进程 fork函数 wait函数

#include
#include
#include
#include

int main()
{
 int n;
  int exit_code;
 char *message;
 pid_t new_pid;
 new_pid = fork();

 
 printf("fork is starting...............\n");
 switch(new_pid)
 {
  case -1: /* Error */
   perror("fork failed.\n");
   exit(1);
  
  case 0: /* This is child */
   message = "This is a child thread.";
   n = 3;
    exit_code = 37;
   break;
  
  default: /* This is parent */
   message = "This is a parent thread.";
   n = 5;
    exit_code = 0;
   break;
 }
 
 for(;n>0;n--)
 {
  puts(message);
  sleep(1);
 }
 
  
 if(new_pid !=0)
 {
  int stat_val;
  pid_t child_pid;
  
  child_pid = wait(&stat_val);
  printf("Child has finished: PID = %d\n",child_pid);
  if(WIFEXITED(stat_val))
   printf("Child exited with code %d\n",WEXITSTATUS(stat_val));
  else
   printf("Child terminated abnormally\n");
  
 }
 exit(exit_code);
  
 
}