What is the main difference between a class and a struct in C?

Table of Contents

• Introduction
• The Concept of Classes vs Structs in C
  • 1. Absence of Classes in C
  • 2. Struct in C
• Key Differences Between Class (C++) and Struct (C)
  • 1. Data and Functions Grouping
  • 2. Object-Oriented Features
  • 3. Access Control
• Practical Example: Encapsulation in C++
  • C++ Example: Encapsulation with Classes
  • C Example: No Encapsulation with Structs
• Conclusion

Introduction

In C, there is no concept of a class as it is a procedural programming language. Instead, C uses structs to group related data. While C++ introduces both structs and classes with specific differences, C remains purely focused on structs.

This guide explains how structs are used in C and highlights the differences between the concepts of class in object-oriented languages like C++ and the struct in C.

The Concept of Classes vs Structs in C

1. Absence of Classes in C

Unlike C++, which supports object-oriented programming (OOP) with concepts like classes, inheritance, and polymorphism, C is a procedural language. There is no built-in support for class in C. As a result, C does not have the class keyword or features like member functions, constructors, destructors, inheritance, or encapsulation that are integral to object-oriented programming.

In C++, a class groups both data (variables) and methods (functions) together in a single unit, enforcing encapsulation and providing object-oriented design. This concept does not exist in C.

2. Struct in C

In C, a struct is used to group related data (variables) of different types. However, it does not support member functions or object-oriented principles like encapsulation. C's struct is purely a data container that holds variables but does not bind functions to the data as classes do in object-oriented languages.

Example of a struct in C:

In this example, struct Point is a simple data structure used to store two integers. It does not have any member functions, constructors, or access control mechanisms like a class would in C++.

Key Differences Between Class (C++) and Struct (C)

1. Data and Functions Grouping

• Class in C++: In C++, a class groups both data members and member functions together. It supports access control (private, protected, public), encapsulation, inheritance, and polymorphism, making it a core part of object-oriented programming.

  Example in C++:

• Struct in C: A struct in C, on the other hand, can only group data. It does not support member functions or access control. It is purely a data structure for holding related variables.

  Example in C:

2. Object-Oriented Features

• Class in C++: Classes in C++ are designed to support object-oriented programming with features like:
  • Encapsulation: By making data members private and exposing functionality through public methods.
  • Inheritance: Allowing classes to inherit from other classes.
  • Polymorphism: Allowing functions to behave differently based on the object invoking them.
• Struct in C: C does not support object-oriented features. Structs in C only group variables, and all members are public by default. There is no encapsulation, inheritance, or polymorphism.

3. Access Control

• Class in C++: Members of a class are private by default, meaning they cannot be accessed directly from outside the class unless specifically allowed using public or protected keywords.
• Struct in C: In C, struct members are always public, meaning there is no built-in mechanism for hiding or protecting data. You can freely access and modify struct members from anywhere in the code.

Practical Example: Encapsulation in C++

While C++ classes use encapsulation to hide data, C structs do not provide any access control. Here's an example showing how C++ encapsulates data in a class, which is not possible in C:

C++ Example: Encapsulation with Classes

C Example: No Encapsulation with Structs

In C++, the Person class uses private members and public methods to control access to the name and age. In C, the Person struct allows direct access to all members with no control over data validation or protection.

Conclusion

In C, struct is the only way to group data, as it lacks the concept of a class and other object-oriented features such as encapsulation, inheritance, and polymorphism. In contrast, C++ supports both struct and class, with class being primarily used for object-oriented programming. The fundamental difference between class and struct lies in their purpose: struct is a simple data container in C, while class in C++ introduces a range of OOP capabilities that allow for greater control, modularity, and abstraction in program design.