What is meant by function overriding in c plus plus?

Answer 1

Function overriding applies to class member functions (methods), where a derived class provides a more specialised implementation of its generic base class method. An override can still call the base class method and augment it with other instructions (before or after the call to the base class method), or it can provide a complete implementation of its own without calling the base class method.

Classes that are intended to act as generic base classes will generally declare their methods to be virtual, meaning they are intended to be overridden, if required.

Abstract base classes will contain one or more pure-virtual methods (which may or may not provide a generic implementation), meaning classes must be derived from the abstract base class and all the pure-virtual methods must be overridden in the derived class (otherwise they, too, become abstract). Only classes that fully implement all the pure-virtual methods they inherit from their base classes can actually be instantiated. That is, you cannot instantiate an instance of an abstract base class, even if it provides generic implementations for all its pure-virtual methods. They can only be instantiated by deriving classes from them.