In C++ object oriented programming, which of the following is not actually a member of a class, even though it can access its private data members?

Introduction / Context:
In C++ object oriented programming, a class encapsulates both data members and member functions. Only some functions are true members of the class, meaning they are part of the class body and are invoked using an object or the class name. Friend functions are often confusing, because they can see private and protected members, yet they are not members of the class itself. This question tests clear understanding of which functions belong to the class and which do not.

Given Data / Assumptions:

• The class can declare normal member functions, static member functions, virtual functions, and const qualified functions.
• The class can also declare non member functions as friends using the friend keyword.
• Friend functions have special access rights, but they are still ordinary functions at global or other namespace scope.
• The question asks which option is not a member of the class, even though it may have access to private data.

Concept / Approach:
Any function defined inside the class body or declared as a member is a true member function. This includes virtual functions, static functions, and const qualified member functions. A friend function is declared with the friend keyword inside the class, but it is not a member. The main effect of friend is to grant access to private and protected members, not to change the function's scope. Member functions are called using object.member() or ClassName::member(), while friend functions are called like normal free functions.

Step-by-Step Solution:
Step 1: Note that a virtual function is simply a member function marked virtual to support dynamic binding. It is still a member of the class. Step 2: A static function is a member function associated with the class rather than any specific object, but it is still declared inside the class and is part of the class interface. Step 3: A const member function is a member whose body is not allowed to modify the object state. It is still clearly a member function. Step 4: A friend function is declared with friend inside the class, but it is defined outside the class without the ClassName:: scope. It is called like a normal function and is not counted as a class member.

Verification / Alternative check:
If you look at how these functions are defined and called, members use ClassName:: and can be virtual, static, or const, while friend functions do not use ClassName:: in their definition. You can also inspect the class interface in documentation tools, where friend functions are usually shown in a separate friends section rather than in the members list. This confirms that the friend function is not a member of the class.

Why Other Options Are Wrong:
The virtual function, static function, and const function are all defined as part of the class, so they are true members. The fact that they have special behaviour does not remove them from the class membership. Only the friend function is external to the class while still having access rights.

Common Pitfalls:
Learners often think that any function declared inside the class body must be a member. They forget that friend is an access grant, not a membership declaration. Another pitfall is to assume that static or virtual status changes membership. Remember that friend functions remain non members with special access privileges.

Final Answer:
The function that is not a class member is a friend function that has been declared as a friend of the class.