Method overriding in C++ - Step-by-Step Execution

Concept Flow - Method overriding

Define Base Class with Method

↓

Define Derived Class with Same Method

↓

Create Derived Object

↓

Call Method on Derived Object

↓

Derived Method Runs, Overrides Base

↓

End

Method overriding happens when a derived class has a method with the same name as its base class, so calling it on a derived object runs the new method instead of the base one.

Execution Sample

C++

#include <iostream>

class Base {
public:
  void greet() { std::cout << "Hello from Base\n"; }
};

class Derived : public Base {
public:
  void greet() { std::cout << "Hello from Derived\n"; }
};

int main() {
  Derived d;
  d.greet();
}

This code defines a base class and a derived class that both have a greet method. Calling greet on the derived object runs the derived version.

Execution Table

Step	Action	Class	Method Called	Output
1	Create object d	Derived	None
2	Call d.greet()	Derived	greet()	Hello from Derived
3	End of main	None	None

💡 Program ends after calling the overridden greet method on Derived object.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
d	undefined	Derived object created	No change	Derived object exists

Key Moments - 2 Insights

Why does calling d.greet() run Derived's greet, not Base's?

Because d is an object of Derived, and Derived has its own greet method that overrides Base's. See execution_table step 2 where Derived's greet runs.

What if Derived did not have greet method?

Then calling d.greet() would run Base's greet method, since Derived inherits it. This is not shown in the table but is the default behavior.

Visual Quiz - 3 Questions

Look at the execution table, what is printed when d.greet() is called?

A No output

B Hello from Derived

C Hello from Base

D Compilation error

💡 Hint

Check execution_table row 2 under Output column.

At which step is the Derived object created?

A Step 1

B Step 2

C Step 3

D Before Step 1

💡 Hint

Look at execution_table row 1 Action column.

If Derived did not override greet(), what would happen when d.greet() is called?

A No method runs

B Derived's greet runs

C Base's greet runs

D Program crashes

💡 Hint

Refer to key_moments second question about default behavior.

Concept Snapshot

Method overriding means a derived class has a method with the same name as its base class.
When calling that method on a derived object, the derived version runs.
This allows customizing behavior in subclasses.
In C++, overriding requires same method signature.
Without overriding, base class method runs.

Full Transcript

Method overriding in C++ happens when a derived class defines a method with the same name as one in its base class. When you create an object of the derived class and call that method, the derived class's version runs instead of the base class's. In the example, the base class has a greet method that prints "Hello from Base". The derived class also has a greet method that prints "Hello from Derived". When we create a Derived object d and call d.greet(), it prints "Hello from Derived". This shows the derived method overrides the base method. If the derived class did not have greet, calling d.greet() would run the base class's greet method. This is how C++ supports customizing behavior in subclasses by overriding methods.