C++ Constructors

C++ Constructors

A constructor in C++ is a special method that is automatically called when an object of a class is created.

It is generally used to initialize the object's attributes with default or starting values.

Rules for Constructors:

1. The constructor must have exactly the same name as the class.
2. It does not have a return type (not even void).
3. It is always declared public (usually, though advanced patterns might use private constructors).

1. Creating a Basic Constructor

#include <iostream>
using namespace std;

class MyClass {
  public:
    // This is the constructor
    MyClass() {
      cout << "Object created! Constructor called.\n";
    }
};
int main() {
  MyClass myObj; // Constructor is called automatically here!
  return 0;
}

Notice that we didn't explicitly call myObj.MyClass(). The constructor ran the exact moment MyClass myObj; was executed.

2. Constructor Parameters

Constructors can also take parameters, just like regular functions. This is incredibly useful for setting initial values for attributes right when the object is created.

#include <iostream>
#include <string>
using namespace std;

class Car {
  public:
    string brand;
    string model;
    int year;
    // Constructor with parameters
    Car(string x, string y, int z) {
      brand = x;
      model = y;
      year = z;
    }
};
int main() {
  // Create objects and pass values to the constructor
  Car carObj1("BMW", "X5", 1999);
  Car carObj2("Ford", "Mustang", 1969);
  // Print values
  cout << carObj1.brand << " " << carObj1.model << " " << carObj1.year << "\n";
  cout << carObj2.brand << " " << carObj2.model << " " << carObj2.year << "\n";
  return 0;
}

This code is much cleaner than creating an object and then setting each attribute one by one on separate lines!