#include "apue.h"static void	sig_quit(int);intmain(void){	sigset_t	newmask, oldmask, pendmask;	if (signal(SIGQUIT, sig_quit) == SIG_ERR)		err_sys("can't catch SIGQUIT");	/*	 * Block SIGQUIT and save current signal mask.	 */	sigemptyset(&newmask);	sigaddset(&newmask, SIGQUIT);	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)		err_sys("SIG_BLOCK error");	sleep(5);	/* SIGQUIT here will remain pending */	if (sigpending(&pendmask) < 0)		err_sys("sigpending error");	if (sigismember(&pendmask, SIGQUIT))		printf("\nSIGQUIT pending\n");	/*	 * Reset signal mask which unblocks SIGQUIT.	 */	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)		err_sys("SIG_SETMASK error");	printf("SIGQUIT unblocked\n");	sleep(5);	/* SIGQUIT here will terminate with core file */	exit(0);}static voidsig_quit(int signo){	printf("caught SIGQUIT\n");	if (signal(SIGQUIT, SIG_DFL) == SIG_ERR)		err_sys("can't reset SIGQUIT");}