Linux C编程的小例子——实现who命令(第二版)

/*
 * who1.c
 *
 *  Created on: Dec 30, 2013
 *      Author: fedora
 */

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


#define SHOWHOST

void showtime(long timeval){
	char* cp;
	cp = ctime(&timeval);

	printf("%12.12s",cp+4);
}

void show_info(struct utmp* utbufp){
	if(utbufp->ut_type != USER_PROCESS){
		return ;
	}

	printf("%-8.8s",utbufp->ut_name);
	printf(" ");
	printf("%-8.8s",utbufp->ut_line);
    printf(" ");
    showtime(utbufp->ut_time);
    printf(" ");

#ifdef SHOWHOST
    if(utbufp->ut_host[0] != '\0'){
    	printf("( %s )",utbufp->ut_host);
    }
#endif

    printf("\n");
}
int main(){
	struct utmp current_record;
	int utmpfd;
	int reclen = sizeof(current_record);

	if((utmpfd = open(UTMP_FILE,O_RDONLY)) == -1){
		perror(UTMP_FILE);

		return 1;
	}

	while( read(utmpfd,&current_record,reclen) == reclen ){
		show_info(&current_record);
	}

	close(utmpfd);

	return 0;
}