c++ 的 坑真多之头文件

#pragma once
#include <string>
#include <iostream>

class Humankind;
class Person {
public:
Person();
void sayHello(Humankind human);
};

#pragma once
#include <string>
#include <iostream>
#include "Humankind.h"
class Person : Humankind{
public:
Person();
void sayHello();
};