 If there are more values than needed,
564 the excess values are thrown away.
565 If there are fewer values than needed,
567 If the list of expressions ends with a function call,
568 then all values returned by that call enter the list of values,
569 before the adjustment
573 <p>
574 The assignment statement first evaluates all its expressions
575 and only then are the assignments performed.
576 Thus the code
578 <pre>
579 i = 3
581 </pre><p>
585 Similarly, the line
587 <pre>
588 x, y = y, x
589 </pre><p>
591 and
593 <pre>
594 x, y, z = y, z, x
595 </pre><p>
599 <p>
600 The meaning of assignments to global variables
601 and table fields can be changed via metatables.
606 This function is not defined or callable in Lua.
607 We use it here only for explanatory purposes.)
610 <p>
612 is equivalent to the assignment
614 which in turn is equivalent to
616 <pre>
617 settable_event(_env, "x", val)
618 </pre><p>
621 We use it here only for explanatory purposes.)
628 The control structures
630 familiar syntax:
635 <pre>
638 stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b>
639 </pre><p>
643 <p>
644 The condition expression of a
645 control structure can return any value.
648 (in particular, the number 0 and the empty string are also true).
651 <p>
654 but only after the condition.
655 So, the condition can refer to local variables
656 declared inside the loop block.
659 <p>
661 from a function or a chunk (which is just a function).
663 Functions and chunks can return more than one value,
666 <pre>
668 </pre>
670 <p>
673 skipping to the next statement after the loop:
676 <pre>
678 </pre><p>
682 <p>
686 middle of a block,
687 then an explicit inner block can be used,
688 as in the idioms
691 their (inner) blocks.
699 <p>
702 one numeric and one generic.
705 <p>
707 control variable runs through an arithmetic progression.
708 It has the following syntax:
710 <pre>
711 stat ::= <b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b>
712 </pre><p>
718 <pre>
720 </pre><p>
721 is equivalent to the code:
723 <pre>
724 do
725 local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>)
727 while (<em>step</em> > 0 and <em>var</em> <= <em>limit</em>) or (<em>step</em> <= 0 and <em>var</em> >= <em>limit</em>) do
731 end
732 end
733 </pre><p>
734 Note the following:
736 <ul>
738 <li>
739 All three control expressions are evaluated only once,
740 before the loop starts.
741 They must all result in numbers.
742 </li>
744 <li>
745 <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables.
746 The names shown here are for explanatory purposes only.
747 </li>
749 <li>
750 If the third expression (the step) is absent,
752 </li>
754 <li>
756 </li>
758 <li>
761 If you need this value,
762 assign it to another variable before breaking or exiting the loop.
763 </li>
765 </ul>
767 <p>
770 On each iteration, the iterator function is called to produce a new value,
774 <pre>
777 </pre><p>
780 <pre>
781 for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end
782 </pre><p>
783 is equivalent to the code:
785 <pre>
786 do
788 while true do
789 local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>)
793 end
794 end
795 </pre><p>
796 Note the following:
798 <ul>
800 <li>
805 </li>
807 <li>
808 <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables.
809 The names are here for explanatory purposes only.
810 </li>
812 <li>
814 </li>
816 <li>
819 If you need these values,
820 then assign them to other variables before breaking or exiting the loop.
821 </li>
823 </ul>
829 To allow possible side-effects,
830 function calls can be executed as statements:
832 <pre>
833 stat ::= functioncall
834 </pre><p>
835 In this case, all returned values are thrown away.
843 Local variables can be declared anywhere inside a block.
844 The declaration can include an initial assignment:
846 <pre>
848 </pre><p>
849 If present, an initial assignment has the same semantics
854 <p>
856 and so local variables can be declared in a chunk outside any explicit block.
857 The scope of such local variables extends until the end of the chunk.
860 <p>
871 <p>
872 The basic expressions in Lua are the following:
874 <pre>
875 exp ::= prefixexp
877 exp ::= Number
878 exp ::= String
879 exp ::= function
880 exp ::= tableconstructor
882 exp ::= exp binop exp
883 exp ::= unop exp
885 </pre>
887 <p>
893 Vararg expressions,
895 directly inside a vararg function;
899 <p>
901 relational operators (see <a href="#2.5.2">§2.5.2</a>), logical operators (see <a href="#2.5.3">§2.5.3</a>),
908 <p>
909 Both function calls and vararg expressions can result in multiple values.
910 If an expression is used as a statement
912 then its return list is adjusted to zero elements,
913 thus discarding all returned values.
914 If an expression is used as the last (or the only) element
915 of a list of expressions,
916 then no adjustment is made
917 (unless the call is enclosed in parentheses).
918 In all other contexts,
919 Lua adjusts the result list to one element,
920 discarding all values except the first one.
923 <p>
924 Here are some examples:
926 <pre>
927 f() -- adjusted to 0 results
928 g(f(), x) -- f() is adjusted to 1 result
929 g(x, f()) -- g gets x plus all results from f()
930 a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil)
931 a,b = ... -- a gets the first vararg parameter, b gets
932 -- the second (both a and b can get nil if there
933 -- is no corresponding vararg parameter)
935 a,b,c = x, f() -- f() is adjusted to 2 results
936 a,b,c = f() -- f() is adjusted to 3 results
937 return f() -- returns all results from f()
938 return ... -- returns all received vararg parameters
939 return x,y,f() -- returns x, y, and all results from f()
940 {f()} -- creates a list with all results from f()
941 {...} -- creates a list with all vararg parameters
942 {f(), nil} -- f() is adjusted to 1 result
943 </pre>
945 <p>
946 Any expression enclosed in parentheses always results in only one value.
947 Thus,
956 Lua supports the usual arithmetic operators:
961 If the operands are numbers, or strings that can be converted to
963 then all operations have the usual meaning.
964 Exponentiation works for any exponent.
966 Modulo is defined as
968 <pre>
969 a % b == a - math.floor(a/b)*b
970 </pre><p>
971 That is, it is the remainder of a division that rounds
972 the quotient towards minus infinity.
979 The relational operators in Lua are
981 <pre>
983 </pre><p>
987 <p>
990 Otherwise, the values of the operands are compared.
991 Numbers and strings are compared in the usual way.
992 Objects (tables, userdata, threads, and functions)
995 Every time you create a new object
996 (a table, userdata, thread, or function),
997 this new object is different from any previously existing object.
1000 <p>
1001 You can change the way that Lua compares tables and userdata
1005 <p>
1010 entries in a table.
1013 <p>
1017 <p>
1018 The order operators work as follows.
1019 If both arguments are numbers, then they are compared as such.
1020 Otherwise, if both arguments are strings,
1021 then their values are compared according to the current locale.
1032 The logical operators in Lua are
1036 and anything else as true.
1039 <p>
1048 that is,
1049 the second operand is evaluated only if necessary.
1050 Here are some examples:
1052 <pre>
1057 false and error() --> false
1058 false and nil --> false
1059 false or nil --> nil
1061 </pre><p>
1062 (In this manual,
1070 The string concatenation operator in Lua is
1072 If both operands are strings or numbers, then they are converted to
1082 <p>
1084 The length of a string is its number of bytes
1085 (that is, the usual meaning of string length when each
1086 character is one byte).
1089 <p>
1096 the index of its last value.
1097 If the array has "holes"
1102 the array).
1109 Operator precedence in Lua follows the table below,
1110 from lower to higher priority:
1112 <pre>
1113 or
1114 and
1116 ..
1117 + -
1118 * / %
1119 not # - (unary)
1120 ^
1121 </pre><p>
1122 As usual,
1123 you can use parentheses to change the precedences of an expression.
1125 operators are right associative.
1126 All other binary operators are left associative.
1133 Table constructors are expressions that create tables.
1134 Every time a constructor is evaluated, a new table is created.
1135 A constructor can be used to create an empty table
1136 or to create a table and initialize some of its fields.
1137 The general syntax for constructors is
1139 <pre>
1141 fieldlist ::= field {fieldsep field} [fieldsep]
1142 field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp
1144 </pre>
1146 <p>
1153 starting with 1.
1154 Fields in the other formats do not affect this counting.
1155 For example,
1157 <pre>
1159 </pre><p>
1160 is equivalent to
1162 <pre>
1163 do
1164 local t = {}
1165 t[f(1)] = g
1172 a = t
1173 end
1174 </pre>
1176 <p>
1178 and the expression is a function call or a vararg expression,
1179 then all values returned by this expression enter the list consecutively
1181 To avoid this,
1182 enclose the function call or the vararg expression
1186 <p>
1187 The field list can have an optional trailing separator,
1188 as a convenience for machine-generated code.
1195 A function call in Lua has the following syntax:
1197 <pre>
1198 functioncall ::= prefixexp args
1199 </pre><p>
1200 In a function call,
1201 first prefixexp and args are evaluated.
1203 then this function is called
1204 with the given arguments.
1205 Otherwise, the prefixexp "call" metamethod is called,
1206 having as first parameter the value of prefixexp,
1207 followed by the original call arguments
1211 <p>
1212 The form
1214 <pre>
1216 </pre><p>
1217 can be used to call "methods".
1223 <p>
1224 Arguments have the following syntax:
1226 <pre>
1228 args ::= tableconstructor
1229 args ::= String
1230 </pre><p>
1231 All argument expressions are evaluated before the call.
1234 that is, the argument list is a single new table.
1238 that is, the argument list is a single literal string.
1241 <p>
1242 As an exception to the free-format syntax of Lua,
1244 This restriction avoids some ambiguities in the language.
1245 If you write
1247 <pre>
1248 a = f
1249 (g).x(a)
1250 </pre><p>
1252 So, if you want two statements, you must add a semi-colon between them.
1257 <p>
1262 in a tail call,
1263 the called function reuses the stack entry of the calling function.
1264 Therefore, there is no limit on the number of nested tail calls that
1265 a program can execute.
1266 However, a tail call erases any debug information about the
1267 calling function.
1268 Note that a tail call only happens with a particular syntax,
1270 this syntax makes the calling function return exactly
1271 the returns of the called function.
1272 So, none of the following examples are tail calls:
1274 <pre>
1275 return (f(x)) -- results adjusted to 1
1276 return 2 * f(x)
1277 return x, f(x) -- additional results
1278 f(x); return -- results discarded
1279 return x or f(x) -- results adjusted to 1
1280 </pre>
1287 <p>
1288 The syntax for function definition is
1290 <pre>
1293 </pre>
1295 <p>
1296 The following syntactic sugar simplifies function definitions:
1298 <pre>
1302 </pre><p>
1303 The statement
1305 <pre>
1307 </pre><p>
1308 translates to
1310 <pre>
1312 </pre><p>
1313 The statement
1315 <pre>
1317 </pre><p>
1318 translates to
1320 <pre>
1322 </pre><p>
1323 The statement
1325 <pre>
1327 </pre><p>
1328 translates to
1330 <pre>
1332 </pre><p>
1335 <pre>
1337 </pre><p>
1338 (This only makes a difference when the body of the function
1342 <p>
1343 A function definition is an executable expression,
1345 When Lua pre-compiles a chunk,
1346 all its function bodies are pre-compiled too.
1347 Then, whenever Lua executes the function definition,
1350 is the final value of the expression.
1351 Different instances of the same function
1352 can refer to different external local variables
1353 and can have different environment tables.
1356 <p>
1357 Parameters act as local variables that are
1358 initialized with the argument values:
1360 <pre>
1362 </pre><p>
1363 When a function is called,
1364 the list of arguments is adjusted to
1365 the length of the list of parameters,
1367 which is
1369 A vararg function does not adjust its argument list;
1370 instead, it collects all extra arguments and supplies them
1372 which is also written as three dots.
1373 The value of this expression is a list of all actual extra arguments,
1374 similar to a function with multiple results.
1375 If a vararg expression is used inside another expression
1376 or in the middle of a list of expressions,
1377 then its return list is adjusted to one element.
1378 If the expression is used as the last element of a list of expressions,
1379 then no adjustment is made
1380 (unless that last expression is enclosed in parentheses).
1383 <p>
1384 As an example, consider the following definitions:
1386 <pre>
1387 function f(a, b) end
1388 function g(a, b, ...) end
1390 </pre><p>
1391 Then, we have the following mapping from arguments to parameters and
1392 to the vararg expression:
1394 <pre>
1395 CALL PARAMETERS
1407 </pre>
1409 <p>
1411 If control reaches the end of a function
1413 then the function returns with no results.
1416 <p>
1420 Thus, the statement
1422 <pre>
1424 </pre><p>
1425 is syntactic sugar for
1427 <pre>
1429 </pre>
1438 <p>
1440 Lua is a lexically scoped language.
1442 their declaration and lasts until the end of the innermost block that
1443 includes the declaration.
1444 Consider the following example:
1446 <pre>
1447 x = 10 -- global variable
1448 do -- new block
1449 local x = x -- new 'x', with value 10
1451 x = x+1
1452 do -- another block
1453 local x = x+1 -- another 'x'
1455 end
1457 end
1459 </pre>
1461 <p>
1467 <p>
1468 Because of the lexical scoping rules,
1469 local variables can be freely accessed by functions
1470 defined inside their scope.
1471 A local variable used by an inner function is called
1473 inside the inner function.
1476 <p>
1478 defines new local variables.
