C ++ virtual functions, pure virtual functions, abstract base classes, and virtual base classes)

Virtual functions:
Purpose: To cause late binding
Implementation Method: Use the virtual keyword when declaring a function

Pure virtual functions:
Objective: To provide abstract Interfaces
Implementation Method: Virtual int Foo () = 0;
Feature: If a class contains pure virtual functions, the vtable of the class is incomplete, so the object of the class cannot be generated. Such a class is called a pure abstract base class.

Pure abstract base class, also known as pure virtual class:
Objective: To provide abstract Interfaces
Implementation Method: contains pure virtual functions
Feature: objects of this class cannot be generated.

Virtual base class:
Objective: to eliminate ambiguity
Implementation Method: Virtual inheritance
Feature: A class can be either a virtual base class of a class or a non-virtual base class of another class.