虛擬繼承、多態的記憶體布局

測試平台，Ubuntu 12.04--x64 代碼如下：

#include <iostream>#include <cstdio>using namespace std;class A {public:    long a;    virtual void a1() { cout << "A:a1()" << endl; }    virtual void a2() { cout << "A:a2()" << endl; }};class B: public virtual A {    public:    long b;        virtual void B1() { cout << "B:b1()" << endl; }        virtual void a2() { cout << "B:a2()" << endl; }};class C: public virtual A {    public:    long c;        virtual void C1() { cout << "C:C1()" << endl; }        virtual void C2() { cout << "C:C2()" << endl; }};class D: public B, public C {public:    long d;        virtual void D1() { cout << "D:D1()" << endl; }        virtual void C2() { cout << "D:C2()" << endl; }};typedef void(*Fun)();int main(){    D d;    cout << "d addr:" << &d << endl;    B *pb = &d;    cout << "d(b) addr:" << pb << endl;    C *pc = &d;    cout << "d(c) addr:" << pc << endl;    A *pa = &d;    cout << "d(a) addr:" << pa << endl;    cout << "d:" << &d.d << endl         << "c:" << &d.c << endl         << "b:" << &d.b << endl         << "a:" << &d.a << endl         << "sizeof(d" << sizeof(D) << endl;    long *pint;    pint = (long*)*(long**)&d;    cout << "d addr:" << pint << endl << pint[-1] << endl << pint[-2] << endl << pint[-3] << endl;    cout << "function" << endl;    Fun pFunc;    pFunc = (Fun)*((long*)*(long*)(&d));    pFunc();    pFunc = (Fun)*((long*)*(long*)(&d)+1);    pFunc();    pFunc = (Fun)*((long*)*(long*)(&d)+2);    pFunc();    pFunc = (Fun)*((long*)*(long*)(&d)+3);    pFunc();    pint = (long*)*(long**)pc;    cout << "c addr:" << pint << endl << pint[-1] << endl << pint[-2] << endl << pint[-3] << endl;    pFunc = (Fun)(pint[0]);    pFunc();    pFunc = (Fun)(pint[1]);    pFunc();    pint = (long*)*(long**)pa;    cout << "a addr:" << pint << endl << pint[-1] << endl << pint[-2] << endl << pint[-3] << endl;    pFunc = (Fun)(pint[0]);    pFunc();    pFunc = (Fun)(pint[1]);    pFunc();    return 0;}