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 *****************