Upcasting

The assignment of child class object to a parent class reference in C++ inheritance is known as up-casting.

Syntax
1. parentClass* objectName = new childClass();
2. parentClass* objectName = &childClassObject;

CODE

EG 1 . Creating a child class, parent class and using Upcasting

#include <iostream>
using namespace std;

class Rectangle2D {
  public:
    double length, width;
    double Area() {
        return length * width;
    }
    double Perimeter() {
        return 2 * (length+width);
    }
};

class Rectangle3D : public Rectangle2D {
  public:
    double height;
    double Volume() {
        return length * width * height;
    }
};

int main() {
    //UPCASTING
    Rectangle2D* r1 = new Rectangle3D();
}

CODE EXPLANATION
In the above code, we created a new child class(Rectangle3D) object and assigned that to Parent class(Rectangle2D) reference called r1. This assignment of child class object to a parent class reference in C++ inheritance is known as up-casting. The above upcasting can be written in an another way where we can create instance of child class and assign its memory address to parent class pointer instance.
Rectangle3D r1;
Rectangle2D* r2 = &r1;


What is the use of Upcasting?
We going to study some important topics is OOPs called Virtual, Pure Virtual method(following Articles) where Upcasting plays a major role.