Interface-like behavior in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an interface in C++?

An interface in C++ is a class that has only pure virtual functions and no data members. It defines a contract that other classes can implement.

beginner

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

You declare a pure virtual function by assigning 0 to the function declaration, like this: virtual void func() = 0;.

beginner

Why can't you create an object of a class with pure virtual functions?

Because such a class is abstract and incomplete. It requires derived classes to provide implementations for the pure virtual functions before objects can be created.

intermediate

How does C++ achieve interface-like behavior without a dedicated interface keyword?

By using abstract classes with only pure virtual functions, C++ simulates interfaces. Classes implementing the interface inherit and override these functions.

intermediate

What is the role of a virtual destructor in an interface-like class?

A virtual destructor ensures that when deleting an object through a pointer to the interface, the derived class's destructor is called properly, avoiding resource leaks.

Which of the following declares a pure virtual function in C++?

A void foo() {}

B virtual void foo() = 0;

C virtual void foo();

D void foo() = 0;

Only 'virtual void foo() = 0;' declares a pure virtual function.

Can you instantiate an object of a class that has at least one pure virtual function?

A No, never.

B Only if the class has a constructor.

C Only if the pure virtual function has a body.

D Yes, always.

Classes with pure virtual functions are abstract and cannot be instantiated.

What keyword does C++ use to indicate a function is virtual?

A virtual

B interface

C abstract

D override

The 'virtual' keyword marks a function as virtual in C++.

Why should an interface-like class have a virtual destructor?

A To make all functions pure virtual.

B To prevent the class from being instantiated.

C To allow derived class destructors to run correctly when deleting via base pointer.

D To improve performance.

A virtual destructor ensures proper cleanup of derived objects.

Which of these best describes an interface-like class in C++?

A A class with private constructors.

B A class with no functions.

C A class with only static functions.

D A class with only pure virtual functions and no data members.

Interface-like classes have only pure virtual functions and no data members.

Explain how C++ uses abstract classes to simulate interfaces.

Think about classes with functions set to zero.

Why is it important to have a virtual destructor in an interface-like class?

Consider what happens when deleting objects via base class pointers.