Can multiple base classes have the same virtual method?

Question

class A has a pure virtual method read()
class B has an implemented virtual method read()
I have a class C that inherits A and B
Can this happen?

What I'm trying to achieve is that the two base classes A and B complement each other.

So C read() method would actually call class B read()

class A {
    virtual int get_data() = 0;

    void print() {
        log(get_data());
    }
}

class B {
    virtual int get_data() {
        return 4;
    }
}

class C : public A, public B {

}

C my_class;
my_class.print(); // should log 4;

I'm not on my computer nor will have opportunity in the next couple of weeks so I can't test this... but I'm designing the architecture and needed to know if this is possible and if not.. how can this be accomplished!

Not an answer to your question, but there are many online compilers you can use to check things like this: coliru.stacked-crooked.com (I'm not saying you're wrong for asking, just mentioning) — Tas
well it doesn't compile in the online compiler you posted.. if this is not allowed then how can I do something like this? — xDGameStudios
@xDGameStudios when something doesn't compile, you should read the error message. — eerorika

eerorika eerorika · Accepted Answer · 2019-03-31T22:13:09

Can multiple base classes have the same virtual method?

Can this happen?

Yes.

So C read() method would actually call class B read()

That doesn't happen automatically. A member function of base doesn't override a function of an unrelated base.

You can add an override to C:

class C : public A, public B {
    int get_data() override;
}

This overrides both A::get_data and B::get_data. In order to "actually call class B read()", you can indeed make such call:

int C::get_data() {
    return B::get_data();
}

Or... that would be possible if you hadn't declared B::get_data private.

Overriding a function in another base without explicitly delegating in derived is possible if you change your hierarchy a bit. In particular, you need a common base, and virtual inheritance:

struct Base {
    virtual int get_data() = 0;
};

struct A : virtual Base {
    void print() {
        std::cout << get_data();
    }
};

struct B : virtual Base {
    int get_data() override {
        return 4;
    }
};

struct C : A, B {};

Can multiple base classes have the same virtual method?

1 Answers