glibc/manual/examples/pipe.c

/* Creating a Pipe
   Copyright (C) 1991-2023 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.

   This program 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 General Public License for more details.

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

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

/* Read characters from the pipe and echo them to @code{stdout}.  */

void
read_from_pipe (int file)
{
  FILE *stream;
  int c;
  stream = fdopen (file, "r");
  while ((c = fgetc (stream)) != EOF)
    putchar (c);
  fclose (stream);
}

/* Write some random text to the pipe. */

void
write_to_pipe (int file)
{
  FILE *stream;
  stream = fdopen (file, "w");
  fprintf (stream, "hello, world!\n");
  fprintf (stream, "goodbye, world!\n");
  fclose (stream);
}

int
main (void)
{
  pid_t pid;
  int mypipe[2];

/*@group*/
  /* Create the pipe.  */
  if (pipe (mypipe))
    {
      fprintf (stderr, "Pipe failed.\n");
      return EXIT_FAILURE;
    }
/*@end group*/

  /* Create the child process.  */
  pid = fork ();
  if (pid == (pid_t) 0)
    {
      /* This is the child process.
	 Close other end first.  */
      close (mypipe[1]);
      read_from_pipe (mypipe[0]);
      return EXIT_SUCCESS;
    }
  else if (pid < (pid_t) 0)
    {
      /* The fork failed.  */
      fprintf (stderr, "Fork failed.\n");
      return EXIT_FAILURE;
    }
  else
    {
      /* This is the parent process.
	 Close other end first.  */
      close (mypipe[0]);
      write_to_pipe (mypipe[1]);
      return EXIT_SUCCESS;
    }
}