深入探討C++父類子類中虛函數的應用

建構函式不能是虛函數，因為在調用建構函式建立對象時，建構函式必須是確定的，所以建構函式不能是虛函數。
解構函式可以是虛函數。

1.父類Father.h：
複製代碼 代碼如下:#pragma once
class Father
{
public:
Father(void);
virtual ~Father(void);
virtual int getCount();
public:
int count;
};

Father.cpp複製代碼 代碼如下:#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.子類Child.h：
複製代碼 代碼如下:#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複製代碼 代碼如下:#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.測試類別Test.cpp
複製代碼 代碼如下:#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.輸出結果：
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 *****************