C++對象記憶體布局–⑤GCC編譯器–單個虛擬繼承

C++對象記憶體布局--⑤GCC編譯器--單個虛擬繼承

　　測試GNU的GCC編譯器在處理虛擬繼承上跟VS不同的地方。衍生類別的虛函數表跟虛基類表合并。

//GCC編譯器--單個虛擬繼承.cpp//2010.8.18//虛基類表到底是那個？，還是說衍生類別的虛函數表的上邊和下邊都是？//GCC編譯器#include <iostream>using   namespace std;//////////////////////////////////////////////////////////////////class Base{    public:        Base(int a = 10):a(a)        {            cout << "Base::Base()" << endl;        }        virtual void show1()        {            cout << "Base::show1()" << endl;            cout << a << endl;        }    private:        int a;};//////////////////////////////////////////////////////////////////class Derived : virtual public Base{    public:        Derived(int b = 100):b(b)        {            cout << "Derived::derived()" << endl;        }        virtual void show2()        {            cout << "Derived::show2()" << endl;            cout << b << endl;        }    private:        int b;};//////////////////////////////////////////////////////////////////int main(){    Derived obj;    int** p = (int**)&obj;    cout << "虛擬繼承了基類的衍生類別的對象記憶體布局：" <<endl;    for (int i = 0; i != sizeof(obj)/4; ++i)    {        cout << p[i] << endl;    }     typedef void (*fun)(void*pThis);//this指標非常重要    cout << endl << "第一虛函數表第一項，虛函數Derived::show2()地址：" << (int*)p[0][0] << endl;    ((fun)(p[0][0]))(p);    cout << "第二虛函數表第一項，虛函數Base::show1()地址   ：" << (int*)p[2][0] << endl;    ((fun)(p[2][0]))(p+2);    cout << endl << "衍生類別虛函數表指標往低地址方向定址：" << endl;    cout << "p[0][-1] = " << (int*)p[0][-1] << endl;    cout << "p[0][-2] = " << (int*)p[0][-2] << endl;    cout << "p[0][-3] = " << (int*)p[0][-3] << endl;    cout << endl << "衍生類別虛函數表指標往高地址方向定址：" << endl;    cout << "p[0][0] = " << (int*)p[0][0] << "(這個是show2()函數地址)" << endl;    cout << "p[0][1] = " << (int*)p[0][1] << endl;    cout << "p[0][2] = " << (int*)p[0][2] << endl;    cout << "p[0][3] = " << (int*)p[0][3] << endl;    cout << endl << "是否往高方向尋找和往地方向尋找所找到的都是虛基類表呢？" << endl;    //system("pause");    return 0;}/*Base::Base()Derived::derived()虛擬繼承了基類的衍生類別的對象記憶體布局：0x472d4c0x640x472d5c0xa第一虛函數表第一項，虛函數Derived::show2()地址：0x41cd50Derived::show2()100第二虛函數表第一項，虛函數Base::show1()地址   ：0x41ccbcBase::show1()10衍生類別虛函數表指標往低地址方向定址：p[0][-1] = 0x471388p[0][-2] = 0p[0][-3] = 0x8衍生類別虛函數表指標往高地址方向定址：p[0][0] = 0x41cd50(這個是show2()函數地址)p[0][1] = 0p[0][2] = 0xfffffff8p[0][3] = 0x471388是否往高方向尋找和往地方向尋找所找到的都是虛基類表呢？*/