标签：c++内存布局   c++对象内存布局   不同平台c++内存布局   

1.前言

本篇文章的所有代码例子，如果是windows上编译运行，则使用的是visual studio 2013。如果是RHEL6.5平台(linux kernal: 2.6.32-431.el6.i686)上编译运行，则其gcc版本为4.4.7，如下所示：

2.菱形继承类的内存分布

2.1.类的结构

                    菱形继承 - 重复继承

2.2.实现代码windows版本

下面的代码运行在windows 7+visual studio 2013平台上。

#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 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 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 Base1, public 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;
	}
};
int main()
{
	typedef void(*Fun)(void);

	int** pVtab = NULL;
	Fun pFun = NULL;

	Derive derive;
	pVtab = (int**)&derive;
	cout << "[0]  Derive::Base1::_vptr->" << endl;
	pFun = (Fun)pVtab[0][0];
	cout << "       [0] ";
	pFun();
	pFun = (Fun)pVtab[0][1];
	cout << "       [1] ";
	pFun();
	pFun = (Fun)pVtab[0][2];
	cout << "       [2] ";
	pFun();
	pFun = (Fun)pVtab[0][3];
	cout << "       [3] ";
	pFun();
	pFun = (Fun)pVtab[0][4];
	cout << "       [4] ";
	pFun();
	pFun = (Fun)pVtab[0][5];
	cout << "       [5] 0x" << pFun << endl;

	cout << "[1]  Base::_iBase = " << (int)pVtab[1] << endl;
	cout << "[2]  Base::_cBase = " << (char)(int)pVtab[2] << endl;
	cout << "[3]  Base1::_iBase1 = " << (int)pVtab[3] << endl;
	cout << "[4]  Base1::_cBase1 = " << (char)(int)pVtab[4] << endl;

	cout << "[5]  Derive::Base2::_vptr->" << endl;
	pFun = (Fun)pVtab[5][0];
	cout << "       [0] ";
	pFun();
	pFun = (Fun)pVtab[5][1];
	cout << "       [1] ";
	pFun();
	pFun = (Fun)pVtab[5][2];
	cout << "       [2] ";
	pFun();
	pFun = (Fun)pVtab[5][3];
	cout << "       [3] ";
	pFun();
	pFun = (Fun)pVtab[5][4];
	cout << "       [4] 0x" << pFun << endl;

	cout << "[6]  Base::_iBase = " << (int)pVtab[6] << endl;
	cout << "[7]  Base::_cBase = " << (char)(int)pVtab[7] << endl;
	cout << "[8]  Base2::_iBase2 = " << (int)pVtab[8] << endl;
	cout << "[9]  Base2::_cBase2 = " << (char)(int)pVtab[9] << endl;

	cout << "[10] Derive::_iDerive = " << (int)pVtab[10] << endl;
	cout << "[11] Derive::_cDerive = " << (char)(int)pVtab[11] << endl;

	return 0;
}

2.3.实现代码linux版本

linux平台下的代码，与上一节中的windows代码，绝大部分是相似的，不同点仅在于linux版本中，会访问并打印出pVtab[0][6]的值。下面给出了完整的main函数。

int main()
{
        typedef void(*Fun)(void);

        int** pVtab = NULL;
        Fun pFun = NULL;

        Derive derive;
        pVtab = (int**)&derive;
        cout << "[0]  Derive::Base1::_vptr->" << endl;
        pFun = (Fun)pVtab[0][0];
        cout << "       [0] ";
        pFun();
        pFun = (Fun)pVtab[0][1];
        cout << "       [1] ";
        pFun();
        pFun = (Fun)pVtab[0][2];
        cout << "       [2] ";
        pFun();
        pFun = (Fun)pVtab[0][3];
        cout << "       [3] ";
        pFun();
        pFun = (Fun)pVtab[0][4];
        cout << "       [4] ";
        pFun();
        pFun = (Fun)pVtab[0][5];
        cout << "       [5] ";
        pFun();
        pFun = (Fun)pVtab[0][6];
        cout << "       [6] 0x" << pFun << endl;

        cout << "[1]  Base::_iBase = " << (int)pVtab[1] << endl;
        cout << "[2]  Base::_cBase = " << (char)(int)pVtab[2] << endl;
        cout << "[3]  Base1::_iBase1 = " << (int)pVtab[3] << endl;
        cout << "[4]  Base1::_cBase1 = " << (char)(int)pVtab[4] << endl;

        cout << "[5]  Derive::Base2::_vptr->" << endl;
        pFun = (Fun)pVtab[5][0];
        cout << "       [0] ";
        pFun();
        pFun = (Fun)pVtab[5][1];
        cout << "       [1] ";
        pFun();
        pFun = (Fun)pVtab[5][2];
        cout << "       [2] ";
        pFun();
        pFun = (Fun)pVtab[5][3];
        cout << "       [3] ";
        pFun();
        pFun = (Fun)pVtab[5][4];
        cout << "       [4] 0x" << pFun << endl;

        cout << "[6]  Base::_iBase = " << (int)pVtab[6] << endl;
        cout << "[7]  Base::_cBase = " << (char)(int)pVtab[7] << endl;
        cout << "[8]  Base2::_iBase2 = " << (int)pVtab[8] << endl;
        cout << "[9]  Base2::_cBase2 = " << (char)(int)pVtab[9] << endl;

        cout << "[10] Derive::_iDerive = " << (int)pVtab[10] << endl;
        cout << "[11] Derive::_cDerive = " << (char)(int)pVtab[11] << endl;

        return 0;
}

2.4.内存分布对比

通过下面的对比图，可以看到，对于菱形非虚继承，在这两种平台上的内存分布几乎一样。

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

C++对象内存分布(2) - 菱形继承(non virtual)

标签：c++内存布局   c++对象内存布局   不同平台c++内存布局   

原文地址：http://blog.csdn.net/shltsh/article/details/46642727