虚基类的作用：消除二义性

前因：

1.C++中多重继承，即一个派生类可以有多个基类。如果多个基类有同名成员或同名函数，派生类对象对其访问时会产生二义性。

举例：

#include <iostream>
using namespace std;

class Base1    
{        
public:                                                
    Base1(int var){cout << "Base1" << endl; };
    int var;
    void fun() { cout << "Base1::fun()" << endl; }
};
 
class Base2            
{
public:                                                
    Base2(int var){cout << "Base2" << endl;};
    int var;
    void fun() { cout << "Base2::fun()" << endl; }
};
 
class Derived : public Base1, public Base2 {        
public:                                                
    Derived(int var) : Base1(var), Base2(var){cout << "Derived" << endl; };
    //int var;
    //void fun() { cout << "Derived::fun()" << endl; }
};
 
int main() {                                    
    Derived d(1);                                
    d.var = 2;                                    
    d.fun();
    //cout<<"d.var = " <<d.var<<endl;
    return 0;
}

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