构造函数不能是虚函数，因为在调用构造函数创建对象时，构造函数必须是确定的，所以构造函数不能是虚函数。

析构函数可以是虚函数。

1.父类Father.h：

复制代码 代码如下:

#pragma once

class Father

{

public:

Father(void);

virtual ~Father(void);

virtual int getCount();

public:

int count;

};

Father.cpp

复制代码 代码如下:

#include "StdAfx.h"

#include "Father.h"

#include <iostream>

using namespace std;

Father::Father(void)

{

count = 1;

cout<<"Father is called. count = "<<count<<endl;

}

Father::~Father(void)

{

cout<<"~Father is called."<<endl;

}

int Father::getCount()

{

cout<<"Father::getCount() count = "<<count<<endl;

return count;

}

2.子类Child.h：

复制代码 代码如下:

#pragma once

#include "father.h"

class Child :

public Father

{

public:

Child(void);

virtual ~Child(void);

virtual int getCount();

int getAge();

public:

int age;

};

Child.cpp

复制代码 代码如下:

#include "StdAfx.h"

#include "Child.h"

#include <iostream>

using namespace std;

Child::Child(void)

{

count = 2;

age = 20;

cout<<"Child is called. count = "<<count<<", age = "<<age<<endl;

}

Child::~Child(void)

{

cout<<"~Child is called."<<endl;

}

int Child::getCount()

{

cout<<"Child::getCount() count = "<<count<<endl;

return count;

}

int Child::getAge()

{

cout<<"Child::getAge() age = "<<age<<endl;

return age;

}

3.测试类Test.cpp

复制代码 代码如下:

#include "stdafx.h"

#include <cstdlib>

#include <iostream>

#include "Child.h"

using namespace std;

int _tmain(int argc, _TCHAR* argv[])

{

Father *father1 = new Father();

cout<<"father1 count = "<<father1->getCount()<<endl;

delete father1;

cout<<"************** father1 end *****************"<<endl<<endl;

Father *father2 = new Child();

cout<<"father2 count = "<<father2->getCount()<<endl; // father2 don't have getAge() method

delete father2;

cout<<"************** father2 end *****************"<<endl<<endl;

Child *child = new Child();

cout<<"child count = "<<child->getCount()<<endl;

cout<<"child age = "<<child->getAge()<<endl;

delete child;

cout<<"************** child end *****************"<<endl<<endl;

getchar();

return 0;

}

4.输出结果：

Father is called. count = 1

Father::getCount() count = 1

father1 count = 1

~Father is called.

************** father1 end *****************

Father is called. count = 1

Child is called. count = 2, age = 20

Child::getCount() count = 2

father2 count = 2

~Child is called.

~Father is called.

************** father2 end *****************

Father is called. count = 1

Child is called. count = 2, age = 20

Child::getCount() count = 2

child count = 2

Child::getAge() age = 20

child age = 20

~Child is called.

~Father is called.

************** child end *****************

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