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

Concept Flow - Function overriding

Base class defines function

↓

Derived class defines function with same name

↓

Create derived class object

↓

Call function on derived object

↓

Derived class function runs, overrides base

↓

End

Function overriding happens when a derived class provides its own version of a function defined in its base class. When called on a derived object, the derived version runs.

Execution Sample

C++

#include <iostream>
class Base {
public:
  virtual void show() { std::cout << "Base show"; }
};
class Derived : public Base {
public:
  void show() override { std::cout << "Derived show"; }
};
int main() {
  Derived d;
  d.show();
}

This code shows a base class and a derived class both having a show() function. Calling show() on derived object runs derived version.

Execution Table

Step	Action	Function Called	Output
1	Create Derived object d	None
2	Call d.show()	Derived::show()	Derived show
3	Program ends	None

💡 No more code to run, program ends

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
d (Derived object)	None	Created	Exists	Exists

Key Moments - 2 Insights

Why does calling show() on derived object run Derived::show() and not Base::show()?

Because Derived class defines its own show() with the same name, it overrides Base's show(). See execution_table step 2 where Derived::show() runs.

What if Derived did not have show()?

Then calling d.show() would run Base::show() because Derived inherits it. Overriding only happens if Derived defines the function.

Visual Quiz - 3 Questions

Look at the execution_table, what function is called at step 2?

A Base::show()

B Derived::show()

C No function called

D Both Base::show() and Derived::show()

💡 Hint

Check the 'Function Called' column at step 2 in execution_table

At which step is the Derived object created?

A Step 2

B Step 3

C Step 1

D No object created

💡 Hint

Look at the 'Action' column in execution_table for object creation

If Derived did not override show(), what would be the output at step 2?

A Base show

B Derived show

C No output

D Compilation error

💡 Hint

Refer to key_moments explanation about overriding and inheritance

Concept Snapshot

Function overriding means a derived class has a function with the same name as in base class.
When called on derived object, derived function runs, hiding base version.
Overriding requires same function signature.
If derived does not override, base function runs.
Used for customizing behavior in derived classes.

Full Transcript

Function overriding in C++ happens when a derived class defines a function with the same name as one in its base class. When you create an object of the derived class and call that function, the derived class's version runs instead of the base class's. In the example, the base class has a show() function that prints "Base show". The derived class also has a show() function that prints "Derived show". When we create a derived object and call show(), it prints "Derived show". This is because the derived class's function overrides the base class's. If the derived class did not have its own show(), calling show() on the derived object would run the base class's version. This lets derived classes customize or replace behavior from base classes.