Friends and Nested Classes in C++

In the previous lesson, Converting C++ Types, we went through namespaces. In today's C++ tutorial, we're going to talk about friends and show how we can nest classes.

Friends

Every class can define its friends. Notice the explicit definition, i.e. "I choose my friends". This is very important because friends are a powerful technique that violates encapsulation and doesn't meet the ideas of the pure OOP. Once defined, friends have the ability to access private members of the class. If you think about it, it's absolutely against the rules that we've been talking about. Not only that a friend can access public and protected members to other class, it can even access private members, which is totally at odds with what we are trying to do - encapsulate the logic. On the other hand, if we really need to get to the fields, it's a better solution than to mark the field as public.

Usage

Friends are not used much and when they are, these are very close objects in the sense of close cooperation - for example, let's consider a Map class and a MapIcon class. When we move the map, we need to move the icon coordinates as well. One solution is to make the map a friend of the icon which makes the map able to rewrite the coordinates of the icons. Another case is


 

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We'll show the concept of friends in C++ and then how to create nested classes.

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Article has been written for you by David Capka
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The author is a programmer, who likes web technologies and being the lead/chief article writer at ICT.social. He shares his knowledge with the community and is always looking to improve. He believes that anyone can do what they set their mind to.
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