C++对象内存分布(2) - 菱形继承(non virtual)

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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：

[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

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。输出Derive类的内存分布。

#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 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;}

运行结果如下：

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;}

运行结果如下：

2.4.Derive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，Derive类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

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