Using member function pointers to simulate polymorphism in C + +

1. Usage of member function pointers

1#include <iostream>2 using namespacestd;3 class Base4 {5  Public:6    intTestintLhsintRHS)7     {8cout<<"Base Test"<<Endl;9         return 1;Ten     } One }; A classDerived Public Base - { -  Public: the     intTestintLhsintRHS) -     { -cout<<"derived Test"<<Endl; -         return 2; +     } - }; + intMain () A { at     Base*p; - derived D; -     int(Base::* basefunction) (int,int); -     int(derived::* derivedfunction) (int,int); -     //base class pointer to child class object + base class member function pointer call base class member function -p=&D; inbasefunction=&Base:: Test; -(p->*basefunction) (1,2);//equivalent to D.base::test (int,int); to     //base class pointer to subclass Object + base class member function pointer call child class member function +p=&D; -Basefunction= (int(Base::*)(int,int)) &derived::test; the(p->*basefunction) (1,2);//equivalent to D.test (int,int); *     return 0; $}

Output

Base Test

Derived test

2. member function pointer simulation polymorphism

1#include <iostream>2 using namespacestd;3 class Base4 {5  Public:6     Base()7     {8virtualfunctionpointer=&Base:: Test;9     }Ten~Base() One     { A          -     } -     int(Base::*virtualfunctionpointer) (); the  -     intTest () -     { -         //determines whether a base class instance prevents infinite recursion +         if(virtualfunctionpointer==&Base:: Test) -         { +cout<<"Base"<<Endl; A             return 1; at         } -         //the subclass object calls test through a base-class pointer, polymorphic -         Else -            return( This->*virtualfunctionpointer) (); -        -     } in  - }; to classDerived Public Base + { -  Public: the    * derived () $     {Panax NotoginsengVirtualfunctionpointer= (int(Base::*) ()) &derived::test; -     } the~derived () +     { A          the     } +     intTest () -     { $cout<<"derived"<<Endl; $         return 2; -     } -  the }; - intMain ()Wuyi { the derived D; -     Base*p=&D; WuCout<<p->test () <<Endl; -     Baseb; Aboutp=&b; $Cout<<p->test () <<Endl; -  -     return 0; -}

Output:

Derived

2

Base

1

Using member function pointers to simulate polymorphism in C + +