Virtuals

#include <iostream>
using namespace std;

class A {
public:
    virtual ~A() {}

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

private:
    int x;
};

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

class B {
public:
    B();
    virtual ~B() {}
    void special() { h(); }
    // Можно сделать чисто виртуальной.
    virtual void h() { cout << "B::h" << endl; }
};

B::B()
{
    special();
}

class C : public A, public B {
public:
    C();
    virtual ~C() {}

    void f() { cout << "C::f" << endl; }
    virtual void g() { cout << "C::g" << endl; }
    virtual void h() { cout << "C::h" << endl; }
};

C::C() :
    A(),
    B()
{
}

int main()
{
    A* a = new A();
    a->f();
    cout << sizeof( A ) << endl;
    delete a;

    C* c2 = new C();
    A* a2 = c2;
    B* b2 = c2;

    a2->f();
    b2->h();

    delete a2;
    return 0;
}