1479 Consider the following example:
1481 <pre>
1482 a = {}
1483 local x = 20
1485 local y = 0
1486 a[i] = function () y=y+1; return x+y end
1487 end
1488 </pre><p>
1489 The loop creates ten closures
1490 (that is, ten instances of the anonymous function).
1500 <p>
1501 Because Lua is an embedded extension language,
1502 all Lua actions start from C code in the host program
1504 Whenever an error occurs during Lua compilation or execution,
1505 control returns to C,
1506 which can take appropriate measures
1507 (such as printing an error message).
1510 <p>
1511 Lua code can explicitly generate an error by calling the
1513 If you need to catch errors in Lua,
1522 <p>
1525 that defines the behavior of the original value
1526 under certain special operations.
1527 You can change several aspects of the behavior
1528 of operations over a value by setting specific fields in its metatable.
1529 For instance, when a non-numeric value is the operand of an addition,
1531 If it finds one,
1532 Lua calls this function to perform the addition.
1535 <p>
1539 and the metamethod is the function that performs the addition.
1542 <p>
1543 You can query the metatable of any value
1547 <p>
1548 You can replace the metatable of tables
1550 function.
1551 You cannot change the metatable of other types from Lua
1552 (except by using the debug library);
1553 you must use the C API for that.
1556 <p>
1557 Tables and full userdata have individual metatables
1558 (although multiple tables and userdata can share their metatables).
1559 Values of all other types share one single metatable per type;
1560 that is, there is one single metatable for all numbers,
1561 one for all strings, etc.
1564 <p>
1565 A metatable controls how an object behaves in arithmetic operations,
1566 order comparisons, concatenation, length operation, and indexing.
1567 A metatable also can define a function to be called when a userdata
1568 is garbage collected.
1569 For each of these operations Lua associates a specific key
1571 When Lua performs one of these operations over a value,
1572 it checks whether this value has a metatable with the corresponding event.
1573 If so, the value associated with that key (the metamethod)
1574 controls how Lua will perform the operation.
1577 <p>
1578 Metatables control the operations listed next.
1579 Each operation is identified by its corresponding name.
1580 The key for each operation is a string with its name prefixed by
1582 for instance, the key for operation "add" is the
1584 The semantics of these operations is better explained by a Lua function
1585 describing how the interpreter executes the operation.
1588 <p>
1589 The code shown here in Lua is only illustrative;
1590 the real behavior is hard coded in the interpreter
1591 and it is much more efficient than this simulation.
1592 All functions used in these descriptions
1593 (<a href="#pdf-rawget"><code>rawget</code></a>, <a href="#pdf-tonumber"><code>tonumber</code></a>, etc.)
1595 In particular, to retrieve the metamethod of a given object,
1596 we use the expression
1598 <pre>
1599 metatable(obj)[event]
1600 </pre><p>
1601 This should be read as
1603 <pre>
1604 rawget(getmetatable(obj) or {}, event)
1605 </pre><p>
1607 That is, the access to a metamethod does not invoke other metamethods,
1608 and the access to objects with no metatables does not fail
1613 <ul>
1620 <p>
1622 for a binary operation.
1623 First, Lua tries the first operand.
1624 If its type does not define a handler for the operation,
1625 then Lua tries the second operand.
1627 <pre>
1628 function getbinhandler (op1, op2, event)
1629 return metatable(op1)[event] or metatable(op2)[event]
1630 end
1631 </pre><p>
1632 By using this function,
1635 <pre>
1636 function add_event (op1, op2)
1637 local o1, o2 = tonumber(op1), tonumber(op2)
1638 if o1 and o2 then -- both operands are numeric?
1639 return o1 + o2 -- '+' here is the primitive 'add'
1640 else -- at least one of the operands is not numeric
1641 local h = getbinhandler(op1, op2, "__add")
1642 if h then
1643 -- call the handler with both operands
1644 return (h(op1, op2))
1645 else -- no handler available: default behavior
1646 error(···)
1647 end
1648 end
1649 end
1650 </pre><p>
1651 </li>
1656 Behavior similar to the "add" operation.
1657 </li>
1662 Behavior similar to the "add" operation.
1663 </li>
1668 Behavior similar to the "add" operation.
1669 </li>
1674 Behavior similar to the "add" operation,
1675 with the operation
1677 </li>
1682 Behavior similar to the "add" operation,
1684 as the primitive operation.
1685 </li>
1691 <pre>
1692 function unm_event (op)
1693 local o = tonumber(op)
1694 if o then -- operand is numeric?
1695 return -o -- '-' here is the primitive 'unm'
1696 else -- the operand is not numeric.
1697 -- Try to get a handler from the operand
1698 local h = metatable(op).__unm
1699 if h then
1700 -- call the handler with the operand
1701 return (h(op))
1702 else -- no handler available: default behavior
1703 error(···)
1704 end
1705 end
1706 end
1707 </pre><p>
1708 </li>
1714 <pre>
1715 function concat_event (op1, op2)
1718 return op1 .. op2 -- primitive string concatenation
1719 else
1720 local h = getbinhandler(op1, op2, "__concat")
1721 if h then
1722 return (h(op1, op2))
1723 else
1724 error(···)
1725 end
1726 end
1727 end
1728 </pre><p>
1729 </li>
1735 <pre>
1736 function len_event (op)
1737 if type(op) == "string" then
1738 return strlen(op) -- primitive string length
1739 elseif type(op) == "table" then
1740 return #op -- primitive table length
1741 else
1742 local h = metatable(op).__len
1743 if h then
1744 -- call the handler with the operand
1745 return (h(op))
1746 else -- no handler available: default behavior
1747 error(···)
1748 end
1749 end
1750 end
1751 </pre><p>
1753 </li>
1759 for comparison operators.
1760 A metamethod only is selected when both objects
1761 being compared have the same type
1762 and the same metamethod for the selected operation.
1764 <pre>
1765 function getcomphandler (op1, op2, event)
1766 if type(op1) ~= type(op2) then return nil end
1767 local mm1 = metatable(op1)[event]
1768 local mm2 = metatable(op2)[event]
1769 if mm1 == mm2 then return mm1 else return nil end
1770 end
1771 </pre><p>
1772 The "eq" event is defined as follows:
1774 <pre>
1775 function eq_event (op1, op2)
1776 if type(op1) ~= type(op2) then -- different types?
1777 return false -- different objects
1778 end
1779 if op1 == op2 then -- primitive equal?
1780 return true -- objects are equal
1781 end
1782 -- try metamethod
1783 local h = getcomphandler(op1, op2, "__eq")
1784 if h then
1785 return (h(op1, op2))
1786 else
1787 return false
1788 end
1789 end
1790 </pre><p>
1792 </li>
1798 <pre>
1799 function lt_event (op1, op2)
1801 return op1 < op2 -- numeric comparison
1803 return op1 < op2 -- lexicographic comparison
1804 else
1805 local h = getcomphandler(op1, op2, "__lt")
1806 if h then
1807 return (h(op1, op2))
1808 else
1809 error(···)
1810 end
1811 end
1812 end
1813 </pre><p>
1815 </li>
1821 <pre>
1822 function le_event (op1, op2)
1824 return op1 <= op2 -- numeric comparison
1826 return op1 <= op2 -- lexicographic comparison
1827 else
1828 local h = getcomphandler(op1, op2, "__le")
1829 if h then
1830 return (h(op1, op2))
1831 else
1832 h = getcomphandler(op1, op2, "__lt")
1833 if h then
1834 return not h(op2, op1)
1835 else
1836 error(···)
1837 end
1838 end
1839 end
1840 end
1841 </pre><p>
1843 Note that, in the absence of a "le" metamethod,
1846 </li>
1852 <pre>
1853 function gettable_event (table, key)
1854 local h
1855 if type(table) == "table" then
1856 local v = rawget(table, key)
1857 if v ~= nil then return v end
1858 h = metatable(table).__index
1859 if h == nil then return nil end
1860 else
1861 h = metatable(table).__index
1862 if h == nil then
1863 error(···)
1864 end
1865 end
1866 if type(h) == "function" then
1867 return (h(table, key)) -- call the handler
1868 else return h[key] -- or repeat operation on it
1869 end
1870 end
1871 </pre><p>
1872 </li>
1878 <pre>
1879 function settable_event (table, key, value)
1880 local h
1881 if type(table) == "table" then
1882 local v = rawget(table, key)
1883 if v ~= nil then rawset(table, key, value); return end
1884 h = metatable(table).__newindex
1885 if h == nil then rawset(table, key, value); return end
1886 else
1887 h = metatable(table).__newindex
1888 if h == nil then
1889 error(···)
1890 end
1891 end
1892 if type(h) == "function" then
1893 h(table, key,value) -- call the handler
1894 else h[key] = value -- or repeat operation on it
1895 end
1896 end
1897 </pre><p>
1898 </li>
1901 called when Lua calls a value.
1904 <pre>
1905 function function_event (func, ...)
1906 if type(func) == "function" then
1907 return func(...) -- primitive call
1908 else
1909 local h = metatable(func).__call
1910 if h then
1911 return h(func, ...)
1912 else
1913 error(···)
1914 end
1915 end
1916 end
1917 </pre><p>
1918 </li>
1920 </ul>
1927 <p>
1928 Besides metatables,
1929 objects of types thread, function, and userdata
1930 have another table associated with them,
1932 Like metatables, environments are regular tables and
1933 multiple objects can share the same environment.
1936 <p>
1937 Threads are created sharing the environment of the creating thread.
1938 Userdata and C functions are created sharing the environment
1939 of the creating C function.
1940 Non-nested Lua functions
1941 (created by <a href="#pdf-loadfile"><code>loadfile</code></a>, <a href="#pdf-loadstring"><code>loadstring</code></a> or <a href="#pdf-load"><code>load</code></a>)
1942 are created sharing the environment of the creating thread.
1943 Nested Lua functions are created sharing the environment of
1944 the creating Lua function.
1947 <p>
1948 Environments associated with userdata have no meaning for Lua.
1949 It is only a convenience feature for programmers to associate a table to
1950 a userdata.
1953 <p>
1954 Environments associated with threads are called
1956 They are used as the default environment for threads and
1957 non-nested Lua functions created by the thread
1961 <p>
1962 The environment associated with a C function can be directly
1964 It is used as the default environment for other C functions
1965 and userdata created by the function.
1968 <p>
1969 Environments associated with Lua functions are used to resolve
1971 They are used as the default environment for nested Lua functions
1972 created by the function.
1975 <p>
1976 You can change the environment of a Lua function or the
1978 You can get the environment of a Lua function or the running thread
1980 To manipulate the environment of other objects
1981 (userdata, C functions, other threads) you must
1982 use the C API.
1990 <p>
1991 Lua performs automatic memory management.
1992 This means that
1993 you have to worry neither about allocating memory for new objects
1994 nor about freeing it when the objects are no longer needed.
1995 Lua manages memory automatically by running
1998 (that is, objects that are no longer accessible from Lua).
1999 All memory used by Lua is subject to automatic management:
2000 tables, userdata, functions, threads, strings, etc.
2003 <p>
2004 Lua implements an incremental mark-and-sweep collector.
2005 It uses two numbers to control its garbage-collection cycles:
2008 Both use percentage points as units
2012 <p>
2013 The garbage-collector pause
2014 controls how long the collector waits before starting a new cycle.
2015 Larger values make the collector less aggressive.
2016 Values smaller than 100 mean the collector will not wait to
2017 start a new cycle.
2018 A value of 200 means that the collector waits for the total memory in use
2019 to double before starting a new cycle.
2022 <p>
2023 The step multiplier
2024 controls the relative speed of the collector relative to
2025 memory allocation.
2026 Larger values make the collector more aggressive but also increase
2027 the size of each incremental step.
2028 Values smaller than 100 make the collector too slow and
2029 can result in the collector never finishing a cycle.
2031 the speed of memory allocation.
2034 <p>
2037 With these functions you can also control
2038 the collector directly (e.g., stop and restart it).
2044 <p>
2045 Using the C API,
2048 Finalizers allow you to coordinate Lua's garbage collection
2049 with external resource management
2050 (such as closing files, network or database connections,
2051 or freeing your own memory).
2054 <p>
2056 collected immediately by the garbage collector.
2057 Instead, Lua puts them in a list.
2058 After the collection,
2059 Lua does the equivalent of the following function
2060 for each userdata in that list:
2062 <pre>
2063 function gc_event (udata)
2064 local h = metatable(udata).__gc
2065 if h then
2066 h(udata)
2067 end
2068 end
2069 </pre>
2071 <p>
2072 At the end of each garbage-collection cycle,
2074 order of their creation,
2075 among those collected in that cycle.
2076 That is, the first finalizer to be called is the one associated
2077 with the userdata created last in the program.
2078 The userdata itself is freed only in the next garbage-collection cycle.
2086 <p>
2089 A weak reference is ignored by the garbage collector.
2090 In other words,
2091 if the only references to an object are weak references,
2092 then the garbage collector will collect this object.
2095 <p>
2096 A weak table can have weak keys, weak values, or both.
2097 A table with weak keys allows the collection of its keys,
2098 but prevents the collection of its values.
2099 A table with both weak keys and weak values allows the collection of
2100 both keys and values.
2101 In any case, if either the key or the value is collected,
2102 the whole pair is removed from the table.
2103 The weakness of a table is controlled by the
2106 the keys in the table are weak.
