9 Iterators library [iterators]

9.7 Iterator adaptors [iterators.predef]

9.7.6 Counted iterators [iterators.counted]

9.7.6.2 counted_iterator operations [counted.iter.ops]

9.7.6.2.11 counted_iterator::operator-= [counted.iter.op.-=]

constexpr counted_iterator& operator-=(difference_type n) requires RandomAccessIterator<I>;

Requires: -n <= cnt

Effects:

current -= n;
cnt += n;

Returns: *this.