C语言实现who

代码实现

#include <stdio.h>
#include <stdlib.h>
#include <utmp.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>

#define	SHOWHOST	

void show_time(long timeval){ 
	char format_time[40]; 
        struct tm *cp;  
        cp = localtime(&timeval);  
        strftime(format_time,40,"%F %R",cp);
        printf("%s",format_time);  
}  

int show_info( struct utmp *utbufp )
{
	if(utbufp->ut_type == USER_PROCESS){

	printf("%-8.8s", utbufp->ut_name);	
	printf(" ");				
	printf("%-8.8s", utbufp->ut_line);	
	printf("     ");				
	show_time(utbufp->ut_time);	
	printf(" ");				
#ifdef	SHOWHOST
	printf("(%s)", utbufp->ut_host);	
#endif
	printf("\n");				
	}
	return 0;
}
int main()
{
	struct utmp	 current_record;	
	int		utmpfd;		
	int		reclen = sizeof(current_record);

	if ( (utmpfd = open(UTMP_FILE, O_RDONLY)) == -1 ){
		perror( UTMP_FILE );	
		exit(1);
	}
	while ( read(utmpfd, &current_record, reclen) == reclen )
		show_info(&current_record);
	close(utmpfd);
	return 0;			
}

mywho与Linux系统who比较