2108 the values in the table are weak.
2111 <p>
2112 After you use a table as a metatable,
2114 Otherwise, the weak behavior of the tables controlled by this
2115 metatable is undefined.
2125 <p>
2126 Lua supports coroutines,
2128 A coroutine in Lua represents an independent thread of execution.
2129 Unlike threads in multithread systems, however,
2130 a coroutine only suspends its execution by explicitly calling
2131 a yield function.
2134 <p>
2135 You create a coroutine with a call to <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>.
2136 Its sole argument is a function
2137 that is the main function of the coroutine.
2140 it does not start the coroutine execution.
2143 <p>
2145 passing as its first argument
2147 the coroutine starts its execution,
2148 at the first line of its main function.
2149 Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed on
2150 to the coroutine main function.
2151 After the coroutine starts running,
2155 <p>
2156 A coroutine can terminate its execution in two ways:
2157 normally, when its main function returns
2158 (explicitly or implicitly, after the last instruction);
2159 and abnormally, if there is an unprotected error.
2160 In the first case, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>,
2161 plus any values returned by the coroutine main function.
2162 In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b>
2163 plus an error message.
2166 <p>
2168 When a coroutine yields,
2169 the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately,
2170 even if the yield happens inside nested function calls
2171 (that is, not in the main function,
2172 but in a function directly or indirectly called by the main function).
2173 In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>,
2175 The next time you resume the same coroutine,
2176 it continues its execution from the point where it yielded,
2177 with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra
2181 <p>
2183 the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine,
2184 but instead of returning the coroutine itself,
2185 it returns a function that, when called, resumes the coroutine.
2186 Any arguments passed to this function
2188 <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>,
2189 except the first one (the boolean error code).
2192 any error is propagated to the caller.
2195 <p>
2196 As an example,
2197 consider the following code:
2199 <pre>
2200 function foo (a)
2201 print("foo", a)
2202 return coroutine.yield(2*a)
2203 end
2205 co = coroutine.create(function (a,b)
2206 print("co-body", a, b)
2207 local r = foo(a+1)
2208 print("co-body", r)
2209 local r, s = coroutine.yield(a+b, a-b)
2210 print("co-body", r, s)
2211 return b, "end"
2212 end)
2218 </pre><p>
2219 When you run it, it produces the following output:
2221 <pre>
2222 co-body 1 10
2223 foo 2
2225 main true 4
2226 co-body r
2228 co-body x y
2229 main true 10 end
2230 main false cannot resume dead coroutine
2231 </pre>
2238 <p>
2240 This section describes the C API for Lua, that is,
2241 the set of C functions available to the host program to communicate
2242 with Lua.
2243 All API functions and related types and constants
2247 <p>
2248 Even when we use the term "function",
2249 any facility in the API may be provided as a macro instead.
2250 All such macros use each of their arguments exactly once
2251 (except for the first argument, which is always a Lua state),
2252 and so do not generate any hidden side-effects.
2255 <p>
2256 As in most C libraries,
2257 the Lua API functions do not check their arguments for validity or consistency.
2258 However, you can change this behavior by compiling Lua
2259 with a proper definition for the macro <a name="pdf-luai_apicheck"><code>luai_apicheck</code></a>,
2266 <p>
2268 Each element in this stack represents a Lua value
2272 <p>
2273 Whenever Lua calls C, the called function gets a new stack,
2274 which is independent of previous stacks and of stacks of
2275 C functions that are still active.
2276 This stack initially contains any arguments to the C function
2277 and it is where the C function pushes its results
2281 <p>
2282 For convenience,
2283 most query operations in the API do not follow a strict stack discipline.
2284 Instead, they can refer to any element in the stack
2291 (that is, the element that was pushed onto the stack first)
2292 and
2295 (that is, the element at the top)
2308 <p>
2309 When you interact with Lua API,
2310 you are responsible for ensuring consistency.
2311 In particular,
2314 to grow the stack size.
2317 <p>
2318 Whenever Lua calls C,
2319 it ensures that at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> stack positions are available.
2321 so that usually you do not have to worry about stack space
2322 unless your code has loops pushing elements onto the stack.
2325 <p>
2326 Most query functions accept as indices any value inside the
2327 available stack space, that is, indices up to the maximum stack size
2331 as follows:
2333 <pre>
2336 </pre><p>
2337 Note that 0 is never an acceptable index.
2345 <p>
2346 Unless otherwise noted,
2347 any function that accepts valid indices can also be called with
2349 which represent some Lua values that are accessible to C code
2350 but which are not in the stack.
2351 Pseudo-indices are used to access the thread environment,
2352 the function environment,
2353 the registry,
2357 <p>
2358 The thread environment (where global variables live) is
2360 The environment of the running C function is always
2364 <p>
2365 To access and change the value of global variables,
2366 you can use regular table operations over an environment table.
2367 For instance, to access the value of a global variable, do
2369 <pre>
2370 lua_getfield(L, LUA_GLOBALSINDEX, varname);
2371 </pre>
2378 <p>
2379 When a C function is created,
2380 it is possible to associate some values with it,
2383 accessible to the function whenever it is called
2387 <p>
2388 Whenever a C function is called,
2389 its upvalues are located at specific pseudo-indices.
2390 These pseudo-indices are produced by the macro
2392 The first value associated with a function is at position
2396 current function (but not greater than 256),
2397 produces an acceptable (but invalid) index.
2405 <p>
2407 a pre-defined table that can be used by any C code to
2408 store whatever Lua value it needs to store.
2409 This table is always located at pseudo-index
2411 Any C library can store data into this table,
2412 but it should take care to choose keys different from those used
2413 by other libraries, to avoid collisions.
2414 Typically, you should use as key a string containing your library name
2415 or a light userdata with the address of a C object in your code.
2418 <p>
2419 The integer keys in the registry are used by the reference mechanism,
2420 implemented by the auxiliary library,
2421 and therefore should not be used for other purposes.
2429 <p>
2431 (You can also choose to use exceptions if you use C++;
2433 When Lua faces any error
2434 (such as memory allocation errors, type errors, syntax errors,
2435 and runtime errors)
2437 that is, it does a long jump.
2439 to set a recover point;
2440 any error jumps to the most recent active recover point.
2443 <p>
2444 Most functions in the API can throw an error,
2445 for instance due to a memory allocation error.
2446 The documentation for each function indicates whether
2447 it can throw errors.
2450 <p>
2451 Inside a C function you can throw an error by calling <a href="#lua_error"><code>lua_error</code></a>.
2459 <p>
2460 Here we list all functions and types from the C API in
2461 alphabetical order.
2462 Each function has an indicator like this:
2466 <p>
2468 is how many elements the function pops from the stack.
2470 is how many elements the function pushes onto the stack.
2471 (Any function always pushes its results after popping its arguments.)
2474 depending on the situation;
2476 we cannot know how many elements the function pops/pushes
2477 by looking only at its arguments
2478 (e.g., they may depend on what is on the stack).
2480 tells whether the function may throw errors:
2483 only due to not enough memory;
2490 <pre>typedef void * (*lua_Alloc) (void *ud,
2491 void *ptr,
2492 size_t osize,
2493 size_t nsize);</pre>
2495 <p>
2496 The type of the memory-allocation function used by Lua states.
2497 The allocator function must provide a
2499 but not exactly the same.
2500 Its arguments are
2501 <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>;
2510 if and only if it cannot fill the request.
2515 Lua assumes that the allocator never fails when
2519 <p>
2520 Here is a simple implementation for the allocator function.
2521 It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>.
2523 <pre>
2524 static void *l_alloc (void *ud, void *ptr, size_t osize,
2525 size_t nsize) {
2526 (void)ud; (void)osize; /* not used */
2527 if (nsize == 0) {
2528 free(ptr);
2529 return NULL;
2530 }
2531 else
2532 return realloc(ptr, nsize);
2533 }
2534 </pre><p>
2535 This code assumes
2538 ANSI C ensures both behaviors.
2548 <p>
2549 Sets a new panic function and returns the old one.
2552 <p>
2553 If an error happens outside any protected environment,
2556 thus exiting the host application.
2557 Your panic function can avoid this exit by
2558 never returning (e.g., doing a long jump).
2561 <p>
2562 The panic function can access the error message at the top of the stack.
2572 <p>
2573 Calls a function.
2576 <p>
2577 To call a function you must use the following protocol:
2578 first, the function to be called is pushed onto the stack;
2579 then, the arguments to the function are pushed
2580 in direct order;
2581 that is, the first argument is pushed first.
2584 All arguments and the function value are popped from the stack
2585 when the function is called.
2586 The function results are pushed onto the stack when the function returns.
2590 Lua takes care that the returned values fit into the stack space.
2591 The function results are pushed onto the stack in direct order
2592 (the first result is pushed first),
2593 so that after the call the last result is on the top of the stack.
2596 <p>
2597 Any error inside the called function is propagated upwards
2601 <p>
2602 The following example shows how the host program can do the
2603 equivalent to this Lua code:
2605 <pre>
2607 </pre><p>
2608 Here it is in C:
2610 <pre>
2611 lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* function to be called */
2613 lua_getfield(L, LUA_GLOBALSINDEX, "t"); /* table to be indexed */
2615 lua_remove(L, -2); /* remove 't' from the stack */
2618 lua_setfield(L, LUA_GLOBALSINDEX, "a"); /* set global 'a' */
2619 </pre><p>
2620 Note that the code above is "balanced":
2621 at its end, the stack is back to its original configuration.
2622 This is considered good programming practice.
2631 <p>
2632 Type for C functions.
2635 <p>
2636 In order to communicate properly with Lua,
2637 a C function must use the following protocol,
2638 which defines the way parameters and results are passed:
2639 a C function receives its arguments from Lua in its stack
2640 in direct order (the first argument is pushed first).
2641 So, when the function starts,
2643 The first argument (if any) is at index 1
2645 To return values to Lua, a C function just pushes them onto the stack,
2646 in direct order (the first result is pushed first),
2647 and returns the number of results.
2648 Any other value in the stack below the results will be properly
2649 discarded by Lua.
2650 Like a Lua function, a C function called by Lua can also return
2651 many results.
2654 <p>
2655 As an example, the following function receives a variable number
2656 of numerical arguments and returns their average and sum:
2658 <pre>
2659 static int foo (lua_State *L) {
2660 int n = lua_gettop(L); /* number of arguments */
2661 lua_Number sum = 0;
2662 int i;
2664 if (!lua_isnumber(L, i)) {
2665 lua_pushstring(L, "incorrect argument");
2666 lua_error(L);
2667 }
2668 sum += lua_tonumber(L, i);
2669 }
2670 lua_pushnumber(L, sum/n); /* first result */
2671 lua_pushnumber(L, sum); /* second result */
2672 return 2; /* number of results */
2673 }
2674 </pre>
2683 <p>
2685 It returns false if it cannot grow the stack to that size.
2686 This function never shrinks the stack;
2687 if the stack is already larger than the new size,
2688 it is left unchanged.
2698 <p>
2699 Destroys all objects in the given Lua state
2700 (calling the corresponding garbage-collection metamethods, if any)
2701 and frees all dynamic memory used by this state.
2702 On several platforms, you may not need to call this function,
2703 because all resources are naturally released when the host program ends.
2704 On the other hand, long-running programs,
2705 such as a daemon or a web server,
2706 might need to release states as soon as they are not needed,
2707 to avoid growing too large.
2717 <p>
2719 pops them, and leaves the result at the top.
2721 (that is, the function does nothing);
2723 Concatenation is performed following the usual semantics of Lua
2734 <p>
2738 In case of errors,
2739 <a href="#lua_cpcall"><code>lua_cpcall</code></a> returns the same error codes as <a href="#lua_pcall"><code>lua_pcall</code></a>,
2740 plus the error object on the top of the stack;
2741 otherwise, it returns zero, and does not change the stack.
2752 <p>
2753 Creates a new empty table and pushes it onto the stack.
2754 The new table has space pre-allocated
2756 This pre-allocation is useful when you know exactly how many elements
2757 the table will have.
2768 <p>
2769 Dumps a function as a binary chunk.
2770 Receives a Lua function on the top of the stack
2771 and produces a binary chunk that,
2772 if loaded again,
2773 results in a function equivalent to the one dumped.
2774 As it produces parts of the chunk,
2775 <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>)
2777 to write them.
2780 <p>
2781 The value returned is the error code returned by the last
2782 call to the writer;
2786 <p>
2787 This function does not pop the Lua function from the stack.
2797 <p>
2801 (that is, may call metamethods).
2813 <p>
2814 Generates a Lua error.
2815 The error message (which can actually be a Lua value of any type)
2816 must be on the stack top.
2817 This function does a long jump,
2818 and therefore never returns.
2829 <p>
2830 Controls the garbage collector.
2833 <p>
2834 This function performs several tasks,
2837 <ul>
2840 stops the garbage collector.
2841 </li>
2844 restarts the garbage collector.
2845 </li>
2848 performs a full garbage-collection cycle.
2849 </li>
2852 returns the current amount of memory (in Kbytes) in use by Lua.
2853 </li>
2856 returns the remainder of dividing the current amount of bytes of
2857 memory in use by Lua by 1024.
2858 </li>
2861 performs an incremental step of garbage collection.
2863 (larger values mean more steps) in a non-specified way.
