Incrementing past end iterator

[Paul]

Suppose C is a random access container. I seem to remember reading that adding positive integers to iterators works fine so long as we don't travel more than 1 unit past the off-the-end iterator.

For example, if vec is a vector, auto z = vec.end() + 1; is fine (of course we can't dereference z, though).

However, auto z = vec.end() + 2; has undefined behaviour. Is this correct? I can't see a reference anywhere.

Thanks.

Paul

[Alf P. Steinbach]

The end() iterator is already one past the end of the sequence. It's an
"after" the sequence iterator. I think that's what you probably read.


Cheers & hth.,

- Alf

[Öö Tiib]

On Monday, 11 January 2016 16:38:37 UTC+2, Paul wrote:
> Suppose C is a random access container. I seem to remember reading that
> adding positive integers to iterators works fine so long as we don't travel
> more than 1 unit past the off-the-end iterator.
>

It was incorrect or you misread it or you misremember it. Traveling one unit
further than the "one past end" iterator is undefined behavior.

> For example, if vec is a vector, auto z = vec.end() + 1; is fine (of course
> we can't dereference z, though).

No. Dereferencing or incrementing past 'vec.end()' is undefined behavior.

>
> However, auto z = vec.end() + 2; has undefined behaviour. Is this correct?
> I can't see a reference anywhere.

That has also undefined behavior and so has 'vec.end() + 3'. 'vec.end()' *is*
one past end iterator already.