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