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1 | .\" Copyright (c) 1990, 1991, 1993 |
2 | .\" The Regents of the University of California. All rights reserved. | |
3 | .\" | |
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. | |
7 | .\" | |
8 | .\" Redistribution and use in source and binary forms, with or without | |
9 | .\" modification, are permitted provided that the following conditions | |
10 | .\" are met: | |
11 | .\" 1. Redistributions of source code must retain the above copyright | |
12 | .\" notice, this list of conditions and the following disclaimer. | |
13 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
14 | .\" notice, this list of conditions and the following disclaimer in the | |
15 | .\" documentation and/or other materials provided with the distribution. | |
16 | .\" 3. All advertising materials mentioning features or use of this software | |
17 | .\" must display the following acknowledgement: | |
18 | .\" This product includes software developed by the University of | |
19 | .\" California, Berkeley and its contributors. | |
20 | .\" 4. Neither the name of the University nor the names of its contributors | |
21 | .\" may be used to endorse or promote products derived from this software | |
22 | .\" without specific prior written permission. | |
23 | .\" | |
24 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
25 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
26 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
27 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
28 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
29 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
30 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
31 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
32 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
33 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
34 | .\" SUCH DAMAGE. | |
35 | .\" | |
36 | .\" @(#)fseek.3 8.1 (Berkeley) 6/4/93 | |
9385eb3d | 37 | .\" $FreeBSD: src/lib/libc/stdio/fseek.3,v 1.24 2002/12/19 09:40:24 ru Exp $ |
5b2abdfb | 38 | .\" |
9385eb3d | 39 | .Dd October 12, 2002 |
5b2abdfb A |
40 | .Dt FSEEK 3 |
41 | .Os | |
42 | .Sh NAME | |
43 | .Nm fgetpos , | |
44 | .Nm fseek , | |
45 | .Nm fseeko , | |
46 | .Nm fsetpos , | |
47 | .Nm ftell , | |
48 | .Nm ftello , | |
49 | .Nm rewind | |
50 | .Nd reposition a stream | |
51 | .Sh LIBRARY | |
52 | .Lb libc | |
53 | .Sh SYNOPSIS | |
54 | .In stdio.h | |
55 | .Ft int | |
56 | .Fn fseek "FILE *stream" "long offset" "int whence" | |
57 | .Ft long | |
58 | .Fn ftell "FILE *stream" | |
59 | .Ft void | |
60 | .Fn rewind "FILE *stream" | |
61 | .Ft int | |
9385eb3d | 62 | .Fn fgetpos "FILE * restrict stream" "fpos_t * restrict pos" |
5b2abdfb A |
63 | .Ft int |
64 | .Fn fsetpos "FILE *stream" "const fpos_t *pos" | |
65 | .In sys/types.h | |
66 | .Ft int | |
67 | .Fn fseeko "FILE *stream" "off_t offset" "int whence" | |
68 | .Ft off_t | |
69 | .Fn ftello "FILE *stream" | |
70 | .Sh DESCRIPTION | |
71 | The | |
72 | .Fn fseek | |
73 | function sets the file position indicator for the stream pointed | |
74 | to by | |
75 | .Fa stream . | |
76 | The new position, measured in bytes, is obtained by adding | |
77 | .Fa offset | |
78 | bytes to the position specified by | |
79 | .Fa whence . | |
80 | If | |
81 | .Fa whence | |
82 | is set to | |
83 | .Dv SEEK_SET , | |
84 | .Dv SEEK_CUR , | |
85 | or | |
86 | .Dv SEEK_END , | |
87 | the offset is relative to the | |
88 | start of the file, the current position indicator, or end-of-file, | |
89 | respectively. | |
90 | A successful call to the | |
91 | .Fn fseek | |
92 | function clears the end-of-file indicator for the stream and undoes | |
93 | any effects of the | |
94 | .Xr ungetc 3 | |
9385eb3d A |
95 | and |
96 | .Xr ungetwc 3 | |
97 | functions on the same stream. | |
5b2abdfb A |
98 | .Pp |
99 | The | |
100 | .Fn ftell | |
101 | function | |
102 | obtains the current value of the file position indicator for the | |
103 | stream pointed to by | |
104 | .Fa stream . | |
105 | .Pp | |
106 | The | |
107 | .Fn rewind | |
108 | function sets the file position indicator for the stream pointed | |
109 | to by | |
110 | .Fa stream | |
