钻石（菱形）继承和虚基类

//Test1.h
#include<iostream>
using namespace std;
class Grandfather
{
public:
    int a;
    Grandfather(int _a):a(_a) 
    {
        cout<<"Grandfather was built. "<<endl;
    }
    ~Grandfather(){cout<<"Grandfather was free. "<<endl;}
};
class Father1 : public virtual Grandfather
{
public:
    int n;
    Father1(int _a) : n(_a),Grandfather(_a)
    {
        cout<<"Father1 was built. "<<endl;
    }
    ~Father1(){cout<<"Father1 was free. "<<endl;}
};
class Father2 : virtual public Grandfather //virtual写在public前后都可以
{
public:
    int n;
    Father2(int _a) : n(_a),Grandfather(_a)
    {
        cout<<"Father2 was built. "<<endl;
    }
    ~Father2(){cout<<"Father2 was free. "<<endl;}
};
class Son : public Father1, public Father2
{
public:
    Son(int _a):Father1(_a),Father2(_a),Grandfather(_a)
    {
        cout<<"Son was built. "<<endl;
    }
    ~Son(){cout<<"Son was free. "<<endl;}
};

#include"Test1.h"
void main()
{
    Son son(10);
    son.Father1::n = 1;
    son.Father2::n = 2;//由于在Father1,Father2内均存在公有数据n，在对其赋值时需要加上作用域
    son.Father1::a = 5;
    son.Father2::a = 6;//两次赋值均对一个数据成员操作
}