Re: [boost] [iterator] UB when implicitly using default constructed counting_iterator<unsigned>

Subject: Re: [boost] [iterator] UB when implicitly using default constructed counting_iterator<unsigned>
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2012-12-07 12:03:07

> On 11/30/2012 4:14 AM, Peter Sommerlad wrote:
> > Hi Jeffrey, hi all,
> ...
> > std::copy_n(boost::make_filter_iterator(is_prime{},boost::make_counting_iterator(1u)
> > // if the following line is omitted we have undefined behavior, because of uninitialized unsigned value
> > // ,boost::make_counting_iterator(std::numeric_limits<unsigned>::max()) // must be different from above value
> > ),40,std::ostream_iterator<unsigned>{std::cout,", "});
>
> IMHO, the counting_iterator concern is misplaced. The true culprit is
> make_filter_iterator's defaulted end iterator argument. Of all the
> iterator types in the standard library, only istream[buf]_iterator(as
> pointed out by Steven Watanabe) is valid in this context.
>
> My preferences is to leave counting_iterator as is, and remove the
> default from make_filter_iterator. 

+1

Regards,
Nate