回顾类/对象大小计算

虚基类表

1.virtual base table
	1.1本类地址与虚基类表指针地址的差
	1.2虚基类地址与虚基类表指针地址的差
	
2.virtual base table pointer(vbptr)

在这里插入图片描述

#include <iostream>

using namespace std;

class BB
{
public:
	int bb_;
};

class B2 : virtual public BB
{
public:
	int b2_;
};

class B1 : virtual public BB
{
public:
	int b1_;
};

class DD : public B1, public B2
{
public:
	int dd_;
};

int main()
{
	cout << sizeof(BB) << endl;

	cout << sizeof(B1) << endl;
	cout << sizeof(B2) << endl;

	cout << sizeof(DD) << endl;

	B1 b1;
	long** p;
	
	cout << &b1 << endl;
	cout << &b1.bb_ << endl;
	cout << &b1.b1_ << endl;

	p = (long**)&b1;
	cout << p[0][0] << endl;
	cout << p[0][1] << endl;

	return 0;
}

在这里插入图片描述

#include <iostream>

using namespace std;

class BB
{
public:
	int bb_;
};

class B2 : virtual public BB
{
public:
	int b2_;
};

class B1 : virtual public BB
{
public:
	int b1_;
};

class DD : public B1, public B2
{
public:
	int dd_;
};

int main()
{
	cout << sizeof(BB) << endl;

	cout << sizeof(B1) << endl;
	cout << sizeof(B2) << endl;

	cout << sizeof(DD) << endl;

	B1 b1;
	long** p;
	
	cout << &b1 << endl;
	cout << &b1.bb_ << endl;
	cout << &b1.b1_ << endl;

	p = (long**)&b1;
	cout << p[0][0] << endl;
	cout << p[0][1] << endl;

	DD dd;
	cout << &dd << endl;
	cout << &dd.bb_ << endl;
	cout << &dd.b1_ << endl;
	cout << &dd.b2_ << endl;
	cout << &dd.dd_ << endl;

	p = (long**)&dd;
	cout << p[0][0] << endl;
	cout << p[0][1] << endl;

	cout << p[2][0] << endl;
	cout << p[2][1] << endl;

	return 0;
}