using signal SIGALRM for timeout

/*******************************************************
* timeout *
* Program to demonstrate a timeout routine *
*******************************************************/
#include < stdio.h >
#include < signal.h >
#include < setjmp.h >
/*
* The environment for setjmp.
*/
jmp_buf env;
main()
{
int i;
char buf[160];
extern void timeout();
/*
* Inform the system we want to catch the
* alarm signal
*/
signal(SIGALRM, timeout);
/*
* The code inside the if gets executed the first
* time through setjmp, the code inside the else
* the second time.
*/
if (setjmp(env) == 0) {
/*
* Issue a request for an alarm to be delivered
* in 5 seconds. alarm() is a system call.
*/
alarm(5);
/*
* Prompt for input. Waits for it forever. If
* it's still waiting and an alarm signal comes,
* we come back to the setjmp() and never get
* any further.
*/
printf("Type a word; if you don't in 5 ");
printf("seconds I'll use 'WORD' instead:");
(void) fgets(buf, sizeof(buf), stdin);
/*
* Turn off the alarm
*/
alarm(0);
}
else {
/*
* Assume the default.
*/
strcpy(buf, "WORD");
}
printf("\n The word is: %s\n", buf);
exit(0);
}
/*
* timeout -- catch the signal
*/
void timeout(sig)
int sig;
{
int i;
/*
* Ignore the signal for the duration of this
* routine.
*/
signal(sig, SIG_IGN);
/*
* We would perform any timeout-related
* functions here.
*/
printf("...Timeout!\n");
/*
* Restore the action of the alarm signal
*/
signal(SIGALRM, timeout);
/*
* Return to the main routine at setjmp,
* and make setjmp return 1.
*/
longjmp(env, 1);
}