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32 .\" @(#)stdio.3 6.5 (Berkeley) 5/6/91
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34 .\" Converted for Linux, Mon Nov 29 16:07:22 1993, faith@cs.unc.edu
35 .\" Modified, 2001-12-26, aeb
36 .\"
37 .TH STDIO 3 2001-12-26 "" "Linux Programmer's Manual"
38 .SH NAME
39 stdio \- standard input/output library functions
40 .SH SYNOPSIS
41 .B #include <stdio.h>
42 .sp
43 .B FILE *stdin;
44 .br
45 .B FILE *stdout;
46 .br
47 .B FILE *stderr;
48 .SH DESCRIPTION
49 The standard I/O library provides a simple and efficient buffered stream
50 I/O interface. Input and output is mapped into logical data streams and the
51 physical I/O characteristics are concealed. The functions and macros are
52 listed below; more information is available from the individual man pages.
53 .PP
54 A stream is associated with an external file (which may be a physical
55 device) by
56 .I opening
57 a file, which may involve creating a new file. Creating an existing file
58 causes its former contents to be discarded. If a file can support
59 positioning requests (such as a disk file, as opposed to a terminal) then a
60 .I file position indicator
61 associated with the stream is positioned at the start of the file (byte
62 zero), unless the file is opened with append mode. If append mode is used,
63 it is unspecified whether the position indicator will be placed at the
64 start or the end of the file. The position indicator is maintained by
65 subsequent reads, writes and positioning requests. All input occurs
66 as if the characters were read by successive calls to the
67 .BR fgetc (3)
68 function; all output takes place as if all characters were written by
69 successive calls to the
70 .BR fputc (3)
71 function.
72 .PP
73 A file is disassociated from a stream by
74 .I closing
75 the file. Output streams are flushed (any unwritten buffer contents are
76 transferred to the host environment) before the stream is disassociated from
77 the file. The value of a pointer to a
78 .B FILE
79 object is indeterminate after a file is closed (garbage).
80 .PP
81 A file may be subsequently reopened, by the same or another program
82 execution, and its contents reclaimed or modified (if it can be
83 repositioned at the start). If the main function returns to its original
84 caller, or the
85 .BR exit (3)
86 function is called, all open files are closed (hence all output streams are
87 flushed) before program termination. Other methods of program termination,
88 such as
89 .BR abort (3)
90 do not bother about closing files properly.
91 .PP
92 At program startup, three text streams are predefined and need not be
93 opened explicitly \(em
94 .I standard input
95 (for reading conventional input), \(em
96 .I standard output
97 (for writing conventional input), and
98 .I standard error
99 (for writing diagnostic output). These streams are abbreviated
100 .IR stdin , stdout
101 and
102 .IR stderr .
103 When opened, the standard error stream is not fully buffered; the standard
104 input and output streams are fully buffered if and only if the streams do
105 not to refer to an interactive device.
106 .PP
107 Output streams that refer to terminal devices are always line buffered by
108 default; pending output to such streams is written automatically whenever
109 an input stream that refers to a terminal device is read. In cases where a
110 large amount of computation is done after printing part of a line on an
111 output terminal, it is necessary to
112 .BR fflush (3)
113 the standard output before going off and computing so that the output will
114 appear.
115 .PP
116 The
117 .B stdio
118 library is a part of the library
119 .B libc
120 and routines are automatically loaded as needed by the compilers
121 .BR cc (1)
122 and
123 .BR pc (1).
124 The
125 .B SYNOPSIS
126 sections of the following manual pages indicate which include files are to
127 be used, what the compiler declaration for the function looks like and
128 which external variables are of interest.
129 .PP
130 The following are defined as macros; these names may not be re-used without
131 first removing their current definitions with
132 .BR #undef :
133 .BR BUFSIZ ,
134 .BR EOF ,
135 .BR FILENAME_MAX ,
136 .BR FOPEN_MAX ,
137 .BR L_cuserid ,
138 .BR L_ctermid ,
139 .BR L_tmpnam,
140 .BR NULL ,
141 .BR SEEK_END ,
142 .BR SEEK_SET ,
143 .BR SEE_CUR ,
144 .BR TMP_MAX ,
145 .BR clearerr ,
146 .BR feof ,
147 .BR ferror ,
148 .BR fileno ,
149 .BR fropen ,
150 .BR fwopen ,
151 .BR getc ,
152 .BR getchar ,
153 .BR putc ,
154 .BR putchar ,
155 .BR stderr ,
156 .BR stdin ,
157 .BR stdout .
