ftell.c revision 1574 
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)
38static char sccsid[] = "@(#)ftell.c	8.1 (Berkeley) 6/4/93";
39#endif /* LIBC_SCCS and not lint */
40
41#include <stdio.h>
42#include <errno.h>
43#include "local.h"
44
45/*
46 * ftell: return current offset.
47 */
48long
49ftell(fp)
50	register const FILE *fp;
51{
52	register fpos_t pos;
53
54	if (fp->_seek == NULL) {
55		errno = ESPIPE;			/* historic practice */
56		return (-1L);
57	}
58
59	/*
60	 * Find offset of underlying I/O object, then
61	 * adjust for buffered bytes.
62	 */
63	if (fp->_flags & __SOFF)
64		pos = fp->_offset;
65	else {
66		pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
67		if (pos == -1L)
68			return (pos);
69	}
70	if (fp->_flags & __SRD) {
71		/*
72		 * Reading.  Any unread characters (including
73		 * those from ungetc) cause the position to be
74		 * smaller than that in the underlying object.
75		 */
76		pos -= fp->_r;
77		if (HASUB(fp))
78			pos -= fp->_ur;
79	} else if (fp->_flags & __SWR && fp->_p != NULL) {
80		/*
81		 * Writing.  Any buffered characters cause the
82		 * position to be greater than that in the
83		 * underlying object.
84		 */
85		pos += fp->_p - fp->_bf._base;
86	}
87	return (pos);
88}
89