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13 .TH FOPEN 3C "Apr 18, 2006"
14 .SH NAME
15 fopen \- open a stream
16 .SH SYNOPSIS
17 .LP
18 .nf
19 #include <stdio.h>
20
21 \fBFILE *\fR\fBfopen\fR(\fBconst char *\fR\fIfilename\fR, \fBconst char *\fR\fImode\fR);
22 .fi
23
24 .SH DESCRIPTION
25 .sp
26 .LP
27 The \fBfopen()\fR function opens the file whose pathname is the string pointed
28 to by \fIfilename\fR, and associates a stream with it.
29 .sp
30 .LP
31 The argument \fImode\fR points to a string beginning with one of the following
32 base sequences:
33 .sp
34 .ne 2
35 .na
36 \fB\fBr\fR\fR
37 .ad
38 .RS 20n
39 Open file for reading.
40 .RE
41
42 .sp
43 .ne 2
44 .na
45 \fB\fBw\fR\fR
46 .ad
47 .RS 20n
48 Truncate to zero length or create file for writing.
49 .RE
50
51 .sp
52 .ne 2
53 .na
54 \fB\fBa\fR\fR
55 .ad
56 .RS 20n
57 Append; open or create file for writing at end-of-file.
58 .RE
59
60 .sp
61 .ne 2
62 .na
63 \fB\fBr+\fR\fR
64 .ad
65 .RS 20n
66 Open file for update (reading and writing).
67 .RE
68
69 .sp
70 .ne 2
71 .na
72 \fB\fBw+\fR\fR
73 .ad
74 .RS 20n
75 Truncate to zero length or create file for update.
76 .RE
77
78 .sp
79 .ne 2
80 .na
81 \fB\fBa+\fR\fR
82 .ad
83 .RS 20n
84 Append; open or create file for update, writing at end-of-file.
85 .RE
86
87 .sp
88 .LP
89 In addition to the base sequences for the \fImode\fR argument above, two
90 additional flags are supported via the \fBb\fR character and the \fBe\fR
91 character. Order of these additional flags (including the \fB+\fR) does
92 not matter.
93 .sp
94 .LP
95 The character \fBb\fR has no effect, but is allowed for ISO C standard
96 conformance (see \fBstandards\fR(5)). Opening a file with read mode (\fBr\fR as
97 the first character in the \fImode\fR argument) fails if the file does not
98 exist or cannot be read.
99 .sp
100 .LP
101 The character \fBe\fR will cause the underlying file descriptor to be
102 opened with the O_CLOEXEC flag as described in \fBopen\fR(2).
103 .sp
104 .LP
105 Opening a file with append mode (\fBa\fR as the first character in the
106 \fImode\fR argument) causes all subsequent writes to the file to be forced to
107 the then current end-of-file, regardless of intervening calls to
108 \fBfseek\fR(3C). If two separate processes open the same file for append, each
109 process may write freely to the file without fear of destroying output being
110 written by the other. The output from the two processes will be intermixed in
111 the file in the order in which it is written.
112 .sp
113 .LP
114 When a file is opened with update mode (\fB+\fR as the second or third
115 character in the \fImode\fR argument), both input and output may be performed
116 on the associated stream. However, output must not be directly followed by
117 input without an intervening call to \fBfflush\fR(3C) or to a file positioning
118 function ( \fBfseek\fR(3C), \fBfsetpos\fR(3C) or \fBrewind\fR(3C)), and input
119 must not be directly followed by output without an intervening call to a file
120 positioning function, unless the input operation encounters end-of-file.
121 .sp
122 .LP
123 When opened, a stream is fully buffered if and only if it can be determined not
124 to refer to an interactive device. The error and end-of-file indicators for the
125 stream are cleared.
126 .sp
127 .LP
128 If \fImode\fR begins with \fIw\fR or \fBa\fR and the file did not previously
129 exist, upon successful completion, \fBfopen()\fR function will mark for update
130 the \fBst_atime\fR, \fBst_ctime\fR and \fBst_mtime\fR fields of the file and
131 the \fBst_ctime\fR and \fBst_mtime\fR fields of the parent directory.
132 .sp
133 .LP
134 If \fImode\fR begins with \fIw\fR and the file did previously exist, upon
135 successful completion, \fBfopen()\fR will mark for update the \fBst_ctime\fR
136 and \fBst_mtime\fR fields of the file. The \fBfopen()\fR function will
137 allocate a file descriptor as \fBopen\fR(2) does.
