linux下fork函数创建进程

linux下fork函数创建进程

#include
#include
#include
#include
#include
int main()
{
pid_t child1,child2,child;  /*创建两个子进程*/
child1=fork();
//child2=fork();        /*子进程1的出错处理*/
 if(child1==-1)
     {
          printf("Child1 fork error\n");
          exit(1);  /*异常退出*/
     }
        /*在子进程1中调用execlp()函数*/
 if(child1!=0)
 {
    child2=fork();
    if(child2==-1)
    {
     printf("Child2 fork error\n");
     exit(1);  /*异常退出*/
    }        /*在子进程2中使其暂停5s*/
    else if(child2==0)
     {
     printf("I am child2.I will sleep for 5 seconds!\n");
     sleep(5);
     printf("I am child2.I have awaked and I will exit!\n");
     exit(0); /*正常退出*/
     }        /*在父进程中等待两个子进程的退出*/


    else
      {
       printf("I am father progress\n");
       child=waitpid(child1,NULL,0);/*阻塞式等待*/
       if(child==child1)
         {
          printf("I am father progress.I get child1 exit code:%d\n",child);
         }
       else
        {
        printf("Error occured!\n");
        }
        do
        {
         child=waitpid(child2,NULL,WNOHANG);/*非阻塞式等待*/
         if(child==0)
            {
              printf("I am father progress.The child2 progress has not exited!\n");
              sleep(1);
            }
        }while(child==0);
        if(child==child2)
        {
         printf("I am father progress.I get child2 exit code:%d\n",child);
        }
        else
        {
         printf("Erroe occured!\n");
        }
    }
 }
 else if(child1==0)
   {
   printf("I am child1 and I execute 'ls -l'\n");
   if(execlp("ls","ls","-l",NULL)<0)
          {
            printf("Child1 execlp error\n");
          }
    }        /*子进程2的出错处理*/
exit(0);

}

运行结果：