学步园

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：

#pragma once<br /> class Father<br /> {<br /> public:<br /> Father(void);<br /> virtual ~Father(void);</p> <p> virtual int getCount();</p> <p>public:<br /> int count;<br /> };

Father.cpp

#include "StdAfx.h"<br /> #include "Father.h"<br /> #include <iostream></p> <p>using namespace std;</p> <p>Father::Father(void)<br /> {<br /> count = 1;<br /> cout<<"Father is called. count = "<<count<<endl;<br /> }</p> <p>Father::~Father(void)<br /> {<br /> cout<<"~Father is called."<<endl;<br /> }</p> <p>int Father::getCount()<br /> {<br /> cout<<"Father::getCount() count = "<<count<<endl;<br /> return count;<br /> }

2.子类Child.h：

#pragma once<br /> #include "father.h"<br /> class Child :<br /> public Father<br /> {<br /> public:<br /> Child(void);<br /> virtual ~Child(void);</p> <p> virtual int getCount();<br /> int getAge();</p> <p>public:<br /> int age;<br /> };

Child.cpp

#include "StdAfx.h"<br /> #include "Child.h"<br /> #include <iostream></p> <p>using namespace std;</p> <p>Child::Child(void)<br /> {<br /> count = 2;<br /> age = 20;<br /> cout<<"Child is called. count = "<<count<<", age = "<<age<<endl;<br /> }</p> <p>Child::~Child(void)<br /> {<br /> cout<<"~Child is called."<<endl;<br /> }</p> <p>int Child::getCount()<br /> {<br /> cout<<"Child::getCount() count = "<<count<<endl;<br /> return count;<br /> }</p> <p>int Child::getAge()<br /> {<br /> cout<<"Child::getAge() age = "<<age<<endl;<br /> return age;<br /> }

3.测试类Test.cpp

#include "stdafx.h"<br /> #include <cstdlib><br /> #include <iostream><br /> #include "Child.h"</p> <p>using namespace std;</p> <p>int _tmain(int argc, _TCHAR* argv[])<br /> {<br /> Father *father1 = new Father();<br /> cout<<"father1 count = "<<father1->getCount()<<endl;<br /> delete father1;<br /> cout<<"************** father1 end *****************"<<endl<<endl;</p> <p> Father *father2 = new Child();<br /> cout<<"father2 count = "<<father2->getCount()<<endl; // father2 don't have getAge() method<br /> delete father2;<br /> cout<<"************** father2 end *****************"<<endl<<endl;</p> <p> Child *child = new Child();<br /> cout<<"child count = "<<child->getCount()<<endl;<br /> cout<<"child age = "<<child->getAge()<<endl;<br /> delete child;<br /> cout<<"************** child end *****************"<<endl<<endl;</p> <p> getchar();</p> <p> return 0;<br /> }

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