2864 If you want to control the step size
2866 The function returns 1 if the step finished a
2867 garbage-collection cycle.
2868 </li>
2873 The function returns the previous value of the pause.
2874 </li>
2879 The function returns the previous value of the step multiplier.
2880 </li>
2882 </ul>
2891 <p>
2892 Returns the memory-allocation function of a given state.
2904 <p>
2905 Pushes onto the stack the environment table of
2906 the value at the given index.
2916 <p>
2919 As in Lua, this function may trigger a metamethod
2930 <p>
2932 It is defined as a macro:
2934 <pre>
2935 #define lua_getglobal(L,s) lua_getfield(L, LUA_GLOBALSINDEX, s)
2936 </pre>
2945 <p>
2946 Pushes onto the stack the metatable of the value at the given
2947 acceptable index.
2948 If the index is not valid,
2949 or if the value does not have a metatable,
2960 <p>
2966 <p>
2967 This function pops the key from the stack
2968 (putting the resulting value in its place).
2969 As in Lua, this function may trigger a metamethod
2980 <p>
2981 Returns the index of the top element in the stack.
2983 this result is equal to the number of elements in the stack
2994 <p>
2995 Moves the top element into the given valid index,
2996 shifting up the elements above this index to open space.
2997 Cannot be called with a pseudo-index,
2998 because a pseudo-index is not an actual stack position.
3007 <p>
3008 The type used by the Lua API to represent integral values.
3011 <p>
3013 which is usually the largest signed integral type the machine handles
3014 "comfortably".
3024 <p>
3025 Returns 1 if the value at the given acceptable index has type boolean,
3036 <p>
3048 <p>
3049 Returns 1 if the value at the given acceptable index is a function
3060 <p>
3061 Returns 1 if the value at the given acceptable index is a light userdata,
3072 <p>
3084 <p>
3085 Returns 1 if the given acceptable index is not valid
3086 (that is, it refers to an element outside the current stack),
3097 <p>
3098 Returns 1 if the given acceptable index is not valid
3099 (that is, it refers to an element outside the current stack)
3111 <p>
3112 Returns 1 if the value at the given acceptable index is a number
3113 or a string convertible to a number,
3124 <p>
3125 Returns 1 if the value at the given acceptable index is a string
3126 or a number (which is always convertible to a string),
3137 <p>
3138 Returns 1 if the value at the given acceptable index is a table,
3149 <p>
3150 Returns 1 if the value at the given acceptable index is a thread,
3161 <p>
3162 Returns 1 if the value at the given acceptable index is a userdata
3173 <p>
3177 (that is, may call metamethods).
3187 <pre>int lua_load (lua_State *L,
3188 lua_Reader reader,
3189 void *data,
3190 const char *chunkname);</pre>
3192 <p>
3193 Loads a Lua chunk.
3194 If there are no errors,
3196 function on top of the stack.
3197 Otherwise, it pushes an error message.
3200 <ul>
3205 syntax error during pre-compilation;</li>
3208 memory allocation error.</li>
3210 </ul>
3212 <p>
3213 This function only loads a chunk;
3214 it does not run it.
3217 <p>
3218 <a href="#lua_load"><code>lua_load</code></a> automatically detects whether the chunk is text or binary,
3222 <p>
3223 The <a href="#lua_load"><code>lua_load</code></a> function uses a user-supplied <code>reader</code> function
3228 <p>
3240 <p>
3241 Creates a new, independent state.
3243 (due to lack of memory).
3245 Lua does all memory allocation for this state through this function.
3247 simply passes to the allocator in every call.
3257 <p>
3258 Creates a new empty table and pushes it onto the stack.
3269 <p>
3270 Creates a new thread, pushes it on the stack,
3271 and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread.
3272 The new state returned by this function shares with the original state
3273 all global objects (such as tables),
3274 but has an independent execution stack.
3277 <p>
3278 There is no explicit function to close or to destroy a thread.
3279 Threads are subject to garbage collection,
3280 like any Lua object.
3290 <p>
3291 This function allocates a new block of memory with the given size,
3292 pushes onto the stack a new full userdata with the block address,
3293 and returns this address.
3296 <p>
3297 Userdata represent C values in Lua.
3299 It is an object (like a table):
3300 you must create it, it can have its own metatable,
3301 and you can detect when it is being collected.
3302 A full userdata is only equal to itself (under raw equality).
3305 <p>
3307 Lua calls the metamethod and marks the userdata as finalized.
3308 When this userdata is collected again then
3309 Lua frees its corresponding memory.
3319 <p>
3320 Pops a key from the stack,
3321 and pushes a key-value pair from the table at the given index
3322 (the "next" pair after the given key).
3323 If there are no more elements in the table,
3327 <p>
3328 A typical traversal looks like this:
3330 <pre>
3331 /* table is in the stack at index 't' */
3332 lua_pushnil(L); /* first key */
3333 while (lua_next(L, t) != 0) {
3335 printf("%s - %s\n",
3336 lua_typename(L, lua_type(L, -2)),
3337 lua_typename(L, lua_type(L, -1)));
3338 /* removes 'value'; keeps 'key' for next iteration */
3339 lua_pop(L, 1);
3340 }
3341 </pre>
3343 <p>
3344 While traversing a table,
3346 unless you know that the key is actually a string.
3348 the value at the given index;
3358 <p>
3359 The type of numbers in Lua.
3363 <p>
3364 Through the configuration file you can change
3365 Lua to operate with another type for numbers (e.g., float or long).
3375 <p>
3376 Returns the "length" of the value at the given acceptable index:
3377 for strings, this is the string length;
3379 for userdata, this is the size of the block of memory allocated
3380 for the userdata;
3391 <p>
3392 Calls a function in protected mode.
3395 <p>
3398 If there are no errors during the call,
3399 <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>.
3400 However, if there is any error,
3402 pushes a single value on the stack (the error message),
3403 and returns an error code.
3406 and its arguments from the stack.
3409 <p>
3411 then the error message returned on the stack
3412 is exactly the original error message.
3415 (In the current implementation, this index cannot be a pseudo-index.)
3416 In case of runtime errors,
3417 this function will be called with the error message
3418 and its return value will be the message returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>.
3421 <p>
3422 Typically, the error handler function is used to add more debug
3423 information to the error message, such as a stack traceback.
3424 Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>,
3425 since by then the stack has unwound.
3428 <p>
3430 or one of the following error codes
3433 <ul>
3436 a runtime error.
3437 </li>
3440 memory allocation error.
3441 For such errors, Lua does not call the error handler function.
3442 </li>
3445 error while running the error handler function.
3446 </li>
3448 </ul>
3457 <p>
3468 <p>
3479 <p>
3480 Pushes a new C closure onto the stack.
3483 <p>
3484 When a C function is created,
3485 it is possible to associate some values with it,
3487 these values are then accessible to the function whenever it is called.
3488 To associate values with a C function,
3489 first these values should be pushed onto the stack
3490 (when there are multiple values, the first value is pushed first).
3492 is called to create and push the C function onto the stack,
3494 associated with the function.
3495 <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack.
3498 <p>
3509 <p>
3510 Pushes a C function onto the stack.
3511 This function receives a pointer to a C function
3513 when called, invokes the corresponding C function.
3516 <p>
3517 Any function to be registered in Lua must
3518 follow the correct protocol to receive its parameters
3522 <p>
3525 <pre>
3526 #define lua_pushcfunction(L,f) lua_pushcclosure(L,f,0)
3527 </pre>
3536 <p>
3537 Pushes onto the stack a formatted string
3538 and returns a pointer to this string.
3540 but has some important differences:
3542 <ul>
3544 <li>
3545 You do not have to allocate space for the result:
3546 the result is a Lua string and Lua takes care of memory allocation
3547 (and deallocation, through garbage collection).
3548 </li>
3550 <li>
3551 The conversion specifiers are quite restricted.
3552 There are no flags, widths, or precisions.
3553 The conversion specifiers can only be
3560 </li>
3562 </ul>
3571 <p>
3582 <p>
3583 Pushes a light userdata onto the stack.
3586 <p>
3587 Userdata represent C values in Lua.
3589 It is a value (like a number):
3590 you do not create it, it has no individual metatable,
3591 and it is not collected (as it was never created).
3592 A light userdata is equal to "any"
3593 light userdata with the same C address.
3603 <p>
3606 In these cases, it automatically provides the string length.
3616 <p>
3618 onto the stack.
3619 Lua makes (or reuses) an internal copy of the given string,
3621 the function returns.
3622 The string can contain embedded zeros.
3632 <p>
3633 Pushes a nil value onto the stack.
3643 <p>
3654 <p>
3656 onto the stack.
3657 Lua makes (or reuses) an internal copy of the given string,
3659 the function returns.
3660 The string cannot contain embedded zeros;
3661 it is assumed to end at the first zero.
3671 <p>
3673 Returns 1 if this thread is the main thread of its state.
3683 <p>
3684 Pushes a copy of the element at the given valid index
3685 onto the stack.
3693 <pre>const char *lua_pushvfstring (lua_State *L,
3694 const char *fmt,
3695 va_list argp);</pre>
3697 <p>
3698 Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code>
3699 instead of a variable number of arguments.
3709 <p>
3712 (that is, without calling metamethods).
3724 <p>
3726 (i.e., without metamethods).
3736 <p>
3739 The access is raw;
3740 that is, it does not invoke metamethods.
3750 <p>
3752 (i.e., without metamethods).
3762 <p>
3768 <p>
3769 This function pops the value from the stack.
3770 The assignment is raw;
3771 that is, it does not invoke metamethods.
3778 <pre>typedef const char * (*lua_Reader) (lua_State *L,
3779 void *data,
3780 size_t *size);</pre>
3782 <p>
3784 Every time it needs another piece of the chunk,
3787 The reader must return a pointer to a block of memory
3788 with a new piece of the chunk
3790 The block must exist until the reader function is called again.
3791 To signal the end of the chunk,
3793 The reader function may return pieces of any size greater than zero.
3801 <pre>void lua_register (lua_State *L,
3802 const char *name,
3803 lua_CFunction f);</pre>
3805 <p>
3807 It is defined as a macro:
3809 <pre>
3810 #define lua_register(L,n,f) \
3811 (lua_pushcfunction(L, f), lua_setglobal(L, n))
3812 </pre>
3821 <p>
3822 Removes the element at the given valid index,
3823 shifting down the elements above this index to fill the gap.
3824 Cannot be called with a pseudo-index,
3825 because a pseudo-index is not an actual stack position.
3835 <p>
3836 Moves the top element into the given position (and pops it),
3837 without shifting any element
3838 (therefore replacing the value at the given position).
3848 <p>
3849 Starts and resumes a coroutine in a given thread.
3852 <p>
3853 To start a coroutine, you first create a new thread
3855 then you push onto its stack the main function plus any arguments;
3858 This call returns when the coroutine suspends or finishes its execution.
3859 When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>,
3860 or all values returned by the body function.
3863 0 if the coroutine finishes its execution
3864 without errors,
3866 In case of errors,
3867 the stack is not unwound,
3868 so you can use the debug API over it.
3869 The error message is on the top of the stack.
3870 To restart a coroutine, you put on its stack only the values to
3882 <p>
3894 <p>
3895 Pops a table from the stack and sets it as
3896 the new environment for the value at the given index.
3897 If the value at the given index is
3898 neither a function nor a thread nor a userdata,
3900 Otherwise it returns 1.
3910 <p>
3916 <p>
3917 This function pops the value from the stack.
3918 As in Lua, this function may trigger a metamethod
3929 <p>
3930 Pops a value from the stack and
3932 It is defined as a macro:
3934 <pre>
3935 #define lua_setglobal(L,s) lua_setfield(L, LUA_GLOBALSINDEX, s)
3936 </pre>
3945 <p>
3946 Pops a table from the stack and
3947 sets it as the new metatable for the value at the given
3948 acceptable index.
3958 <p>
3965 <p>
3966 This function pops both the key and the value from the stack.
3967 As in Lua, this function may trigger a metamethod
3978 <p>
3980 and sets the stack top to this index.
3981 If the new top is larger than the old one,
3992 <p>
3993 Opaque structure that keeps the whole state of a Lua interpreter.
3994 The Lua library is fully reentrant:
3995 it has no global variables.
3996 All information about a state is kept in this structure.
3999 <p>
4000 A pointer to this state must be passed as the first argument to
4001 every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>,
4002 which creates a Lua state from scratch.
4012 <p>
4016 <p>
4017 The status can be 0 for a normal thread,
4018 an error code if the thread finished its execution with an error,
4029 <p>
4030 Converts the Lua value at the given acceptable index to a C boolean
4032 Like all tests in Lua,
4035 otherwise it returns 0.
4036 It also returns 0 when called with a non-valid index.
4037 (If you want to accept only actual boolean values,
4048 <p>
4049 Converts a value at the given acceptable index to a C function.
4050 That value must be a C function;
4061 <p>
4062 Converts the Lua value at the given acceptable index
4064 The Lua value must be a number or a string convertible to a number
4069 <p>
4070 If the number is not an integer,
4071 it is truncated in some non-specified way.
4081 <p>
4082 Converts the Lua value at the given acceptable index to a C string.
4085 The Lua value must be a string or a number;
4087 If the value is a number,
4091 when <a href="#lua_tolstring"><code>lua_tolstring</code></a> is applied to keys during a table traversal.)
