C++多重继承虚表的内存分布

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接前面虚表的内存分布，今天重点看多重继承的虚表内存分布，简单的说，继承几个类便有几个虚表，如下代码

class Drive : public Base1, public Base2, public Base3 {

public:

    virtual void fd() { cout << "Drive::fd" << endl; }

    virtual void gd() { cout << "Drive::gd" << endl; }

};

则虚表有3个，如下图所示：

添加更多的测试代码：

// trytest.cpp : 定义控制台应用程序的入口点。

//

#include "stdafx.h"

#include <WTypes.h>

#include < iostream >

using namespace std;

class Base1 {

    virtual void f() { cout << "Base1::f" << endl; }

    virtual void g() { cout << "Base1::g" << endl; }

};

class Base2 {

    virtual void f() { cout << "Base2::f" << endl; }

    virtual void g() { cout << "Base2::g" << endl; }

};

class Base3 {

    virtual void f() { cout << "Base3::f" << endl; }

    virtual void g() { cout << "Base3::g" << endl; }

};

class Drive : public Base1, public Base2, public Base3 {

public:

    virtual void fd() { cout << "Drive::fd" << endl; }

    virtual void gd() { cout << "Drive::gd" << endl; }

};

typedef void(*Fun)(void);

int main() {

    Drive objDrive;

    cout << "Size is = " << sizeof(objDrive) << endl; 

    Fun pFun = NULL;

    cout<<"sizeof(int)="<<sizeof(int)<<endl;

    cout<<"sizeof(int*)="<<sizeof(int*)<<endl;

    // 调用Base1的第一个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    // 调用Base1的第二个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    cout << "Address of virtual pointer 1 " << (int*)(&objDrive + ) << endl;

    cout << "Value at virtual pointer i.e. Address of virtual table "

        << (int*)*(int*)((int*)&objDrive + ) << endl;

    cout << "Information about VTable 1" << endl;

    cout << "Value at 1st entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl;

    cout << "Value at 2nd entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl; 

    // 调用Base2的第一个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    // 调用Base2的第二个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    cout << "Address of virtual pointer 2 " << (int*)((int*)&objDrive + ) << endl;

    cout << "Value at virtual pointer i.e. Address of virtual table "

        << (int*)*(int*)((int*)&objDrive + ) << endl;

    cout << "Information about VTable 2" << endl;

    cout << "Value at 1st entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl;

    cout << "Value at 2nd entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl; 

    // 调用Base3的第一个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    // 调用Base3的第二个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    cout << "Address of virtual pointer 3 " << (int*)((int*)&objDrive + ) << endl;

    cout << "Value at virtual pointer i.e. Address of virtual table "

        << (int*)*(int*)((int*)&objDrive + ) << endl;

    cout << "Information about VTable 3" << endl;

    cout << "Value at 1st entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl;

    cout << "Value at 2nd entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl; 

    // 调用派生类的第一个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    // 调用派生类的第二个虚函数

    pFun = (Fun)*((int*)*(int*)((int*)&objDrive + ) + );

    pFun();

    cout << "Value at 3rd entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl;

    cout << "Value at 4th entry of VTable "

        << (int*)*((int*)*(int*)((int*)&objDrive + ) + ) << endl; 

    //明确多重继承中虚函数的内存位置

    cout <<"Address at 1st entry of VTable "

        << (int*)*((int*)&objDrive + ) +  << endl; 

    cout <<"Address at 2nd entry of VTable "

        << (int*)*((int*)&objDrive + ) +  << endl; 

    cout <<"Address at 3rd entry of VTable "

        << (int*)*((int*)&objDrive + ) +  << endl; 

    cout <<"Address at 4th entry of VTable "

        << (int*)*((int*)&objDrive + ) +  << endl; 

    pFun = (Fun)*((int*)*((int*)&objDrive + ) + );

    pFun();

    pFun = (Fun)*((int*)*((int*)&objDrive + ) + );

    pFun();

    pFun = (Fun)*((int*)*((int*)&objDrive + ) + );

    pFun();

    pFun = (Fun)*((int*)*((int*)&objDrive + ) + );

    pFun();

    return ;

}