libio/ioftell.c

   1 /* Copyright (C) 1993-2017 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 Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the 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    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <http://www.gnu.org/licenses/>.
  17
  18    As a special exception, if you link the code in this file with
  19    files compiled with a GNU compiler to produce an executable,
  20    that does not cause the resulting executable to be covered by
  21    the GNU Lesser General Public License.  This exception does not
  22    however invalidate any other reasons why the executable file
  23    might be covered by the GNU Lesser General Public License.
  24    This exception applies to code released by its copyright holders
  25    in files containing the exception.  */
  26
  27 #include "libioP.h"
  28 #include <stdlib.h>
  29 #include <errno.h>
  30 /* ANSI explicily requires setting errno to a positive value on failure. */
  31
  32 long int
  33 _IO_ftell (_IO_FILE *fp)
  34 {
  35   _IO_off64_t pos;
  36   CHECK_FILE (fp, -1L);
  37   _IO_acquire_lock (fp);
  38   pos = _IO_seekoff_unlocked (fp, 0, _IO_seek_cur, 0);
  39   if (_IO_in_backup (fp) && pos != _IO_pos_BAD)
  40     {
  41       if (_IO_vtable_offset (fp) != 0 || fp->_mode <= 0)
  42         pos -= fp->_IO_save_end - fp->_IO_save_base;
  43     }
  44   _IO_release_lock (fp);
  45   if (pos == _IO_pos_BAD)
  46     {
  47 #ifdef EIO
  48       if (errno == 0)
  49         __set_errno (EIO);
  50 #endif
  51       return -1L;
  52     }
  53   if ((_IO_off64_t) (long int) pos != pos)
  54     {
  55 #ifdef EOVERFLOW
  56       __set_errno (EOVERFLOW);
  57 #endif
  58       return -1L;
  59     }
  60   return pos;
  61 }
  62 libc_hidden_def (_IO_ftell)
  63
  64 #ifdef weak_alias
  65 weak_alias (_IO_ftell, ftell)
  66 #endif