Linux C編程的小例子——實現who命令(第二版)

Linux C編程的小例子——實現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;
}