Pure virtual functions in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a pure virtual function in C++?

A pure virtual function is a function declared in a base class that has no implementation and is set to 0. It forces derived classes to provide their own implementation.

beginner

How do you declare a pure virtual function in C++?

You declare a pure virtual function by adding = 0 at the end of the function declaration inside a class, for example: virtual void func() = 0;

beginner

What happens if a class has at least one pure virtual function?

The class becomes abstract, meaning you cannot create objects of that class directly. You must derive a subclass and implement the pure virtual functions.

intermediate

Why use pure virtual functions in a base class?

They define an interface that derived classes must follow, ensuring certain functions are implemented in subclasses, which helps design flexible and extendable programs.

advanced

Can a pure virtual function have a body (implementation) in C++?

Yes, a pure virtual function can have a body, but it still makes the class abstract. Derived classes can call the base class implementation if needed.

How do you mark a function as pure virtual in C++?

A By adding = 0 after the function declaration

B By using the keyword pure

C By declaring the function static

D By defining the function inside the class

A pure virtual function is declared by adding = 0 after its declaration inside the class.

What is true about a class with at least one pure virtual function?

A It cannot have derived classes

B It can be instantiated directly

C It must have no other functions

D It is called an abstract class

A class with at least one pure virtual function is abstract and cannot be instantiated directly.

Can a pure virtual function have an implementation in C++?

A No, it cannot have any implementation

B Yes, but the class remains abstract

C Yes, and the class becomes concrete

D Only if it is static

A pure virtual function can have a body, but the class remains abstract.

Why would you use a pure virtual function?

A To make the function private

B To prevent inheritance

C To force derived classes to implement the function

D To allow multiple definitions

Pure virtual functions force derived classes to provide their own implementation.

What keyword is used to declare a pure virtual function?

A = 0

B override

C abstract

D virtual

The = 0 syntax marks a function as pure virtual.

Explain what a pure virtual function is and how it affects a class in C++.

Think about how pure virtual functions create a blueprint for subclasses.

Describe why and when you would use pure virtual functions in your C++ programs.

Consider how pure virtual functions help organize code and design.