Question

I’d like my code to print:

B B
A B
B A

But it prints

Item Item
Item Item
Item Item

The code:

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

struct Item {
    Item(){}
    virtual void method1 (Item x, Item y) {cout << "Item Item\n";}
};

struct A : public Item {
    A(){}
};

struct B : public Item {
    B(){}
    virtual void method1 (B x, B y) {cout << "B B\n";}
    virtual void method1 (A x, B y) {cout << "A B\n";}
    virtual void method1 (B x, A y) {cout << "B A\n";}
};

int main ( void ) {
    Item * a[2];
    a[0] = new B; a[1] = new A;
    a[0]->method1(*a[0], *a[0]);
    a[0]->method1(*a[1], *a[0]);
    a[0]->method1(*a[0], *a[1]);
}

Answer 1

Your overloads of method1 in B don’t override the virtual method in Item. So, when you call someItem->method1, it is not going to use them.

It looks like you want what is called “multiple dispatch”, which C++ doesn’t support directly. See http://en.wikipedia.org/wiki/Multiple_dispatch#C.2B.2B for some discussion and workarounds.