Question

Is there a way you can invoke a member function of a base class upon a class derived from it?

Class Bass{
    public:
        void func();
};

Class Derived: public Base{
    public:
        void func();
};

I have a practice midterm, and I suspect no, because how would the Base class know about the Derived, but I am not sure.

Answer 1

Is there a way you can invoke a member function of a base class upon a class derived from it?

Not sure exactly what you mean by this, but given your Base and Derived classes you can do the following. Just make sure you use a reference or pointer, not pass-by-value because of the slicing problem.

---

Call Base::func() from within Derived::func():

void Derived::func()
{
    Base::func();
}

---

Call Base::func() explicitly on a Derived object:

Derived d;
d.Base::func();

---

I […] am wondering if you could do something like Base::func(Derived d)

As others have pointed out, you can do this using a forward declaration:

// Tell the compiler "Derived" is a class name.
class Derived;

class Base
{
    // Can use the class name since it has been declared.
    void func(Derived& derived);
};

// Define the class named "Derived".
class Derived : public Base
{
    // ...
};

// Use the derived class.
void Base::func(Derived& derived)
{
    // For this bit to work, the definition of `Derived` must
    // be visible at this point (like putting the class above
    // or including your "Derived.h" from "Base.cpp").
    derived.some_derived_method();
}

However, you won’t be able to define the Base::func(Derived&) directly in the class definition since you need to finished defining Base and to define Derived first.