1 /* $NetBSD: ftell.c,v 1.20 2012/03/27 15:05:42 christos Exp $ */
2
3 /*-
4 * Copyright (c) 1990, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Chris Torek.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
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
16 * notice, this list of conditions and the following disclaimer in the
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
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35 #include <sys/cdefs.h>
36 #if defined(LIBC_SCCS) && !defined(lint)
37 #if 0
38 static char sccsid[] = "@(#)ftell.c 8.2 (Berkeley) 5/4/95";
39 #else
40 __RCSID("$NetBSD: ftell.c,v 1.20 2012/03/27 15:05:42 christos Exp $");
41 #endif
42 #endif /* LIBC_SCCS and not lint */
43
44 #include <assert.h>
45 #include <errno.h>
46 #include <stdio.h>
47 #include "reentrant.h"
48 #include "local.h"
49
50 /*
51 * ftell: return current offset.
52 */
53 long
ftell(FILE * fp)54 ftell(FILE *fp)
55 {
56 off_t pos;
57
58
59 FLOCKFILE(fp);
60
61 if (fp->_seek == NULL) {
62 FUNLOCKFILE(fp);
63 errno = ESPIPE; /* historic practice */
64 return -1L;
65 }
66
67 /*
68 * Find offset of underlying I/O object, then
69 * adjust for buffered bytes.
70 */
71 (void)__sflush(fp); /* may adjust seek offset on append stream */
72 if (fp->_flags & __SOFF)
73 pos = fp->_offset;
74 else {
75 pos = (*fp->_seek)(fp->_cookie, (off_t)0, SEEK_CUR);
76 if (pos == -1L) {
77 FUNLOCKFILE(fp);
78 return (long)pos;
79 }
80 }
81 if (fp->_flags & __SRD) {
82 /*
83 * Reading. Any unread characters (including
84 * those from ungetc) cause the position to be
85 * smaller than that in the underlying object.
86 */
87 pos -= fp->_r;
88 if (HASUB(fp))
89 pos -= fp->_ur;
90 } else if (fp->_flags & __SWR && fp->_p != NULL) {
91 /*
92 * Writing. Any buffered characters cause the
93 * position to be greater than that in the
94 * underlying object.
95 */
96 pos += fp->_p - fp->_bf._base;
97 }
98 FUNLOCKFILE(fp);
99
100 if (__long_overflow(pos)) {
101 errno = EOVERFLOW;
102 return -1L;
103 }
104
105 return (long)pos;
106 }
107