派生类赋值给基类指针，调用成员函数

#include <iostream>
using namespace std;

class A{
public:
int v;
void fun(){ cout<<"Member of A:"<<v<<endl;}

A(){ v=3;cout<<"constructor of A:"<<v<<endl;}
~A(){ cout<<"Delete A:"<<endl;}
};

class B1:virtual public A{
public:
int v;
void fun(){ cout<<"Member of B1:"<<v<<endl;}

B1(){ cout<<"constructor of B1:"<<endl;}
~B1(){ cout<<"Delete B1:"<<endl;}
};

class B2:virtual public A{
public:
int v;
void fun(){ cout<<"Member of B2:"<<v<<endl;}

B2(){ cout<<"constructor of B2:"<<endl;}
~B2(){ cout<<"Delete B2:"<<endl;}

};

class D1: public B2, public B1 {
public:
int v;