Question

What happens if a class contains at least one pure virtual function?

• A. It must be defined as final
• B. It cannot be inherited by other classes
• C. It forces the base class constructor to be private
• D. It becomes an abstract class and cannot be instantiated

Hint:

One pure virtual function makes the class abstract, so no direct objects can be created.

Answer 1

The Correct Option is D

Step 1: Marking a member function with $= 0$ makes it pure virtual, meaning the class promises the interface but leaves the body to derived classes.

Step 2: A class holding at least one such unfinished function is incomplete as a concrete type, so it is labelled abstract.

Step 3: The direct consequence is that you cannot write an object of it; attempting to instantiate it is a compile error. You may still use pointers or references to it.

Step 4: It can absolutely be inherited, is not required to be final, and does not force a private constructor. Only when a subclass implements all pure virtual functions does that subclass become instantiable.

\[\boxed{\text{It becomes an abstract class and cannot be instantiated}}\]