# std::sort

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< cpp‎ | algorithm

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

Sorts the elements in the range `[first, last)` in ascending order. The order of equal elements is not guaranteed to be preserved.

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

### Parameters

first, last | - | the range of elements to sort
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 RandomIt can be dereferenced and then implicitly converted to both of them. ​

Type requirements
- `RandomIt` must meet the requirements of `ValueSwappable` and `RandomAccessIterator`.
- The type of dereferenced `RandomIt` must meet the requirements of `MoveAssignable` and `MoveConstructible`.
- `Compare` must meet the requirements of `Compare`.

### Return value

(none)

### Complexity

O(N·log(N)), where N = std::distance(first, last) comparisons on average. | (until C++11)
O(N·log(N)), where N = std::distance(first, last) comparisons. | (since C++11)

### 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.

### Example

Run this code

    #include <algorithm>
    #include <functional>
    #include <array>
    #include <iostream>

    int main()
    {
        std::array<int, 10> s = {5, 7, 4, 2, 8, 6, 1, 9, 0, 3};

        // sort using the default operator<
        std::sort(s.begin(), s.end());
        for (auto a : s) {
            std::cout << a << " ";
        }
        std::cout << '\n';

        // sort using a standard library compare function object
        std::sort(s.begin(), s.end(), std::greater<int>());
        for (auto a : s) {
            std::cout << a << " ";
        }
        std::cout << '\n';

        // sort using a custom function object
        struct {
            bool operator()(int a, int b)
            {
                return a < b;
            }
        } customLess;
        std::sort(s.begin(), s.end(), customLess);
        for (auto a : s) {
            std::cout << a << " ";
        }
        std::cout << '\n';

        // sort using a lambda expression
        std::sort(s.begin(), s.end(), [](int a, int b) {
            return b < a;
        });
        for (auto a : s) {
            std::cout << a << " ";
        }
        std::cout << '\n';
    }

Output:

    0 1 2 3 4 5 6 7 8 9
    9 8 7 6 5 4 3 2 1 0
    0 1 2 3 4 5 6 7 8 9
    9 8 7 6 5 4 3 2 1 0

### See also

partial_sort | sorts the first N elements of a range (function template)
stable_sort | sorts a range of elements while preserving order between equal elements (function template)

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