C++菱形继承内存模型

#include 
using namespace std;

class Animal
{
public:
	Animal(){}
	~Animal(){}
	int m_A = 1;
private:
	
};

class Needy : virtual public Animal
{
public:
	Needy(){}
	~Needy(){}

private:

};

class Horse :virtual public Animal

{
public:
	Horse(){}
	~Horse(){}

private:

};

class Mule : public Needy,  public Horse
{
public:
	Mule(){}
	~Mule(){}

private:

};

void test01()
{
	Mule mule1;
	cout << mule1.m_A << endl;
}


int main()
{
	test01();
}

继承关系

class Horse :virtual public Animal
class Needy : virtual public Animal

class Mule : public Needy,  public Horse

Horse和Needy进行的是虚继承，这样Mule只会从Animal类继承一份 int m_A

使用VS Tools 中的VS 2017 开发者命令提示符查看，Mule的内存模型

F:Visual Studio IDE>cd F:DesktopC++this指针继承

F:DesktopC++this指针继承>cl /d1 reportSingleClassLayoutMule main.cpp

命令如上

class Mule      size(12):
        +---
 0      | +--- (base class Needy)
 0      | | {vbptr}
        | +---
 4      | +--- (base class Horse)
 4      | | {vbptr}
        | +---
        +---
        +--- (virtual base Animal)
 8      | m_A
        +---

Mule::$vbtable@Needy@:
 0      | 0
 1      | 8 (Muled(Needy+0)Animal)

Mule::$vbtable@Horse@:
 0      | 0
 1      | 4 (Muled(Horse+0)Animal)
vbi:       class  offset o.vbptr  o.vbte fVtorDisp
          Animal       8       0       4 0
Microsoft (R) Incremental Linker Version 14.16.27045.0
Copyright (C) Microsoft Corporation.  All rights reserved.

/out:main.exe
main.obj

Mule中只会存衣服Animal中的int m_A ,Needy和Horse区域只会存一份指向int m_A的指针偏移量