< cpp‎ | algorithm
Defined in header <algorithm>
template< class ForwardIt >
bool is_sorted( ForwardIt first, ForwardIt last );
(1) (since C++11)
template< class ForwardIt, class Compare >
bool is_sorted( ForwardIt first, ForwardIt last, Compare comp );
(2) (since C++11)

Checks if the elements in range [first, last) are sorted in ascending order. The first version of the function uses operator< to compare the elements, the second uses the given comparison function comp.


[edit] Parameters

first, last - the range of elements to examine
comp - comparison function object (i.e. an object that satisfies the requirements of Compare) which returns ​true if the first argument is less than (i.e. is ordered before) the second.

The signature of the comparison function should be equivalent to the following:

 bool cmp(const Type1 &a, const Type2 &b);

The signature does not need to have const &, but the function object must not modify the objects passed to it.
The types Type1 and Type2 must be such that an object of type ForwardIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
ForwardIt must meet the requirements of ForwardIterator.

[edit] Return value

true if the elements in the range are sorted in ascending order

[edit] Complexity

linear in the distance between first and last

[edit] Possible implementation

First version
template<class ForwardIt>
bool is_sorted(ForwardIt first, ForwardIt last)
    return std::is_sorted_until(first, last) == last;
Second version
template<class ForwardIt, class Compare>
bool is_sorted(ForwardIt first, ForwardIt last, Compare comp)
    return std::is_sorted_until(first, last, comp) == last;

[edit] Example

#include <iostream>
#include <algorithm>
int main() 
    const int N = 5;
    int digits[N] = {3, 1, 4, 1, 5};
    for (auto i : digits) std::cout << i << ' ';
    std::cout << ": is_sorted: " << std::is_sorted(digits, digits+N) << '\n';
    std::sort(digits, digits+N);
    for (auto i : digits) std::cout << i << ' ';
    std::cout << ": is_sorted: " << std::is_sorted(digits, digits+N) << '\n';


3 1 4 1 5 : is_sorted: 0
1 1 3 4 5 : is_sorted: 1

[edit] See also

finds the largest sorted subrange
(function template)
parallelized version of std::is_sorted
(function template)