glibc/stdio-common/errnobug.c

/* Regression test for reported old bug that errno is clobbered
   by the first successful output to a stream on an unseekable object.
   Copyright (C) 1995-2020 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <stdio.h>
#include <unistd.h>

int
main (void)
{
  int fd[2];
  FILE *f;

  /* Get a stream that cannot seek.  */

  if (pipe (fd))
    {
      perror ("pipe");
      return 1;
    }
  f = fdopen (fd[1], "w");
  if (f == NULL)
    {
      perror ("fdopen");
      return 1;
    }

  errno = 0;
  if (fputs ("fnord", f) == EOF)
    {
      perror ("fputs");
      return 1;
    }

  if (errno)
    {
      perror ("errno gratuitously set -- TEST FAILED");
      return 1;
    }

  puts ("Test succeeded.");
  return 0;
}