138 .sp
139 .LP
140 Normally, 32-bit applications return an \fBEMFILE\fR error when attempting to
141 associate a stream with a file accessed by a file descriptor with a value
142 greater than 255. If the last character of \fImode\fR is \fBF\fR, 32-bit
143 applications will be allowed to associate a stream with a file accessed by a
144 file descriptor with a value greater than 255. A \fBFILE\fR pointer obtained in
145 this way must never be used by any code that might directly access fields in
146 the \fBFILE\fR structure. If the fields in the \fBFILE\fR structure are used
147 directly by 32-bit applications when the last character of mode is \fBF\fR,
148 data corruption could occur. See the USAGE section of this manual page and the
149 \fBenable_extended_FILE_stdio\fR(3C) manual page for other options for enabling
150 the extended FILE facility.
151 .sp
152 .LP
153 In 64-bit applications, the last character of \fImode\fR is silently ignored if
154 it is \fBF\fR. 64-bit applications are always allowed to associate a stream
155 with a file accessed by a file descriptor with any value.
156 .sp
157 .LP
158 The largest value that can be represented correctly in an object of type
159 \fBoff_t\fR will be established as the offset maximum in the open file
160 description.
161 .SH RETURN VALUES
162 .sp
163 .LP
164 Upon successful completion, \fBfopen()\fR returns a pointer to the object
165 controlling the stream. Otherwise, a null pointer is returned and \fBerrno\fR
166 is set to indicate the error.
167 .sp
168 .LP
169 The \fBfopen()\fR function may fail and not set \fBerrno\fR if there are no
170 free \fBstdio\fR streams.
171 .SH ERRORS
172 .sp
173 .LP
174 The \fBfopen()\fR function will fail if:
175 .sp
176 .ne 2
177 .na
178 \fB\fBEACCES\fR\fR
179 .ad
180 .RS 16n
181 Search permission is denied on a component of the path prefix, or the file
182 exists and the permissions specified by \fImode\fR are denied, or the file does
183 not exist and write permission is denied for the parent directory of the file
184 to be created.
185 .RE
186
187 .sp
188 .ne 2
189 .na
190 \fB\fBEINTR\fR\fR
191 .ad
192 .RS 16n
193 A signal was caught during the execution of \fBfopen()\fR.
194 .RE
195
196 .sp
197 .ne 2
198 .na
199 \fB\fBEISDIR\fR\fR
200 .ad
201 .RS 16n
202 The named file is a directory and \fImode\fR requires write access.
203 .RE
204
205 .sp
206 .ne 2
207 .na
208 \fB\fBELOOP\fR\fR
209 .ad
210 .RS 16n
211 Too many symbolic links were encountered in resolving \fIpath\fR.
212 .RE
213
214 .sp
215 .ne 2
216 .na
217 \fB\fBEMFILE\fR\fR
218 .ad
219 .RS 16n
220 There are {\fBOPEN_MAX\fR} file descriptors currently open in the calling
221 process.
222 .RE
223
224 .sp
225 .ne 2
226 .na
227 \fB\fBENAMETOOLONG\fR\fR
228 .ad
229 .RS 16n
230 The length of the \fIfilename\fR exceeds \fIPATH_MAX\fR or a pathname component
231 is longer than \fINAME_MAX\fR.
232 .RE
233
234 .sp
235 .ne 2
236 .na
237 \fB\fBENFILE\fR\fR
238 .ad
239 .RS 16n
240 The maximum allowable number of files is currently open in the system.
241 .RE
242
243 .sp
244 .ne 2
245 .na
246 \fB\fBENOENT\fR\fR
247 .ad
248 .RS 16n
249 A component of \fIfilename\fR does not name an existing file or \fIfilename\fR
250 is an empty string.
251 .RE
252
253 .sp
254 .ne 2
255 .na
256 \fB\fBENOSPC\fR\fR
257 .ad
258 .RS 16n
259 The directory or file system that would contain the new file cannot be
260 expanded, the file does not exist, and it was to be created.
261 .RE
262
263 .sp
264 .ne 2
265 .na
266 \fB\fBENOTDIR\fR\fR
267 .ad
268 .RS 16n
269 A component of the path prefix is not a directory.
270 .RE
271
272 .sp
273 .ne 2
274 .na
275 \fB\fBENXIO\fR\fR
276 .ad
277 .RS 16n
278 The named file is a character special or block special file, and the device
279 associated with this special file does not exist.
