linux下的who.c编写

来源：互联网发布：最新版淘宝下载安装编辑：程序博客网时间：2024/05/17 02:37

/**********************
data:2010-11-21
**********************/
#include <stdio.h>
#include <utmp.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>

#define SHOWHOST
void show_info(struct utmp *utbufp);
void show_time(long);

int main(int argc, char *argv[])
{
    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;
}

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(" ");
    printf("%ld", utbufp->ut_pid);
    printf(" ");
    show_time(utbufp->ut_time);
    printf(" ");

    #ifdef SHOWHOST
       printf("(%s)",utbufp->ut_host);
    #endif

printf("/n");
}

void show_time(long timeval)
{
    char *cp;
    cp = ctime(&timeval);
    printf("%12.12s", cp+4);
}