xref: /freebsd/share/doc/psd/20.ipctut/pipe.c (revision 97759ccc715c4b365432c16d763c50eecfcb1100)

.\" Copyright (c) 1986, 1993
.\"	The Regents of the University of California.  All rights reserved.
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.\" modification, are permitted provided that the following conditions
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.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
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.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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#include <stdio.h>

#define DATA "Bright star, would I were steadfast as thou art . . ."

/*
 * This program creates a pipe, then forks.  The child communicates to the
 * parent over the pipe. Notice that a pipe is a one-way communications
 * device.  I can write to the output socket (sockets[1], the second socket
 * of the array returned by pipe()) and read from the input socket
 * (sockets[0]), but not vice versa.
 */

main()
{
	int sockets[2], child;

	/* Create a pipe */
	if (pipe(sockets) < 0) {
		perror("opening stream socket pair");
		exit(10);
	}

	if ((child = fork()) == -1)
		perror("fork");
	else if (child) {
		char buf[1024];

		/* This is still the parent.  It reads the child's message. */
		close(sockets[1]);
		if (read(sockets[0], buf, 1024) < 0)
			perror("reading message");
		printf("-->%s\en", buf);
		close(sockets[0]);
	} else {
		/* This is the child.  It writes a message to its parent. */
		close(sockets[0]);
		if (write(sockets[1], DATA, sizeof(DATA)) < 0)
			perror("writing message");
		close(sockets[1]);
	}
}