Compare two list iterators which point to different lists

Question

As pointed out in other questions here on SO, equality comparison between two iterators from different containers is UB.

In my case I have two list iterators, which might not be from the same container:

std::list< int >::iterator a, b;

Suppose that I know for sure that none of them is an end iterator, my question is if I am allowed to do:

&(*a) == &(*b)

Why not? if they are not end-iterators, dereferencing them yields an `lvalue`, whose address you surely can get. — lisyarus, Mar 21 '14 at 18:53

jrok · Accepted Answer · 2014-03-21T19:01:54.383

2

Sure, you can do that, as you're not comapring the iterators but the addresses of their referands.

Assuming iterators are from different containers, this comparison cannot ever be true in a well-formed program, though.

edited Mar 21 '14 at 19:01

answered Mar 21 '14 at 18:53

jrok

Why not? If the two iterator belong to the same container and points to the same element how can it be false? – sbabbi Mar 21 '14 at 18:55
I though you said the iterators are not from the same container? – jrok Mar 21 '14 at 18:56
Sorry, what I really meant was *might* be from the same container, I'll fix that. – sbabbi Mar 21 '14 at 19:00
In that case, yes, it's fine and it can be true. – jrok Mar 21 '14 at 19:02

1 Answers1