280 .RE
281
282 .sp
283 .ne 2
284 .na
285 \fB\fBEOVERFLOW\fR\fR
286 .ad
287 .RS 16n
288 The current value of the file position cannot be represented correctly in an
289 object of type \fBfpos_t\fR.
290 .RE
291
292 .sp
293 .ne 2
294 .na
295 \fB\fBEROFS\fR\fR
296 .ad
297 .RS 16n
298 The named file resides on a read-only file system and \fImode\fR requires write
299 access.
300 .RE
301
302 .sp
303 .LP
304 The \fBfopen()\fR function may fail if:
305 .sp
306 .ne 2
307 .na
308 \fB\fBEINVAL\fR\fR
309 .ad
310 .RS 16n
311 The value of the \fImode\fR argument is not valid.
312 .RE
313
314 .sp
315 .ne 2
316 .na
317 \fB\fBEMFILE\fR\fR
318 .ad
319 .RS 16n
320 {\fBFOPEN_MAX\fR} streams are currently open in the calling process.
321 .sp
322 {\fBSTREAM_MAX\fR} streams are currently open in the calling process.
323 .RE
324
325 .sp
326 .ne 2
327 .na
328 \fB\fBENAMETOOLONG\fR\fR
329 .ad
330 .RS 16n
331 Pathname resolution of a symbolic link produced an intermediate result whose
332 length exceeds {\fBPATH_MAX\fR}.
333 .RE
334
335 .sp
336 .ne 2
337 .na
338 \fB\fBENOMEM\fR\fR
339 .ad
340 .RS 16n
341 Insufficient storage space is available.
342 .RE
343
344 .sp
345 .ne 2
346 .na
347 \fB\fBETXTBSY\fR\fR
348 .ad
349 .RS 16n
350 The file is a pure procedure (shared text) file that is being executed and
351 \fImode\fR requires write access.
352 .RE
353
354 .SH USAGE
355 .sp
356 .LP
357 A process is allowed to have at least {\fBFOPEN_MAX\fR} \fBstdio\fR streams
358 open at a time. For 32-bit applications, however, the underlying ABIs formerly
359 required that no file descriptor used to access the file underlying a
360 \fBstdio\fR stream have a value greater than 255. To maintain binary
361 compatibility with earlier Solaris releases, this limit still constrains 32-bit
362 applications. However, when a 32-bit application is aware that no code that has
363 access to the \fBFILE\fR pointer returned by \fBfopen()\fR will use the
364 \fBFILE\fR pointer to directly access any fields in the \fBFILE\fR structure,
365 the \fBF\fR character can be used as the last character in the \fImode\fR
366 argument to circumvent this limit. Because it could lead to data corruption,
367 the \fBF\fR character in \fImode\fR must never be used when the \fBFILE\fR
368 pointer might later be used by binary code unknown to the user. The \fBF\fR
369 character in \fImode\fR is intended to be used by library functions that need a
370 \fBFILE\fR pointer to access data to process a user request, but do not need to
371 pass the \fBFILE\fR pointer back to the user. 32-bit applications that have
372 been inspected can use the extended FILE facility to circumvent this limit if
373 the inspection shows that no \fBFILE\fR pointers will be used to directly
374 access \fBFILE\fR structure contents.
375 .sp
376 .LP
377 The \fBfopen()\fR function has a transitional interface for 64-bit file
378 offsets. See \fBlf64\fR(5).
379 .SH ATTRIBUTES
380 .sp
381 .LP
382 See \fBattributes\fR(5) for descriptions of the following attributes:
383 .sp
384
385 .sp
386 .TS
387 box;
388 c | c
389 l | l .
390 ATTRIBUTE TYPE ATTRIBUTE VALUE
391 _
392 Interface Stability See below.
393 _
394 MT-Level MT-Safe
395 .TE
396
397 .sp
398 .LP
399 The \fBF\fR character in the \fImode\fR argument is Evolving. In all other
400 respects this function is Standard.
401 .SH SEE ALSO
402 .sp
403 .LP
404 \fBenable_extended_FILE_stdio\fR(3C), \fBfclose\fR(3C), \fBfdopen\fR(3C),
405 \fBfflush\fR(3C), \fBfreopen\fR(3C), \fBfsetpos\fR(3C), \fBrewind\fR(3C),
406 \fBopen\fR(2), \fBattributes\fR(5), \fBlf64\fR(5), \fBstandards\fR(5)