Question

I’ve some little question about STL iterator implementation.

• why iterator defining as a struct but not as class?
• what is the main reason?

Answer 1

This is defined in the standard, 24.2 which describes the <iterator> header, which are struct. This choice was probably made because iterators provide access to container elements and making them class would be useless, the only difference being that class has private access level by default, whereas struct has public access level.

So there were 2 choices if declaring iterators class instead of struct:

• make all members public, which is useless since the same effect can be obtained by making it directly struct.
• make getters, which would provide unnecessary overhead and abstraction.