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Abstract Classes in C++: Creating Frameworks for Code Reusability

Definition of Abstract Classes in C++

Well, a C++ abstract class comes with at least one pure virtual function. This means that neither these classes nor a function without a definition can be instantiated. To prevent the child class from becoming an abstract class in and of itself, the abstract class's child classes must give the body to the pure virtual function. 

Table of Content —

Purpose of Abstract Classes in C++

Broad notions are expressed using an abstract class in C++, from which more specific classes can be descended. It is not possible to create an abstract class-type object. However, you can utilize pointers and references to abstract class types. 

Create an abstract class with a minimum of one pure virtual member feature. Enforcing polymorphism is another objective of abstract classes. The capacity to treat objects of various types similarly is known as polymorphism. 

A base class that incorporates abstract classes and specifies a common interface for a set of derived classes can be created. After that, you can refer to any objects of derived classes using pointers or references to the base class. 

Abstract Classes in Cpp

Learn More: Hierarchical Inheritance In Java

Abstract Classes in C++ vs. Concrete Classes

Below is the quick comparison of Abstract class in C++ Vs concrete classes:

Basis Abstract Class Concrete Class
Supported  Methods Both abstract and concrete methods can be found in abstract classes. There are only permitted types of methods for a concrete class. The class becomes abstract even with just one abstract method.
Abstract Method Abstract methods can or cannot be present in abstract classes. An abstract method cannot be part of a concrete class.
Inheritance The extend keyword allows abstract classes to inherit from other classes and implement interfaces. There is only one interface that an interface can inherit.
Instantiation A new keyword cannot be used to instantiate an abstract class. The new keyword can be used to Instantiate a concrete class.
Final You cannot declare/specify an abstract class as a final class. You can declare a concrete class as a final class.
Interface An abstract class cannot implement an interface by itself. To utilize the interface for instantiation, a child class must be present.  Implementing an interface is simple. 

Creating Abstract Classes in C++

Here’s how to create an abstract class in C++:


using namespace std;

class Shape {
  virtual void draw() = 0;

Implementing Concrete Classes

Concrete class implementation in C++ is a rather simple procedure. Firstly, define the class. The class definition should outline the class's data members and member functions. Implementing the class's member functions is the next step. 

Finally, you may use a concrete class object to engage with the outside world. Concrete class implementation in C++ is a potent technique for producing reusable and maintainable code. 

Understanding Polymorphism and Its Relationship to Abstract Classes

The idea of polymorphism is especially useful when dealing with a single abstract term implemented in various forms. You can design a single abstract class using polymorphism and modify it to fit your techniques and ideas. 

For instance, describe the common methods and properties shared by all shapes in Shape's abstract class. Subclasses of Shape might then be created for other shapes, like a Circle, a Rectangle, and a Triangle. Since it cannot be instantiated, the Shape class would be abstract. 

On the other hand, the Shape class's subclasses may all be instantiated and have access to the same functions and attributes. This would enable you to treat all shapes equally, even though they can be different. 

Utilizing Abstract Classes in C++ to Achieve Polymorphic Behavior

When it comes to OOP, a C++ abstract class serves the purpose of a powerful and efficient tool for achieving polymorphic behavior. Subclasses that can differ in how they specifically implement a common behavior can be made by declaring that behavior in a C++ abstract class. 

As a result, you may design code that can be applied to various object types without worrying about how the behavior would be implemented specifically. 

As an illustration, you could develop the general behavior of all shapes into an abstract class named Shape. Methods for drawing the shape and figuring out its area and perimeter could all be a part of this behavior. 

After that, you may make subclasses of Shapes for particular forms like Circles, Rectangles, and Triangles. Each of these subclasses would implement the common functionality of Shape in a manner unique to the type of shape it represents. 

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Benefits of Abstract Classes in C++

Below are the key benefits of Abstract class in C++ for your better understanding:

  • Reusability: Code reuse is possible with abstract classes. You save time, energy, and effort as you won’t have to rewrite the existing code. 
  • Abstraction: Implementation specifics can be abstracted away using abstract classes. This may make it simpler to read and update your code. 
  • Polymorphism: It can be implemented by using the C++ abstract class. Your code may become more expandable and adaptable as a result. 
  • Error Checking: An abstract class in C++ may require error-checking to reduce coding errors. 
  • Code Documentation: Abstract classes can be used as a tool for code documentation. This may make it simpler to read and update your code. 

Comparing Abstract Classes with Interfaces in C++

C++ Abstract Class Interface
Using the Extend keyword, an abstract class in C++ can enforce an interface and inherit from another class. Regarding inheritance, an interface can only inherit from another interface. 
Inheriting from an abstract class is possible with the extends keyword. The implements keyword is the only way to put an interface into use.

Examples of Abstract Classes in C++

Consider creating a calculator that outputs the perimeter when a shape is entered. Think about the kind of code you would implement in such a calculator. You can start with a few fundamental forms and hardcode the perimeter if you create unique functions inside the Shape class. That’s how the class might show up on display:

class Shape {  
// All the functions of both square and rectangle are clubbed together in a single class.  
void width(int w) {  
shape_width = w;  
void height(int h) {  
shape_height = h;  
int areaOfSquare(int s) {  
return 4 * s;  
int areaOfRectange(int l, int b) {  
return (l * b);  
int shape_width;  
int shape_height;  
int main (){  
shapes R;  
cout<<"The area of rectangle is"<

Abstract Classes in Cpp


An effective tool for building frameworks for code reuse is abstract classes. You can provide a group of classes with a common interface and require subclasses to implement specific methods by utilizing abstract classes. 

Your code may become more adaptable, extendable, and simple to comprehend and maintain. You must learn more about them if you're seeking a technique to increase the reusability of your code. To do so, check out Hero Vired’s data science and analytics course certification offer!


An abstract class type cannot be created as an object. To abstract class types, you can utilize references and pointers. You can establish an abstract class by defining a minimum of one pure virtual member function.

Only one abstract class may be inherited by a class. However, numerous interfaces can be used to extend a class. To its descendant classes, an abstract class offers fundamental functionality. An interface, on the other hand, gives the classes it extends ancillary functionality.

Those classes are abstract base classes if they have at least one pure virtual function. The most advantageous polymorphism features of C++ are provided via virtual members and abstract classes.

Generally, abstract classes share code and functionality with other classes. When a class needs to implement a certain set of methods, interfaces define those methods.

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