Runtime polymorphism in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is runtime polymorphism in C++?

Runtime polymorphism means that the program decides which function to call during execution, not while compiling. It allows a base class pointer to call derived class functions using virtual functions.

beginner

How do you enable runtime polymorphism in C++?

By declaring a function as virtual in the base class. This tells the compiler to use dynamic dispatch to call the correct function at runtime.

intermediate

What happens if a base class function is not virtual but overridden in a derived class?

The base class pointer will call the base class version of the function, not the derived class version. This is because without <code>virtual</code>, the function call is resolved at compile time.

advanced

Explain the role of the vtable in runtime polymorphism.

The vtable is a hidden table created by the compiler that stores pointers to virtual functions. Each class with virtual functions has a vtable. At runtime, the program uses the vtable to call the correct function version.

intermediate

What is a pure virtual function and how does it relate to runtime polymorphism?

A pure virtual function is declared by assigning 0 in the base class (e.g., <code>virtual void f() = 0;</code>). It makes the class abstract and forces derived classes to implement the function, enabling polymorphism.

Which keyword enables runtime polymorphism in C++?

A virtual

B static

C const

D inline

The virtual keyword tells the compiler to use dynamic dispatch for function calls, enabling runtime polymorphism.

What will happen if a base class pointer calls a non-virtual function overridden in a derived class?

A Compilation error

B Derived class function is called

C Base class function is called

D Program crashes

Without virtual, the function call is resolved at compile time, so the base class function is called.

What is the purpose of a vtable?

A Store data members

B Store pointers to virtual functions

C Store global variables

D Store function parameters

The vtable stores pointers to virtual functions to enable dynamic dispatch at runtime.

What does a pure virtual function do?

A Provides a default implementation

B Disables polymorphism

C Prevents inheritance

D Makes the class abstract

A pure virtual function makes the class abstract and forces derived classes to implement the function.

Which of these is true about runtime polymorphism?

A It requires virtual functions

B Function calls are decided at compile time

C It only works with static functions

D It disables inheritance

Runtime polymorphism requires virtual functions to decide which function to call during program execution.

Describe how runtime polymorphism works in C++ and why virtual functions are important.

Think about how the program decides which function to call when using a base class pointer.

Explain the difference between compile-time and runtime polymorphism with examples.

Consider when the program decides which function to call: before running or while running.