Since only random access iterators provide + and - operators, the library provides two function templates advance and distance. These function templates use + and - for random access iterators (and are, therefore, constant time for them); for input, forward and bidirectional iterators they use ++ to provide linear time implementations.
template <class InputIterator, class Distance>
constexpr void advance(InputIterator& i, Distance n);
template <class InputIterator>
constexpr typename iterator_traits<InputIterator>::difference_type
distance(InputIterator first, InputIterator last);
Effects: If InputIterator meets the requirements of random access iterator, returns (last - first); otherwise, returns the number of increments needed to get from first to last.
Requires: If InputIterator meets the requirements of random access iterator, last shall be reachable from first or first shall be reachable from last; otherwise, last shall be reachable from first.
template <class InputIterator>
constexpr InputIterator next(InputIterator x,
typename iterator_traits<InputIterator>::difference_type n = 1);
template <class BidirectionalIterator>
constexpr BidirectionalIterator prev(BidirectionalIterator x,
typename iterator_traits<BidirectionalIterator>::difference_type n = 1);