C + + Basic (vii) function overlay, virtual function, pure virtual function comparison

1. Function overrides

ClassA, ClassB, where ClassB inherited ClassA

The class definition is as follows:

#ifndef _classa_h#define _classa_h#include <iostream>using namespace Std;class classa{public:classa (void); ~ ClassA (void); void method ();}; #endif

#include "stdafx.h" #include "ClassA.h" Classa::classa (void) {}classa::~classa (void) {}void classa::method (void) {cout << "I am from Class Classa:methoda" <<ENDL;}

#ifndef _class_b#define _class_b#include "ClassA.h" CLASS classb:public classa{public:classb (void); ~classb (void); void method ();}; #endif

#include "stdafx.h" #include "ClassB.h" classb::classb (void) {}classb::~classb (void) {}void classb::method () {cout< < "I am from Class Classb:methoda" <<ENDL;}

2. Virtual function overrides

Virtualclassa, VIRTUALCLASSB, where Virtualclassb inherited Virtualclassa

The class definition is as follows:

#ifndef _virtual_class_a#define _virtual_class_a#include <iostream>using namespace Std;class VirtualClassA{ Public:virtualclassa (void); ~virtualclassa (void); virtual void method ();}; #endif

#include "stdafx.h" #include "VirtualClassA.h" Virtualclassa::virtualclassa (void) {}virtualclassa::~virtualclassa ( void) {}void virtualclassa::method () {cout<< "I am from Class Virtualclassa:method" <<ENDL;}

#ifndef _virtual_class_b#define _virtual_class_b#include "VirtualClassA.h" CLASS virtualclassb:public virtualclassa{ Public:virtualclassb (void); ~virtualclassb (void); virtual void method ();}; #endif

#include "stdafx.h" #include "VirtualClassB.h" virtualclassb::virtualclassb (void) {}VIRTUALCLASSB::~VIRTUALCLASSB ( void) {}void  virtualclassb::method () {cout<< "I am from Class Virtualclassb:method" <<ENDL;}

3. Pure virtual function overrides

Purevirtualclassa, PUREVIRTUALCLASSB, where Purevirtualclassb inherited Purevirtualclassa

The class definition is as follows:

#ifndef _pure_virtual_class_a#define _pure_virtual_class_a#include <iostream>using namespace Std;class Purevirtualclassa{public:purevirtualclassa (void); ~purevirtualclassa (void); virtual void method () =0;/* Typically, The pure virtual function of the abstract base class is not implemented; Of course, it can also provide implementation for pure virtual function; */}; #endif

#include "stdafx.h" #include "PureVirtualClassA.h" Purevirtualclassa::P Urevirtualclassa (void) {}purevirtualclassa:: ~purevirtualclassa (void) {}

#ifndef _pure_virtual_class_b#define _pure_virtual_class_b#include "Purevirtualclassa.h" CLASS PUREVIRTUALCLASSB: Public purevirtualclassa{public:purevirtualclassb (void); ~purevirtualclassb (void); virtual void method ();}; #endif

#include "stdafx.h" #include "PureVirtualClassB.h" PUREVIRTUALCLASSB::P urevirtualclassb (void) {}PUREVIRTUALCLASSB:: ~purevirtualclassb (void) {}void purevirtualclassb::method (void) {cout<< "I am from class Purevirtualclassb: Method "<<ENDL;}

The test code is as follows:

VirtualMethodTest.cpp: Defines the entry point of the console application. #include "stdafx.h" #include "ClassA.h" #include "ClassB.h" #include "VirtualClassA.h" #include "VirtualClassB.h" # Include "PureVirtualClassA.h" #include "PureVirtualClassB.h" #include <iostream>using namespace Std;int _tmain ( int argc, _tchar* argv[]) {cout<< "--------Overlay---------" <<endl; ClassA *pclassa=new ClassA ();p classa->method ();d elete (Pclassa); ClassB *pclassb=new ClassB ();p classb->method ();//pclassb->classa::method ();--You can call the method of the parent class implicitly//(*PCLASSB). Classa::method ();d elete (PCLASSB); ClassA *pclassb2=new ClassB ();p classb2->method ();d elete (pClassB2);cout<< "-------polymorphic----------" << Endl Virtualclassa *pvirtualclassa=new Virtualclassa ();p virtualclassa->method ();d elete (Pvirtualclassa); VIRTUALCLASSB *pvirtualclassb=new virtualclassb ();p virtualclassb->method ();d elete (PVIRTUALCLASSB); Virtualclassa *pvirtualclassb2=new virtualclassb ();p virtualclassb2->method ();d elete (pVirtualClassB2);cout< < "-------Pure virtual function----------"<<endl;//purevirtualclassa *ppurevirtualclassa=new Purevirtualclassa ();//ppurevirtualclassa->method ( );//delete (Ppurevirtualclassa); PUREVIRTUALCLASSB *ppurevirtualclassb=new purevirtualclassb ();pP urevirtualclassb->method ();d elete ( PPUREVIRTUALCLASSB); Purevirtualclassa *ppurevirtualclassb2=new purevirtualclassb ();pP urevirtualclassb2->method ();d elete ( pPureVirtualClassB2); return 0;}

The printing results are as follows:

Function overlay can not achieve polymorphism;

virtual function and pure virtual function can realize polymorphism.

Classes that contain pure virtual functions cannot be instantiated.

Code Address: http://download.csdn.net/detail/zz7zz7zz/8096231

C + + Basic (vii) function overlay, virtual function, pure virtual function comparison