#include <algorithm>
  bool is_sorted( iterator start, iterator end );
  bool is_sorted( iterator start, iterator end, StrictWeakOrdering cmp );

The is_sorted() algorithm returns true if the elements in the range [start,end) are sorted in ascending order.

By default, the < operator is used to compare elements. If the strict weak order function object cmp is given, then it is used instead.

is_sorted() runs in linear time.