c - 在 C 中先于父执行子

Question

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

int main(int argc, char ** argv)
{

    int pid;
    int status;
    pid = fork();

    if (pid < 0)
    {
        printf("Cannot create a child process");
        exit(1);
    }
    else if (pid == 0)
    {

        printf("I am the child process. %d \n", getpid());
        printf("The child process is done. \n");
        fflush(stdout); // it does not write immediately to a disk.
        exit(0);
    }
    else
    {

        printf("I am the parent process.%d \n", getpid());
        sleep(5); // sleep does not works
        pid = wait(&status); // want to wait until the child is complited
        printf("The parent process is done. \n");
        fflush(stdout); // it does not write immediately to a disk.
        exit(1);
    }
}

大家好，我目前正在尝试创建一个子进程。然而，到目前为止一切顺利，我现在正在尝试的是首先执行子进程并打印出来，并且总是最后打印出消息“父进程已完成”。

I am the parent process.28847  
I am the child process. 28848 
The child process is done.
The parent process is done.

目前正在打印:

I am the parent process.28847 
The parent process is done.
I am the child process. 28848 
The child process is done.

这是我第一次使用 fork ，所以我对自己在做什么不太有信心，我试过 sleep 和等待(&status)来尝试等到子进程完成然后执行父进程，但有些事情不是工作。

附言抱歉布局不好，第一次使用 stackoverflow。

Answer 1

试试 waitpid(-1, NULL, 0);或等待(NULL)；这将阻塞父进程，直到所有子进程都完成。如果有效，则您无需使用 sleep 。

对您的代码稍作修改:

else
{
    int status =0;
    printf("I am the parent process.%d \n", getpid());
    status= waitpid(-1, NULL, 0); // want to wait until the child is complete
    //Also check if child process terminated properly
    if(status==0)
    {
        printf("Child process terminated properly");
    }   
    else
    {
       printf("Child process terminated with error");
    }

    printf("The parent process is done. \n");

    fflush(stdout); // it does not write immediately to a disk.

    exit(1);
}