C++ 一目了然虚基类！

#include <IOSTREAM.H>  
//基类  
class CBase  
...{  
protected:  
    int a;  
public:  
    CBase(int na)  
    ...{  
        a=na;  
        cout<<"CBase constructor! ";  
    }  
  
    ~CBase()...{cout<<"CBase deconstructor! ";}  
};  
  
//派生类1(声明CBase为虚基类)  
class CDerive1:virtual public CBase  
...{  
public:  
    CDerive1(int na):CBase(na)  
    ...{  
        cout<<"CDerive1 constructor! ";  
    }  
      
    ~CDerive1()...{cout<<"CDerive1 deconstructor! ";}  
  
    int GetA()...{return a;}  
};  
  
//派生类2(声明CBase为虚基类)  
class CDerive2:virtual public CBase  
...{  
public:  
    CDerive2(int na):CBase(na)  
    ...{  
        cout<<"CDerive2 constructor! ";  
    }  
    ~CDerive2()...{cout<<"CDerive2 deconstructor! ";}  
    int GetA()...{return a;}  
};  
  
//子派生类  
class CDerive12:public CDerive1,public CDerive2  
...{  
public:  
    CDerive12(int na1,int na2,int na3):CDerive1(na1),CDerive2(na2),CBase(na3)  
    ...{  
        cout<<"CDerive12 constructor! ";  
    }  
    ~CDerive12()...{cout<<"CDerive12 deconstructor! ";}  
};  
void main()  
...{  
    CDerive12 obj(100,200,300);  
    //得到从CDerive1继承的值  
    cout<<" from CDerive1 : a = "<<obj.CDerive1::GetA();  
    //得到从CDerive2继承的值  
    cout<<" from CDerive2 : a = "<<obj.CDerive2::GetA()<<endl<<endl;  
}  

从上例可以看出，在类CDerived12的构造函数初始化表中，调用了间接基类CBase的构造函数，这对于非虚基类是非法的，但对于虚基类则是合法且必要的。
　　对于派生类CDerived1和CDerived2，不论是其内部实现，还是实例化的对象，基类CBase是否是它们的虚基类是没有影响的。受到影响的是它们的派生类CDerived12，因为它从两条路径都能到达CBase。

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/livelylittlefish/archive/2008/03/11/2171267.aspx