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4 .\" This code is derived from software contributed to Berkeley by
5 .\" Chris Torek and the American National Standards Committee X3,
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36 .\" @(#)fopen.3 8.1 (Berkeley) 6/4/93
37 .\" $FreeBSD: src/lib/libc/stdio/fopen.3,v 1.7.2.6 2001/12/14 18:33:57 ru Exp $
38 .\" $DragonFly: src/lib/libc/stdio/fopen.3,v 1.4 2007/04/04 18:36:55 swildner Exp $
39 .\"
40 .Dd June 8, 2004
41 .Dt FOPEN 3
42 .Os
43 .Sh NAME
44 .Nm fopen ,
45 .Nm fdopen ,
46 .Nm freopen
47 .Nd stream open functions
48 .Sh LIBRARY
49 .Lb libc
50 .Sh SYNOPSIS
51 .In stdio.h
52 .Ft FILE *
53 .Fn fopen "const char *path" "const char *mode"
54 .Ft FILE *
55 .Fn fdopen "int fildes" "const char *mode"
56 .Ft FILE *
57 .Fn freopen "const char *path" "const char *mode" "FILE *stream"
58 .Sh DESCRIPTION
59 The
60 .Fn fopen
61 function
62 opens the file whose name is the string pointed to by
63 .Fa path
64 and associates a stream with it.
65 .Pp
66 The argument
67 .Fa mode
68 points to a string beginning with one of the following
69 sequences (Additional characters may follow these sequences.):
70 .Bl -tag -width indent
71 .It Dq Li r
72 Open text file for reading.
73 The stream is positioned at the beginning of the file.
74 .It Dq Li r+
75 Open for reading and writing.
76 The stream is positioned at the beginning of the file.
77 .It Dq Li w
78 Truncate file to zero length or create text file for writing.
79 The stream is positioned at the beginning of the file.
80 .It Dq Li w+
81 Open for reading and writing.
82 The file is created if it does not exist, otherwise it is truncated.
83 The stream is positioned at the beginning of the file.
84 .It Dq Li a
85 Open for writing.
86 The file is created if it does not exist.
87 The stream is positioned at the end of the file.
88 Subsequent writes to the file will always end up at the then current
89 end of file, irrespective of any intervening
90 .Xr fseek 3
91 or similar.
92 .It Dq Li a+
93 Open for reading and writing.
94 The file is created if it does not exist.
95 The stream is positioned at the end of the file.
96 Subsequent writes to the file will always end up at the then current
97 end of file, irrespective of any intervening
98 .Xr fseek 3
99 or similar.
100 .El
101 .Pp
102 The
103 .Fa mode
104 string can also include the letter ``b'' either as a third character or
105 as a character between the characters in any of the two-character strings
106 described above.
107 This is strictly for compatibility with
108 .St -isoC
109 and has no effect; the ``b'' is ignored.
110 .Pp
111 Any created files will have mode
112 .Pf \\*q Dv S_IRUSR
113 \&|
114 .Dv S_IWUSR
115 \&|
116 .Dv S_IRGRP
117 \&|
118 .Dv S_IWGRP
119 \&|
120 .Dv S_IROTH
121 \&|
122 .Dv S_IWOTH Ns \\*q
123 .Pq Li 0666 ,
124 as modified by the process'
125 umask value (see
126 .Xr umask 2 ) .
127 .Pp
128 Reads and writes may be intermixed on read/write streams in any order,
129 and do not require an intermediate seek as in previous versions of
130 .Em stdio .
131 This is not portable to other systems, however;
132 .Tn ANSI C
133 requires that
134 a file positioning function intervene between output and input, unless
135 an input operation encounters end-of-file.
136 .Pp
137 The
138 .Fn fdopen
139 function associates a stream with the existing file descriptor,
140 .Fa fildes .
141 The mode
142 of the stream must be compatible with the mode of the file descriptor.
143 When the stream is closed via
144 .Xr fclose 3 ,
145 .Fa fildes
146 is closed also.
147 .Pp
148 The
149 .Fn freopen
150 function
151 opens the file whose name is the string pointed to by
152 .Fa path
153 and associates the stream pointed to by
154 .Fa stream
155 with it.
156 The original stream (if it exists) is closed.
157 The
158 .Fa mode
159 argument is used just as in the
160 .Fn fopen
161 function.
162 .Pp
163 If the
164 .Fa path
165 argument is
166 .Dv NULL ,
167 .Fn freopen
168 attempts to re-open the file associated with
169 .Fa stream
170 with a new mode.
171 The new mode must be compatible with the mode that the stream was originally
172 opened with:
173 .Bl -bullet -offset indent
174 .It
175 Streams originally opened with mode
176 .Dq Li r
177 can only be reopened with that same mode.
178 .It
179 Streams originally opened with mode
180 .Dq Li a
181 can be reopened with the same mode, or mode
182 .Dq Li w .
183 .It
184 Streams originally opened with mode
185 .Dq Li w
186 can be reopened with the same mode, or mode
187 .Dq Li a .
188 .It
189 Streams originally opened with mode
190 .Dq Li r+ ,
191 .Dq Li w+ ,
192 or
193 .Dq Li a+
194 can be reopened with any mode.
195 .El
196 .Pp
197 The primary use of the
198 .Fn freopen
199 function
200 is to change the file associated with a
201 standard text stream
202 .Dv ( stderr , stdin ,
203 or
204 .Dv stdout ) .
205 .Sh RETURN VALUES
206 Upon successful completion
207 .Fn fopen ,
208 .Fn fdopen
209 and
210 .Fn freopen
211 return a
212 .Tn FILE
213 pointer.
214 Otherwise,
215 .Dv NULL
216 is returned and the global variable
217 .Va errno
218 is set to indicate the error.
219 .Sh ERRORS
220 .Bl -tag -width Er
221 .It Bq Er EINVAL
222 The
223 .Fa mode
224 argument
225 to
226 .Fn fopen ,
227 .Fn fdopen ,
228 or
229 .Fn freopen
230 was invalid.
231 .El
232 .Pp
233 The
234 .Fn fopen ,
235 .Fn fdopen
236 and
237 .Fn freopen
238 functions
239 may also fail and set
240 .Va errno
241 for any of the errors specified for the routine
242 .Xr malloc 3 .
243 .Pp
244 The
245 .Fn fopen
246 function
247 may also fail and set
248 .Va errno
249 for any of the errors specified for the routine
250 .Xr open 2 .
251 .Pp
252 The
253 .Fn fdopen
254 function
255 may also fail and set
256 .Va errno
257 for any of the errors specified for the routine
258 .Xr fcntl 2 .
259 .Pp
260 The
261 .Fn freopen
262 function
263 may also fail and set
264 .Va errno
265 for any of the errors specified for the routines
266 .Xr open 2 ,
267 .Xr fclose 3
268 and
269 .Xr fflush 3 .
270 .Sh SEE ALSO
271 .Xr open 2 ,
272 .Xr fclose 3 ,
273 .Xr fileno 3 ,
274 .Xr fseek 3 ,
275 .Xr funopen 3
276 .Sh STANDARDS
277 The
278 .Fn fopen
279 and
280 .Fn freopen
281 functions
282 conform to
283 .St -isoC .
284 The
285 .Fn fdopen
286 function
287 conforms to
288 .St -p1003.1-88 .