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16 <p>C's standard library contains many features and functions
17 which we haven't seen.
19 but not all.
20 Besides format specifier characters for a few types we haven't seen,
22 you can also control the width, precision,
23 justification (left or right)
25 (In their full complexity,
32 </p><p>The
34 functions
35 let you
36 ``print'' and ``read''
37 to and from in-memory strings instead of files.
39 string into an integer;
41 <pre>
42 int i = 10;
43 char str[10];
44 sprintf(str, "%d", i);
45 </pre>
48 to read and write characters.
49 There are also functions
51 for reading and writing lines
52 (though we rarely need these,
56 for reading or writing arbitrary numbers of characters.
57 </p><p>It's possible to ``un-read'' a character,
58 that is,
60 (This is useful if you accidentally read one character too far,
61 and would prefer that some other part of your program
62 read that character instead.)
63 </p><p>You can use the
65 to jump around in files,
66 performing random access (as opposed to sequential) I/O.
69 condition or due to a read error of some sort.
70 You can clear errors and end-of-file conditions with
72 </p><p>You can open files in ``binary'' mode, or for
73 simultaneous
75 reading and writing.
76 (These options involve extra characters
81 A second set of string functions
83 all
84 accept a third argument telling them to
89 operate on blocks of memory
90 which aren't necessarily strings
93 find characters in strings.
94 There is a motley collection
95 of ``span'' and ``scan'' functions,
97 for searching out or skipping over sequences of characters all
98 drawn from a specified set of characters.
100 into words or ``tokens,''
103 which let you classify and manipulate characters:
104 check for letters or digits,
105 convert between upper- and lower-case,
106 etc.
107 </p><p>A host of mathematical functions
110 you may on some Unix systems
111 have to ask for a special library containing the math functions
112 while compiling/linking.)
119 <pre>
121 </pre>
122 Another way is
123 <pre>
125 </pre>
126 It seems like it would be simpler to just say
127 <pre>
128 rand() % n + 1
129 </pre>
130 but this method is imperfect
131 (or rather, it's imperfect if
133 and
135 as all too many of them are).
136 </p><p>Several functions let you interact with
137 the operating system under which your program is running.
139 returns control to the operating system immediately,
140 terminating your program
141 and returning an ``exit status.''
143 your operating system's
144 or process's
145 ``environment variables''
146 (if any).
148 allows you to invoke an operating-system command
149 (i.e. another program)
150 from within your program.
152 (of any type);
153 you supply a comparison function
154 (via a function pointer)
155 which knows how to compare two array elements,
158 search for elements in sorted arrays;
159 it, too, operates in terms of a caller-supplied comparison function.
167 and
169 you to determine the current date and time,
170 print dates and times,
171 and perform other date/time manipulations.
172 For example, to print today's date in a program,
173 you can write
174 <pre>
177 time_t now;
178 now = time((time_t *)NULL);
180 </pre>
182 variable-length function argument lists
185 let you write your own functions which accept
187 variable numbers of arguments but call on the
189 </p><p>There are facilities for dealing with
190 multibyte and ``wide'' characters and strings,
191 for use with multinational character sets.
192 </p><hr>
193 <p>
194 Read sequentially:
198 </p>
199 <p>
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