异步回收fork出的子进程(僵尸进程)

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <sys/wait.h>   

void handler(int num) {
    //我接受到了SIGCHLD的信号啦
    int status;
    int pid = waitpid(-, &status, WNOHANG);
    if (WIFEXITED(status)) {
        printf("The child %d exit with code %d\n", pid, WEXITSTATUS(status));
    }
}   

int main() {
    //子进程的pid
    int c_pid;
    int pid;   

    signal(SIGCHLD, handler);   

    if ((pid = fork())) {
        //父进程
        c_pid = pid;
        printf("The child process is %d\n", c_pid);   

        //父进程不用等待，做自己的事情吧～
        for (int i = ; i < ; i++) {
            printf("Do parent things.\n");
            sleep();
        }   

        exit();
    } else {
        //子进程
        printf("I 'm a child.\n");
        sleep();
        exit();
    }
}