一目了然c++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(,,);
     //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