写的小闹钟程序

原理很简单，就是像闹钟一样，隔一段时间就滴答一次，可以设置时间间隔的。

#include <apue.h>

static volatile sig_atomic_t sigalrm;

static void sig_alrm(int signo)
{
    sigalrm = 1;
    write(STDERR_FILENO, "\a", 2);
}

int main(int argc, char **argv)
{
    int                 nsec;
    sigset_t            set;
    struct    sigaction    act;
    struct     itimerval    timer;

    if (argc != 2)
        err_quit("argc == 2");

    daemon(0, 1);

    nsec = atoi(argv[1]);

    timer.it_value.tv_sec = nsec;
    timer.it_value.tv_usec = 0;
    timer.it_interval.tv_sec = nsec;
    timer.it_interval.tv_usec = 0;

    if (setitimer(ITIMER_REAL, &timer, NULL))
        err_sys("setitimer error");

    if (sigemptyset(&set) < 0)
        err_sys("sigemptyset error");

    if (sigaddset(&set, SIGALRM) < 0)
        err_sys("sigaddset error");

    if (sigprocmask(SIG_BLOCK, &set, NULL) < 0)
        err_sys("sigprocmask error");

    if (sigemptyset(&set) < 0)
        err_sys("sigemptyset error");

    act.sa_flags = 0;
    act.sa_handler = sig_alrm;

    if (sigemptyset(&act.sa_mask) < 0)
        err_sys("sigemptyset error");

    if (sigaction(SIGALRM, &act, NULL) < 0)
        err_sys("sigaction error");

    for ( ; ; ) {

        sigsuspend(&set);

        if (sigalrm) {
            sigalrm = 0;
        }

    }

    return 0;
}