stdio/freopen.c

   1 /* Copyright (C) 1991, 1994, 1995, 1996, 1997 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, write to the Free
  16    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  17    02111-1307 USA.  */
  18
  19 #include <errno.h>
  20 #include <stdio.h>
  21
  22
  23 /* Defined in fopen.c.  */
  24 extern int __getmode __P ((const char *, __io_mode *));
  25
  26 /* Defined in sysd-stdio.c.  */
  27 extern int __stdio_reopen __P ((const char *filename, __io_mode mode,
  28                                 void *cookieptr, __io_close_fn closefn));
  29
  30 /* Replace STREAM, opening it on FILENAME.  */
  31 FILE *
  32 freopen (filename, mode, stream)
  33      const char *filename;
  34      const char *mode;
  35      register FILE *stream;
  36 {
  37   __io_mode m;
  38   void *cookie;
  39
  40   if (!__getmode (mode, &m))
  41     {
  42       (void) fclose (stream);
  43       __set_errno (EINVAL);
  44       return NULL;
  45     }
  46
  47   if (stream->__mode.__write)
  48     /* Flush the stream.  */
  49     (void) fflush (stream);
  50
  51   /* Open the file, attempting to preserve the old cookie value.  */
  52   cookie = stream->__cookie;
  53   if (__stdio_reopen (filename, m, &cookie,
  54                       stream->__seen ?
  55                       stream->__io_funcs.__close :
  56                       __stdio_close))
  57     {
  58       int save = errno;
  59       (void) fclose (stream);
  60       __set_errno (save);
  61       return NULL;
  62     }
  63
  64   /* Close the stream, first disabling its cookie close function because
  65      __stdio_reopen has already dealt with closing the old cookie.  */
  66   stream->__seen = 1;           /* It might have no functions yet.  */
  67   stream->__io_funcs.__close = NULL;
  68   (void) fclose (stream);
  69
  70   stream->__magic = _IOMAGIC;
  71   stream->__cookie = cookie;
  72   stream->__mode = m;
  73
  74   return stream;
  75 }