Question

我不完全确定何时使用fork（）进行子进程处理即使作为其他处理的父亲的子处理（状态0），也有创建其他子处理的子处理吗？

#include <stdio.h>

int main()
{
    printf("new proces");

    if (fork() == 0) {
        printf("child parent");

        if (fork() == 0)
            printf("child child");
    }

    printf("\n");
}

我很困惑因为我不确定当子进程调用fork（）时它是否会创建新进程？因为在这段代码中

#include<stdio.h>
int main(){
printf(" do ");
if(fork()!=0) printf("ma ");
if(fork()==0) printf("to \n");
else printf("\n");


}

我的结果就像在这个代码中有没有状态0的子父进程而我不知道为什么因为它是第一个父进程的子进程

do ma 
do ma to
do to
do

不喜欢这个

do ma
do do to
to

子进程调用fork没有返回0因为我有两个ma不仅一个而且我不知道为什么

Answer 1

是。该过程创建一个孩子，然后创建另一个孩子，成为它的父母您可以使用fork返回号来区分child和parent。来自fork：

On success, the PID of the child process is returned in the parent, 
and 0 is returned in the child. On failure, -1 is returned in the parent, 
no child process is created, and errno is set appropriately.

您需要检查fork（）返回值。如果它返回0，则表示此过程是子进程。如果返回的值大于0，则此进程为父进程，返回值为子进程ID。看看这个程序。我添加了usleep次调用以使进程一个接一个地打印出来：

#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
int main(){
    // lets create a family!
    pid_t grandpa_pid = getpid();
    pid_t child_pid;
    if ((child_pid = fork()) == 0){
        pid_t parent_pid = getpid();
        pid_t child_child_pid;
        if ((child_child_pid = fork()) == 0) {
            usleep(200);
            printf("I am child and I will write third. My pid is %d, %d is my parent and %d is my parents parent, so my grandpa.", getpid(), parent_pid, grandpa_pid);
        } else {
            usleep(100);
            // parent_pid = getpid()
            printf("I am parent and I will write second. My pid is %d, %d is my child and %d is my parent.", getpid(), child_child_pid, grandpa_pid);
        }
    } else {
        // grandpa_pid == getpid()
        printf("I am grandpa and I will write first. My pid is %d and %d is my child.", getpid(), child_pid);
    }
    printf("\n");
}

产生以下输出：

I am grandpa and I will write first. My pid is 5 and 6 is my child.                                                                                                                
I am parent and I will write second. My pid is 6, 7 is my child and 5 is my parent.                                                                                                
I am child and I will write third. My pid is 7, 6 is my parent and 5 is my parents parent, so my grandpa.

从孩子创建子进程

1 个答案: