哪位高手看看，问题出在哪

#include "apue.h"

static void sig_quit(int);

int main()
{
sigset_t newmask, oldmask, pendmask;

if (signal(SIGQUIT, sig_quit) == SIG_ERR)
err_sys("can't catch SIGQUIT");

sigemptyset(&newmask);
sigaddset(&newmask, SIGQUIT - 1);

if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)
err_sys("SIG_BLOCK error");

sleep(5);

if (sigpending(&pendmask) < 0)
err_sys("sigpending error");
if (sigismember(&pendmask, SIGQUIT - 1) < 0)
printf("\nSIGQUIT pending\n");

if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)
err_sys("SIG_SETMASK error");
printf("SIGQUIT unblocked\n");

sleep(5);
exit(0);
}

static void sig_quit(int signo)
{
printf("caught SIGQUIT\n");
if (signal(SIGQUIT, SIG_DFL) == SIG_ERR)
err_sys("can't reset SIGQUIT");
}
按书本说，运行时，第一次休眠5秒钟时，按下ctrl+\输出结果是
SIGQUIT pending
catch SIGQUIT
SIGQUIT unblocked
但是我的运行结果没有输出SIGQUIT pending，即
catch SIGQUIT
SIGQUIT unblocked
这是什么原因呢?