fork()函数的理解

#include <sys/types.h>

#include <stdio.h>
#include <sys/wait.h>
#include <unistd.h>

int main(){
        int status;
        pid_t pc,pr;

        pc=fork();//在调用了fork函数之后，子进程和父进程就此开始分道扬镳，也就是这里fork()返回值子进程和父进程是得到了不同的值

         //对于子进程：fork()函数返回的是0，所以子进程的pc=0；而对于父进程，fork()函数返回的是子进程的PID

        //pc=fork();之后的代码子进程和父进程都继续往下执行，因为子进程和父进程具有相同的代码区

        if(pc<0){
                printf("fork failed");
                exit(1);
        }else if(pc==0){   //所以，子进程执行到这里的时候符合判断条件，而父进程不符合，子进程进入else if {..}，而父进程pc=pid_chidl，所以继续往下执行
                int i;
                for(i=3;i>0;i--){
                        printf("this is the child\n");
                        sleep(3);
                }
                exit(3);
        }else{  //父进程执行到这里以后，满足条件，所以进入else{...}
                pr=wait(&status);
                if(WIFEXITED(status)){
                        printf("the child process %d exit normally.\n",pr);
                        printf("the WEXITSTATUS return code id %d \n",WEXITSTATUS(status));
                        printf("the WIFEXITED return code id %d \n",WIFEXITED(status));
                }else{
                        printf("the child process %d exit abnormally.\n",pr);
                        printf("status is %d",status);
                }
        }
        return 0;
}

输出的结果：

this is the child
this is the child
this is the child
the child process 15446 exit normally.
the WEXITSTATUS return code id 3
the WIFEXITED return code id 1