4094 <p>
4096 to a string inside the Lua state.
4098 after its last character (as in C),
4099 but can contain other zeros in its body.
4100 Because Lua has garbage collection,
4101 there is no guarantee that the pointer returned by <a href="#lua_tolstring"><code>lua_tolstring</code></a>
4102 will be valid after the corresponding value is removed from the stack.
4112 <p>
4113 Converts the Lua value at the given acceptable index
4114 to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>).
4115 The Lua value must be a number or a string convertible to a number
4127 <p>
4128 Converts the value at the given acceptable index to a generic
4130 The value can be a userdata, a table, a thread, or a function;
4132 Different objects will give different pointers.
4133 There is no way to convert the pointer back to its original value.
4136 <p>
4137 Typically this function is used only for debug information.
4147 <p>
4148 Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>.
4158 <p>
4159 Converts the value at the given acceptable index to a Lua thread
4161 This value must be a thread;
4172 <p>
4173 If the value at the given acceptable index is a full userdata,
4174 returns its block address.
4175 If the value is a light userdata,
4176 returns its pointer.
4187 <p>
4188 Returns the type of the value in the given acceptable index,
4190 (that is, an index to an "empty" stack position).
4191 The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants
4201 and
4212 <p>
4221 <pre>typedef int (*lua_Writer) (lua_State *L,
4222 const void* p,
4223 size_t sz,
4224 void* ud);</pre>
4226 <p>
4228 Every time it produces another piece of chunk,
4235 <p>
4236 The writer returns an error code:
4239 calling the writer again.
4249 <p>
4253 <p>
4265 <p>
4266 Yields a coroutine.
4269 <p>
4270 This function should only be called as the
4271 return expression of a C function, as follows:
4273 <pre>
4274 return lua_yield (L, nresults);
4275 </pre><p>
4277 the running coroutine suspends its execution,
4278 and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns.
4290 <p>
4291 Lua has no built-in debugging facilities.
4292 Instead, it offers a special interface
4294 This interface allows the construction of different
4295 kinds of debuggers, profilers, and other tools
4296 that need "inside information" from the interpreter.
4301 <pre>typedef struct lua_Debug {
4302 int event;
4303 const char *name; /* (n) */
4304 const char *namewhat; /* (n) */
4305 const char *what; /* (S) */
4306 const char *source; /* (S) */
4307 int currentline; /* (l) */
4308 int nups; /* (u) number of upvalues */
4309 int linedefined; /* (S) */
4310 int lastlinedefined; /* (S) */
4311 char short_src[LUA_IDSIZE]; /* (S) */
4312 /* private part */
4314 } lua_Debug;</pre>
4316 <p>
4317 A structure used to carry different pieces of
4318 information about an active function.
4320 of this structure, for later use.
4321 To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information,
4325 <p>
4328 <ul>
4331 If the function was defined in a string,
4333 If the function was defined in a file,
4335 </li>
4339 </li>
4342 the line number where the definition of the function starts.
4343 </li>
4346 the line number where the definition of the function ends.
4347 </li>
4354 In the latter case,
4355 Lua has no other information about the function.
4356 </li>
4359 the current line where the given function is executing.
4360 When no line information is available,
4362 </li>
4365 a reasonable name for the given function.
4366 Because functions in Lua are first-class values,
4367 they do not have a fixed name:
4368 some functions can be the value of multiple global variables,
4369 while others can be stored only in a table field.
4371 called to find a suitable name.
4372 If it cannot find a name,
4374 </li>
4381 according to how the function was called.
4382 (Lua uses the empty string when no other option seems to apply.)
4383 </li>
4386 the number of upvalues of the function.
4387 </li>
4389 </ul>
4398 <p>
4399 Returns the current hook function.
4409 <p>
4410 Returns the current hook count.
4420 <p>
4421 Returns the current hook mask.
4431 <p>
4432 Returns information about a specific function or function invocation.
4435 <p>
4436 To get information about a function invocation,
4442 <p>
4443 To get information about a function you push it onto the stack
4445 (In that case,
4448 you can write the following code:
4450 <pre>
4451 lua_Debug ar;
4452 lua_getfield(L, LUA_GLOBALSINDEX, "f"); /* get global 'f' */
4454 printf("%d\n", ar.linedefined);
4455 </pre>
4457 <p>
4460 a value to be pushed on the stack:
4462 <ul>
4465 </li>
4470 </li>
4473 </li>
4476 </li>
4479 pushes onto the stack the function that is
4480 running at the given level;
4481 </li>
4484 pushes onto the stack a table whose indices are the
4485 numbers of the lines that are valid on the function.
4487 that is, a line where you can put a break point.
4488 Non-valid lines include empty lines and comments.)
4489 </li>
4491 </ul>
4493 <p>
4494 This function returns 0 on error
4505 <p>
4506 Gets information about a local variable of a given activation record.
4511 (1 is the first parameter or active local variable, and so on,
4512 until the last active local variable).
4513 <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack
4514 and returns its name.
4517 <p>
4519 represent internal variables
4520 (loop control variables, temporaries, and C function locals).
4523 <p>
4525 when the index is greater than
4526 the number of active local variables.
4536 <p>
4537 Get information about the interpreter runtime stack.
4540 <p>
4543 of the function executing at a given level.
4547 when called with a level greater than the stack depth,
4548 it returns 0.
4558 <p>
4559 Gets information about a closure's upvalue.
4560 (For Lua functions,
4561 upvalues are the external local variables that the function uses,
4562 and that are consequently included in its closure.)
4563 <a href="#lua_getupvalue"><code>lua_getupvalue</code></a> gets the index <code>n</code> of an upvalue,
4564 pushes the upvalue's value onto the stack,
4565 and returns its name.
4567 (Upvalues have no particular order,
4568 as they are active through the whole function.
4569 So, they are numbered in an arbitrary order.)
4572 <p>
4574 when the index is greater than the number of upvalues.
4576 as a name for all upvalues.
4585 <p>
4586 Type for debugging hook functions.
4589 <p>
4592 Lua identifies these events with the following constants:
4593 <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>,
4594 <a name="pdf-LUA_HOOKTAILRET"><code>LUA_HOOKTAILRET</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>,
4601 In the latter case, Lua is simulating a return from
4602 a function that did a tail call;
4606 <p>
4607 While Lua is running a hook, it disables other calls to hooks.
4608 Therefore, if a hook calls back Lua to execute a function or a chunk,
4609 this execution occurs without any calls to hooks.
4619 <p>
4620 Sets the debugging hook function.
4623 <p>
4626 it is formed by a bitwise or of the constants
4633 For each event, the hook is called as explained below:
4635 <ul>
4638 The hook is called just after Lua enters the new function,
4639 before the function gets its arguments.
4640 </li>
4643 The hook is called just before Lua leaves the function.
4644 You have no access to the values to be returned by the function.
4645 </li>
4648 start the execution of a new line of code,
4649 or when it jumps back in the code (even to the same line).
4650 (This event only happens while Lua is executing a Lua function.)
4651 </li>
4655 (This event only happens while Lua is executing a Lua function.)
4656 </li>
4658 </ul>
4660 <p>
4671 <p>
4672 Sets the value of a local variable of a given activation record.
4673 Parameters <code>ar</code> and <code>n</code> are as in <a href="#lua_getlocal"><code>lua_getlocal</code></a>
4675 <a href="#lua_setlocal"><code>lua_setlocal</code></a> assigns the value at the top of the stack
4676 to the variable and returns its name.
4677 It also pops the value from the stack.
4680 <p>
4682 when the index is greater than
4683 the number of active local variables.
4693 <p>
4694 Sets the value of a closure's upvalue.
4695 It assigns the value at the top of the stack
4696 to the upvalue and returns its name.
4697 It also pops the value from the stack.
4698 Parameters <code>funcindex</code> and <code>n</code> are as in the <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>
4702 <p>
4704 when the index is greater than the number of upvalues.
4714 <p>
4717 to interface C with Lua.
4718 While the basic API provides the primitive functions for all
4719 interactions between C and Lua,
4720 the auxiliary library provides higher-level functions for some
4721 common tasks.
4724 <p>
4725 All functions from the auxiliary library
4730 <p>
4731 All functions in the auxiliary library are built on
4732 top of the basic API,
4733 and so they provide nothing that cannot be done with this API.
4736 <p>
4737 Several functions in the auxiliary library are used to
4738 check C function arguments.
4740 All of these functions throw an error if the check is not satisfied.
4741 Because the error message is formatted for arguments
4742 (e.g., "<code>bad argument #1</code>"),
4743 you should not use these functions for other stack values.
4749 <p>
4750 Here we list all functions and types from the auxiliary library
4751 in alphabetical order.
4759 <p>
4771 <p>
4775 The string may contain embedded zeros.
4785 <p>
4798 <p>
4802 The string may not contain embedded zeros.
4812 <p>
4813 Adds the value at the top of the stack
4816 Pops the value.
4819 <p>
4820 This is the only function on string buffers that can (and must)
4821 be called with an extra element on the stack,
4822 which is the value to be added to the buffer.
4830 <pre>void luaL_argcheck (lua_State *L,
4831 int cond,
4832 int narg,
4833 const char *extramsg);</pre>
4835 <p>
4837 If not, raises an error with the following message,
4840 <pre>
4842 </pre>
4851 <p>
4852 Raises an error with the following message,
4855 <pre>
4857 </pre>
4859 <p>
4860 This function never returns,
4861 but it is an idiom to use it in C functions
4871 <p>
4875 <p>
4876 A string buffer allows C code to build Lua strings piecemeal.
4877 Its pattern of use is as follows:
4879 <ul>
4881 <li>First you declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li>
4885 <li>
4886 Then you add string pieces to the buffer calling any of
4888 </li>
4890 <li>
4892 This call leaves the final string on the top of the stack.
4893 </li>
4895 </ul>
4897 <p>
4898 During its normal operation,
4899 a string buffer uses a variable number of stack slots.
4900 So, while using a buffer, you cannot assume that you know where
4901 the top of the stack is.
4902 You can use the stack between successive calls to buffer operations
4903 as long as that use is balanced;
4904 that is,
4905 when you call a buffer operation,
4906 the stack is at the same level
4907 it was immediately after the previous buffer operation.
4909 After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its
4910 level when the buffer was initialized,
4911 plus the final string on its top.
4921 <p>
4923 This function does not allocate any space;
4924 the buffer must be declared as a variable
4935 <p>
4936 Calls a metamethod.
4939 <p>
4942 this function calls this field and passes the object as its only argument.
4943 In this case this function returns 1 and pushes onto the
4944 stack the value returned by the call.
4945 If there is no metatable or no metamethod,
4946 this function returns 0 (without pushing any value on the stack).
4956 <p>
4957 Checks whether the function has an argument
4968 <p>
4980 <p>
4992 <p>
5004 <p>
5006 and returns this string;
5008 with the string's length.
5011 <p>
5013 so all conversions and caveats of that function apply here.
5023 <p>
5025 and returns this number.
5033 <pre>int luaL_checkoption (lua_State *L,
5034 int narg,
5035 const char *def,
5036 const char *const lst[]);</pre>
5038 <p>
5041 (which must be NULL-terminated).
5042 Returns the index in the array where the string was found.
5043 Raises an error if the argument is not a string or
5044 if the string cannot be found.
5047 <p>
5053 <p>
5054 This is a useful function for mapping strings to C enums.
5055 (The usual convention in Lua libraries is
5056 to use strings instead of numbers to select options.)
5066 <p>
5068 raising an error if the stack cannot grow to that size.
5079 <p>
5081 and returns this string.
5084 <p>
5086 so all conversions and caveats of that function apply here.
5096 <p>
5098 See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>.
5108 <p>
5110 of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>).
5120 <p>
5121 Loads and runs the given file.
5122 It is defined as the following macro:
5124 <pre>
5126 </pre><p>
5127 It returns 0 if there are no errors
5128 or 1 in case of errors.
5138 <p>
5139 Loads and runs the given string.
5140 It is defined as the following macro:
5142 <pre>
5144 </pre><p>
5145 It returns 0 if there are no errors
5146 or 1 in case of errors.
5156 <p>
5157 Raises an error.
5159 plus any extra arguments,
5161 It also adds at the beginning of the message the file name and
5162 the line number where the error occurred,
5163 if this information is available.
5166 <p>
5167 This function never returns,
5168 but it is an idiom to use it in C functions
5179 <p>
5182 If the object does not have a metatable,
5183 or if the metatable does not have this field,
5184 returns 0 and pushes nothing.
5194 <p>
5204 <pre>const char *luaL_gsub (lua_State *L,
5205 const char *s,
5206 const char *p,
5207 const char *r);</pre>
5209 <p>
5213 Pushes the resulting string on the stack and returns it.
5221 <pre>int luaL_loadbuffer (lua_State *L,
5222 const char *buff,
5223 size_t sz,
5224 const char *name);</pre>
5226 <p>
5227 Loads a buffer as a Lua chunk.
5232 <p>
5235 used for debug information and error messages.
5245 <p>
5246 Loads a file as a Lua chunk.
5250 then it loads from the standard input.
5254 <p>
5257 if it cannot open/read the file.
5260 <p>
5262 it does not run it.
5272 <p>
5273 Loads a string as a Lua chunk.
5278 <p>
5282 <p>
5284 it does not run it.
5294 <p>
5296 returns 0.
5297 Otherwise,
5298 creates a new table to be used as a metatable for userdata,
5300 and returns 1.
5303 <p>
5304 In both cases pushes onto the stack the final value associated
5315 <p>
5316 Creates a new Lua state.
5319 and then sets a panic function (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) that prints
5320 an error message to the standard error output in case of fatal
5321 errors.
5324 <p>
5325 Returns the new state,
5336 <p>
5337 Opens all standard Lua libraries into the given state.
5347 <p>
5352 Otherwise, raises an error.
5360 <pre>lua_Integer luaL_optinteger (lua_State *L,
5361 int narg,
5362 lua_Integer d);</pre>
5364 <p>
5369 Otherwise, raises an error.
5379 <p>
5384 Otherwise, raises an error.
5392 <pre>const char *luaL_optlstring (lua_State *L,
5393 int narg,
5394 const char *d,
5395 size_t *l);</pre>
5397 <p>
5399 returns this string.
5402 Otherwise, raises an error.
5405 <p>
5417 <p>
5419 returns this number.
5422 Otherwise, raises an error.
5430 <pre>const char *luaL_optstring (lua_State *L,
5431 int narg,
5432 const char *d);</pre>
5434 <p>
5436 returns this string.
5439 Otherwise, raises an error.
5449 <p>
5450 Returns an address to a space of size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>
5453 After copying the string into this space you must call
5454 <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add
5455 it to the buffer.
5465 <p>
5467 the top of the stack.
5477 <p>
5480 for the object at the top of the stack (and pops the object).
5483 <p>
5484 A reference is a unique integer key.
5489 Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object.
5492 <p>
5494 <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>.
5503 <pre>typedef struct luaL_Reg {
5504 const char *name;
5505 lua_CFunction func;
5506 } luaL_Reg;</pre>
5508 <p>
5509 Type for arrays of functions to be registered by
5512 the function.
5522 <pre>void luaL_register (lua_State *L,
5523 const char *libname,
5524 const luaL_Reg *l);</pre>
5526 <p>
5527 Opens a library.
5530 <p>
5536 <p>
5544 reuses this table instead of creating a new one.
5547 <p>
5548 In any case the function leaves the table
5549 on the top of the stack.
5559 <p>
5560 Returns the name of the type of the value at the given index.
5570 <p>
5571 Generates an error with a message like the following:
5573 <pre>
5574 <em>location</em>: bad argument <em>narg</em> to '<em>func</em>' (<em>tname</em> expected, got <em>rt</em>)
5575 </pre><p>
5576 where <code><em>location</em></code> is produced by <a href="#luaL_where"><code>luaL_where</code></a>,
5588 <p>
5591 The entry is removed from the table,
5592 so that the referred object can be collected.
5596 <p>
5597 If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>,
5608 <p>
5609 Pushes onto the stack a string identifying the current position
5611 Typically this string has the following format:
5613 <pre>
5615 </pre><p>
5618 etc.
5621 <p>
5622 This function is used to build a prefix for error messages.
5632 <p>
5633 The standard Lua libraries provide useful functions
5634 that are implemented directly through the C API.
5635 Some of these functions provide essential services to the language
5636 (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>);
5637 others provide access to "outside" services (e.g., I/O);
5638 and others could be implemented in Lua itself,
5639 but are quite useful or have critical performance requirements that
5643 <p>
5644 All libraries are implemented through the official C API
5645 and are provided as separate C modules.
5646 Currently, Lua has the following standard libraries:
5648 <ul>
5666 </ul><p>
5667 Except for the basic and package libraries,
5668 each library provides all its functions as fields of a global table
5669 or as methods of its objects.
5672 <p>
5673 To have access to these libraries,
5674 the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function,
5675 which opens all standard libraries.
5676 Alternatively,
5677 it can open them individually by calling
5687 and should not be called directly:
5688 you must call them like any other Lua C function,
5695 <p>
5696 The basic library provides some core functions to Lua.
5697 If you do not include this library in your application,
5698 you should check carefully whether you need to provide
5699 implementations for some of its facilities.
5702 <p>
5704 Issues an error when
5706 otherwise, returns all its arguments.
5708 when absent, it defaults to "assertion failed!"
5713 <p>
5717 <p>
5718 This function is a generic interface to the garbage collector.
5721 <ul>
5724 performs a full garbage-collection cycle.
5725 This is the default option.
5726 </li>
5729 stops the garbage collector.
5730 </li>
5733 restarts the garbage collector.
5734 </li>
5737 returns the total memory in use by Lua (in Kbytes).
5738 </li>
5741 performs a garbage-collection step.
5743 (larger values mean more steps) in a non-specified way.
5744 If you want to control the step size
5747 </li>
5753 </li>
5759 </li>
5761 </ul>
5765 <p>
5767 Opens the named file and executes its contents as a Lua chunk.
5768 When called without arguments,
5770 Returns all values returned by the chunk.
5777 <p>
5779 Terminates the last protected function called
5784 <p>
5786 at the beginning of the message.
5793 to the message.
5798 <p>
5800 A global variable (not a function) that
5802 Lua itself does not use this variable;
5803 changing its value does not affect any environment,
5804 nor vice-versa.
5810 <p>
5812 Returns the current environment in use by the function.
5814 that specifies the function at that stack level:
5816 If the given function is not a Lua function,
5824 <p>
5828 <p>
5830 Otherwise,
5832 returns the associated value.
5833 Otherwise, returns the metatable of the given object.
5838 <p>
5842 <p>
5844 so that the construction
5846 <pre>
5848 </pre><p>
5849 will iterate over the pairs (<code>1,t[1]</code>), (<code>2,t[2]</code>), ···,
5850 up to the first integer key absent from the table.
5855 <p>
5859 <p>
5862 with previous results.
5866 <p>
5867 If there are no errors,
5868 returns the compiled chunk as a function;
5870 The environment of the returned function is the global environment.
5873 <p>
5875 and debug information.
5876 When absent,
5877 it defaults to "<code>=(load)</code>".
5882 <p>
5886 <p>
5889 or from the standard input,
5890 if no file name is given.
5895 <p>
5899 <p>
5901 but gets the chunk from the given string.
5904 <p>
5905 To load and run a given string, use the idiom
5907 <pre>
5908 assert(loadstring(s))()
5909 </pre>
5911 <p>
5912 When absent,
5918 <p>
5922 <p>
5923 Allows a program to traverse all fields of a table.
5924 Its first argument is a table and its second argument
5925 is an index in this table.
5927 and its associated value.
5930 and its associated value.
5931 When called with the last index,
5935 In particular,
5939 <p>
5940 The order in which the indices are enumerated is not specified,
5942 (To traverse a table in numeric order,
5946 <p>
5948 during the traversal,
5949 you assign any value to a non-existent field in the table.
5950 You may however modify existing fields.
5951 In particular, you may clear existing fields.
5956 <p>
5960 <p>
5961 Returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>,
5962 so that the construction
5964 <pre>
5966 </pre><p>
5970 <p>
5972 the table during its traversal.
5977 <p>
5981 <p>
5986 and returns a status code.
5987 Its first result is the status code (a boolean),
5988 which is true if the call succeeds without errors.
5990 after this first result.
5996 <p>
5998 Receives any number of arguments,
6000 using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert them to strings.
6002 but only as a quick way to show a value,
6003 typically for debugging.
6009 <p>
6012 without invoking any metamethod.
6013 Returns a boolean.
6018 <p>
6021 without invoking any metamethod.
6028 <p>
6031 without invoking any metamethod.
6037 <p>
6043 <p>
6047 <p>
6056 <p>
6060 <p>
6061 Sets the environment to be used by the given function.
6063 that specifies the function at that stack level:
6068 <p>
6070 the environment of the running thread.
6076 <p>
6080 <p>
6081 Sets the metatable for the given table.
6082 (You cannot change the metatable of other types from Lua, only from C.)
6084 removes the metatable of the given table.
6086 raises an error.
6089 <p>
6095 <p>
6097 Tries to convert its argument to a number.
6098 If the argument is already a number or a string convertible
6103 <p>
6104 An optional argument specifies the base to interpret the numeral.
6109 In base 10 (the default), the number can have a decimal part,
6111 In other bases, only unsigned integers are accepted.
6116 <p>
6118 Receives an argument of any type and
6119 converts it to a string in a reasonable format.
6120 For complete control of how numbers are converted,
6124 <p>
6128 and uses the result of the call as its result.
6133 <p>
6135 Returns the type of its only argument, coded as a string.
6136 The possible results of this function are
6138 "<code>number</code>",
6139 "<code>string</code>",
6140 "<code>boolean</code>",
6141 "<code>table</code>",
6142 "<code>function</code>",
6143 "<code>thread</code>",
6144 and "<code>userdata</code>".
6149 <p>
6151 Returns the elements from the given table.
6152 This function is equivalent to
6154 <pre>
6156 </pre><p>
6157 except that the above code can be written only for a fixed number
6158 of elements.
6165 <p>
6167 A global variable (not a function) that
6168 holds a string containing the current interpreter version.
6169 The current contents of this variable is "<code>Lua 5.1</code>".
6174 <p>
6178 <p>
6180 except that you can set a new error handler.
6183 <p>
6189 and returns a status code.
6190 Its first result is the status code (a boolean),
6191 which is true if the call succeeds without errors.
6193 after this first result.
6194 In case of any error,
6205 <p>
6206 The operations related to coroutines comprise a sub-library of
6207 the basic library and come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>.
6211 <p>
6215 <p>
6218 Returns this new coroutine,
6224 <p>
6225 <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3>
6228 <p>
6230 The first time you resume a coroutine,
6231 it starts running its body.
6233 as the arguments to the body function.
6234 If the coroutine has yielded,
6237 as the results from the yield.
6240 <p>
6241 If the coroutine runs without any errors,
6243 (if the coroutine yields) or any values returned by the body function
6244 (if the coroutine terminates).
6245 If there is any error,
6251 <p>
6255 <p>
6256 Returns the running coroutine,
6262 <p>
6266 <p>
6271 or if it has not started running yet;
6273 (that is, it has resumed another coroutine);
6275 or if it has stopped with an error.
6280 <p>
6284 <p>
6287 Returns a function that resumes the coroutine each time it is called.
6288 Any arguments passed to the function behave as the
6291 except the first boolean.
6292 In case of error, propagates the error.
6297 <p>
6298 <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3>
6301 <p>
6302 Suspends the execution of the calling coroutine.
6303 The coroutine cannot be running a C function,
6304 a metamethod, or an iterator.
6315 <p>
6316 The package library provides basic
6317 facilities for loading and building modules in Lua.
6318 It exports two of its functions directly in the global environment:
6319 <a href="#pdf-require"><code>require</code></a> and <a href="#pdf-module"><code>module</code></a>.
6323 <p>
6327 <p>
6328 Creates a module.
6330 this table is the module.
6332 this table is the module.
6339 (the full module name minus last component; see below).
6345 <p>
6347 (that is, one with components separated by dots),
6349 tables for each component.
6355 <p>
6357 the module name,
6358 where each option is a function to be applied over the module.
6363 <p>
6367 <p>
6368 Loads the given module.
6369 The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table
6376 <p>
6377 To find a loader,
6378 <code>require</code> is guided by the <a href="#pdf-package.loaders"><code>package.loaders</code></a> array.
6379 By changing this array,
6381 The following explanation is based on the default configuration
6385 <p>
6387 If it has a value,
6388 this value (which should be a function) is the loader.
6391 If that also fails, it searches for a C loader using the
6393 If that also fails,
6394 it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.loaders"><code>package.loaders</code></a>).
6397 <p>
6398 Once a loader is found,
6400 If the loader returns any value,
6402 If the loader returns no value and
6409 <p>
6410 If there is any error loading or running the module,
6411 or if it cannot find any loader for the module,
6417 <p>
6421 <p>
6422 The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader.
6425 <p>
6426 Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way
6434 <p>
6439 <p>
6441 modules are already loaded.
6449 <p>
6453 <p>
6454 A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules.
6457 <p>
6459 When looking for a module,
6460 <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order,
6461 with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its
6462 sole parameter.
6464 or a string explaining why it did not find that module
6466 Lua initializes this table with four functions.
6469 <p>
6470 The first searcher simply looks for a loader in the
6474 <p>
6475 The second searcher looks for a loader as a Lua library,
6478 For each template,
6479 the searcher will change each interrogation
6481 which is the module name with each dot replaced by a
6483 then it will try to open the resulting file name.
6484 So, for instance, if the Lua path is the string
6486 <pre>
6487 "./?.lua;./?.lc;/usr/local/?/init.lua"
6488 </pre><p>
6490 will try to open the files
6495 <p>
6496 The third searcher looks for a loader as a C library,
6497 using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>.
6498 For instance,
6499 if the C path is the string
6501 <pre>
6502 "./?.so;./?.dll;/usr/local/?/init.so"
6503 </pre><p>
6507 Once it finds a C library,
6508 this searcher first uses a dynamic link facility to link the
6509 application with the library.
6510 Then it tries to find a C function inside the library to
6511 be used as the loader.
6513 concatenated with a copy of the module name where each dot
6514 is replaced by an underscore.
6515 Moreover, if the module name has a hyphen,
6516 its prefix up to (and including) the first hyphen is removed.
