ftell.c revision 43782 
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 1.9 1998/04/11 07:40:44 jb Exp $";
43#endif /* LIBC_SCCS and not lint */
44
45#include <sys/types.h>
46#include <stdio.h>
47#include <errno.h>
48#include "local.h"
49#include "libc_private.h"
50
51/*
52 * standard ftell function.
53 */
54long
55ftell(fp)
56	register FILE *fp;
57{
58	register off_t rv;
59	rv = ftello(fp);
60	if ((long)rv != rv) {
61		errno = EOVERFLOW;
62		return (-1);
63	}
64	return (rv);
65}
66
67/*
68 * ftello: return current offset.
69 */
70off_t
71ftello(fp)
72	register FILE *fp;
73{
74	register fpos_t pos;
75
76	if (fp->_seek == NULL) {
77		errno = ESPIPE;			/* historic practice */
78		return (-1L);
79	}
80
81	FLOCKFILE(fp);
82	/*
83	 * Find offset of underlying I/O object, then
84	 * adjust for buffered bytes.
85	 */
86	if (fp->_flags & __SOFF)
87		pos = fp->_offset;
88	else {
89		pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
90		if (pos == -1) {
91			FUNLOCKFILE(fp);
92			return (pos);
93		}
94	}
95	if (fp->_flags & __SRD) {
96		/*
97		 * Reading.  Any unread characters (including
98		 * those from ungetc) cause the position to be
99		 * smaller than that in the underlying object.
100		 */
101		pos -= fp->_r;
102		if (HASUB(fp))
103			pos -= fp->_ur;
104	} else if (fp->_flags & __SWR && fp->_p != NULL) {
105		/*
106		 * Writing.  Any buffered characters cause the
107		 * position to be greater than that in the
108		 * underlying object.
109		 */
110		pos += fp->_p - fp->_bf._base;
111	}
112	FUNLOCKFILE(fp);
113	return (pos);
114}
115