linux fork详解

一、fork写时复制测试

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
int a = 200;
int main(int argc,char *argv[])
{
        pid_t pid;
        pid = fork();
        if (pid == 0)
        {
                a = 100;
                printf("子进程的a=%d\n", a);
        }
        else
        {
                printf("父进程的a=%d\n", a);
        }
        return 0;
}

result:

#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
int a = 200;
int main(int argc,char *argv[])
{
        pid_t pid;
        pid = fork();
        if (pid == 0)
        {

                printf("子进程的a=%p\n", &a);
        }
        else
        {
                printf("父进程的a=%p\n", &a);
        }
        return 0;
}

result:

二、 循环创建n个子进程

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

int main(int argc, char *argv[])
{
  int n = 5, i;        //默认创建5个子进程

  if (argc == 2) 
  {  
    n = atoi(argv[1]);
  }

  for (i = 0; i < n; i++)  //出口1,父进程专用出口
    if (fork() == 0)
      break;      //出口2,子进程出口,i不自增

  if (n == i) 
  {
    sleep(n);
    printf("I am parent, pid = %d\n", getpid());
  } else 
  {
    sleep(i);
    printf("I'm %dth child, pid = %d\n", 
        i+1, getpid());
  }

  return 0;
}

result: