EBO，c++编译器有empty继承优化（编译期）

#include <iostream>

using namespace std;

class empty
{
//null
};

class A : private empty//这种情况下用private
{
int s;
};

class AA
{
int s;
empty e;
};

void main()
{
empty e;
A a;
AA aa;
cout << sizeof(e) << " " << endl;//1
cout << sizeof(a) << " " << endl;//4
cout << sizeof(aa) << " " << endl;//8
}

//还必须是单继承
// EBO