一目了然c++虚基类！

 1 #include <IOSTREAM.H>
 2 //基类
 3 class CBase
 4 ...{
 5 protected:
 6     int a;
 7 public:
 8     CBase(int na)
 9     ...{
10         a=na;
11         cout<<"CBase constructor! ";
12     }
13
14     ~CBase()...{cout<<"CBase deconstructor! ";}
15 };
16
17 //派生类1(声明CBase为虚基类)
18 class CDerive1:virtual public CBase
19 ...{
20 public:
21     CDerive1(int na):CBase(na)
22     ...{
23         cout<<"CDerive1 constructor! ";
24     }
25
26     ~CDerive1()...{cout<<"CDerive1 deconstructor! ";}
27
28     int GetA()...{return a;}
29 };
30
31 //派生类2(声明CBase为虚基类)
32 class CDerive2:virtual public CBase
33 ...{
34 public:
35     CDerive2(int na):CBase(na)
36     ...{
37         cout<<"CDerive2 constructor! ";
38     }
39     ~CDerive2()...{cout<<"CDerive2 deconstructor! ";}
40     int GetA()...{return a;}
41 };
42
43 //子派生类
44 class CDerive12:public CDerive1,public CDerive2
45 ...{
46 public:
47     CDerive12(int na1,int na2,int na3):CDerive1(na1),CDerive2(na2),CBase(na3)
48     ...{
49         cout<<"CDerive12 constructor! ";
50     }
51     ~CDerive12()...{cout<<"CDerive12 deconstructor! ";}
52 };
53 void main()
54 ...{
55     CDerive12 obj(100,200,300);
56     //得到从CDerive1继承的值
57     cout<<" from CDerive1 : a = "<<obj.CDerive1::GetA();
58     //得到从CDerive2继承的值
59     cout<<" from CDerive2 : a = "<<obj.CDerive2::GetA()<<endl<<endl;
60 }  

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