类/对象的大小问题，关于virtual虚继承

Question

class A{};
class B{
virtual void func0() {}
};
class C{
virtual void func1() {}
};
class D:public B, public C{
virtual void func2() {}
};
class E:public B, public C{
};
这里D和E大小一样，为啥，本身的虚基类表指针呢？发生了什么操作

Answer 1

#include <iostream>

using namespace std;

class A{};

class B
{
    virtual void func0() {
        cout << "B func0"<<endl;
    }
};

class C
{
    virtual void func1()
    {
        cout << "C func1"<<endl;
    }
};

class D:public B , public C
{
    virtual void func2()
    {
        cout << "D func2()" <<endl;
    }
};

class E:public B, public C
{
};

int main()
{
    D d;

    long *p2Class = (long *)&d;

    long *p2VTB = (long *) ( *p2Class );


    //第一张虚函数表 begin
    long *p2Fun = NULL;

    p2Fun = (long *)(*(p2VTB));
    ((void (*) ())p2Fun)();           //cout-->B func0

    p2Fun = (long *)(*(p2VTB + 1));
    ((void (*) ())p2Fun)();           //cout-->D func2
    //第一张虚函数表 end

    //第二张虚函数表 begin
    long *p2VTC = (long *) ( *(p2Class + 1) );

    p2Fun = (long *)(*(p2VTC));
    ((void (*) ())p2Fun)();           //cout-->C func1

    /*
    p2Fun = (long *)(*(p2VTC + 1));
    ((void (*) ())p2Fun)();           //报错
     */
    //第二张虚函数表 end

    return 0;
}

我是64位的, 验证得出, 本身的虚基类表指针被和B的虚函数指针放在同一张虚函数表里, C的虚函数表里没有.