lib/freopen.c

   1 /* Open a stream to a file.
   2    Copyright (C) 2007-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation, either version 3 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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 Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2007.  */
  18
  19 /* If the user's config.h happens to include <stdio.h>, let it include only
  20    the system's <stdio.h> here, so that orig_freopen doesn't recurse to
  21    rpl_freopen.  */
  22 #define _GL_ALREADY_INCLUDING_STDIO_H
  23 #include <config.h>
  24
  25 /* Get the original definition of freopen.  It might be defined as a macro.  */
  26 #include <stdio.h>
  27 #undef _GL_ALREADY_INCLUDING_STDIO_H
  28
  29 #include <errno.h>
  30
  31 static FILE *
  32 orig_freopen (const char *filename, const char *mode, FILE *stream)
  33 {
  34   return freopen (filename, mode, stream);
  35 }
  36
  37 /* Specification.  */
  38 #ifdef __osf__
  39 /* Write "stdio.h" here, not <stdio.h>, otherwise OSF/1 5.1 DTK cc eliminates
  40    this include because of the preliminary #include <stdio.h> above.  */
  41 # include "stdio.h"
  42 #else
  43 # include <stdio.h>
  44 #endif
  45
  46 #include <fcntl.h>
  47 #include <string.h>
  48 #include <unistd.h>
  49
  50 FILE *
  51 rpl_freopen (const char *filename, const char *mode, FILE *stream)
  52 {
  53   FILE *result;
  54 #if defined _WIN32 && ! defined __CYGWIN__
  55   char const *null_device = "NUL";
  56   if (filename && strcmp (filename, "/dev/null") == 0)
  57     filename = null_device;
  58 #else
  59   char const *null_device = "/dev/null";
  60 #endif
  61
  62 #ifdef __KLIBC__
  63   errno = 0;
  64 #endif
  65
  66   result = orig_freopen (filename, mode, stream);
  67
  68   if (!result)
  69     {
  70 #ifdef __KLIBC__
  71       /* On OS/2 kLIBC, freopen returns NULL even if it is successful
  72          if filename is NULL. */
  73       if (!filename && !errno)
  74         result = stream;
  75 #endif
  76     }
  77   else if (filename)
  78     {
  79       int fd = fileno (result);
  80       if (dup2 (fd, fd) < 0 && errno == EBADF)
  81         {
  82           int nullfd = open (null_device, O_RDONLY | O_CLOEXEC);
  83           int err = 0;
  84           if (nullfd != fd)
  85             {
  86               if (dup2 (nullfd, fd) < 0)
  87                 err = 1;
  88               close (nullfd);
  89             }
  90           if (!err)
  91             result = orig_freopen (filename, mode, result);
  92         }
  93     }
  94
  95   return result;
  96 }