regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
const regex_type& re,
regex_constants::match_flag_type m = regex_constants::match_default);
Effects: Initializes begin and end to
a and b, respectively, sets
pregex to addressof(re), sets flags to
m, then calls regex_search(begin, end, match, *pregex, flags).
If this
call returns false the constructor sets *this to the end-of-sequence
iterator.