10.2.c

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <pwd.h>
#include <string.h>

static void my_alarm(int signo)
{
    struct passwd  *rootptr;

    printf("in signal handler\n");
    if (NULL == (rootptr = getpwnam("root"))) {
        printf("getpwnam(root) error\n");
        exit(-1);
    }

    alarm(1);
}

int main(void)
{
    struct passwd   *ptr;
    
    signal(SIGALRM, my_alarm);
    alarm(1);

    for (; ;) {
        if (NULL == (ptr = getpwnam("vagrant"))) {
            printf("getpwnam error\n");
            exit(-1);
        }

        if (strcmp(ptr->pw_name, "vagrant") != 0) {
            printf("return value corrupted, pw_name = %s\n", ptr->pw_name);
        }
    }
}