//-------------------------------------------------------------------
//	myitimer.cpp
//
//	This program shows how to setup an interval timer in a Linux 
//	program so that it will periodically issue a SIGALRM signal.
//
//		     compile using:  $ make myitimer 
//
//	programmer: ALLAN CRUSE
//	written on: 16 SEP 2004
//	revised on: 20 SEP 2005
//-------------------------------------------------------------------

#include <stdio.h>	// for printf() 
#include <signal.h>	// for signal()
#include <sys/time.h>	// for setitimer()	

int	signaled = 0;				// global variable 

void on_alarm( int signum ) { signaled = 1; }	// signal handler


int main( int argc, char **argv )
{
	// install our signal-handler 
	signal( SIGALRM, on_alarm );

	// initialize and install our interval-timer
	struct itimerval    ourit, oldit;
	// specify the initial delay (i.e., one second)
	ourit.it_value.tv_sec = 1;
	ourit.it_value.tv_usec = 0;
	// specify the periodic delay (i.e., one-half second)
	ourit.it_interval.tv_sec = 0;
	ourit.it_interval.tv_usec = 500000;
	// replace the default itimer with our itimer
	setitimer( ITIMER_REAL, &ourit, &oldit ); 

	// loop to print another line each time 'SIGALRM' is received
	printf( "\ec" ); // reset the terminal (this clears the screen) 
	int	letter = 'A', count = 0;
	do	{
		if ( !signaled ) continue;
	       	else	++count;
		signaled = 0;
		printf( "%20s", " " );
		for (int i = 0; i < 40; i++) printf( "%c", letter );
		printf( "\n" );
		if ( letter == 'Z' ) letter = 'A'; else ++letter;
		}
	while ( count < 52 );
	
	// restore original interval-timer and signal-handler
	setitimer( ITIMER_REAL, &oldit, NULL );
	signal( SIGALRM, SIG_DFL );
	printf( "\n" );
}