pipedemo2.c

介绍和编写和IO重定向的使用

/* pipedemo2.c	* Demonstrates how pipe is duplicated in fork()
 *		* Parent continues to write and read pipe,
 *		  but child also writes to the pipe
 */
#include	<stdio.h>

#define	CHILD_MESS	"I want a cookie\n"
#define	PAR_MESS	"testing..\n"
#define	oops(m,x)	{ perror(m); exit(x); }

main()
{
	int	pipefd[2];		/* the pipe	*/
	int	len;			/* for write	*/
	char	buf[BUFSIZ];		/* for read	*/
	int	read_len;

	if ( pipe( pipefd ) == -1 )
		oops("cannot get a pipe", 1);

	switch( fork() ){
		case -1:
			oops("cannot fork", 2);
	
		/* child writes to pipe every 5 seconds */
		case 0:			
			len = strlen(CHILD_MESS);
			while ( 1 ){
				if (write( pipefd[1], CHILD_MESS, len) != len )
					oops("write", 3);
				sleep(5);
			}

		/* parent reads from pipe and also writes to pipe */
		default:		
			len = strlen( PAR_MESS );
			while ( 1 ){
				if ( write( pipefd[1], PAR_MESS, len)!=len )
					oops("write", 4);
				sleep(1);
				read_len = read( pipefd[0], buf, BUFSIZ );
				if ( read_len <= 0 )
					break;
				write( 1 , buf, read_len );
			}
	}
}