fork新建进程

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

int main()
{
  pid_t pid;                                  //记录fork（）的返回值，用于区别父子进程
  char *Message;                              //用于记录输出信息
  int LoopVal;      //用于记录父子进程的循环次数
  int LoopVal1;      //用于循环
  int ExitCode;

  printf("the new fork starting\n");
  pid=fork();                                        //新建子进程
  switch(pid)
    {
    case -1:      //建立进程错误       
     printf("creat new fork error!");
     exit(1);
    case 0:                                           //子进程
      Message = "This is in the child process";
      LoopVal = 7;
      ExitCode = 25;
      break;
    default:                                         //父进程
      Message = "This is in the parent process,waiting the child finished........";
      LoopVal = 5;
      ExitCode = 15;
      break;
    }
  for(LoopVal1=0;LoopVal1<LoopVal;LoopVal1++)
    {
      puts(Message);
      sleep(1);
    }
  if(pid!=0)         //父进程
    {
      int StateVal;
      pid_t ChildPid;
      ChildPid = wait(&StateVal);         //用StateVal记录状态信息,wait返回的是子进程退出时，子进程的进程id。
      printf("The child has finished with  the PID of %d\n",ChildPid);
      if(WIFEXITED(StateVal))             //如果子进程正常结束，它就取一个非零值
 　　{

　　　　//宏WEXITSTATUS(StateVal)是如果子进程正常结束，该宏函数的值为0，否则为非零值，与WIFEXITED(StateVal)刚好相反。
  　　 　　printf("the child process has exit with code %d\n",WEXITSTATUS(StateVal));

            //如果WIFEXITED非零，它返回子进程的退出码
      }                                              

      else
          printf("the child has terminated abnormally\n");
    }                                                   //子进程非正常结束
    exit(ExitCode);
}