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

int main()
{
	pid_t pid;
	if((pid = fork()) < 0){
		perror("fork");
	/*子進程1*/	
	}else if(pid == 0){
		if((pid = fork()) < 0) 
			perror("fork");
		/*子進程2退出*/
		else if(pid > 0)
			exit(0);
		/*等待兩妙，以確保在打印父進程ID時第一個子進程已終止*/
		sleep(2);
		/*打印子進程的父進程號*/
		printf("second child, parent pid = %d\n", getppid());
		exit(0);
	}else{
	/*在父進程中等待子進程退出*/
	if(waitpid(pid, NULL, 0) != pid)
		perror("waitpid");
	exit(0);
	}
}