C + + type compatibility

#include <iostream>using namespacestd;classcfather{ Public:    voidDisplay ()Const{cout<<"cfather::d isplay ()"<<Endl;}};classCSon: Publiccfather{ Public:    voidDisplay ()Const{cout<<"CSon::d isplay ()"<<Endl;}};classCgrandson: Publiccson{ Public:    voidDisplay ()Const{cout<<"Cgrandson::d isplay ()"<<Endl;}};voidShow (Cfather *ptr) {ptr-display ();}voidShowson (CSon *ptr) {ptr-display ();}intMain () {Cfather father;    CSon Son;    Cgrandson grandson; Show (&father); Show (&son); Show (&grandson); Showson (&grandson);    GetChar (); return 0;}

Output Result:

Type compatibility principle: You can assign the address of a derived class object to a base class

Conclusion: But through this pointer to the base class type, only the members inherited from the base class can be accessed.

Effect: When a base class object occurs, the derived class only plays the role of the base class when overridden by a derived class object.

change the code below to access the data members:

#include <iostream>using namespacestd;classcfather{ Public: Cfather (): ITest ( -){}//Constructor member initialization    voidDisplay ()Const{cout<<"cfather::d isplay ()"<<itest<<endl;}//contains itest    intiTest;};classCSon: Publiccfather{ Public:    voidDisplay ()Const{cout<<"CSon::d isplay ()"<<itest<<endl;}////Includes ITest};classCgrandson: Publiccson{ Public:    voidDisplay ()Const{cout<<"Cgrandson::d isplay ()"<<itest<<endl;}////Includes ITest};voidShow (Cfather *ptr) {ptr-display ();}voidShowson (CSon *ptr) {ptr-display ();}intMain () {Cfather father;    CSon Son;    Cgrandson grandson; Show (&father);//ParentShow (&son);//ChildShow (&grandson);//SunShowson (&grandson);//ChildGetChar (); return 0;}

Results:

C + + type compatibility