/*
 * Sample program for pipe system call  - No.42
 *
 * pipe - create pipe
 *
 * Synopsis
 *     #include <unistd.h>
 *
 *     int pipe(int filedes[2]);
 *
 * Description
 *     pipe creates a pair of file descriptors, pointing to a
 *     pipe inode, and places them in the array pointed to by
 *     filedes. filedes[0] is for reading, filedes[1] is for
 *     writing.
 */

#include <stdio.h>
#include <string.h>

main()
{
	int	fd[2];
	int	pid;
	char	buf[BUFSIZ];
	char	*str = "hello, world\n";

	if (pipe(fd) == -1) {	/* fd[0] is for reading, fd[1] for writing */
		perror("pipe");
		exit(1);
	}

	switch (pid = fork()) {
	case -1:
		perror("fork");
		exit(1);
		break;
	case 0:			/* spawn a child process as upstream */
		close(fd[0]);	/* file descriptor for reading need to be closed */
		strncpy(buf, str, strlen(str) + 1);
		write(fd[1], buf, sizeof buf);
		break;
	default:		/* parent process works as downstream */
		close(fd[1]);	/* file descriptor for writing need to be closed */
		read(fd[0], buf, sizeof buf);
		printf("%s", buf);
		break;
	}

	exit(0);
}