对象内存布局 (15)

前篇：http://blog.youkuaiyun.com/pathuang68/archive/2009/04/24/4105851.aspx

和对象内存布局 (14)差不多，只是改动了两个继承关系。几个类的继承关系如下图，这种继承方式不是很有实际意义，在此纯粹是探究类的memory layout。

代码如下：

#include <iostream>

using namespace std;

class Base

{

public:

int base_member;

};

class Derived1 : public virtual Base

{

public:

int derived1_member;

};

class Derived2 : public virtual Base

{

public:

int derived2_member;

};

class ChildDerived : public virtual Derived1, public virtual Derived2

{

public:

int childderived_member;

};

int main(void)

{

ChildDerived cd;

cout << "sizeof(Base) = /t/t" << sizeof(Base) << endl;

cout << "sizeof(Derived1) = /t" << sizeof(Derived1) << endl;

cout << "sizeof(Derived2) = /t" << sizeof(Derived2) << endl;

cout << "sizeof(ChildDerived) = /t" << sizeof(ChildDerived) << endl;

cout << endl;

cout << "ChildDerived object's vbptr = " << (int*)&cd << endl;

cout << endl;

cout << "Address of virtual base class table of ChildDerived object = " << (int*)(*((int*)&cd)) << endl;

cout << "Item 1 in ChildDerived's virtual base class table = " << *((int*)*(int*)(&cd) + 0) << endl;

cout << "Item 2 in ChildDerived's virtual base class table = " << *((int*)*(int*)(&cd) + 1) << endl;

cout << "Item 3 in ChildDerived's virtual base class table = " << *((int*)*(int*)(&cd) + 2) << endl;

cout << "Item 4 in ChildDerived's virtual base class table = " << *((int*)*(int*)(&cd) + 3) << endl;

cout << "Item 4 in ChildDerived's virtual base class table = " << *((int*)*(int*)(&cd) + 4) << endl;

cout << endl;

cout << "Address of virtual base class table of Derived1 object = " << (int*)*((int*)&cd + 3) << endl;

cout << "Item 1 in Derived1's virtual base class table = " << *((int*)*((int*)&cd + 3) + 0) << endl;

cout << "Item 2 in Derived1's virtual base class table = " << *((int*)*((int*)&cd + 3) + 1) << endl;

cout << "Item 3 in Derived1's virtual base class table = " << *((int*)*((int*)&cd + 3) + 2) << endl;

cout << endl;

cout << "Address of virtual base class table of Derived2 object = " << (int*)*((int*)&cd + 5) << endl;

cout << "Item 1 in Derived2's virtual base class table = " << *((int*)*((int*)&cd + 5) + 0) << endl;

cout << "Item 2 in Derived2's virtual base class table = " << *((int*)*((int*)&cd + 5) + 1) << endl;

cout << "Item 3 in Derived2's virtual base class table = " << *((int*)*((int*)&cd + 5) + 2) << endl;

cout << endl;

cout << "The address of base class Derived1's instance = " << (Derived1*)&cd << endl;

cout << "The address of base class Derived2's instance = " << (Derived2*)&cd << endl;

cout << "The address of base class Base's instance = /t" << (Base*)&cd << endl;

return 0;

}

注意：因为可能出现负数，所以在上面的程序中，将原来的unsigned long* 改为了int*。运行结果：

图解如下：

后篇：http://blog.youkuaiyun.com/pathuang68/archive/2009/04/24/4105922.aspx