stdio/ftell.c

   1 /* Copyright (C) 1991, 1992, 1994, 1996 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   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.
   8
   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.
  13
  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
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 #include <errno.h>
  20 #include <stdio.h>
  21
  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;
  27 {
  28   long int pos;
  29
  30   if (!__validfp (stream))
  31     {
  32       __set_errno (EINVAL);
  33       return -1L;
  34     }
  35
  36   if (__stdio_check_offset (stream) == EOF)
  37     return -1L;
  38
  39   /* Start with the file position associated with the beginning
  40      of our buffer.  */
  41   pos = stream->__target;
  42
  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;
  52
  53   return pos;
  54 }