ftell.c revision 35129 
1/*-
2 * Copyright (c) 1990, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Chris Torek.
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
37#if defined(LIBC_SCCS) && !defined(lint)
38#if 0
39static char sccsid[] = "@(#)ftell.c	8.2 (Berkeley) 5/4/95";
40#endif
41static const char rcsid[] =
42		"$Id: ftell.c,v 1.8 1997/03/11 11:40:40 peter Exp $";
43#endif /* LIBC_SCCS and not lint */
44
45#include <stdio.h>
46#include <errno.h>
47#include "local.h"
48#include "libc_private.h"
49
50/*
51 * ftell: return current offset.
52 */
53long
54ftell(fp)
55	register FILE *fp;
56{
57	register fpos_t pos;
58
59	if (fp->_seek == NULL) {
60		errno = ESPIPE;			/* historic practice */
61		return (-1L);
62	}
63
64	FLOCKFILE(fp);
65	/*
66	 * Find offset of underlying I/O object, then
67	 * adjust for buffered bytes.
68	 */
69	if (fp->_flags & __SOFF)
70		pos = fp->_offset;
71	else {
72		pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
73		if (pos == -1) {
74			FUNLOCKFILE(fp);
75			return (pos);
76		}
77	}
78	if (fp->_flags & __SRD) {
79		/*
80		 * Reading.  Any unread characters (including
81		 * those from ungetc) cause the position to be
82		 * smaller than that in the underlying object.
83		 */
84		pos -= fp->_r;
85		if (HASUB(fp))
86			pos -= fp->_ur;
87	} else if (fp->_flags & __SWR && fp->_p != NULL) {
88		/*
89		 * Writing.  Any buffered characters cause the
90		 * position to be greater than that in the
91		 * underlying object.
92		 */
93		pos += fp->_p - fp->_bf._base;
94	}
95	FUNLOCKFILE(fp);
96	return (pos);
97}
98