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: