使用fork()产生1个父级及其3个子进程

编程以创建四个进程(1个父级和3个子级)，它们按以下顺序终止：
(a)父流程最终终止
(b)第一个孩子在父母之前和第二个孩子之后终止。
(c)第二个孩子在最后一个孩子之后和第一个孩子之前终止。
(d)第三个孩子先终止。

先决条件：fork()，

// CPP code to create three child
// process of a parent
#include 
#include 
#include 
  
// Driver code
int main()
{
    int pid, pid1, pid2;
  
    // variable pid will store the
    // value returned from fork() system call
    pid = fork();
  
    // If fork() returns zero then it
    // means it is child process.
    if (pid == 0) {
  
        // First child needs to be printed
        // later hence this process is made
        // to sleep for 3 seconds.
        sleep(3);
  
        // This is first child process
        // getpid() gives the process
        // id and getppid() gives the
        // parent id of that process.
        printf("child[1] --> pid = %d and ppid = %d\n",
               getpid(), getppid());
    }
  
    else {
        pid1 = fork();
        if (pid1 == 0) {
            sleep(2);
            printf("child[2] --> pid = %d and ppid = %d\n",
                   getpid(), getppid());
        }
        else {
            pid2 = fork();
            if (pid2 == 0) {
                // This is third child which is
                // needed to be printed first.
                printf("child[3] --> pid = %d and ppid = %d\n",
                       getpid(), getppid());
            }
  
            // If value returned from fork()
            // in not zero and >0 that means
            // this is parent process.
            else {
                // This is asked to be printed at last
                // hence made to sleep for 3 seconds.
                sleep(3);
                printf("parent --> pid = %d\n", getpid());
            }
        }
    }
  
    return 0;
}

输出：

child[3]-->pid=50 and ppid=47
child[2]-->pid=49 and ppid=47
child[1]-->pid=48 and ppid=47
parent-->pid=47

此代码在Linux平台上运行。

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