c - 使用报警功能

Question

该程序实现了多个警报，以允许进程定义多个计时器(使用 alarm 函数)。问题是当我编译时我收到了一些警告，我该如何摆脱它们？另外，我觉得实现的不太好，我也想收到这方面的反馈

警告:

main.c:16:55: warning: implicit declaration of function ‘getppid’ [-Wimplicit-function-declaration]
   16 |     printf("sending kill SIGALRM to the parent %d\n", getppid());
      |                                                       ^~~~~~~
main.c: In function ‘set_alarm’:
main.c:26:9: warning: implicit declaration of function ‘fork’ [-Wimplicit-function-declaration]
   26 |     if( fork() == 0 ){
      |         ^~~~
main.c:28:9: warning: implicit declaration of function ‘alarm’ [-Wimplicit-function-declaration]
   28 |         alarm(secs);
      |         ^~~~~
main.c:30:9: warning: implicit declaration of function ‘pause’ [-Wimplicit-function-declaration]
   30 |         pause();
      |         ^~~~~

代码:

#include <stdio.h>
#include <signal.h>
#include <stdlib.h>
/*
    The OPTIONAL parent SIGALRM handler. Does nothing useful apart from logging the SIGALRM received from the child.
*/
void parent_alrm_handler(int signo) {
    printf("Parent proc caught alrm signal\n");
    return;
}

/*
    The child SIGALRM handler.Replays the SIGALRM back to the parent when it receives it.
*/
void child_alrm_handler(int signo){
    printf("sending kill SIGALRM to the parent %d\n", getppid());
    kill(getppid(), SIGALRM);
}

/*
    Since each proc has single timer. I create child proceses when the req for new alarms is made.
*/
void set_alarm(int secs){
    signal(SIGALRM, parent_alrm_handler);
    if( fork() == 0 ){
        signal(SIGALRM, child_alrm_handler);
        alarm(secs);
        printf ("setting an alarm\n");
        pause();
        exit(0);        
    }   
}

int
main(void) {
    set_alarm(1); //alarm 1     
    set_alarm(4); //alarm 2     
    for(;;)
        pause();
    return 0;
}

Answer 1

您没有包含定义这些函数的 unistd.h。