What is a constructor in C++?

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A constructor in C++ is a special type of function that is automatically called when an object of a class is created. The main purpose of a constructor is to initialize the member variables of the class. Constructors have the same name as the class and do not have a return type.

Key Features of Constructors:

Automatic Invocation: Constructors are called automatically when an object is created.
No Return Type: Constructors do not have a return type, not even void.
Same Name as Class: The name of the constructor must be the same as the class name.

Types of Constructors in C++:

1. Default Constructor

A default constructor is a constructor that either has no parameters or has parameters with default values. If no constructor is provided by the user, C++ provides an implicit default constructor.

class MyClass {
public:
    MyClass() {  // Default constructor
        std::cout << "Object created!" << std::endl;
    }
};

2. Parameterized Constructor

A constructor that takes arguments to initialize objects with specific values is known as a parameterized constructor.

class MyClass {
private:
    int x;
public:
    MyClass(int a) {  // Parameterized constructor
        x = a;
    }
};

3. Copy Constructor

A copy constructor is used to initialize a new object as a copy of an existing object. The default copy constructor performs a shallow copy, but you can define your own to perform deep copying.

class MyClass {
private:
    int x;
public:
    MyClass(const MyClass &obj) {  // Copy constructor
        x = obj.x;
    }
};

Use Cases of Constructors:

Initialization: Constructors are primarily used to initialize object data when they are created.
Resource Allocation: In more complex applications, constructors may allocate resources such as dynamic memory.

Example:

#include <iostream>
using namespace std;

class Car {
public:
    string brand;
    int year;

    // Parameterized constructor
    Car(string b, int y) {
        brand = b;
        year = y;
    }

    // Display function
    void display() {
        cout << "Brand: " << brand << ", Year: " << year << endl;
    }
};

int main() {
    Car car1("Toyota", 2020);
    car1.display();  // Outputs: Brand: Toyota, Year: 2020

    return 0;
}