图解C++ Vtable

下面给出一个完整的C++代码实例（结合图解，相信大家一定会真正理解多态思想）：

#include<stdio.h>
#include<stdlib.h>
#include<iostream>
#include<iomanip>
using namespace std;
 
 
class A
{
public:
    int m_data1;
    int m_data2;
    void func1() {}
    void func2() {}
    virtual void vfunc1(){}
    virtual void vfunc2(){}
};
 
 
class B : public A
{
public:
    int m_data3;
    void func2() {}
    virtual void vfunc1(){}
};
 
 
class C : public B
{
public:
    int m_data1;
    int m_data4;
    void func2() {}
    virtual void vfunc1(){}
};
 
 
void main()
{
    cout << "sizeof(A):" << sizeof(A) << endl;
    cout << "sizeof(B):" << sizeof(B) << endl;
    cout << "sizeof(C):" << sizeof(C) << endl;
 
 
    A a;B b;C c;
    b.m_data1 = 1;
    b.m_data2 = 2;
    b.m_data3 = 3;
 
 
    c.m_data1 = 11;
    c.m_data2 = 22;
    c.m_data3 = 33;
    c.m_data4 = 44;
    c.A::m_data1 = 111;
 
 
 
 
    cout << "The offset of object b:" << endl;
    cout << &b << " : " << "vptr from A" << endl;
    cout << &(b.m_data1) << " : " << b.m_data1 << endl;
    cout << &(b.m_data2) << " : " << b.m_data2 << endl;
    cout << &(b.m_data3) << " : " << b.m_data3 << endl << endl;
 
 
    cout << "The offset of object c:" << endl;
    cout << &c << " : " << "vptr fron B" << endl;
    cout << &(c.A::m_data1) << " : " << c.A::m_data1 << endl;
    cout << &(c.m_data1) << " : " << c.m_data1 << endl;
    cout << &(c.m_data2) << " : " << c.m_data2 << endl;
    cout << &(c.m_data3) << " : " << c.m_data3 << endl;
    cout << &(c.m_data4) << " : " << c.m_data4 << endl << endl;
    system("pause");
}
 

原理解释：