111 | to the beginning of the file. | |
112 | It is equivalent to: | |
113 | .Pp | |
114 | .Dl (void)fseek(stream, 0L, SEEK_SET) | |
115 | .Pp | |
116 | except that the error indicator for the stream is also cleared | |
117 | (see | |
118 | .Xr clearerr 3 ) . | |
119 | .Pp | |
120 | Since | |
121 | .Fn rewind | |
122 | does not return a value, | |
123 | an application wishing to detect errors should clear | |
124 | .Va errno , | |
125 | then call | |
126 | .Fn rewind , | |
127 | and if | |
128 | .Va errno | |
129 | is non-zero, assume an error has occurred. | |
130 | .Pp | |
131 | The | |
132 | .Fn fseeko | |
133 | function is identical to | |
134 | .Fn fseek , | |
135 | except it takes an | |
136 | .Fa off_t | |
137 | argument | |
138 | instead of a | |
139 | .Fa long . | |
140 | Likewise, the | |
141 | .Fn ftello | |
142 | function is identical to | |
143 | .Fn ftell , | |
144 | except it returns an | |
145 | .Fa off_t . | |
146 | .Pp | |
147 | The | |
148 | .Fn fgetpos | |
149 | and | |
150 | .Fn fsetpos | |
151 | functions | |
152 | are alternate interfaces equivalent to | |
153 | .Fn ftell | |
154 | and | |
155 | .Fn fseek | |
156 | (with whence set to | |
157 | .Dv SEEK_SET ) , | |
158 | setting and storing the current value of | |
159 | the file offset into or from the object referenced by | |
160 | .Fa pos . | |
161 | On some | |
162 | .Pq non- Ns Tn UNIX | |
163 | systems an | |
164 | .Dq Fa fpos_t | |
165 | object may be a complex object | |
166 | and these routines may be the only way to portably reposition a text stream. | |
9385eb3d A |
167 | .Pp |
168 | If the stream is a wide character stream (see | |
169 | .Xr fwide 3 ) , | |
170 | the position specified by the combination of | |
171 | .Fa offset | |
172 | and | |
173 | .Fa whence | |
174 | must contain the first byte of a multibyte sequence. | |
5b2abdfb A |
175 | .Sh RETURN VALUES |
176 | The | |
177 | .Fn rewind | |
178 | function | |
179 | returns no value. | |
180 | .Pp | |
181 | .Rv -std fgetpos fseek fseeko fsetpos | |
182 | .Pp | |
183 | Upon successful completion, | |
184 | .Fn ftell | |
185 | and | |
186 | .Fn ftello | |
187 | return the current offset. | |
188 | Otherwise, \-1 is returned and the global variable | |
189 | .Va errno | |
190 | is set to indicate the error. | |
191 | .Sh ERRORS | |
192 | .Bl -tag -width Er | |
193 | .It Bq Er EBADF | |
194 | The | |
195 | .Fa stream | |
9385eb3d | 196 | argument |
5b2abdfb A |
197 | is not a seekable stream. |
198 | .It Bq Er EINVAL | |
199 | The | |
200 | .Fa whence | |
201 | argument is invalid or | |
202 | the resulting file-position | |
203 | indicator would be set to a negative value. | |
204 | .It Bq Er EOVERFLOW | |
205 | The resulting file offset would be a value which | |
206 | cannot be represented correctly in an object of type | |
207 | .Fa off_t | |
208 | for | |
209 | .Fn fseeko | |
210 | and | |
211 | .Fn ftello | |
212 | or | |
213 | .Fa long | |
214 | for | |
215 | .Fn fseek | |
216 | and | |
217 | .Fn ftell . | |
218 | .It Bq Er ESPIPE | |
219 | The file descriptor underlying stream is associated with a pipe or FIFO | |
220 | or file-position indicator value is unspecified | |
221 | (see | |
222 | .Xr ungetc 3 ) . | |
223 | .El | |
224 | .Pp | |
225 | The functions | |
226 | .Fn fgetpos , | |
227 | .Fn fseek , | |
228 | .Fn fseeko , | |
229 | .Fn fsetpos , | |
230 | .Fn ftell , | |
231 | and | |
232 | .Fn ftello | |
233 | may also fail and set | |
234 | .Va errno | |
235 | for any of the errors specified for the routines | |
236 | .Xr fflush 3 , | |
237 | .Xr fstat 2 , | |
238 | .Xr lseek 2 , | |
239 | and | |
240 | .Xr malloc 3 . | |
241 | .Sh SEE ALSO | |
242 | .Xr lseek 2 , | |
243 | .Xr clearerr 3 , | |
9385eb3d A |
244 | .Xr fwide 3 , |
245 | .Xr ungetc 3 , | |
246 | .Xr ungetwc 3 | |
5b2abdfb A |
247 | .Sh STANDARDS |
248 | The | |
249 | .Fn fgetpos , | |
250 | .Fn fsetpos , | |
251 | .Fn fseek , | |
252 | .Fn ftell , | |
253 | and | |
254 | .Fn rewind | |
255 | functions | |
256 | conform to | |
257 | .St -isoC . | |
258 | .Pp | |
259 | The | |
260 | .Fn fseeko | |
261 | and | |
262 | .Fn ftello | |
263 | functions conform to | |
9385eb3d | 264 | .St -p1003.1-2001 . |