manual/examples/pipe.c

   1 /* Creating a Pipe
   2    Copyright (C) 1991-2024 Free Software Foundation, Inc.
   3
   4    This program is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU General Public License
   6    as published by the Free Software Foundation; either version 2
   7    of the License, or (at your option) any later version.
   8
   9    This program 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 General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program; if not, see <https://www.gnu.org/licenses/>.
  16 */
  17
  18 #include <sys/types.h>
  19 #include <unistd.h>
  20 #include <stdio.h>
  21 #include <stdlib.h>
  22
  23 /* Read characters from the pipe and echo them to @code{stdout}.  */
  24
  25 void
  26 read_from_pipe (int file)
  27 {
  28   FILE *stream;
  29   int c;
  30   stream = fdopen (file, "r");
  31   while ((c = fgetc (stream)) != EOF)
  32     putchar (c);
  33   fclose (stream);
  34 }
  35
  36 /* Write some random text to the pipe. */
  37
  38 void
  39 write_to_pipe (int file)
  40 {
  41   FILE *stream;
  42   stream = fdopen (file, "w");
  43   fprintf (stream, "hello, world!\n");
  44   fprintf (stream, "goodbye, world!\n");
  45   fclose (stream);
  46 }
  47
  48 int
  49 main (void)
  50 {
  51   pid_t pid;
  52   int mypipe[2];
  53
  54 /*@group*/
  55   /* Create the pipe.  */
  56   if (pipe (mypipe))
  57     {
  58       fprintf (stderr, "Pipe failed.\n");
  59       return EXIT_FAILURE;
  60     }
  61 /*@end group*/
  62
  63   /* Create the child process.  */
  64   pid = fork ();
  65   if (pid == (pid_t) 0)
  66     {
  67       /* This is the child process.
  68          Close other end first.  */
  69       close (mypipe[1]);
  70       read_from_pipe (mypipe[0]);
  71       return EXIT_SUCCESS;
  72     }
  73   else if (pid < (pid_t) 0)
  74     {
  75       /* The fork failed.  */
  76       fprintf (stderr, "Fork failed.\n");
  77       return EXIT_FAILURE;
  78     }
  79   else
  80     {
  81       /* This is the parent process.
  82          Close other end first.  */
  83       close (mypipe[0]);
  84       write_to_pipe (mypipe[1]);
  85       return EXIT_SUCCESS;
  86     }
  87 }