1fopen(3C) Standard C Library Functions fopen(3C)
2
6 fopen - open a stream
7
9 #include <stdio.h>
10 FILE *fopen(const char *filename, const char *mode);
12
15 The fopen() function opens the file whose pathname is the string
16 pointed to by filename, and associates a stream with it.
17 The argument mode points to a string beginning with one of the follow‐
20 ing sequences:
21 r or rb Open file for reading.
23 w or wb Truncate to zero length or create file for writ‐
26 ing.
27 a or ab Append; open or create file for writing at end-of-
30 file.
31 r+ or rb+ or r+b Open file for update (reading and writing).
34 w+ or wb+ or w+b Truncate to zero length or create file for update.
37 a+ or ab+ or a+b Append; open or create file for update, writing at
40 end-of-file.
41 The character b has no effect, but is allowed for ISO C standard con‐
45 formance (see standards(5)). Opening a file with read mode (r as the
46 first character in the mode argument) fails if the file does not exist
47 or cannot be read.
48 Opening a file with append mode (a as the first character in the mode
51 argument) causes all subsequent writes to the file to be forced to the
52 then current end-of-file, regardless of intervening calls to fseek(3C).
53 If two separate processes open the same file for append, each process
54 may write freely to the file without fear of destroying output being
55 written by the other. The output from the two processes will be inter‐
56 mixed in the file in the order in which it is written.
57 When a file is opened with update mode (+ as the second or third char‐
60 acter in the mode argument), both input and output may be performed on
61 the associated stream. However, output must not be directly followed by
62 input without an intervening call to fflush(3C) or to a file position‐
63 ing function ( fseek(3C), fsetpos(3C) or rewind(3C)), and input must
64 not be directly followed by output without an intervening call to a
65 file positioning function, unless the input operation encounters end-
66 of-file.
67 When opened, a stream is fully buffered if and only if it can be deter‐
70 mined not to refer to an interactive device. The error and end-of-file
71 indicators for the stream are cleared.
72 If mode begins with w or a and the file did not previously exist, upon
75 successful completion, fopen() function will mark for update the
76 st_atime, st_ctime and st_mtime fields of the file and the st_ctime and
77 st_mtime fields of the parent directory.
78 If mode begins with w and the file did previously exist, upon success‐
81 ful completion, fopen() will mark for update the st_ctime and st_mtime
82 fields of the file. The fopen() function will allocate a file descrip‐
83 tor as open(2) does.
84 Normally, 32-bit applications return an EMFILE error when attempting to
87 associate a stream with a file accessed by a file descriptor with a
88 value greater than 255. If the last character of mode is F, 32-bit
89 applications will be allowed to associate a stream with a file accessed
90 by a file descriptor with a value greater than 255. A FILE pointer
91 obtained in this way must never be used by any code that might directly
92 access fields in the FILE structure. If the fields in the FILE struc‐
93 ture are used directly by 32-bit applications when the last character
94 of mode is F, data corruption could occur. See the USAGE section of
95 this manual page and the enable_extended_FILE_stdio(3C) manual page for
96 other options for enabling the extended FILE facility.
97 In 64-bit applications, the last character of mode is silently ignored
100 if it is F. 64-bit applications are always allowed to associate a
101 stream with a file accessed by a file descriptor with any value.
102 The largest value that can be represented correctly in an object of
105 type off_t will be established as the offset maximum in the open file
106 description.
107
109 Upon successful completion, fopen() returns a pointer to the object
110 controlling the stream. Otherwise, a null pointer is returned and
111 errno is set to indicate the error.
112 The fopen() function may fail and not set errno if there are no free
115 stdio streams.
116
118 The fopen() function will fail if:
119 EACCES Search permission is denied on a component of the path
121 prefix, or the file exists and the permissions speci‐
122 fied by mode are denied, or the file does not exist and
123 write permission is denied for the parent directory of
124 the file to be created.
125 EINTR A signal was caught during the execution of fopen().
128 EISDIR The named file is a directory and mode requires write
131 access.
132 ELOOP Too many symbolic links were encountered in resolving
135 path.
136 EMFILE There are {OPEN_MAX} file descriptors currently open in
139 the calling process.
140 ENAMETOOLONG The length of the filename exceeds PATH_MAX or a path‐
143 name component is longer than NAME_MAX.
144 ENFILE The maximum allowable number of files is currently open
147 in the system.
148 ENOENT A component of filename does not name an existing file
151 or filename is an empty string.
152 ENOSPC The directory or file system that would contain the new
155 file cannot be expanded, the file does not exist, and
156 it was to be created.
157 ENOTDIR A component of the path prefix is not a directory.
160 ENXIO The named file is a character special or block special
163 file, and the device associated with this special file
164 does not exist.
165 EOVERFLOW The current value of the file position cannot be repre‐
168 sented correctly in an object of type fpos_t.
169 EROFS The named file resides on a read-only file system and
172 mode requires write access.
173 The fopen() function may fail if:
177 EINVAL The value of the mode argument is not valid.
179 EMFILE {FOPEN_MAX} streams are currently open in the calling
182 process.
183 {STREAM_MAX} streams are currently open in the calling
185 process.
186 ENAMETOOLONG Pathname resolution of a symbolic link produced an
189 intermediate result whose length exceeds {PATH_MAX}.
190 ENOMEM Insufficient storage space is available.
193 ETXTBSY The file is a pure procedure (shared text) file that is
196 being executed and mode requires write access.
197
200 A process is allowed to have at least {FOPEN_MAX} stdio streams open at
201 a time. For 32-bit applications, however, the underlying ABIs formerly
202 required that no file descriptor used to access the file underlying a
203 stdio stream have a value greater than 255. To maintain binary compati‐
204 bility with earlier Solaris releases, this limit still constrains
205 32-bit applications. However, when a 32-bit application is aware that
206 no code that has access to the FILE pointer returned by fopen() will
207 use the FILE pointer to directly access any fields in the FILE struc‐
208 ture, the F character can be used as the last character in the mode
209 argument to circumvent this limit. Because it could lead to data cor‐
210 ruption, the F character in mode must never be used when the FILE
211 pointer might later be used by binary code unknown to the user. The F
212 character in mode is intended to be used by library functions that need
213 a FILE pointer to access data to process a user request, but do not
214 need to pass the FILE pointer back to the user. 32-bit applications
215 that have been inspected can use the extended FILE facility to circum‐
216 vent this limit if the inspection shows that no FILE pointers will be
217 used to directly access FILE structure contents.
218 The fopen() function has a transitional interface for 64-bit file off‐
221 sets. See lf64(5).
222
224 See attributes(5) for descriptions of the following attributes:
225 ┌─────────────────────────────┬─────────────────────────────┐
230 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
231 ├─────────────────────────────┼─────────────────────────────┤
232 │Interface Stability │See below. │
233 ├─────────────────────────────┼─────────────────────────────┤
234 │MT-Level │MT-Safe │
235 └─────────────────────────────┴─────────────────────────────┘
236 The F character in the mode argument is Evolving. In all other respects
239 this function is Standard.
240
242 enable_extended_FILE_stdio(3C), fclose(3C), fdopen(3C), fflush(3C),
243 freopen(3C), fsetpos(3C), rewind(3C), attributes(5), lf64(5), stan‐
244 dards(5)
245SunOS 5.11 18 Apr 2006 fopen(3C)