1 /* $OpenBSD: ftell.c,v 1.10 2012/05/21 22:24:19 matthew Exp $ */
2 /*-
3 * Copyright (c) 1990, 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.
8 *
9 * Redistribution and use in source and binary forms, with or without
10 * modification, are permitted provided that the following conditions
11 * are met:
12 * 1. Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 * 2. Redistributions in binary form must reproduce the above copyright
15 * notice, this list of conditions and the following disclaimer in the
16 * documentation and/or other materials provided with the distribution.
17 * 3. Neither the name of the University nor the names of its contributors
18 * may be used to endorse or promote products derived from this software
19 * without specific prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
31 * SUCH DAMAGE.
32 */
33
34 #include <stdio.h>
35 #include <errno.h>
36 #include <limits.h>
37 #include "local.h"
38
39 /*
40 * ftello: return current offset.
41 */
42 off_t
ftello(FILE * fp)43 ftello(FILE *fp)
44 {
45 fpos_t pos;
46
47 if (fp->_seek == NULL) {
48 errno = ESPIPE; /* historic practice */
49 pos = -1;
50 goto out;
51 }
52
53 /*
54 * Find offset of underlying I/O object, then
55 * adjust for buffered bytes.
56 */
57 FLOCKFILE(fp);
58 __sflush(fp); /* may adjust seek offset on append stream */
59 if (fp->_flags & __SOFF)
60 pos = fp->_offset;
61 else {
62 pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
63 if (pos == -1)
64 goto out;
65 }
66 if (fp->_flags & __SRD) {
67 /*
68 * Reading. Any unread characters (including
69 * those from ungetc) cause the position to be
70 * smaller than that in the underlying object.
71 */
72 pos -= fp->_r;
73 if (HASUB(fp))
74 pos -= fp->_ur;
75 } else if (fp->_flags & __SWR && fp->_p != NULL) {
76 /*
77 * Writing. Any buffered characters cause the
78 * position to be greater than that in the
79 * underlying object.
80 */
81 pos += fp->_p - fp->_bf._base;
82 }
83 out: FUNLOCKFILE(fp);
84 return (pos);
85 }
86
87 long
ftell(FILE * fp)88 ftell(FILE *fp)
89 {
90 off_t offset = ftello(fp);
91 if (offset > LONG_MAX) {
92 errno = EOVERFLOW;
93 return (-1);
94 }
95 return ((long)offset);
96 }
97