6521 <p>
6523 It searches the C path for a library for
6524 the root name of the given module.
6527 If found, it looks into it for an open function for
6528 the submodule;
6530 With this facility, a package can pack several C submodules
6531 into one single library,
6532 with each submodule keeping its original open function.
6537 <p>
6538 <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3>
6541 <p>
6544 and returns this function as a C function.
6545 (So, <code>funcname</code> must follow the protocol (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>)).
6548 <p>
6549 This is a low-level function.
6550 It completely bypasses the package and module system.
6552 it does not perform any path searching and
6553 does not automatically adds extensions.
6555 including if necessary a path and extension.
6557 (which may depend on the C compiler and linker used).
6560 <p>
6561 This function is not supported by ANSI C.
6562 As such, it is only available on some platforms
6563 (Windows, Linux, Mac OS X, Solaris, BSD,
6569 <p>
6573 <p>
6577 <p>
6578 At start-up, Lua initializes this variable with
6581 if the environment variable is not defined.
6582 Any "<code>;;</code>" in the value of the environment variable
6583 is replaced by the default path.
6588 <p>
6592 <p>
6593 A table to store loaders for specific modules
6599 <p>
6603 <p>
6606 so that this module inherits values
6607 from the global environment.
6618 <p>
6619 This library provides generic functions for string manipulation,
6620 such as finding and extracting substrings, and pattern matching.
6623 Indices are allowed to be negative and are interpreted as indexing backwards,
6624 from the end of the string.
6625 Thus, the last character is at position -1, and so on.
6628 <p>
6629 The string library provides all its functions inside the table
6631 It also sets a metatable for strings
6633 Therefore, you can use the string functions in object-oriented style.
6638 <p>
6639 The string library assumes one-byte character encodings.
6642 <p>
6650 <p>
6651 Note that numerical codes are not necessarily portable across platforms.
6656 <p>
6658 Receives zero or more integers.
6659 Returns a string with length equal to the number of arguments,
6660 in which each character has the internal numerical code equal
6661 to its corresponding argument.
6664 <p>
6665 Note that numerical codes are not necessarily portable across platforms.
6670 <p>
6674 <p>
6675 Returns a string containing a binary representation of the given function,
6677 a copy of the function.
6683 <p>
6684 <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3>
6685 Looks for the first match of
6688 where this occurrence starts and ends;
6691 where to start the search;
6694 turns off the pattern matching facilities,
6695 so the function does a plain "find substring" operation,
6700 <p>
6701 If the pattern has captures,
6702 then in a successful match
6703 the captured values are also returned,
6704 after the two indices.
6709 <p>
6710 <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3>
6711 Returns a formatted version of its variable number of arguments
6712 following the description given in its first argument (which must be a string).
6714 standard C functions.
6715 The only differences are that the options/modifiers
6720 back by the Lua interpreter:
6721 the string is written between double quotes,
6722 and all double quotes, newlines, embedded zeros,
6723 and backslashes in the string
6724 are correctly escaped when written.
6725 For instance, the call
6727 <pre>
6728 string.format('%q', 'a string with "quotes" and \n new line')
6729 </pre><p>
6730 will produce the string:
6732 <pre>
6734 new line"
6735 </pre>
6737 <p>
6739 <code>g</code>, <code>G</code>, <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> all
6740 expect a number as argument,
6744 <p>
6745 This function does not accept string values
6746 containing embedded zeros,
6752 <p>
6754 Returns an iterator function that,
6755 each time it is called,
6758 then the whole match is produced in each call.
6761 <p>
6762 As an example, the following loop
6764 <pre>
6765 s = "hello world from Lua"
6766 for w in string.gmatch(s, "%a+") do
6767 print(w)
6768 end
6769 </pre><p>
6771 printing one per line.
6773 given string into a table:
6775 <pre>
6776 t = {}
6777 s = "from=world, to=Lua"
6778 for k, v in string.gmatch(s, "(%w+)=(%w+)") do
6779 t[k] = v
6780 end
6781 </pre>
6783 <p>
6785 work as an anchor, as this would prevent the iteration.
6790 <p>
6796 which can be a string, a table, or a function.
6798 the total number of matches that occurred.
6801 <p>
6811 <p>
6813 using the first capture as the key;
6814 if the pattern specifies no captures,
6815 then the whole match is used as the key.
6818 <p>
6820 match occurs, with all captured substrings passed as arguments,
6821 in order;
6822 if the pattern specifies no captures,
6823 then the whole match is passed as a sole argument.
6826 <p>
6827 If the value returned by the table query or by the function call
6828 is a string or a number,
6829 then it is used as the replacement string;
6831 then there is no replacement
6832 (that is, the original match is kept in the string).
6835 <p>
6836 Here are some examples:
6838 <pre>
6852 return loadstring(s)()
6853 end)
6859 </pre>
6863 <p>
6865 Receives a string and returns its length.
6867 Embedded zeros are counted,
6873 <p>
6875 Receives a string and returns a copy of this string with all
6876 uppercase letters changed to lowercase.
6877 All other characters are left unchanged.
6878 The definition of what an uppercase letter is depends on the current locale.
6883 <p>
6888 the captures from the pattern;
6891 then the whole match is returned.
6893 where to start the search;
6899 <p>
6907 <p>
6914 <p>
6920 (which is the same as the string length).
6921 In particular,
6930 <p>
6932 Receives a string and returns a copy of this string with all
6933 lowercase letters changed to uppercase.
6934 All other characters are left unchanged.
6935 The definition of what a lowercase letter is depends on the current locale.
6944 The following combinations are allowed in describing a character class:
6946 <ul>
6952 </li>
6978 This is the standard way to escape the magic characters.
6979 Any punctuation character (even the non magic)
6981 when used to represent itself in a pattern.
6982 </li>
6985 represents the class which is the union of all
6987 A range of characters can be specified by
6993 represents all alphanumeric characters plus the underscore,
6999 <p>
7000 The interaction between ranges and classes is not defined.
7002 have no meaning.
7003 </li>
7008 </li>
7010 </ul><p>
7012 the corresponding uppercase letter represents the complement of the class.
7016 <p>
7017 The definitions of letter, space, and other character groups
7018 depend on the current locale.
7028 <ul>
7030 <li>
7031 a single character class,
7032 which matches any single character in the class;
7033 </li>
7035 <li>
7037 which matches 0 or more repetitions of characters in the class.
7038 These repetition items will always match the longest possible sequence;
7039 </li>
7041 <li>
7043 which matches 1 or more repetitions of characters in the class.
7044 These repetition items will always match the longest possible sequence;
7045 </li>
7047 <li>
7049 which also matches 0 or more repetitions of characters in the class.
7052 </li>
7054 <li>
7057 </li>
7059 <li>
7062 (see below);
7063 </li>
7065 <li>
7069 This means that, if one reads the string from left to right,
7073 balanced parentheses.
7074 </li>
7076 </ul>
7084 beginning of the subject string.
7086 end of the subject string.
7087 At other positions,
7095 A pattern can contain sub-patterns enclosed in parentheses;
7097 When a match succeeds, the substrings of the subject string
7099 Captures are numbered according to their left parentheses.
7107 <p>
7109 the current string position (a number).
7114 <p>
7128 This library provides generic functions for table manipulation.
7132 <p>
7133 Most functions in the table library assume that the table
7134 represents an array or a list.
7135 For these functions, when we talk about the "length" of a table
7136 we mean the result of the length operator.
7139 <p>
7140 <hr><h3><a name="pdf-table.concat"><code>table.concat (table [, sep [, i [, j]]])</code></a></h3>
7141 Given an array where all elements are strings or numbers,
7151 <p>
7155 <p>
7157 shifting up other elements to open space, if necessary.
7166 <p>
7170 <p>
7171 Returns the largest positive numerical index of the given table,
7172 or zero if the table has no positive numerical indices.
7173 (To do its job this function does a linear traversal of
7174 the whole table.)
7179 <p>
7183 <p>
7185 shifting down other elements to close the space, if necessary.
7186 Returns the value of the removed element.
7195 <p>
7201 then it must be a function that receives two table elements,
7202 and returns true
7203 when the first is less than the second
7209 <p>
7210 The sort algorithm is not stable;
7211 that is, elements considered equal by the given order
7212 may have their relative positions changed by the sort.
7222 <p>
7223 This library is an interface to the standard C math library.
7227 <p>
7231 <p>
7237 <p>
7241 <p>
7247 <p>
7251 <p>
7257 <p>
7261 <p>
7267 <p>
7271 <p>
7273 but uses the signs of both parameters to find the
7274 quadrant of the result.
7280 <p>
7284 <p>
7290 <p>
7294 <p>
7300 <p>
7304 <p>
7310 <p>
7314 <p>
7320 <p>
7324 <p>
7330 <p>
7334 <p>
7340 <p>
7344 <p>
7346 that rounds the quotient towards zero.
7351 <p>
7355 <p>
7364 <p>
7368 <p>
7370 a value larger than or equal to any other numerical value.
7375 <p>
7379 <p>
7385 <p>
7389 <p>
7395 <p>
7399 <p>
7405 <p>
7409 <p>
7410 Returns the maximum value among its arguments.
7415 <p>
7419 <p>
7420 Returns the minimum value among its arguments.
7425 <p>
7429 <p>
7430 Returns two numbers,
7436 <p>
7440 <p>
7446 <p>
7450 <p>
7457 <p>
7461 <p>
7467 <p>
7471 <p>
7472 This function is an interface to the simple
7474 (No guarantees can be given for its statistical properties.)
7477 <p>
7478 When called without arguments,
7479 returns a uniform pseudo-random real number
7491 <p>
7495 <p>
7497 for the pseudo-random generator:
7498 equal seeds produce equal sequences of numbers.
7503 <p>
7507 <p>
7513 <p>
7517 <p>
7523 <p>
7527 <p>
7534 <p>
7538 <p>
7544 <p>
7548 <p>
7559 <p>
7560 The I/O library provides two different styles for file manipulation.
7561 The first one uses implicit file descriptors;
7562 that is, there are operations to set a default input file and a
7563 default output file,
7564 and all input/output operations are over these default files.
7565 The second style uses explicit file descriptors.
7568 <p>
7569 When using implicit file descriptors,
7571 When using explicit file descriptors,
7573 and then all operations are supplied as methods of the file descriptor.
7576 <p>
7578 three predefined file descriptors with their usual meanings from C:
7579 <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>.
7580 The I/O library never closes these files.
7583 <p>
7584 Unless otherwise stated,
7586 (plus an error message as a second result and
7587 a system-dependent error code as a third result)
7591 <p>
7595 <p>
7602 <p>
7606 <p>
7612 <p>
7616 <p>
7617 When called with a file name, it opens the named file (in text mode),
7618 and sets its handle as the default input file.
7619 When called with a file handle,
7620 it simply sets this file handle as the default input file.
7621 When called without parameters,
7622 it returns the current default input file.
7625 <p>
7626 In case of errors this function raises the error,
7627 instead of returning an error code.
7632 <p>
7636 <p>
7637 Opens the given file name in read mode
7638 and returns an iterator function that,
7639 each time it is called,
7640 returns a new line from the file.
7641 Therefore, the construction
7643 <pre>
7645 </pre><p>
7646 will iterate over all lines of the file.
7647 When the iterator function detects the end of file,
7651 <p>
7654 that is, it iterates over the lines of the default input file.
7655 In this case it does not close the file when the loop ends.
7660 <p>
7664 <p>
7665 This function opens a file,
7667 It returns a new file handle,
7671 <p>
7674 <ul>
7681 writing is only allowed at the end of file.</li>
7682 </ul><p>
7684 which is needed in some systems to open the file in binary mode.
7685 This string is exactly what is used in the
7691 <p>
7695 <p>
7696 Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file.
7701 <p>
7705 <p>
7707 a file handle that you can use to read data from this program
7709 or to write data to this program
7713 <p>
7714 This function is system dependent and is not available
7715 on all platforms.
7720 <p>
7724 <p>
7730 <p>
7734 <p>
7735 Returns a handle for a temporary file.
7736 This file is opened in update mode
7737 and it is automatically removed when the program ends.
7742 <p>
7746 <p>
7755 <p>
7759 <p>
7765 <p>
7769 <p>
7771 Note that files are automatically closed when
7772 their handles are garbage collected,
7773 but that takes an unpredictable amount of time to happen.
7778 <p>
7782 <p>
7788 <p>
7792 <p>
7793 Returns an iterator function that,
7794 each time it is called,
7795 returns a new line from the file.
7796 Therefore, the construction
7798 <pre>
7800 </pre><p>
7801 will iterate over all lines of the file.
7802 (Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file
7803 when the loop ends.)
7808 <p>
7812 <p>
7814 according to the given formats, which specify what to read.
7815 For each format,
7816 the function returns a string (or a number) with the characters read,
7818 When called without formats,
7819 it uses a default format that reads the entire next line
7820 (see below).
7823 <p>
7824 The available formats are
7826 <ul>
7829 reads a number;
7830 this is the only format that returns a number instead of a string.
7831 </li>
7834 reads the whole file, starting at the current position.
