Function overriding in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is function overriding in C++?

Function overriding occurs when a derived class provides its own version of a function that is already defined in its base class. The function in the derived class has the same name and parameters as the one in the base class.

beginner

Why do we use function overriding?

We use function overriding to change or extend the behavior of a base class function in a derived class. It allows polymorphism, so the program can decide at runtime which function to call based on the object type.

intermediate

What keyword is used in C++11 and later to explicitly indicate a function is overriding a base class function?

The keyword <code>override</code> is used after the function declaration in the derived class to indicate that the function is meant to override a base class function. This helps catch errors if the base function signature changes.

intermediate

What happens if the base class function is not declared as <code>virtual</code> but the derived class overrides it?

If the base class function is not <code>virtual</code>, then the function call is resolved at compile time (static binding). This means the base class version will be called even if the object is of the derived class type, which is usually not what we want.

beginner

Example: What will be the output of this code?<br><pre>#include &lt;iostream&gt;
class Base { public: virtual void show() { std::cout << "Base"; } }; class Derived : public Base { public: void show() override { std::cout << "Derived"; } }; int main() { Base* b = new Derived(); b->show(); delete b; return 0; }</pre>

The output will be <code>Derived</code>. Because <code>show()</code> is virtual in the base class and overridden in the derived class, the call <code>b->show()</code> uses the derived class version at runtime.

What must be true for function overriding to work correctly in C++?

A The base class function must be declared virtual.

B The derived class function must have a different name.

C The base class function must be private.

D The derived class function must be static.

For runtime polymorphism and proper overriding, the base class function should be declared virtual.

What does the override keyword do in C++?

A It makes the function static.

B It makes the function inline.

C It prevents the function from being overridden.

D It tells the compiler the function is intended to override a base class function.

The override keyword helps the compiler check that the function correctly overrides a base class virtual function.

If a base class function is not virtual, what kind of binding is used when calling it through a base class pointer?

A No binding

B Dynamic binding (runtime)

C Static binding (compile-time)

D Late binding

Without virtual, the function call is resolved at compile time (static binding), so the base class version is called.

Which of these is a correct signature for overriding a base class function void display() const;?

A void display() override;

B void display() const override;

C int display() const override;

D void display(int) const override;

The overriding function must match the base function signature exactly, including const qualifier.

What will happen if you use override keyword but the base class function does not exist?

A Compiler error

B Program runs normally

C Warning only

D Undefined behavior

Using override when no base function matches causes a compiler error, helping catch mistakes.

Explain function overriding and why it is important in C++.

Think about how derived classes change base class behavior.

Describe the difference between function overriding and function overloading.

Focus on how the functions differ in name, parameters, and class relationships.