C++对象模型----重复继承

Code:

#include <iostream>

using namespace std;

class A

{
public:

A(int a):x(a){}

virtual void f(){cout << "A::f() called." << endl;}

virtual void g(){cout << "A::g() called." << endl;}

virtual void h(){cout << "A::h() called." << endl;}

private:
int x;

};
class B:public A

{
public:

B(int a,int b):A(a),y(b){}

void f(){cout << "B::f() called." << endl;}

virtual void m(){cout << "B::m() called." << endl;}

virtual void n(){cout << "B::n() called." << endl;}

private:
int y;

};
class C:public A

{
public:

C(int a,int c):A(a),z(c){}

void g(){cout << "C::g() called." << endl;}

virtual void cfun(){cout << "C::cfun() called." << endl;}

private:

int z;
};
class D:public B,public C

{
public:
D(int a,int b,int c,int d):B(a,b),C(a,c),d(d){}

void h(){cout << "D::h() called." << endl;}

void m(){cout << "D::m() called." << endl;}

virtual void t(){cout << "D::t() called." << endl;}

private:

int d;
};
int main()
{
D tp(2,3,4,5);
typedef void (*PFUN)(void);

PFUN pfun;
pfun = (PFUN)(*((int*)(*(int*)(&tp))));

pfun();
pfun = (PFUN)(*((int*)(*(int*)(&tp))+1));

pfun();
pfun = (PFUN)(*((int*)(*(int*)(&tp))+2));

pfun();
pfun = (PFUN)(*((int*)(*(int*)(&tp))+3));

pfun();
pfun = (PFUN)(*((int*)(*(int*)(&tp))+4));

pfun();
pfun = (PFUN)(*((int*)(*(int*)(&tp))+5));

pfun();
cout << *((int*)(&tp) + 1) << endl;

cout << *((int*)(&tp) + 2) << endl;

pfun = (PFUN)(*(int*)(*((int*)(&tp) + 3)));

pfun();
pfun = (PFUN)(*((int*)(*((int*)(&tp) + 3))+1));

pfun();
pfun = (PFUN)(*((int*)(*((int*)(&tp) + 3))+2));

pfun();
pfun = (PFUN)(*((int*)(*((int*)(&tp) + 3))+3));

pfun();
cout << *((int*)(&tp) + 4) << endl;

cout << *((int*)(&tp) + 5) << endl;

cout << *((int*)(&tp) + 6) << endl;

return 0;
}

对像模型:




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从输出结果上我们可以看到A::x在对象D中有两份。一份来自于B,一份来自于C。这不仅浪费的存储空间，而且容易造成歧义。故此引入了虚拟继承。