linux alarm函数

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本文介绍如何使用POSIX标准下的alarm函数来为进程安排信号定时器，并通过一个示例程序展示了如何设定和调整定时器，以及如何在定时器触发时执行特定操作。

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首先 man alarm

NAME
       alarm - set an alarm clock for delivery of a signal

SYNOPSIS
       #include <unistd.h>

       unsigned int alarm(unsigned int seconds);

DESCRIPTION
       alarm() arranges for a SIGALRM signal to be delivered to the process in seconds seconds.

       If seconds is zero, no new alarm() is scheduled.

       In any event any previously set alarm() is cancelled.

RETURN VALUE
       alarm() returns the number of seconds remaining until any previously scheduled alarm was due to be delivered,

or zero if there was no previously scheduled alarm.

测试程序

#include<stdio.h>
#include<signal.h>
#include<unistd.h>

void alarm_test(int i) //需要加int i
{
        printf("hello world\n");
        signal(SIGALRM,alarm_test);
        alarm(3);
}

int main()
{
        int i ;

int a =0;

alarm_test(i);

        for(i=1;i<17;i++)
        {
                printf("sleep %d s\n",i);
                sleep(1);
                if(i == 7)
                 {
                        a = alarm(5); //重新设置定时时间
               //     a = alarm(0); //取消定时任务

   printf("a=[%d]\n",a); //返回剩余时间
                }
        }

return 0;

}