hide_stderr.c

// avp 2014 save-restore stderr by fd
#ifdef __cplusplus
#include <iostream>
using namespace std;
#endif

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

int hide_stderr (const char *dst)
{
  int fd, efd = fileno(stderr), save = dup(efd), olderr = errno;
  if (dup2(fd = open(dst, O_WRONLY | O_CREAT | O_TRUNC, 0664), efd) == -1) {
    olderr = errno;
    close(save);
    save = -1;
  }
  close(fd);
  errno = olderr;
  return save;
}

int rest_stderr (int savefd)
{
  int drc = dup2(savefd, fileno(stderr));
  if (drc != -1)
    close(savefd);
  return drc;
}



int main (int ac, char *av[])
{
#ifdef __cplusplus
  cerr << "c++ 1\n";
#endif

  perror("xaxa");
#if 0
  int fd, stderrfd = fileno(stderr), save = dup(stderrfd);
  printf ("stderrfd: %d save: %d\n", stderrfd, save);
  printf ("dup2 xaxa to %d\n",
      dup2(fd = open("xaxa", O_WRONLY | O_CREAT | O_TRUNC, 0664), stderrfd));
  close(fd);
  printf ("fd = %d\n", fd);
#else
  int save = hide_stderr(av[1] ? av[1] : "/dev/null");
#endif
  perror("xoxo");
  errno = 0;
  fprintf (stderr, " after perror %m\n");
#ifdef __cplusplus
  cerr << "c++ 2\n";
#endif

#if 0
  int drc = dup2(save, stderrfd);
  if (close(save) == -1)
    perror("close");
  else
    perror("success");
#else
  int drc = rest_stderr(save);
#endif
  if (drc == -1)
    perror("dup2");
  else
    perror("xixi");

#ifdef __cplusplus
  cerr << "c++ 3\n";
#endif

  printf ("drc = %d\n", drc);

}