158 Function versions of the macro functions
159 .BR feof ,
160 .BR ferror ,
161 .BR clearerr ,
162 .BR fileno ,
163 .BR getc ,
164 .BR getchar ,
165 .BR putc ,
166 and
167 .B putchar
168 exist and will be used if the macros definitions are explicitly removed.
169 .SH "LIST OF FUNCTIONS"
170 .TP 10n
171 .B Function
172 .B Description
173 .TP
174 .B clearerr
175 check and reset stream status
176 .TP
177 .B fclose
178 close a stream
179 .TP
180 .B fdopen
181 stream open functions
182 .TP
183 .B feof
184 check and reset stream status
185 .TP
186 .B ferror
187 check and reset stream status
188 .TP
189 .B fflush
190 flush a stream
191 .TP
192 .B fgetc
193 get next character or word from input stream
194 .\" .TP
195 .\" .B fgetline
196 .\" get a line from a stream (BSD only; renamed to fgetln())
197 .TP
198 .B fgetpos
199 reposition a stream
200 .TP
201 .B fgets
202 get a line from a stream
203 .TP
204 .B fileno
205 return the integer descriptor of the argument stream
206 .TP
207 .B fopen
208 stream open functions
209 .TP
210 .B fprintf
211 formatted output conversion
212 .TP
213 .B fpurge
214 flush a stream
215 .TP
216 .B fputc
217 output a character or word to a stream
218 .TP
219 .B fputs
220 output a line to a stream
221 .TP
222 .B fread
223 binary stream input/output
224 .TP
225 .B freopen
226 stream open functions
227 .TP
228 .B fropen
229 open a stream
230 .TP
231 .B fscanf
232 input format conversion
233 .TP
234 .B fseek
235 reposition a stream
236 .TP
237 .B fsetpos
238 reposition a stream
239 .TP
240 .B ftell
241 reposition a stream
242 .TP
243 .B fwrite
244 binary stream input/output
245 .TP
246 .B getc
247 get next character or word from input stream
248 .TP
249 .B getchar
250 get next character or word from input stream
251 .TP
252 .B gets
253 get a line from a stream
254 .TP
255 .B getw
256 get next character or word from input stream
257 .TP
258 .B mktemp
259 make temporary file name (unique)
260 .TP
261 .B perror
262 system error messages
263 .TP
264 .B printf
265 formatted output conversion
266 .TP
267 .B putc
268 output a character or word to a stream
269 .TP
270 .B putchar
271 output a character or word to a stream
272 .TP
273 .B puts
274 output a line to a stream
275 .TP
276 .B putw
277 output a character or word to a stream
278 .TP
279 .B remove
280 remove directory entry
281 .TP
282 .B rewind
283 reposition a stream
284 .TP
285 .B scanf
286 input format conversion
287 .TP
288 .B setbuf
289 stream buffering operations
290 .TP
291 .B setbuffer
292 stream buffering operations
293 .TP
294 .B setlinebuf
295 stream buffering operations
296 .TP
297 .B setvbuf
298 stream buffering operations
299 .TP
300 .B sprintf
301 formatted output conversion
302 .TP
303 .B sscanf
304 input format conversion
305 .TP
306 .B strerror
307 system error messages
308 .TP
309 .B sys_errlist
310 system error messages
311 .TP
312 .B sys_nerr
313 system error messages
314 .TP
315 .B tempnam
316 temporary file routines
317 .TP
318 .B tmpfile
319 temporary file routines
320 .TP
321 .B tmpnam
322 temporary file routines
323 .TP
324 .B ungetc
325 un-get character from input stream
326 .TP
327 .B vfprintf
328 formatted output conversion
329 .TP
330 .B vfscanf
331 input format conversion
332 .TP
333 .B vprintf
334 formatted output conversion
335 .TP
336 .B vscanf
337 input format conversion
338 .TP
339 .B vsprintf
340 formatted output conversion
341 .TP
342 .B vsscanf
343 input format conversion
344 .SH "CONFORMING TO"
345 The
346 .B stdio
347 library conforms to ANSI X3.159-1989 (``ANSI C'').
348 .SH "SEE ALSO"
349 .BR open (2),
350 .BR close (2),
351 .BR read (2),
352 .BR write (2),
353 .BR stdout (3)