Pure Virtual Function and Abstract Class

Definition

Abstract class

• In a base class, we don't provide the implementation of certain functions. Such a class is called abstract class.
• An abstract class cannot have an instance of itself created.

Pure Virtual Function

• a virtual function for which we don’t have implementation, we only declare it.

• declared by assigning 0 in declaration.

  // An abstract class
  class Test
  {   
    // Data members of class
  public:
    // Pure Virtual Function
    virtual void show() = 0;
  
   /* Other members */
  };
  

When

• create a pure virtual function when it doesn’t make sense to provide a definition for a virtual function in the base class itself, within the context of inheritance
• For example: for a base class "Figure", it does not make sense to provide the implementation draw() function in the abstract class.