虚函数的实现机制

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#include <iostream>using namespace std;class CBase1 {private:int a;int b;void sayBye() {            cout << "Bye, CBase1!" << endl;}public:CBase1() {cout << "Hello CBase1!" << endl;}virtual ~CBase1() {cout << "Bye CBase1!" << endl;}virtual void sayHi() {            cout << "Hello, CBase1!" << endl;            sayBye();}};class CBase2 {private:int a;int b;public:CBase2() {cout << "Hello CBase2!" << endl;}~CBase2() {cout << "Bye CBase2!" << endl;}virtual void sayHi() {            cout << "Hello, CBase2!" << endl;}};class CSub2: public CBase2 { //继承方式public:CSub2() {cout << "Hello CSub2" << endl;}~CSub2() {cout << "Bye CSub2" << endl;}};class CSub1: public CBase1, public CBase2 { //继承方式public:CSub1() {cout << "Hello CSub1" << endl;}~CSub1() {cout << "Bye CSub1" << endl;}        void sayHi() {            cout << "Hello, CSub1!" << endl;        }        void sayLove() {            cout << "I love you!" << endl;        }private:};int main(){    CBase1* a = new CSub1();    a->sayHi();    dynamic_cast<CSub1*>(a)->sayLove();    return 0;}

#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;    /*    Derive::f    Base1::g    Base1::h    Derive::g1    1    Derive::f    Base2::g    Base2::h    1    Derive::f    Base3::g    Base3::h    0    */    return 0;}

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