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What is a constructor in C++ Programming Language

In C++, a constructor is a special member function of a class that is automatically called when an object of that class is created. Its purpose is to initialize the object’s data members and perform any necessary setup operations.

Here are some key points about constructors in C++:

  1. Name: Constructors have the same name as the class they belong to and do not have a return type, not even void.
  2. Initialization: Constructors initialize the object’s data members to appropriate values, ensuring that the object is in a valid state when created.
  3. Default Constructor: If a class does not define any constructors, C++ automatically generates a default constructor, which is a constructor with no parameters. It initializes the data members with their default values (e.g., 0 for numbers, nullptr for pointers, etc.).
  4. Parameterized Constructor: You can define constructors with parameters to initialize the data members with specific values provided during object creation.
  5. Multiple Constructors: A class can have multiple constructors with different parameter lists. This allows you to create objects with various initialization options.
  6. Initialization List: Inside a constructor, you can use an initialization list to initialize data members directly, rather than assigning values in the constructor’s body. Initialization lists are more efficient and can be used to initialize const members and reference members.
  7. Copy Constructor: The copy constructor is a special constructor that is used to create a new object as a copy of an existing object of the same class. It is invoked when a new object is initialized with an existing object.
  8. Destructor: While not a constructor, it’s worth mentioning that C++ also has destructors, which are special member functions called when an object is destroyed. Destructors clean up resources used by the object, such as freeing memory or releasing file handles.

Constructors play a crucial role in C++ classes, allowing you to initialize objects and perform any necessary setup. They ensure that objects are properly initialized and ready for use as soon as they are created.


Characteristics of a Constructor

  • Have the same names a class
  • Do not have any return type not even void
  • constructor cannot be virtual
  • Like any other function they have parameters
  • They should be declared in public section
  • They cannot be inherited
  • They are called automatically while new object is created

Types of constructors

  • Do nothing constructor
  • Default /unparameterized-is a type of constructor that does not take any arguments it has no parameters but programmer can write some intializations
  • Parameterized

Copy constructor

Write Simple C++ Program to show Constructor

Certainly! Here’s a simple C++ program that demonstrates the usage of a constructor:

#include <iostream>

// Class definition
class MyClass {
    int myNumber;

    // Constructor
    MyClass(int number) {
        myNumber = number;
        std::cout << "Constructor called. Number: " << myNumber << std::endl;

    // Member function
    void printNumber() {
        std::cout << "Number: " << myNumber << std::endl;

int main() {
    // Creating an object of MyClass
    MyClass obj(42);

    // Calling a member function

    return 0;

In this program, we have a class named MyClass that has a constructor and a member function. The constructor takes an integer parameter and initializes the myNumber data member. It also prints a message to indicate that the constructor is called.

In the main() function, we create an object obj of MyClass and pass the value 42 to the constructor. The constructor is automatically called during object creation. Afterward, we call the printNumber() member function of the object, which simply prints the value of myNumber.

When you run the program, you should see the following output:

Constructor called. Number: 42
Number: 42

This demonstrates how the constructor is invoked during object creation and initializes the object’s data member.

Difference Between Class and Object In C++ Programming

In C++ programming, a class and an object are related concepts but have different meanings and roles:

  1. Class:
    • A class is a blueprint or a template that defines the structure and behavior of objects.
    • It is an abstract representation of a real-world entity or a concept, defining the properties (data members) and actions (member functions) associated with it.
    • A class encapsulates data and functions into a single unit, allowing you to create multiple objects based on the class template.
    • It serves as a template for creating objects with similar characteristics and behaviors.
    • Classes are defined using the class keyword in C++.
  2. Object:
    • An object is an instance of a class.
    • It is a specific entity created based on the structure defined by a class.
    • Objects have their own unique identity and can hold data (state) and perform operations (behavior) defined in the class.
    • Objects can interact with other objects and manipulate their own data.
    • Objects are created from a class using the new keyword or by simply declaring them as variables of the class type.
    • Objects have a specific memory representation, where their data members occupy memory based on the class’s definition.

In simpler terms, a class is like a blueprint or a template that defines the structure and behavior of objects, while an object is a specific instance or realization of that blueprint. A class defines what an object should contain and what it can do, while an object is an actual entity that holds data and performs operations as defined by the class.

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