stdinredir2.c

介绍和编写和IO重定向的使用

/* stdinredir2.c
 * 	shows two more methods for redirecting standard input
 *	use #define to set one or the other
 */
#include	<stdio.h>
#include	<fcntl.h>

/* #define	CLOSE_DUP		/* open, close, dup, close */
/* #define	USE_DUP2	/* open, dup2, close */

main()
{
	int	fd ;
	int	newfd;
	char	line[100];

	/* read and print three lines */

	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );

	/* redirect input */
	fd = open("data", O_RDONLY);	/* open the disk file	*/
#ifdef CLOSE_DUP
	close(0);
	newfd = dup(fd);		/* copy open fd to 0	*/
#else
	newfd = dup2(fd,0);		/* close 0, dup fd to 0 */
#endif
	if ( newfd != 0 ){
		fprintf(stderr,"Could not duplicate fd to 0\n");
		exit(1);
	}
	close(fd);			/* close original fd	*/

	/* read and print three lines */

	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );
	fgets( line, 100, stdin ); printf("%s", line );
}