A member function can always access the data in __________ , (in C++).

Concept: A member function is declared as a member of its CLASS, and an ordinary (non-static) member function is invoked ON a specific object; through the implicit this pointer it can access the data members that object holds for its class — the private ones as well as the public ones. Encapsulation hides those members from code OUTSIDE the class, but a member function, being inside the class, can always reach the object it is working on. (A static member function is the exception — it has no this and no bound object — so, by the standard textbook convention, the item means an ordinary member function.)

Application: The blank names where a member function can always access the data. That place is the object it operates on — “the object of which it is a member,” in the item’s wording — because the object holds the private and public data members declared in its class. Consider a class with a private field and a public field:

class Account {
    double balance;   // private
public:
    int id;           // public
    void show() {
        cout << balance << id;   // reads BOTH members of THIS object
    }
};

When show() runs on an Account object it can read that object’s private balance and its public id alike, because a member function can access the data the object holds for its own class.

Why not the others:

• the class of which it is member — a member function does belong to its class, but the phrase asks about the DATA: instance data lives in the object at run time, while the class itself only defines the layout, so it is not where the data is accessed.

• the public part of its class — too narrow: from inside the class the member function also reaches the private and protected data of its object, not only the public members.

• the private part of its class — too narrow in the other direction: it leaves out the public (and protected) members the same function can equally read.

Answer: the object of which it is a member.