1.前言

本篇文章的全部代码样例。假设是windows上编译执行。则使用的是visual studio 2013。假设是RHEL6.5平台(linux kernal: 2.6.32-431.el6.i686)上编译执行，则其gcc版本号为4.4.7，例如以下所看到的：

[root@MiWiFi-R1CM ~]# gcc --version

gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4)

2.菱形继承类的内存分布

本篇文章主要讨论的是虚继承(virtual)下的内存分布。

2.1.类的结构

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2.2.实现代码windows版本号

以下的代码执行在windows 7+visual studio 2013平台上。

分别打印类Base1对象的内存分布。和类Derive对象的内存分布。

#include <iostream>

using namespace std;

class Base

{

public:

	int _iBase;

	char _cBase;

public:

	Base() : _iBase(1111), _cBase('A')

	{

	}

	virtual void func()

	{

		cout << "Base::func()" << endl;

	}

	virtual void baseFunc()

	{

		cout << "Base::baseFunc()" << endl;

	}

};

class Base1 : public virtual Base

{

public:

	int _iBase1;

	char _cBase1;

public:

	Base1() : _iBase1(2222), _cBase1('B')

	{

	}

	virtual void func()

	{

		cout << "Base1::func()" << endl;

	}

	virtual void func1()

	{

		cout << "Base1::func1()" << endl;

	}

	virtual void baseFunc1()

	{

		cout << "Base1::baseFunc1()" << endl;

	}

};

class Base2 : public virtual Base

{

public:

	int _iBase2;

	char _cBase2;

public:

	Base2() : _iBase2(3333), _cBase2('C')

	{

	}

	virtual void func()

	{

		cout << "Base2::func()" << endl;

	}

	virtual void func2()

	{

		cout << "Base2::func2()" << endl;

	}

	virtual void baseFunc2()

	{

		cout << "Base2::baseFunc2()" << endl;

	}

};

class Derive : public virtual Base1, public virtual Base2

{

public:

	int _iDerive;

	char _cDerive;

public:

	Derive() : _iDerive(4444), _cDerive('D')

	{

	}

	virtual void func()

	{

		cout << "Derive::func()" << endl;

	}

	virtual void func1()

	{

		cout << "Derive::func1()" << endl;

	}

	virtual void func2()

	{

		cout << "Derive::func2()" << endl;

	}

	virtual void deriveFunc()

	{

		cout << "Derive::deriveFunc()" << endl;

	}

};

typedef void(*Fun)();

int main() {

	int **pVtab = NULL;

	Fun pFun = NULL;

	Base1 bb1;

	cout << "sizeof(Base)" << sizeof(Base) << endl;

	cout << "sizeof(Base1)" << sizeof(Base1) << endl;

	//Base1 layout

	pVtab = (int**)&bb1;

	cout << "[0] Base1::_vptr->" << "  addr:" << &pVtab[0] << endl;

	pFun = (Fun)pVtab[0][0];

	cout << "    [0]";

	pFun(); //Base1::func1()

	pFun = (Fun)pVtab[0][1];

	cout << "    [1]";

	pFun(); //Base1::baseFunc1()

	cout << "    [2]";

	cout << pVtab[0][2] << endl;

	cout << "[1] Base1::_vbptr->" << "  addr:" << &pVtab[1] << endl;

	cout << "    [0]";

	cout << pVtab[1][0] << endl;

	cout << "    [1]offset->";

	cout << pVtab[1][1] << endl;

	cout << "    [2]";

	cout << pVtab[1][2] << endl;

	cout << "[2] Base1:_iBase1 -> ";

	cout << (int)pVtab[2] << endl; //Base1:_iBase1

	cout << "[3] Base1:_cBase1 -> ";

	cout << (char)(int)pVtab[3] << endl; //Base1:_cBase1

	cout << "[4] unknown ";

	cout << (int)pVtab[4] << endl;

	cout << "[5] Base::_vfptr->" << "  addr:" << &pVtab[4] << endl;

	cout << "    [0]";

	pFun = (Fun)pVtab[5][0];

	pFun();

	cout << "    [1]";

	pFun = (Fun)pVtab[5][1];

	pFun();

	cout << "    [2]";

	cout << (int)pVtab[5][2] << endl;

	cout << "[6] Base:_iBase -> ";

	cout << (int)pVtab[6] << endl; //Base:_iBase

	cout << "[7] Base:_cBase -> ";

	cout << (char)(int)pVtab[7] << endl; //Base:_cBase

	cout << endl;

	cout << "###########################" << endl;

	cout << endl;

