Re: Can iterator be checked to be at end of vector?

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Thu, 30 Jul 2009 11:10:51 -0400

Message-ID:

<a9ydnd-IV5JhKuzXnZ2dnUVZ_gydnZ2d@giganews.com>

Michael Doubez wrote:

On 30 juil, 14:59, Pete Becker <p...@versatilecoding.com> wrote:

cornelis van der bent wrote:

On 29 jul, 17:44, Victor Bazarov <v.Abaza...@comAcast.net> wrote:

cornelis van der bent wrote:

Is there a way to ask a vector<Class*>::iterator if it's at the end of
its vector?

No. An iterator does not know who "its" vector is.

(Background: I know I could compare with myVector.end(), but don't
want to do this. I want to pass two iterators to a method and do some
side by side comparison until one of the iterators is at the end. I
don't want to pass the vectors as well.)

You need to pass the *ends* [as well], not the vectors.

Thanks!
Is there a meaningful (not technical) reason why an iterator does not
have this information? You write my "its" between ""; is there
perhaps any clue in why you do this, in how you conceptually see an
iterator and "its" container?

Iterators aren't based on containers. That's looking at it the wrong way
around. Sequences are the fundamental notion in STL. A pair of iterators
specifies a range of objects within a sequence. Containers are one way
to create sequences, but not the only way.

What is misleading is that:
- the Iterator pattern of the GoF book is described as a way "to
access the elements of an aggregate object sequentially"

Shrug. That doesn't describe STL iterators.

- the Iterator concept of the STL (SGI) "Iterators are a
generalization of pointers: they are objects that point to other
objects."

In OOP case, it can make sense to keep a reference to the container in
order to stop the iteration ( prev()/next() and done() methods).

C++ is a multi-paradigm language. Applying general OOP principles
(whether valid or not) to try to understand the design of the C++
standard library will often be misleading. In particular, as I said,
iterators are not defined in terms of containers, but in terms of the
abstraction of a sequence.

So "misleading" here seems to mean that applying inapplicable analytic
approaches can lead to incorrect results.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of
"The Standard C++ Library Extensions: a Tutorial and Reference"
(www.petebecker.com/tr1book)