下面是一个关于多重继承的虚函数表访问的例程：
c++ 编译器将虚函数表的地址放在了实例对象内存的最前面，实际上这个虚函数表是一个二维数组。
如果是单继承那么这个虚函数表实际上是一个一位数组。
#include <iostream>
using namespace std;
class Base1 {
public:
virtual void f() { cout << "Base1::f" << endl; }
virtual void g() { cout << "Base1::g" << endl; }
virtual void h() { cout << "Base1::h" << endl; }
};
class Base2 {
public:
virtual void f() { cout << "Base2::f" << endl; }
virtual void g() { cout << "Base2::g" << endl; }
virtual void h() { cout << "Base2::h" << endl; }
};
class Base3 {
public:
virtual void f() { cout << "Base3::f" << endl; }
virtual void g() { cout << "Base3::g" << endl; }
virtual void h() { cout << "Base3::h" << endl; }
};
class Derive : public Base1, public Base2, public Base3 {
public:
virtual void f() { cout << "Derive::f" << endl; }
virtual void g1() { cout << "Derive::g1" << endl; }
};
typedef void(*Fun)(void);
int main()
{
Fun pFun = NULL;
Derive d;
int** pVtab = (int**)&d;
//Base1's vtable
//pFun = (Fun)*((int*)*(int*)((int*)&d+0)+0);
pFun = (Fun)pVtab[0][0];
pFun();
//pFun = (Fun)*((int*)*(int*)((int*)&d+0)+1);
pFun = (Fun)pVtab[0][1];
pFun();
//pFun = (Fun)*((int*)*(int*)((int*)&d+0)+2);
pFun = (Fun)pVtab[0][2];
pFun();
//Derive's vtable
//pFun = (Fun)*((int*)*(int*)((int*)&d+0)+3);
pFun = (Fun)pVtab[0][3];
pFun();
//The tail of the vtable
pFun = (Fun)pVtab[0][4];
cout<<pFun<<endl;
//Base2's vtable
//pFun = (Fun)*((int*)*(int*)((int*)&d+1)+0);
pFun = (Fun)pVtab[1][0];
pFun();
//pFun = (Fun)*((int*)*(int*)((int*)&d+1)+1);
pFun = (Fun)pVtab[1][1];
pFun();
pFun = (Fun)pVtab[1][2];
pFun();
//The tail of the vtable
pFun = (Fun)pVtab[1][3];
cout<<pFun<<endl;
//Base3's vtable
//pFun = (Fun)*((int*)*(int*)((int*)&d+1)+0);
pFun = (Fun)pVtab[2][0];
pFun();
//pFun = (Fun)*((int*)*(int*)((int*)&d+1)+1);
pFun = (Fun)pVtab[2][1];
pFun();
pFun = (Fun)pVtab[2][2];
pFun();
//The tail of the vtable
pFun = (Fun)pVtab[2][3];
cout<<pFun<<endl;
return 0;
}