通过实例体会 fork()同时创建多个子进程

来源：互联网发布：网络基础设施建设方案编辑：程序博客网时间：2024/05/19 19:44

特点：同时创建多个子进程，每个子进程可以执行不同的任务，程序可读性较好，便于分析，易扩展为多个子进程

#include <stdio.h>#include <stdlib.h>int main(){    pid_t p1,p2;    printf("before fork(),pid=%d\n",getpid());p1=fork();if(p1==0){printf("in child 1, pid = %d\n", getpid());return 0;}p2 = fork();if( p2 == 0 ){printf("in child 2, pid = %d\n", getpid());return 0; //程序结束不再执行printf("Hello world\n");}/*int st1, st2;waitpid(p1, &st1, 0);waitpid(p2, &st2, 0);printf("in parent, child 1 pid = %d\n", p1);printf("in parent, child 2 pid = %d\n", p2);printf("in parent, pid = %d\n", getpid());printf("in parent, child 1 exited with %d\n", st1);printf("in parent, child 2 exited with %d\n", st2);*/return 0;}

执行结果：

before fork(),pid=2381in child 1, pid = 2382in child 2, pid = 2383

第二种方法

特点：同时创建两个子进程，结构比较繁琐，程序可读性不好，不易扩展

#include <stdio.h>#include <unistd.h>//查查在windows下能编译吗？Linux函数。#include <sys/types.h>//这个头文件不能少，否则pid_t没有定义main(){ printf("This is parent process  %d\n",getpid()); pid_t p1,p2; if((p1=fork())==0)printf("This is child_1 process  %d\n",getpid()); else if((p2=fork())==0)   printf("This is child_2 process  %d\n",getpid()); else {   wait(p1,NULL,0);   wait(p2,NULL,0);   printf("This is parent process  %d\n",getpid()); }}

执行结果：

This is parent process3553This is child_1 process3554This is child_2 process3555This is parent process3553

注意：if .......else if .........else........语句只执行一次。

当执行完if语句的时候子进程结束if...else if...else语句，父进程并没有结束。

第三种方法：for循环方法

特点：其实每次循环只是创建了单个进程，并没有同时创建多个进程

#include<stdio.h>#include<sys/types.h>main() {printf("This is parent process  %d\n",getpid());pid_t p1,p2;int i;for(i=0;i<=2;i++){if((p1=fork())==0){printf("This is child_1 process  %d\n",getpid());return 0;//这个地方非常关键，父进程结束}/*wait(p1,NULL,0);printf("This is parent process  %d\n",getpid());/}

执行结果：

This is parent process2655This is child_1 process2656This is child_1 process2657This is child_1 process2658

注意：标注的return 0 对程序结果影响很大

无return 0 情况

#include <stdio.h>#include <unistd.h>#include <sys/types.h>main(){ printf("This is parent process  %d\n",getpid()); pid_t p1,p2; int i; for(i=0;i<=2;i++) {  if((p1=fork())==0)   {    printf("This is child_1 process  %d\n",getpid());     //return 0;//这个地方非常关键，父进程继续执行    }  /* wait(p1,NULL,0);   printf("This is parent process  %d\n",getpid());*/  }}

执行结果：

This is parent process2620This is child_1 process  2621This is child_1 process  2622This is child_1 process  2625This is child_1 process  2626This is child_1 process  2624This is child_1 process  2623This is child_1 process  2627

结论：父进程会生成2N-1个子进程，N为循环次数，本例中共有7个子进程，但实际上只有3个是父进程产生的，其余都为子进程fork（）出来的

0 0