who

who.c

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#include <utmpx.h>

int main(void)
{
    struct timeval last_hour;
    struct timeval last_login; 
    struct utmpx *entry = NULL;
    gettimeofday(&last_hour, NULL);
    last_hour.tv_sec = last_hour.tv_sec - 3600;

    while ((entry = getutxent()) != NULL) {   
        
        printf("User %s is using %s. The pid is %d\n", 
            entry->ut_user, entry->ut_line, entry->ut_pid);

        if (0 == timercmp(&(entry->ut_tv), &(last_hour), <)){
            printf("%s logged in within the last hour\n", entry->ut_user);
        }
    }

    return 0; 
}