Inheritance. Call child class function from parent class

Question

class C1 {
    void A();
    void B();
}

void C1::A(){ return B(); }

class C2 : public C1 {
    void B();
}

C2 *obj = new C2;
obj->A(); // returns B() from C1

Why does B() from C1 called? How to make A() exist only in C1 and call B() from C2?

Solution 1

You need to make B() in C1 a virtual function.

Virtual functions are basically function pointers that take their value upon initialization of the object. If you new C1, the function pointer would point to C1::B while if you new C2 that function pointer would point to C2::B.

Note: To read more about virtual and related subjects, search for function overriding and polymorphism.

Solution 2

Member methods are not virtual by default in C++ (do you come from Java)?

When you write:

class C1 {
    void A();
    void B();
}

class C2 : public C1 {
    void B();
}

you're not overriding B() in C2, but hiding it.

To override it, you must declare it virtual in the base class (virtual in subsequent classes is not necessary).