C++ Class Default Constructor Example

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Jul 01, 2024

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C++ Class Default Constructor Example

A default constructor in C++ is a special member function that is automatically called when an object of a class is created without any arguments. It provides a way to initialize the member variables of the object with default values.

Here is an example of a C++ class with a default constructor:

#include 

class Rectangle {
public:
  // Default constructor
  Rectangle() {
    width = 0;
    height = 0;
  }

  // Member functions
  int getArea() {
    return width * height;
  }

private:
  int width;
  int height;
};

int main() {
  // Create a Rectangle object using the default constructor
  Rectangle rect;

  // Print the area of the rectangle
  std::cout << "Area of the rectangle: " << rect.getArea() << std::endl;

  return 0;
}

Explanation:

• Class Declaration: We define a class named Rectangle with private member variables width and height.
• Default Constructor: The default constructor is defined as Rectangle(). It initializes the width and height to 0.
• Member Function: The getArea() function calculates the area of the rectangle.
• Object Creation: In the main function, we create an object of Rectangle named rect. Since we don't pass any arguments, the default constructor is called automatically.
• Output: The code prints the area of the rectangle, which is 0 because both width and height are initialized to 0 by the default constructor.

Benefits of Default Constructors:

• Initialization: Ensures that all member variables are initialized with a default value.
• Object Creation: Allows you to create objects without explicitly providing values for all member variables.
• Consistency: Provides a consistent starting point for objects of a class.

Note:

• If a class does not define any constructors, the compiler will automatically generate a default constructor for you. This constructor will not initialize the member variables, so they will have undefined values.
• You can define multiple constructors in a class, but only one can be a default constructor (the one that takes no arguments).

The default constructor is a fundamental part of C++ object-oriented programming and is essential for ensuring proper initialization of class objects.