# std::swap_ranges

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< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
| (1) |
template< class ForwardIt1, class ForwardIt2 > ForwardIt2 swap_ranges( ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2 ); |  | (until C++20)
template< class ForwardIt1, class ForwardIt2 > constexpr ForwardIt2 swap_ranges( ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2 ); |  | (since C++20)
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt2 swap_ranges( ExecutionPolicy&& policy, ForwardIt1 first1, ForwardIt1 last1, ForwardIt2 first2 ); | (2) | (since C++17)

1) Exchanges elements between range `[first1, last1)` and another range starting at `first2`.
2) Same as (1), but executed according to `policy`. This overload does not participate in overload resolution unless std::is_execution_policy_v < std::decay_t <ExecutionPolicy>> is true

### Parameters

first1, last1 | - | the first range of elements to swap
first2 | - | beginning of the second range of elements to swap
policy | - | the execution policy to use. See execution policy for details.
Type requirements
- `ForwardIt1, ForwardIt2` must meet the requirements of LegacyForwardIterator.
- The types of dereferenced `ForwardIt1` and `ForwardIt2` must meet the requirements of Swappable

### Return value

Iterator to the element past the last element exchanged in the range beginning with `first2`.

### Exceptions

The overload with a template parameter named `ExecutionPolicy` reports errors as follows:

- If execution of a function invoked as part of the algorithm throws an exception and `ExecutionPolicy` is one of the 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.

### Possible implementation

    template<class ForwardIt1, class ForwardIt2>
    constexpr ForwardIt2 swap_ranges(ForwardIt1 first1,
                                 ForwardIt1 last1,
                                 ForwardIt2 first2)
    {
        while (first1 != last1) {
            std::iter_swap(first1++, first2++);
        }
        return first2;
    }

### Example

Demonstrates swapping of subranges from different containers

Run this code

    #include <algorithm>
    #include <list>
    #include <vector>
    #include <iostream>
    int main()
    {
        std::vector<int> v = {1, 2, 3, 4, 5};
        std::list<int> l = {-1, -2, -3, -4, -5};

        std::swap_ranges(v.begin(), v.begin()+3, l.begin());

        for(int n : v)
           std::cout << n << ' ';
        std::cout << '\n';
        for(int n : l)
           std::cout << n << ' ';
        std::cout << '\n';
    }

Output:

    -1 -2 -3 4 5
    1 2 3 -4 -5

### Complexity

linear in the distance between `first1` and `last1`

### See also

iter_swap | swaps the elements pointed to by two iterators (function template)
swap | swaps the values of two objects (function template)

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