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1 .\" $NetBSD: fopen.3,v 1.24 2010/04/05 21:34:47 joerg Exp $
2 .\"
3 .\" Copyright (c) 1990, 1991, 1993
4 .\" The Regents of the University of California. All rights reserved.
5 .\"
6 .\" This code is derived from software contributed to Berkeley by
7 .\" Chris Torek and the American National Standards Committee X3,
8 .\" on Information Processing Systems.
9 .\"
10 .\" Redistribution and use in source and binary forms, with or without
11 .\" modification, are permitted provided that the following conditions
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13 .\" 1. Redistributions of source code must retain the above copyright
14 .\" notice, this list of conditions and the following disclaimer.
15 .\" 2. Redistributions in binary form must reproduce the above copyright
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17 .\" documentation and/or other materials provided with the distribution.
18 .\" 3. Neither the name of the University nor the names of its contributors
19 .\" may be used to endorse or promote products derived from this software
20 .\" without specific prior written permission.
21 .\"
22 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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33 .\"
34 .\" @(#)fopen.3 8.1 (Berkeley) 6/4/93
35 .\"
36 .Dd June 4, 1993
37 .Dt FOPEN 3
38 .Os
39 .Sh NAME
40 .Nm fopen ,
41 .Nm fdopen ,
42 .Nm freopen
43 .Nd stream open functions
44 .Sh LIBRARY
45 .Lb libc
46 .Sh SYNOPSIS
47 .In stdio.h
48 .Ft FILE *
49 .Fn fopen "const char * restrict path" "const char * restrict mode"
50 .Ft FILE *
51 .Fn fdopen "int fildes" "const char *mode"
52 .Ft FILE *
53 .Fn freopen "const char * restrict path" "const char * restrict mode" "FILE * restrict stream"
54 .Sh DESCRIPTION
55 The
56 .Fn fopen
57 function
58 opens the file whose name is the string pointed to by
59 .Fa path
60 and associates a stream with it.
61 .Pp
62 The argument
63 .Fa mode
64 points to a string beginning with one of the following
65 sequences (Additional characters may follow these sequences.):
66 .Bl -tag -width indent
67 .It Dq Li r
68 Open for reading.
69 .It Dq Li r+
70 Open for reading and writing.
71 .It Dq Li w
72 Open for writing.
73 Truncate file to zero length or create file.
74 .It Dq Li w+
75 Open for reading and writing.
76 Truncate file to zero length or create file.
77 .It Dq Li a
78 Append; open for writing.
79 The file is created if it does not exist.
80 .It Dq Li a+
81 Append; open for reading and writing.
82 The file is created if it does not exist.
83 .El
84 .Pp
85 The
86 .Fa mode
87 string can also include the letter ``b'' either as a last character or
88 as a character between the characters in any of the two-character strings
89 described above.
90 This is strictly for compatibility with
91 .St -ansiC
92 and has no effect; the ``b'' is ignored.
93 .Pp
94 The letter ``f'' in the mode string restricts fopen to regular
95 files; if the file opened is not a regular file,
96 .Fn fopen
97 will fail.
98 This is a non
99 .St -ansiC
100 extension.
101 .Pp
102 Any created files will have mode
103 .Pf \*q Dv S_IRUSR
104 \&|
105 .Dv S_IWUSR
106 \&|
107 .Dv S_IRGRP
108 \&|
109 .Dv S_IWGRP
110 \&|
111 .Dv S_IROTH
112 \&|
113 .Dv S_IWOTH Ns \*q
114 .Pq Li 0666 ,
115 as modified by the process'
116 umask value (see
117 .Xr umask 2 ) .
118 .Pp
119 Opening a file with append mode causes all subsequent writes to it
120 to be forced to the then current end of file, regardless of intervening
121 repositioning of the stream.
122 .Pp
123 The
124 .Fn fopen
125 and
126 .Fn freopen
127 functions initially position the stream at the start of the file
128 unless the file is opened with append mode,
129 in which case the stream is initially positioned at the end of the file.
