pclose返回值为什么要和256比较

include <errno.h>

include <stdio.h>

include <stdlib.h>

include <string.h>

include <unistd.h>

int main(int argc, char *argv[])
{
int status;
pid_t pid;

  pid = fork();

  if (0 == pid)
  {
  	exit(atoi(argv[1]));
  } else 
  {
  	wait(&status);
  	printf("status = %d\n", status);
  	if (WIFEXITED(status))
  	{
  		printf("WEXITSTATUS(status)=%d\n", WEXITSTATUS(status));
  	}
  }

  return 0;

}
该程序运行结果

pclose的返回值就是这里wait(&status)中status的值。