xref: /netbsd-src/share/doc/psd/20.ipctut/pipe.c (revision 075022b349321510ad14036d70908681ed02f117)
1*075022b3Sagc .\"	$NetBSD: pipe.c,v 1.3 2003/08/07 10:30:50 agc Exp $
26d400d56Sperry .\"
3d9158b13Scgd .\" Copyright (c) 1986, 1993
4d9158b13Scgd .\"	The Regents of the University of California.  All rights reserved.
5d9158b13Scgd .\"
6d9158b13Scgd .\" Redistribution and use in source and binary forms, with or without
7d9158b13Scgd .\" modification, are permitted provided that the following conditions
8d9158b13Scgd .\" are met:
9d9158b13Scgd .\" 1. Redistributions of source code must retain the above copyright
10d9158b13Scgd .\"    notice, this list of conditions and the following disclaimer.
11d9158b13Scgd .\" 2. Redistributions in binary form must reproduce the above copyright
12d9158b13Scgd .\"    notice, this list of conditions and the following disclaimer in the
13d9158b13Scgd .\"    documentation and/or other materials provided with the distribution.
14*075022b3Sagc .\" 3. Neither the name of the University nor the names of its contributors
15d9158b13Scgd .\"    may be used to endorse or promote products derived from this software
16d9158b13Scgd .\"    without specific prior written permission.
17d9158b13Scgd .\"
18d9158b13Scgd .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
19d9158b13Scgd .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
20d9158b13Scgd .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
21d9158b13Scgd .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
22d9158b13Scgd .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
23d9158b13Scgd .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
24d9158b13Scgd .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
25d9158b13Scgd .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
26d9158b13Scgd .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
27d9158b13Scgd .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
28d9158b13Scgd .\" SUCH DAMAGE.
29d9158b13Scgd .\"
30d9158b13Scgd .\"	@(#)pipe.c	8.1 (Berkeley) 6/8/93
31d9158b13Scgd .\"
32d9158b13Scgd #include <stdio.h>
33d9158b13Scgd 
34d9158b13Scgd #define DATA "Bright star, would I were steadfast as thou art . . ."
35d9158b13Scgd 
36d9158b13Scgd /*
37d9158b13Scgd  * This program creates a pipe, then forks.  The child communicates to the
38d9158b13Scgd  * parent over the pipe. Notice that a pipe is a one-way communications
39d9158b13Scgd  * device.  I can write to the output socket (sockets[1], the second socket
40d9158b13Scgd  * of the array returned by pipe()) and read from the input socket
41d9158b13Scgd  * (sockets[0]), but not vice versa.
42d9158b13Scgd  */
43d9158b13Scgd 
44d9158b13Scgd main()
45d9158b13Scgd {
46d9158b13Scgd 	int sockets[2], child;
47d9158b13Scgd 
48d9158b13Scgd 	/* Create a pipe */
49d9158b13Scgd 	if (pipe(sockets) < 0) {
50d9158b13Scgd 		perror("opening stream socket pair");
51d9158b13Scgd 		exit(10);
52d9158b13Scgd 	}
53d9158b13Scgd 
54d9158b13Scgd 	if ((child = fork()) == -1)
55d9158b13Scgd 		perror("fork");
56d9158b13Scgd 	else if (child) {
57d9158b13Scgd 		char buf[1024];
58d9158b13Scgd 
59d9158b13Scgd 		/* This is still the parent.  It reads the child's message. */
60d9158b13Scgd 		close(sockets[1]);
61d9158b13Scgd 		if (read(sockets[0], buf, 1024) < 0)
62d9158b13Scgd 			perror("reading message");
63d9158b13Scgd 		printf("-->%s\en", buf);
64d9158b13Scgd 		close(sockets[0]);
65d9158b13Scgd 	} else {
66d9158b13Scgd 		/* This is the child.  It writes a message to its parent. */
67d9158b13Scgd 		close(sockets[0]);
68d9158b13Scgd 		if (write(sockets[1], DATA, sizeof(DATA)) < 0)
69d9158b13Scgd 			perror("writing message");
70d9158b13Scgd 		close(sockets[1]);
71d9158b13Scgd 	}
72d9158b13Scgd }
73