130 .\" PR 6072 claims this paragraph is not correct.
131 .\" .Pp
132 .\" Reads and writes may be intermixed on read/write streams in any order,
133 .\" and do not require an intermediate seek as in previous versions of
134 .\" .Em stdio .
135 .\" This is not portable to other systems, however;
136 .\" .Tn ANSI C
137 .\" requires that
138 .\" a file positioning function intervene between output and input, unless
139 .\" an input operation encounters end-of-file.
140 .Pp
141 The
142 .Fn fdopen
143 function associates a stream with the existing file descriptor,
144 .Fa fildes .
145 The
146 .Fa mode
147 of the stream must be compatible with the mode of the file descriptor.
148 The stream is positioned at the file offset of the file descriptor.
149 .Pp
150 The
151 .Fn freopen
152 function
153 opens the file whose name is the string pointed to by
154 .Fa path
155 and associates the stream pointed to by
156 .Fa stream
157 with it.
158 The original stream (if it exists) is closed.
159 The
160 .Fa mode
161 argument is used just as in the
162 .Fn fopen
163 function.
164 The primary use of the
165 .Fn freopen
166 function
167 is to change the file associated with a
168 standard text stream
169 .Pf ( Em stderr ,
170 .Em stdin ,
171 or
172 .Em stdout ) .
173 .Sh RETURN VALUES
174 Upon successful completion
175 .Fn fopen ,
176 .Fn fdopen
177 and
178 .Fn freopen
179 return a
180 .Tn FILE
181 pointer.
182 Otherwise,
183 .Dv NULL
184 is returned and the global variable
185 .Va errno
186 is set to indicate the error.
187 .Sh ERRORS
188 .Bl -tag -width Er
189 .It Bq Er EINVAL
190 The
191 .Fa mode
192 provided to
193 .Fn fopen ,
194 .Fn fdopen ,
195 or
196 .Fn freopen
197 was invalid.
198 .It Bq Er EFTYPE
199 The file is not a regular file and the character ``f'' is specified
200 in the mode.
201 .El
202 .Pp
203 The
204 .Fn fopen ,
205 .Fn fdopen
206 and
207 .Fn freopen
208 functions
209 may also fail and set
210 .Va errno
211 for any of the errors specified for the routine
212 .Xr malloc 3 .
213 .Pp
214 The
215 .Fn fopen
216 function
217 may also fail and set
218 .Va errno
219 for any of the errors specified for the routine
220 .Xr open 2 .
221 .Pp
222 The
223 .Fn fdopen
224 function
225 may also fail and set
226 .Va errno
227 for any of the errors specified for the routine
228 .Xr fcntl 2 .
229 .Pp
230 The
231 .Fn freopen
232 function
233 may also fail and set
234 .Va errno
235 for any of the errors specified for the routines
236 .Xr open 2 ,
237 .Xr fclose 3
238 and
239 .Xr fflush 3 .
240 .Sh SEE ALSO
241 .Xr open 2 ,
242 .Xr fclose 3 ,
243 .Xr fileno 3 ,
244 .Xr fseek 3 ,
245 .Xr funopen 3
246 .Sh STANDARDS
247 The
248 .Fn fopen
249 and
250 .Fn freopen
251 functions
252 conform to
253 .St -ansiC .
254 The
255 .Fn fdopen
256 function conforms to
257 .St -p1003.1-90 .
258 .Sh CAVEATS
259 Proper code using
260 .Fn fdopen
261 with error checking should
262 .Xr close 2
263 .Fa fildes
264 in case of failure, and
265 .Xr fclose 3
266 the resulting FILE * in case of success.
267 .Bd -literal
268 FILE *file;
269 int fd;
271 if ((file = fdopen(fd, "r")) != NULL) {
272 /* perform operations on the FILE * */
273 fclose(file);
274 } else {
275 /* failure, report the error */
276 close(fd);
277 }
278 .Ed