Ways to detect whether a C++ virtual function has been redefined in a derived class

Question

In brief: From a C++ base-class pointer which points to an instance of a derived class, how can one determine at run-time whether a non-pure virtual functio

Answer 1

Perhaps this helps. It alone doesn't answer your original question, but you can augment your base class (here, Foo) to use a certain interface if it is supplied or use a default method otherwise.

#include 

struct X {
    virtual void x () = 0;
};

struct Y {
    virtual void y () = 0;
};


struct Foo {
    virtual ~ Foo () {}

    bool does_x () {
        return NULL != dynamic_cast  (this);
    }

    bool does_y () {
        return NULL != dynamic_cast  (this);
    }

    void do_x () {
        dynamic_cast  (*this) .x ();
    }

    void do_y () {
        dynamic_cast  (*this) .y ();
    }
};

struct foo_x : public Foo, public X {
    void x () {
        std :: cout << __PRETTY_FUNCTION__ << std :: endl;
    }
};


struct foo_y : public Foo, public Y {
    void y () {
        std :: cout << __PRETTY_FUNCTION__ << std :: endl;
    }
};

struct foo_xy : public Foo, public X, public Y {
    void x () {
        std :: cout << __PRETTY_FUNCTION__ << std :: endl;
    }

    void y () {
        std :: cout << __PRETTY_FUNCTION__ << std :: endl;
    }
};

void test (Foo & f)
{
    std :: cout << &f << " "
        << "{"
        << "X:" << f .does_x () << ", "
        << "Y:" << f .does_y ()
        << "}\n";

    if (f .does_x ())
        f .do_x ();

    if (f .does_y ())
        f .do_y ();
}

int main ()
{
    foo_x x;
    foo_y y;
    foo_xy xy;
    test (x);
    test (y);
    test (xy);
}