7835 On end of file, it returns the empty string.
7836 </li>
7839 reads the next line (skipping the end of line),
7841 This is the default format.
7842 </li>
7845 reads a string with up to this number of characters,
7847 If number is zero,
7848 it reads nothing and returns an empty string,
7850 </li>
7852 </ul>
7856 <p>
7860 <p>
7861 Sets and gets the file position,
7862 measured from the beginning of the file,
7866 <ul>
7870 </ul><p>
7872 measured in bytes from the beginning of the file.
7874 plus a string describing the error.
7877 <p>
7881 file position, without changing it;
7883 beginning of the file (and returns 0);
7885 end of the file, and returns its size.
7890 <p>
7894 <p>
7895 Sets the buffering mode for an output file.
7896 There are three available modes:
7898 <ul>
7901 no buffering; the result of any output operation appears immediately.
7902 </li>
7905 full buffering; output operation is performed only
7908 </li>
7911 line buffering; output is buffered until a newline is output
7912 or there is any input from some special files
7913 (such as a terminal device).
7914 </li>
7916 </ul><p>
7918 specifies the size of the buffer, in bytes.
7919 The default is an appropriate size.
7924 <p>
7928 <p>
7929 Writes the value of each of its arguments to
7931 The arguments must be strings or numbers.
7932 To write other values,
7933 use <a href="#pdf-tostring"><code>tostring</code></a> or <a href="#pdf-string.format"><code>string.format</code></a> before <code>write</code>.
7943 <p>
7947 <p>
7951 <p>
7952 Returns an approximation of the amount in seconds of CPU time
7953 used by the program.
7958 <p>
7962 <p>
7963 Returns a string or a table containing date and time,
7967 <p>
7969 this is the time to be formatted
7970 (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value).
7974 <p>
7976 then the date is formatted in Coordinated Universal Time.
7977 After this optional character,
7987 <p>
7993 <p>
7994 When called without arguments,
7996 the host system and on the current locale
8002 <p>
8006 <p>
8008 In POSIX, Windows, and some other systems,
8014 <p>
8018 <p>
8021 It returns a status code, which is system-dependent.
8023 and zero otherwise.
8028 <p>
8032 <p>
8035 to terminate the host program.
8041 <p>
8045 <p>
8052 <p>
8056 <p>
8057 Deletes the file or directory with the given name.
8058 Directories must be empty to be removed.
8060 plus a string describing the error.
8065 <p>
8069 <p>
8072 plus a string describing the error.
8077 <p>
8081 <p>
8082 Sets the current locale of the program.
8088 The function returns the name of the new locale,
8092 <p>
8094 the current locale is set to an implementation-defined native locale.
8096 the current locale is set to the standard C locale.
8099 <p>
8101 this function only returns the name of the current locale
8102 for the given category.
8107 <p>
8111 <p>
8112 Returns the current time when called without arguments,
8113 or a time representing the date and time specified by the given table.
8115 and may have fields <code>hour</code>, <code>min</code>, <code>sec</code>, and <code>isdst</code>
8116 (for a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function).
8119 <p>
8120 The returned value is a number, whose meaning depends on your system.
8121 In POSIX, Windows, and some other systems, this number counts the number
8122 of seconds since some given start time (the "epoch").
8123 In other systems, the meaning is not specified,
8130 <p>
8134 <p>
8135 Returns a string with a file name that can
8136 be used for a temporary file.
8137 The file must be explicitly opened before its use
8138 and explicitly removed when no longer needed.
8141 <p>
8142 On some systems (POSIX),
8143 this function also creates a file with that name,
8144 to avoid security risks.
8145 (Someone else might create the file with wrong permissions
8146 in the time between getting the name and creating the file.)
8147 You still have to open the file to use it
8148 and to remove it (even if you do not use it).
8151 <p>
8152 When possible,
8154 which automatically removes the file when the program ends.
8164 <p>
8165 This library provides
8166 the functionality of the debug interface to Lua programs.
8167 You should exert care when using this library.
8168 The functions provided here should be used exclusively for debugging
8169 and similar tasks, such as profiling.
8170 Please resist the temptation to use them as a
8171 usual programming tool:
8172 they can be very slow.
8173 Moreover, several of these functions
8174 violate some assumptions about Lua code
8175 (e.g., that variables local to a function
8176 cannot be accessed from outside or
8177 that userdata metatables cannot be changed by Lua code)
8178 and therefore can compromise otherwise secure code.
8181 <p>
8182 All functions in this library are provided
8184 All functions that operate over a thread
8185 have an optional first argument which is the
8186 thread to operate over.
8187 The default is always the current thread.
8190 <p>
8194 <p>
8195 Enters an interactive mode with the user,
8196 running each string that the user enters.
8197 Using simple commands and other debug facilities,
8198 the user can inspect global and local variables,
8199 change their values, evaluate expressions, and so on.
8201 so that the caller continues its execution.
8204 <p>
8206 within any function, and so have no direct access to local variables.
8211 <p>
8218 <p>
8222 <p>
8223 Returns the current hook settings of the thread, as three values:
8224 the current hook function, the current hook mask,
8225 and the current hook count
8231 <p>
8232 <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] function [, what])</code></a></h3>
8235 <p>
8236 Returns a table with information about a function.
8237 You can give the function directly,
8240 of the given thread:
8243 and so on.
8248 <p>
8249 The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>,
8252 except the table of valid lines.
8253 If present,
8256 If present,
8259 valid lines.
8262 <p>
8264 a table with a name for the current function,
8265 if a reasonable name can be found,
8267 returns a table with all available information
8273 <p>
8274 <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] level, local)</code></a></h3>
8277 <p>
8278 This function returns the name and the value of the local variable
8281 until the last active local variable.)
8283 variable with the given index,
8285 (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.)
8288 <p>
8290 represent internal variables
8291 (loop control variables, temporaries, and C function locals).
8296 <p>
8300 <p>
8307 <p>
8311 <p>
8317 <p>
8321 <p>
8322 This function returns the name and the value of the upvalue
8329 <p>
8333 <p>
8340 <p>
8341 <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3>
8344 <p>
8345 Sets the given function as a hook.
8347 when the hook will be called.
8348 The string mask may have the following characters,
8349 with the given meaning:
8351 <ul>
8355 </ul><p>
8360 <p>
8361 When called without arguments,
8365 <p>
8366 When the hook is called, its first parameter is a string
8367 describing the event that has triggered its call:
8369 when simulating a return from a tail call),
8371 For line events,
8372 the hook also gets the new line number as its second parameter.
8373 Inside a hook,
8375 the running function
8379 In this case, Lua is only simulating the return,
8385 <p>
8386 <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3>
8389 <p>
8393 variable with the given index,
8396 Otherwise, it returns the name of the local variable.
8401 <p>
8402 <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (object, table)</code></a></h3>
8405 <p>
8412 <p>
8413 <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (func, up, value)</code></a></h3>
8416 <p>
8420 with the given index.
8421 Otherwise, it returns the name of the upvalue.
8426 <p>
8427 <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3>
8430 <p>
8431 Returns a string with a traceback of the call stack.
8433 at the beginning of the traceback.
8435 to start the traceback
8446 <p>
8447 Although Lua has been designed as an extension language,
8448 to be embedded in a host C program,
8449 it is also frequently used as a stand-alone language.
8450 An interpreter for Lua as a stand-alone language,
8452 is provided with the standard distribution.
8453 The stand-alone interpreter includes
8454 all standard libraries, including the debug library.
8455 Its usage is:
8457 <pre>
8458 lua [options] [script [args]]
8459 </pre><p>
8460 The options are:
8462 <ul>
8468 <li><b><code>-</code>:</b> executes <code>stdin</code> as a file and stops handling options.</li>
8469 </ul><p>
8472 When called without arguments,
8478 <p>
8479 Before running any argument,
8480 the interpreter checks for an environment variable <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a>.
8486 <p>
8488 For instance, an invocation like
8490 <pre>
8491 $ lua -e'a=1' -e 'print(a)' script.lua
8492 </pre><p>
8493 will first set <code>a</code> to 1, then print the value of <code>a</code> (which is '<code>1</code>'),
8498 <p>
8499 Before starting to run the script,
8502 The script name is stored at index 0,
8503 the first argument after the script name goes to index 1,
8504 and so on.
8505 Any arguments before the script name
8506 (that is, the interpreter name plus the options)
8507 go to negative indices.
8508 For instance, in the call
8510 <pre>
8511 $ lua -la b.lua t1 t2
8512 </pre><p>
8514 then creates a table
8516 <pre>
8520 </pre><p>
8523 as arguments;
8527 <p>
8528 In interactive mode,
8529 if you write an incomplete statement,
8530 the interpreter waits for its completion
8531 by issuing a different prompt.
8534 <p>
8536 then its value is used as the prompt.
8537 Similarly, if the global variable <a name="pdf-_PROMPT2"><code>_PROMPT2</code></a> contains a string,
8538 its value is used as the secondary prompt
8539 (issued during incomplete statements).
8540 Therefore, both prompts can be changed directly on the command line
8542 See the next example:
8544 <pre>
8545 $ lua -e"_PROMPT='myprompt> '" -i
8546 </pre><p>
8547 (The outer pair of quotes is for the shell,
8548 the inner pair is for Lua.)
8550 otherwise,
8551 the program would just end silently
8555 <p>
8556 To allow the use of Lua as a
8557 script interpreter in Unix systems,
8558 the stand-alone interpreter skips
8560 Therefore, Lua scripts can be made into executable programs
8562 as in
8564 <pre>
8565 #!/usr/local/bin/lua
8566 </pre><p>
8567 (Of course,
8568 the location of the Lua interpreter may be different in your machine.
8570 then
8572 <pre>
8573 #!/usr/bin/env lua
8574 </pre><p>
8575 is a more portable solution.)
8581 <p>
8582 Here we list the incompatibilities that you may find when moving a program
8584 You can avoid most of the incompatibilities compiling Lua with
8586 However,
8587 all these compatibility options will be removed in the next version of Lua.
8592 <ul>
8594 <li>
8596 table with the extra arguments to the vararg expression.
8598 </li>
8600 <li>
8601 There was a subtle change in the scope of the implicit
8603 </li>
8605 <li>
8607 does not allow nesting.
8610 </li>
8612 </ul>
8618 <ul>
8620 <li>
8621 Function <code>string.gfind</code> was renamed <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>.
8623 </li>
8625 <li>
8627 third argument,
8629 replacement string is the whole match,
8630 instead of the empty string.
8631 </li>
8633 <li>
8637 use the operator instead of the function.
8639 </li>
8641 <li>
8642 Function <code>loadlib</code> was renamed <a href="#pdf-package.loadlib"><code>package.loadlib</code></a>.
8644 </li>
8646 <li>
8647 Function <code>math.mod</code> was renamed <a href="#pdf-math.fmod"><code>math.fmod</code></a>.
8649 </li>
8651 <li>
8654 </li>
8656 <li>
8657 There were substantial changes in function <a href="#pdf-require"><code>require</code></a> due to
8658 the new module system.
8659 However, the new behavior is mostly compatible with the old,
8660 but <code>require</code> gets the path from <a href="#pdf-package.path"><code>package.path</code></a> instead
8662 </li>
8664 <li>
8665 Function <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> has different arguments.
8668 </li>
8670 </ul>
8676 <ul>
8678 <li>
8680 cannot be called directly,
8681 like a regular C function.
8682 They must be called through Lua,
8683 like a Lua function.
8684 </li>
8686 <li>
8687 Function <code>lua_open</code> was replaced by <a href="#lua_newstate"><code>lua_newstate</code></a> to
8688 allow the user to set a memory-allocation function.
8689 You can use <a href="#luaL_newstate"><code>luaL_newstate</code></a> from the standard library to
8690 create a state with a standard allocation function
8692 </li>
8694 <li>
8696 (from the auxiliary library) are deprecated.
8699 </li>
8701 <li>
8702 Function <code>luaL_openlib</code> was replaced by <a href="#luaL_register"><code>luaL_register</code></a>.
8703 </li>
8705 <li>
8707 is not a userdata of the expected type.
8709 </li>
8711 </ul>
8718 <p>
8719 Here is the complete syntax of Lua in extended BNF.
8720 (It does not describe operator precedences.)
8725 <pre>
8729 block ::= chunk
8732 functioncall |
8736 <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> |
8737 <b>for</b> Name `<b>=</b>´ exp `<b>,</b>´ exp [`<b>,</b>´ exp] <b>do</b> block <b>end</b> |
8749 var ::= Name | prefixexp `<b>[</b>´ exp `<b>]</b>´ | prefixexp `<b>.</b>´ Name
8755 exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Number | String | `<b>...</b>´ | function |
8756 prefixexp | tableconstructor | exp binop exp | unop exp
8772 fieldlist ::= field {fieldsep field} [fieldsep]
8774 field ::= `<b>[</b>´ exp `<b>]</b>´ `<b>=</b>´ exp | Name `<b>=</b>´ exp | exp
8778 binop ::= `<b>+</b>´ | `<b>-</b>´ | `<b>*</b>´ | `<b>/</b>´ | `<b>^</b>´ | `<b>%</b>´ | `<b>..</b>´ |
8779 `<b><</b>´ | `<b><=</b>´ | `<b>></b>´ | `<b>>=</b>´ | `<b>==</b>´ | `<b>~=</b>´ |
8784 </pre>
8786 <p>
8794 <HR>
8796 Last update:
8798 </SMALL>
8799 <!--
8800 Last change: revised for Lua 5.1.5
8801 -->
8803 </body></html>