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  • 虚基类的作用

    当一个基类被声明为虚基类后,即使它成为了多继承链路上的公共基类,最后的派生类中也只有它的一个备份。例如:
    class CBase { };
    class CDerive1:virtual public CBase{ };
    class CDerive2:virtual public CBase{ };
    class CDerive12:public CDerive1,CDerive2{ };
    则在类CDerive12的对象中,仅有类CBase的一个对象数据

    虚基类的特点:

           虚基类构造函数的参数必须由最新派生出来的类负责初始化(即使不是直接继承);
                   虚基类的构造函数先于非虚基类的构造函数执行。

    /**//************************************************************************
    * 混合继承:多基类继承与多重继承
    ************************************************************************/
    #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;
    }

    运行结果:

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  • 原文地址:https://www.cnblogs.com/ikaka/p/3416567.html
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