lib/ftello.c

   1 /* An ftello() function that works around platform bugs.
   2    Copyright (C) 2007, 2009-2020 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation; either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program 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
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 #include <config.h>
  18
  19 /* Specification.  */
  20 #include <stdio.h>
  21
  22 /* Get lseek.  */
  23 #include <unistd.h>
  24
  25 #include "stdio-impl.h"
  26
  27 off_t
  28 ftello (FILE *fp)
  29 #undef ftello
  30 #if !HAVE_FTELLO
  31 # undef ftell
  32 # define ftello ftell
  33 #endif
  34 #if _GL_WINDOWS_64_BIT_OFF_T
  35 # undef ftello
  36 # if HAVE__FTELLI64 /* msvc, mingw64 */
  37 #  define ftello _ftelli64
  38 # else /* mingw */
  39 #  define ftello ftello64
  40 # endif
  41 #endif
  42 {
  43 #if LSEEK_PIPE_BROKEN
  44   /* mingw gives bogus answers rather than failure on non-seekable files.  */
  45   if (lseek (fileno (fp), 0, SEEK_CUR) == -1)
  46     return -1;
  47 #endif
  48
  49 #if FTELLO_BROKEN_AFTER_SWITCHING_FROM_READ_TO_WRITE /* Solaris */
  50   /* The Solaris stdio leaves the _IOREAD flag set after reading from a file
  51      reaches EOF and the program then starts writing to the file.  ftello
  52      gets confused by this.  */
  53   if (fp_->_flag & _IOWRT)
  54     {
  55       off_t pos;
  56
  57       /* Call ftello nevertheless, for the side effects that it does on fp.  */
  58       ftello (fp);
  59
  60       /* Compute the file position ourselves.  */
  61       pos = lseek (fileno (fp), (off_t) 0, SEEK_CUR);
  62       if (pos >= 0)
  63         {
  64           if ((fp_->_flag & _IONBF) == 0 && fp_->_base != NULL)
  65             pos += fp_->_ptr - fp_->_base;
  66         }
  67       return pos;
  68     }
  69 #endif
  70
  71 #if defined __SL64 && defined __SCLE /* Cygwin */
  72   if ((fp->_flags & __SL64) == 0)
  73     {
  74       /* Cygwin 1.5.0 through 1.5.24 failed to open stdin in 64-bit
  75          mode; but has an ftello that requires 64-bit mode.  */
  76       FILE *tmp = fopen ("/dev/null", "r");
  77       if (!tmp)
  78         return -1;
  79       fp->_flags |= __SL64;
  80       fp->_seek64 = tmp->_seek64;
  81       fclose (tmp);
  82     }
  83 #endif
  84   return ftello (fp);
  85 }