who1top.c

understanding unix/linux programming source code(bruce molay)

/* who1.c  - a first version of the who program
 *              open, read UTMP file, and show results
 */
#include	<stdio.h>
#include	<utmp.h>
#include	<fcntl.h>
#include	<unistd.h>

#define	SHOWHOST	/* include remote machine on output */

int main()
{
	struct utmp	current_record;	/* read info into here       */
	int		utmpfd;		/* read from this descriptor */
	int		reclen = sizeof(current_record);

	if ( (utmpfd = open(UTMP_FILE, O_RDONLY)) == -1 ){
		perror( UTMP_FILE );	/* UTMP_FILE is in utmp.h    */
		exit(1);
	}

	while ( read(utmpfd, &current_record, reclen) == reclen )
		show_info(&current_record);
	close(utmpfd);
	return 0;			/* went ok */
}