• A derived class provides its own implementation of a method already defined in its base class, using the same function signature (name, parameters, return type)
• Distinct from overloading: overriding happens across base/derived classes with an identical signature; overloading happens within the same class with different signatures
• To get true runtime dispatch (the derived version being called even through a base-class pointer), the base method must be declared virtual — see the Polymorphism page

class Animal
{
public:
    void speak() { cout << "Some sound\n"; }
};

class Dog : public Animal
{
public:
    void speak() { cout << "Bark!\n"; }   // overrides Animal::speak()
};

Dog d;
d.speak();   // "Bark!" -- Dog's version is used

Overriding vs Overloading — the distinction examiners test most

class Printer
{
public:
    void print(int x) { cout << "int: " << x; }      // OVERLOADING --
    void print(string s) { cout << "string: " << s; } // -- same class, different signatures
};

class Animal
{
public:
    void speak() { cout << "Some sound\n"; }
};
class Dog : public Animal
{
public:
    void speak() { cout << "Bark!\n"; }   // OVERRIDING -- same signature, different class
};

Overriding WITHOUT virtual — the trap

class Animal { public: void speak() { cout << "Some sound\n"; } };
class Dog : public Animal { public: void speak() { cout << "Bark!\n"; } };

Animal* a = new Dog();
a->speak();   // prints "Some sound" -- NOT "Bark!" -- because speak() isn't virtual, static binding applies

Without virtual, the compiler decides which speak() to call based on the pointer's declared type (Animal*), not the actual object type (Dog). This is called static binding, and it's the #1 reason overriding "doesn't work" for students — see the Virtual Function page for the fix.

Important MCQs

1. Overriding requires the derived class method to have:
   • a) A different name b) The exact same signature (name, parameters, return type) as the base method c) No parameters d) A different return type only
2. Without the virtual keyword on the base method, calling it through a base-class pointer to a derived object uses:
   • a) Dynamic binding b) Static binding — the pointer's declared type decides, not the actual object type c) No binding at all d) Runtime polymorphism
3. Overloading differs from overriding mainly because overloading:
   • a) Requires inheritance b) Happens within the same class/scope with different signatures c) Is resolved at runtime d) Requires virtual functions

Self-Test Questions

1. What's the key structural difference between overloading and overriding?
2. In the trap example above, why does a->speak() print "Some sound" instead of "Bark!"?
3. What single keyword fixes the trap example, and where does it need to be added?

📌 Sample & Repeated FPSC Questions (2016–2026)

2026, Paper I, Q4(c) (8 marks) — Demonstrate method overriding using a base class Account and a derived class Current Account. Make balance a protected data member.