C++对象模型4--有重写的单继承

有重写的单继承

派生类中重写了基类的print()函数。

 

//Derived_Overwrite.h

#pragma once

#include "base.h"



class Derived_Overrite : public Base

{

public:

    Derived_Overrite(int);

    virtual ~Derived_Overrite(void);

    virtual void print(void) const;

 

protected:

    int iDerived;

};

 

　　

//Derived_Overwrite.cpp



#include "stdafx.h"

#include "Derived_Overwrite.h"





Derived_Overrite::Derived_Overrite(int i):Base(0)

{

	iDerived = i;

	cout<<"Derived_Overwrite::Derived_Overwrite()"<<endl;

}



Derived_Overrite::~Derived_Overrite(void)

{

	cout<<"Derived_Overwrite::~Derived_Overwrite()"<<endl;

}



void Derived_Overrite::print(void) const

{

	cout<<"Derived_Overwrite::print()， iDerived " << iDerived << endl;

}

　　Base、Derived_Overwrite的类图如下所示：

重写print()函数在虚函数表中表现如下：

 

为了验证上述C++对象模型，我们编写如下测试代码。

 

void test_single_inherit_rewrite()

{

	Derived_Overwrite d(11111);

	cout << "对象d的起始内存地址：" << &d << endl;

	cout << "虚函数表地址：" << (int*)(&d) << endl;



	//虚函数信息

	cout << "虚函数表中第1个函数占位符的地址：" << (int*)*(int*)(&d) << "即析构函数在虚函数表中占位符的地址" << endl;

	cout << "虚函数表中第2个函数占位符的地址：" << ((int*)*(int*)(&d) + 1) << endl;



	typedef void(*Fun)(void);

	Fun pFun = (Fun)*((int*)*(int*)(&d) + 1);

	pFun();

	d.print();

	cout << endl;



	cout << "虚函数表中第3个函数占位符的内容：" << *((int*)*(int*)(&d) + 2) << endl;

	cout << endl;





	cout << "推测数据成员iBase地址：" << ((int*)(&d) +1) << "通过地址取得的值：" << *((int*)(&d) +1) << endl;

    cout << "推测数据成员iDerived地址：" << ((int*)(&d) +2) << "通过地址取得的值：" << *((int*)(&d) +2) << endl;

}

　　代码执行结果：

特别注意下，前面的模型虚函数表中最后一项没有打印出来，本实例中共2个虚函数，打印虚函数表第3项为0。其实虚函数表以0x0000000结束，类似字符串以’\0’结束。