cppreference.com > C++ Algorithms > is_sorted is_sorted Syntax:
      #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. Related topics: binary_search partial_sort partial_sort_copy sort stable_sort