How does friend operator function differ from member operator function?

In C++, we know that private members cannot be accessed from the outside class.

That is a non-member function cannot have an access to the private data of a class.

However there could be a situation where we would like two classes to share a particular function.

For example consider a case where two classes, manager and scientist have been defined.

We would like to use a function income_ tax () to operate on the objects of both these classes.

In such situation, C++ allows the common function to be made friendly with both the classes. Such a function needs not be member of any these classes.

To make outside function friendly to a class, we have to simply declare this function as a friend of a class as shown below:

Class ABC

{

……

…..

Public:

……..

……..

Friend void xyz (void); //declaration

};

When the function is logically coupled with the class (like your maze connectedness example)

When the function needs to access private or protected members, it's better to make it a member than a friend. when it's a generic function that can be templatized to naturally work on other classes (look at the header for good example) .