Question

Consider the following simple polymorphism …

class Parent {
public:
    someFunc() { /* implementation A */ };
};

class Child : public Parent {
public:
    someFunc() { /* implementation B */ };
};

int main ()
{
    Parent* ptr;

    ptr = new Parent();
    ptr->someFunc();
    delete ptr;

    ptr = new Child();
    ptr->someFunc();
    delete ptr;

    return 0;
}

As far as I can tell, in both cases implementation A will be called.

How can I call the “most derived” implementation of someFunc, depending on the dynamic type of ptr?

In my real code there are many children types, so it wouldn’t be practical to use dynamic_cast to check per child class.

Answer 1

Try:

class Parent 
{
    public:
         virtual someFunc() { /* implementation A */ };
       //^^^^^^^
};

Though technically not required.
I always find it good style to also declare the derived function virtual:

class Child : public Parent 
{
    public:
        virtual someFunc() { /* implementation B */ };
};

Unlike Java functions are not virtual by default.