/*  In alarm.c, the first function, ding, simulates an alarm clock.  */#include <signal.h>#include <stdio.h>#include <unistd.h>static int alarm_fired = 0;void ding(int sig){    alarm_fired = 1;}/*  In main, we tell the child process to wait for five seconds    before sending a SIGALRM signal to its parent.  */int main(){    int pid;    printf("alarm application starting\n");    if((pid = fork()) == 0) {        sleep(5);        kill(getppid(), SIGALRM);        exit(0);    }/*  The parent process arranges to catch SIGALRM with a call to signal    and then waits for the inevitable.  */    printf("waiting for alarm to go off\n");    (void) signal(SIGALRM, ding);    pause();    if (alarm_fired)        printf("Ding!\n");    printf("done\n");    exit(0);}