Friend classes and functions

It is sometimes useful to let the functions of one class have access to the components of another class without making the components public and without the overhead of having to call member functions to get private data.

The following shows how one class (in this case Another) can let another class (in this case Base) be a ``friend'' class

class Another {
friend class Base;
int value;
...
}

For the sake of clarity it's a good idea to have the friend lines at the start of the class definition. Note that friendship is granted by the class being accessed, not claimed by the class wanting access.

A friend may be a non-member function, a member function of another class, or an entire class. Friends and derived classes differ in that derived classes might not be able to access all the members of the base class.