	//Derive layout

	// sub Derive vtbl layout

	Derive d;

	cout << "sizeof(Derive)" << sizeof(Derive) << endl;

	pVtab = (int**)&d;

	cout << "[0] Derive::_vfptr->" << "  addr:" << &pVtab[0] << endl;

	cout << "     [0] ";

	pFun = (Fun)pVtab[0][0];

	pFun(); //Derive::func1();

	cout << "     [1] ";

	cout << pVtab[0][1] << endl;

	cout << "[1] Derive::_vbptr->" << "  addr:" << &pVtab[1] << endl;

	cout << "     [0] ";

	cout << pVtab[1][0] << endl;

	cout << "     [1]offset-> ";

	cout << pVtab[1][1] << endl;

	cout << "     [2] ";

	cout << pVtab[1][2] << endl;

	cout << "     [3] ";

	cout << pVtab[1][3] << endl;

	cout << "     [4] ";

	cout << pVtab[1][4] << endl;

	cout << "[2] Derive::_iDerive -> ";

	cout << (int)pVtab[2] << endl; //Derive:_iDerive

	cout << "[3] Derive::_cDerive -> ";

	cout << (char)(int)pVtab[3] << endl; //Derive::_cDerive

	cout << "[4] unknown-> " << (int)pVtab[4] << endl;

	// sub Base vtbl layout

	cout << "[5] Base::_vfptr->" << "  addr:" << &pVtab[5] << endl;

	cout << "     [0] ";

	pFun = (Fun)pVtab[5][0];

	pFun();

	pFun = (Fun)pVtab[5][1];

	cout << "     [1] ";

	pFun();

	cout << "     [2] ";

	cout << pVtab[5][2] << endl;

	cout << "[6] Base::_iBase -> ";

	cout << (int)pVtab[6] << endl;

	cout << "[7] Base::_cBase -> ";

	cout << (char)(int)pVtab[7] << endl;

	cout << "[8] unknown-> ";

	cout << (int)pVtab[8] << endl;

	// sub Base1 vtbl layout

	cout << "[9] Base1::_vfptr->" << "  addr:" << &pVtab[9] << endl;

	cout << "     [0] ";

	cout << pVtab[9][0] << endl;

	pFun = (Fun)pVtab[9][1];

	cout << "     [1] ";

	pFun();

	pFun = (Fun)pVtab[9][2];

	cout << "     [2] ";

	cout << (int)pFun << endl;

	pFun = (Fun)pVtab[9][3];

	cout << "     [3] ";

	cout << (int)pFun << endl;

	cout << "[10] unknown-> ";

	cout << (int)pVtab[10] << endl;

	cout << "[11] Base1::_iBase1 -> ";

	cout << (int)pVtab[11] << endl;

	cout << "[12] Base1::_cBase1 -> ";

	cout << (char)(int)pVtab[12] << endl;

	cout << "[13] unknown-> ";

	cout << (int)pVtab[13] << endl;

	// sub Base2 vtbl layout

	cout << "[14] Base2::_vfptr->" << "  addr:" << &pVtab[14] << endl;

	cout << "     [0] ";

	cout << pVtab[14][0] << endl;

	pFun = (Fun)pVtab[14][1];

	cout << "     [1] ";

	pFun();

	cout << "     [2] ";

	cout << pVtab[14][2] << endl;

	cout << "     [3] ";

	cout << pVtab[14][3] << endl;

	cout << "[15] unknown-> ";

	cout << (int)pVtab[15] << endl;

	cout << "[16] Base2::_iBase2 -> ";

	cout << (int)pVtab[16] << endl;

	cout << "[17] Base2::_cBase2 -> ";

	cout << (char)(int)pVtab[17] << endl;

	return 0;

}

Base1对象的内存分布为：

watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc2hsdHNo/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt="">

Derive对象的内存分布为：

2.3.实现代码linux版本号

以下代码中，对于这4个类的定义，与前面的windows代码中对类的定义是全然一样的，所以这里省略掉了。仅仅列出用于输出内存分布的代码：

int main()

{

	int **pVtab = NULL;

	Fun pFun = NULL;

	Base1 bb1;

	cout << "sizeof(Base)" << sizeof(Base) << endl;

	cout << "sizeof(Base1)" << sizeof(Base1) << endl;

	//Base1 layout

	pVtab = (int**)&bb1;

	cout << "[0] Base1::_vptr->" << "  addr:" << &pVtab[0] << endl;

	pFun = (Fun)pVtab[0][0];

	cout << "    [0]";

	pFun(); //Base1::func1()

	pFun = (Fun)pVtab[0][1];

	cout << "    [1]";

	pFun(); //Base1::baseFunc1()

	pFun = (Fun)pVtab[0][2];

	cout << "    [2]";

	pFun();

	cout << "    [3]";

	cout << pVtab[0][3];

	cout << "[1] Base1:_iBase1 -> ";

	cout << (int)pVtab[1] << endl;  //Base1:_iBase1

	cout << "[2] Base1:_cBase1 -> ";

	cout << (char)(int)pVtab[2] << endl;  //Base1:_cBase1

	// Base layout

	cout << "[3] Base::_vptr->" << "  addr:" << &pVtab[3] << endl;

	pFun = (Fun)pVtab[3][0];

	cout << "    [0]";

	pFun(); //Base1::func()

	pFun = (Fun)pVtab[3][1];

	cout << "    [1]";

	pFun(); //Base::baseFunc()

	cout << "    [2]";

	cout << pVtab[3][2] << endl;

	cout << "[4] Base:_iBase -> ";

	cout << (int)pVtab[4] << endl; //Base:_iBase

	cout << "[5] Base:_cBase -> ";

	cout << (char)(int)pVtab[5] << endl; //Base:_cBase

	cout << "[6] " << (int)pVtab[6] << "  addr:" << &pVtab[6] << endl; //dirty data

	cout << endl;

	cout << "###########################" << endl;

	cout << endl;

