Virtual Function

虚函数，直接上个代码吧，这份代码很长，因为其中研究了一下虚函数的实现，虽说好像什么也没懂。

#include <iostream>
#include <stdio.h>
using namespace std;

class Base {
  
  public:
    Base() {}
    virtual ~Base() {}
    void non_virtual_show() {
        cout << "it shows I am a Base(non_virtual)" << endl;
    }
    virtual void virtual_show() {
        cout << "it shows I am a Base(virtual)" << endl;
    }
    virtual void virtual_show_1() {}
    virtual void virtual_show_2() {
        cout << "successfully call virtual_show_2 in base" << endl;
    }
};

class Derive_1 : public Base {
    
  public:
    void non_virtual_show() {
        cout << "it shows I am a Derive_1(non_virtual)" << endl;
    }
    virtual void virtual_show() {
        cout << "it shows I am a Derive_1(virtual)" << endl;
    }
    virtual void virtual_show_1() {}
    virtual void virtual_show_2() {
        cout << "successfully call virtual_show_2 in derive_1" << endl;
    }
};

int main() {
    
    //PART 1 without pointer
    Base b1;
    Derive_1 d1;
    b1.non_virtual_show();
    b1.virtual_show();
    d1.non_virtual_show();
    d1.virtual_show();
    cout << endl;
    
    //PART 2 with pointer
    Base *p1 = new Base;
    Base *p2 = new Derive_1;
    Derive_1 *p3 = new Derive_1;
    //Derive_1 *p4 = new Base; invalid conversion
    p1->non_virtual_show();
    p1->virtual_show();
    p2->non_virtual_show();
    p2->virtual_show();
    cout << endl;
    
    //PART 3 address
    void (Base::*B_pointer)();
    B_pointer = &Base::non_virtual_show;
    printf("%p\n", B_pointer);
    B_pointer = &Base::virtual_show;
    printf("%p\n", B_pointer);
    B_pointer = &Base::virtual_show_1;
    printf("%p\n", B_pointer);
    B_pointer = &Base::virtual_show_2;
    printf("%p\n", B_pointer);
    cout << endl;
    
    void (Derive_1::*D_pointer)();
    D_pointer = &Derive_1::non_virtual_show;
    printf("%p\n", D_pointer);
    D_pointer = &Derive_1::virtual_show;
    printf("%p\n", D_pointer);
    D_pointer = &Derive_1::virtual_show_1;
    printf("%p\n", D_pointer);
    D_pointer = &Derive_1::virtual_show_2;
    printf("%p\n", D_pointer);
    cout << endl;
    
    //PART 4 call the virtual function through their address
    void (Base::*pointer1)();
    Base *p4 = new Derive_1;
    pointer1 = &Base::non_virtual_show;
    (p4->*pointer1)();
    pointer1 = &Base::virtual_show;
    printf("%p\n", pointer1);
    pointer1 = &Base::virtual_show_1;
    printf("%p\n", pointer1);
    pointer1 = &Base::virtual_show_2;
    printf("%p\n", pointer1);
    (p4->*pointer1)();
    (p4->*(&Base::virtual_show_2))();
    (p4->Base::virtual_show_2)();
    p4->Base::virtual_show_2();
    //pointer1 = &Derive_1::non_virtual_show; cannot convert 'void (Derive_1::*)' to 'void (Base::*)()' in assignment
    //pointer1 = &Derive_1::virtual_show; cannot convert 'void (Derive_1::*)' to 'void (Base::*)()' in assignment
    cout << endl;
    
    void (Base::*pointer2)();
    Derive_1 *p5 = new Derive_1;
    pointer2 = &Base::non_virtual_show;
    (p5->*pointer2)();
    pointer2 = &Base::virtual_show;
    printf("%p\n", pointer2);
    pointer2 = &Base::virtual_show_1;
    printf("%p\n", pointer2);
    pointer2 = &Base::virtual_show_2;
    printf("%p\n", pointer2);
    (p5->*pointer2)();
    (p5->*(&Base::virtual_show_2))();
    (p5->Base::virtual_show_2)();
    p5->Base::virtual_show_2();
    cout << endl;
    
    void (Derive_1::*pointer3)();
    Derive_1 *p6 = new Derive_1;
    pointer3 = &Base::non_virtual_show;
    (p6->*pointer3)();
    pointer3 = &Base::virtual_show;
    printf("%p\n", pointer3);
    pointer3 = &Base::virtual_show_1;
    printf("%p\n", pointer3);
    pointer3 = &Base::virtual_show_2;
    printf("%p\n", pointer3);
    (p6->*pointer3)();
    (p6->*(&Base::virtual_show_2))();
    (p6->Base::virtual_show_2)();
    p6->Base::virtual_show_2();
    
    return 0;
}

 这似乎说明，虚函数的所谓地址只是virtual table中的相对地址（猜测是下标），因为间隔都是一样的，而且基类和派生类的相对地址是一样的（但这并不能说明地址一样，只是相对于virtual table起始距离一样）。不知道这种情况应该怎么解释。

Virtual Function

原文：http://blog.csdn.net/u012925008/article/details/44575335