https://blog.csdn.net/jiangtaigong/article/details/83255471
https://blog.csdn.net/alpha_love/article/details/75222175

#include <iostream>
using namespace std;

class P {
private:
	virtual void showMeImpl();
public:
	void showMe();
};
void P::showMeImpl() {
	cout << "here is the parent" << endl;
}

void P::showMe() {
	showMeImpl();
}

class C : public P {
private:
	void showMeImpl();
public:
	void showMe();
};

void C::showMeImpl() {
	cout << "here is the child" << endl;
}

void C::showMe() {
	cout << "here is the childhhhhhhhhhhhhh" << endl;
}
int main() {
	C c;
	P& p = c;
	p.showMe();
	P* p2 = &c;
	p2->showMe();
}
 

基類中是否出現virtual很關鍵，無論virtual是出現在私有區域還是共有區域，只要在基類中出現，就會創建出虛擬函式表，派生類即會繼承這個虛擬函式表，實現執行時的多型
若基類中沒有出現virtual，那麼派生類繼承了父類，只能表現出靜態多型
注意virtual的位置
若virtual修飾的是showMeImpl，那麼結果為
here is the child
here is the child
若virtual修飾的是showMe，那麼結果為
here is the childhhhhhhhhhhhhh
here is the childhhhhhhhhhhhhh