#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.