/* 虚基类 */

#include <iostream>
using namespace std;

class A
{
public:
 virtual void show() {
 cout << "A::show()" << endl;
 }

 void operator delete(void *ptr) {
 cout << "A::opeartor delete p: " << ptr << endl;
 free(ptr);
 }

private:
 int ma;
};

class B : virtual public A
{
public:
 void show() {
 cout << "B::show()" << endl;
 }

 void* operator new(size_t size) {
 void *p = malloc(size);
 cout << "operator new p: " << p << endl;
 return p;
 }

 void operator delete(void *ptr) {
 cout << "B::opeartor delete p: " << ptr << endl;
 free(ptr);
 }
private:
 int mb;
};


int main() 
{
 /** @brief 基类指针指向派生类对象,永远指向的都是派生类基类部分数据的起始地址
 * 1. windows 下 VS 编译器会有问题,delete p 从 vfptr 开始,但是 new 的其实地址是 vbptr
 * 2. Linux 下 g++ 编译器没有问题,delete p 会从 vbptr 开始释放内存
 * 
 * B 的内存布局
 * +---
 * | {vbptr} virtual base ptr
 * | mb
 * +---
 * +--- (virutal base A)
 * | {vfptr} virtual function ptr
 * | ma
 * +---
 * 
 * B::$vbtable@:
 * | 0 (vbptr 起始偏移量,因为在最上面所以偏移量为 0)
 * | 8
 * 
 * B::$vftable@:
 * | -16 (vptr 起始偏移量,vptr 上面有`vbptr`--8字节和`mb`--4字节,对齐为 8 字节,所以偏移量为 -16)
 * | &B::show
 * */
 A *p = new B();
 cout << "A *p " << p << endl;
 p->show();
 delete p;

 return 0;
}