	// Derive layout

	// sub Derive vtbl layout

	Derive d;

	cout << "sizeof(Derive)" << sizeof(Derive) << endl;

	pVtab = (int**)&d;

	cout << "[0] Derive::_vfptr->" << "  addr:" << &pVtab[0] << endl;

	cout << "     [0] ";

	pFun(); //Derive::func1();

	pFun = (Fun)pVtab[0][1];

	cout << "     [1] ";

	pFun(); //Base1::baseFunc1();

	pFun = (Fun)pVtab[0][2];

	cout << "     [2] ";

	pFun(); //Derive::deriveFunc();

	pFun = (Fun)pVtab[0][3];

	cout << "     [3] ";

	pFun();

	cout << "     [4] ";

	cout << pVtab[0][4] << endl;

	cout << "[1] Derive:_iDerive -> ";

	cout << (int)pVtab[1] << endl; //Derive:_iDerive

	cout << "[2] Derive:_cDerive -> ";

	cout << (char)(int)pVtab[2] << endl; //Derive:_cDerive

	// sub Base1 vtbl layout

	cout << "[3] Base1::_vptr->" << "  addr:" << &pVtab[3] << endl;

	pFun = (Fun)pVtab[3][0];

	cout << "     [0] ";

	pFun();

	pFun = (Fun)pVtab[3][1];

	cout << "     [1] ";

	pFun();

	pFun = (Fun)pVtab[3][2];

	cout << "     [2] ";

	pFun();

	cout << "     [3] ";

	cout << pVtab[3][3] << endl;

	cout << "[4] Base1::_iBase1 -> ";

	cout << (int)pVtab[4] << endl;

	cout << "[5] Base1::_cBase1 -> ";

	cout << (char)(int)pVtab[5] << endl;

	// sub Base vtbl layout

	cout << "[6] Base::_vptr->" << "  addr:" << &pVtab[6] << endl;

	pFun = (Fun)pVtab[6][0];

	cout << "     [0] ";

	pFun();

	pFun = (Fun)pVtab[6][1];

	cout << "     [1] ";

	pFun();

	pFun = (Fun)pVtab[6][2];

	cout << "     [2] ";

	cout << (int)pFun << endl;

	cout << "[7] Base::_iBase -> ";

	cout << (int)pVtab[7] << endl;

	cout << "[8] Base::_cBase -> ";

	cout << (char)(int)pVtab[8] << endl;

	// sub Base2 vtbl layout

	cout << "[9] Base2::_vptr->" << "  addr:" << &pVtab[9] << endl;

	pFun = (Fun)pVtab[9][0];

	cout << "     [0] ";

	pFun();

	pFun = (Fun)pVtab[9][1];

	cout << "     [1] ";

	pFun();

	pFun = (Fun)pVtab[9][2];

	cout << "     [2] ";

	pFun();

	cout << "     [3] ";

	cout << pVtab[9][3] << endl;

	cout << "[10] Base2::_iBase2 -> ";

	cout << (int)pVtab[10] << endl;

	cout << "[11] Base2::_cBase2 -> ";

	cout << (char)(int)pVtab[11] << endl;

	return 0;

}

Base1对象的内存分布为：

watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvc2hsdHNo/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/SouthEast" alt="">

Derive对象的内存分布为：

2.4.Base1类的内存分布对照

Windows 7 + Visual studio 2013 Linux RHEL6.5 + gcc 4.4.7

2.5.Derive类的内存分布对照

Windows 7 + Visual studio 2013 Linux RHEL6.5 + gcc 4.4.7

2.6.Derive类在虚继承与非虚继承中的内存对照

在前面的章节(2.5)中，已经列出了Derive在虚继承(virtual)的情况下，在windows以及linux平台下的具体内存分布。

在前一篇文章中，我们获得了非虚继承(non virtual)的情况下，Derive类的内存分布。

这里将它与本篇文章中获得的虚继承的分布。进行一个对照。

下图是windows平台下。非虚继承与虚继承对类的内存分布的影响对照。

非虚继承(non virtual) 虚继承(virtual)

下图是linux平台下。非虚继承与虚继承对类的内存分布的影响对照。

非虚继承(non virtual) 虚继承(virtual)

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C++对象内存分布(3) - 菱形继承(virtual)

1.前言

2.菱形继承类的内存分布

2.1.类的结构

2.2.实现代码windows版本号

2.3.实现代码linux版本号

2.4.Base1类的内存分布对照

2.5.Derive类的内存分布对照

2.6.Derive类在虚继承与非虚继承中的内存对照

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