#include "apue.h"volatile sig_atomic_t	quitflag;	/* set nonzero by signal handler */static voidsig_int(int signo)	/* one signal handler for SIGINT and SIGQUIT */{	if (signo == SIGINT)		printf("\ninterrupt\n");	else if (signo == SIGQUIT)		quitflag = 1;	/* set flag for main loop */}intmain(void){	sigset_t	newmask, oldmask, zeromask;	if (signal(SIGINT, sig_int) == SIG_ERR)		err_sys("signal(SIGINT) error");	if (signal(SIGQUIT, sig_int) == SIG_ERR)		err_sys("signal(SIGQUIT) error");	sigemptyset(&zeromask);	sigemptyset(&newmask);	sigaddset(&newmask, SIGQUIT);	/*	 * Block SIGQUIT and save current signal mask.	 */	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)		err_sys("SIG_BLOCK error");	while (quitflag == 0)		sigsuspend(&zeromask);	/*	 * SIGQUIT has been caught and is now blocked; do whatever.	 */	quitflag = 0;	/*	 * Reset signal mask which unblocks SIGQUIT.	 */	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)		err_sys("SIG_SETMASK error");	exit(0);}