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# std::is_sorted

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class ForwardIt > bool is_sorted( ForwardIt first, ForwardIt last ); | (1) | (since C++11)
template< class ExecutionPolicy, class ForwardIt > bool is_sorted( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last ); | (2) | (since C++17)
template< class ForwardIt, class Compare > bool is_sorted( ForwardIt first, ForwardIt last, Compare comp ); | (3) | (since C++11)
template< class ExecutionPolicy, class ForwardIt, class Compare > bool is_sorted( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, Compare comp ); | (4) | (since C++17)

Checks if the elements in range `[first, last)` are sorted in non-descending order.

1) Elements are compared using `operator<`.
3) Elements are compared using the given binary comparison function `comp`.
2,4) Same as (1,3), but executed according to `policy`. These overloads do not participate in overload resolution unless std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

### [edit] Parameters

first, last | - | the range of elements to examine
policy | - | the execution policy to use. See execution policy for details.
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] Exceptions

The overloads with a template parameter named `ExecutionPolicy` report errors as follows:

- If execution of a function invoked as part of the algorithm throws an exception and `ExecutionPolicy` is one of the three standard policies, std::terminate is called. For any other `ExecutionPolicy`, the behavior is implementation-defined.
- If the algorithm fails to allocate memory, std::bad_alloc is thrown.

### [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

Run this code

    #include <iostream>
    #include <algorithm>
    #include <iterator>
    int main()
    {
        int digits[] = {3, 1, 4, 1, 5};

        for (auto i : digits) std::cout << i << ' ';
        std::cout << ": is_sorted: " << std::boolalpha
                  << std::is_sorted(std::begin(digits), std::end(digits)) << '\n';

        std::sort(std::begin(digits), std::end(digits));

        for (auto i : digits) std::cout << i << ' ';
        std::cout << ": is_sorted: "
                  << std::is_sorted(std::begin(digits), std::end(digits)) << '\n';
    }

Output:

    3 1 4 1 5 : is_sorted: false
    1 1 3 4 5 : is_sorted: true

### [edit] See also

is_sorted_until (C++11) | finds the largest sorted subrange (function template) [edit]

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