1 .\" Copyright (c) 1990, 1991 The Regents of the University of California.
2 .\" All rights reserved.
4 .\" This code is derived from software contributed to Berkeley by
5 .\" Chris Torek and the American National Standards Committee X3,
6 .\" on Information Processing Systems.
8 .\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
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19 .\" This product includes software developed by the University of
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38 .\" @(#)fopen.3 6.8 (Berkeley) 6/29/91
40 .\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu
41 .\" Modified, aeb, 960421, 970806
42 .\" Modified, joey, aeb, 2002-01-03
44 .TH FOPEN 3 2012-04-22 "GNU" "Linux Programmer's Manual"
46 fopen, fdopen, freopen \- stream open functions
51 .BI "FILE *fopen(const char *" path ", const char *" mode );
53 .BI "FILE *fdopen(int " fd ", const char *" mode );
55 .BI "FILE *freopen(const char *" path ", const char *" mode ", FILE *" stream );
59 Feature Test Macro Requirements for glibc (see
60 .BR feature_test_macros (7)):
64 _POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _POSIX_SOURCE
68 function opens the file whose name is the string pointed to by
70 and associates a stream with it.
74 points to a string beginning with one of the following sequences
75 (possibly followed by additional characters, as described below):
78 Open text file for reading.
79 The stream is positioned at the beginning of the file.
82 Open for reading and writing.
83 The stream is positioned at the beginning of the file.
86 Truncate file to zero length or create text file for writing.
87 The stream is positioned at the beginning of the file.
90 Open for reading and writing.
91 The file is created if it does not exist, otherwise it is truncated.
92 The stream is positioned at the beginning of
96 Open for appending (writing at end of file).
97 The file is created if it does not exist.
98 The stream is positioned at the end of the file.
101 Open for reading and appending (writing at end of file).
102 The file is created if it does not exist.
103 The initial file position for reading is at the beginning of the file,
104 but output is always appended to the end of the file.
108 string can also include the letter \(aqb\(aq either as a last character or as
109 a character between the characters in any of the two-character strings
111 This is strictly for compatibility with C89
112 and has no effect; the \(aqb\(aq is ignored on all POSIX
113 conforming systems, including Linux.
114 (Other systems may treat text files and binary files differently,
115 and adding the \(aqb\(aq may be a good idea if you do I/O to a binary
116 file and expect that your program may be ported to non-UNIX
119 See NOTES below for details of glibc extensions for
122 Any created files will have mode
123 .BR S_IRUSR " | " S_IWUSR " | " S_IRGRP " | " S_IWGRP " | " S_IROTH " | " S_IWOTH
124 (0666), as modified by the process's umask value (see
127 Reads and writes may be intermixed on read/write streams in any order.
128 Note that ANSI C requires that a file positioning function intervene
129 between output and input, unless an input operation encounters end-of-file.
130 (If this condition is not met, then a read is allowed to return the
131 result of writes other than the most recent.)
132 Therefore it is good practice (and indeed sometimes necessary
133 under Linux) to put an
137 operation between write and read operations on such a stream.
138 This operation may be an apparent no-op
139 (as in \fIfseek(..., 0L, SEEK_CUR)\fP
140 called for its synchronizing side effect).
142 Opening a file in append mode (\fBa\fP as the first character of
144 causes all subsequent write operations to this stream to occur
145 at end-of-file, as if preceded the call:
148 fseek(stream, 0, SEEK_END);
153 function associates a stream with the existing file descriptor,
157 of the stream (one of the values "r", "r+", "w", "w+", "a", "a+")
158 must be compatible with the mode of the file descriptor.
159 The file position indicator of the new stream is set to that
162 and the error and end-of-file indicators are cleared.
163 Modes "w" or "w+" do not cause truncation of the file.
164 The file descriptor is not dup'ed, and will be closed when
165 the stream created by
168 The result of applying
170 to a shared memory object is undefined.
174 function opens the file whose name is the string pointed to by
176 and associates the stream pointed to by
179 The original stream (if it exists) is closed.
182 argument is used just as in the
185 The primary use of the
187 function is to change the file associated with a standard text stream
188 .RI ( stderr ", " stdin ", or " stdout ).
190 Upon successful completion
198 Otherwise, NULL is returned and
200 is set to indicate the error.
218 functions may also fail and set
220 for any of the errors specified for the routine
225 function may also fail and set
227 for any of the errors specified for the routine
232 function may also fail and set
234 for any of the errors specified for the routine
239 function may also fail and set
241 for any of the errors specified for the routines
251 functions conform to C89.
254 function conforms to POSIX.1-1990.
257 The GNU C library allows the following extensions for the string specified in
260 .BR c " (since glibc 2.3.3)"
261 Do not make the open operation,
262 or subsequent read and write operations,
263 thread cancellation points.
264 This flag is ignored for
267 .BR e " (since glibc 2.7)"
268 Open the file with the
273 for more information.
274 This flag is ignored for
277 .BR m " (since glibc 2.3)"
278 Attempt to access the file using
280 rather than I/O system calls
287 is attempted only for a file opened for reading.
291 .\" FIXME C11 specifies this flag
292 Open the file exclusively
297 If the file already exists,
303 This flag is ignored for
306 In addition to the above characters,
310 support the following syntax
318 is taken as the name of a coded character set and
319 the stream is marked as wide-oriented.
320 Thereafter, internal conversion functions convert I/O
321 to and from the character set
325 syntax is not specified,
326 then the wide-orientation of the stream is
327 determined by the first file operation.
328 If that operation is a wide-character operation,
329 the stream is marked wide-oriented,
330 and functions to convert to the coded character set are loaded.
332 When parsing for individual flag characters in
334 (i.e., the characters preceding the "ccs" specification),
335 the glibc implementation of
336 .\" FIXME http://sourceware.org/bugzilla/show_bug.cgi?id=12685
340 limits the number of characters examined in
342 to 7 (or, in glibc versions before 2.14, to 6,
343 which was not enough to include possible specifications such as "rb+cmxe").
344 The current implementation of
346 parses at most 5 characters in
355 This page is part of release 3.68 of the Linux
358 A description of the project,
359 information about reporting bugs,
360 and the latest version of this page,
362 \%http://www.kernel.org/doc/man\-pages/.