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。