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[glibc.git] / stdio / ftell.c
blobcb770b67797ca2be7834f6f3fbc47281ec821a88
1 /* Copyright (C) 1991, 1992, 1994, 1996, 1997 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Library General Public License as
6 published by the Free Software Foundation; either version 2 of the
7 License, or (at your option) any later version.
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Library General Public License for more details.
14 You should have received a copy of the GNU Library General Public
15 License along with the GNU C Library; see the file COPYING.LIB. If not,
16 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
17 Boston, MA 02111-1307, USA. */
19 #include <errno.h>
20 #include <stdio.h>
22 /* Return the offset in bytes from the beginning
23 of the file of the file position of STREAM. */
24 long int
25 ftell (stream)
26 FILE *stream;
28 long int pos;
30 if (!__validfp (stream))
32 __set_errno (EINVAL);
33 return -1L;
36 if (__stdio_check_offset (stream) == EOF)
37 return -1L;
39 /* Start with the file position associated with the beginning
40 of our buffer. */
41 pos = stream->__target;
43 if (stream->__pushed_back)
44 /* ungetc was just called, so our real buffer pointer is squirreled
45 away in STREAM->__pushback_bufp, not in STREAM->__bufp as normal.
46 Calling ungetc is supposed to decrement the file position. ANSI
47 says the file position is unspecified if you ungetc when the
48 position is zero; -1 seems as good as anything to me. */
49 pos += stream->__pushback_bufp - stream->__buffer - 1;
50 else
51 pos += stream->__bufp - stream->__buffer;
53 return pos;