What is the difference between a constructor and a destructor in C?

Table of Contents

• Introduction
• Constructor and Destructor in C
  • 1. What is a Constructor in C?
    • Example of a "Constructor" in C:
  • 2. What is a Destructor in C?
    • Example of a "Destructor" in C:
• Key Differences Between C and C++ Regarding Constructors and Destructors
• Practical Examples
  • Example 1: Mimicking Constructor and Destructor in C for Dynamic Memory Allocation
• Conclusion

Introduction

Unlike object-oriented languages like C++, the C programming language does not have native support for constructors and destructors. In C++, constructors and destructors manage the lifecycle of objects, allocating and freeing resources such as memory or file handles. However, in C, developers must manually implement initialization and cleanup functions. This leads to key differences in how resource management is handled in C compared to C++.

This guide explores the differences and explains how similar functionality is achieved in C.

Constructor and Destructor in C

1. What is a Constructor in C?

In C, there is no direct equivalent of a constructor as there is in C++. C does not support classes or objects, so there are no built-in mechanisms for automatically initializing variables or structures. However, the concept of initialization can be implemented manually through functions that serve a similar purpose.

Example of a "Constructor" in C:

Explanation:

• We use the function create_person to allocate memory for the Person structure and initialize its fields.
• This function mimics a constructor by setting initial values for the fields.

2. What is a Destructor in C?

Similar to constructors, C does not have destructors built into the language. In C++, destructors are automatically called to free resources when an object goes out of scope. In C, programmers must manually define and call a function to free any allocated memory or resources, especially when dealing with dynamic memory.

Example of a "Destructor" in C:

Explanation:

• The function destroy_person is explicitly called to release the memory allocated for the Person structure and its members.
• This approach mimics the functionality of a destructor in C++.

Key Differences Between C and C++ Regarding Constructors and Destructors

Feature	Constructor/Destructor in C++	"Constructor"/"Destructor" in C
Automatic Invocation	Automatically called when objects are created or destroyed.	Must be manually implemented and called by the programmer.
Built-in Support	Constructors and destructors are part of the C++ language for class objects.	No native support in C; similar functionality is created using functions.
Object-Oriented	C++ uses constructors and destructors for object-oriented programming.	C is a procedural language, so manual memory management is required.
Memory Management	Automatically manages memory, file handles, etc. in destructors.	Manual memory allocation and deallocation with malloc() and free().
Overloading	Constructors can be overloaded in C++.	C does not support function overloading; only one function for each task.

Practical Examples

Example 1: Mimicking Constructor and Destructor in C for Dynamic Memory Allocation

In this example, we implement a "constructor" and "destructor" to manage dynamic memory for a custom Rectangle structure.

Explanation:

• The function create_rectangle dynamically allocates memory for the Rectangle structure and initializes its fields, mimicking a constructor.
• The function destroy_rectangle frees the memory allocated, acting as a destructor.

Conclusion

In C, there is no native concept of constructors and destructors as found in C++, since C is a procedural language without built-in support for object-oriented features. However, similar functionality can be achieved by writing custom functions for initialization and cleanup, particularly for managing dynamically allocated memory. While these functions perform similar tasks, they must be manually called in C, unlike in C++ where constructors and destructors are automatically invoked during the object's lifecycle.