[Bug libstdc++/64814] std::copy_n advances InputIterator one *less* time than necessary.

[alex-j-a at hotmail dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64814

--- Comment #2 from Anquietas <alex-j-a at hotmail dot co.uk> ---
(In reply to Jonathan Wakely from comment #1)
> The problem is that increments to the input iterator happen inside
> the copy_n call, to a copy of the iterator not to readIter itself.
The copy_n implementation I provided produces the same behaviour as the for
loop, even with copying the iterator.