abstract class Pure Virtual Functions

An abstract class identifies the properties that need to be defined through pure virtual functions. For instance, if a Shape has a volume, then the abstract Shape class would include a pure virtual function for volume.

The term interface refers to an abstract class that contains no data members.

and / or

A class that includes at least one pure virtual function is an abstract base class. (may contains data members on this situation)

Pure Virtual Functions

A pure virtual function is a virtual function that has form but no implementation. The declaration of a pure virtual function takes the form

 virtual type identifier(parameters) = 0;