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# std::rotate_copy

From cppreference.com
< cpp‎ | algorithm

Defined in header `<algorithm>` |  |
template< class ForwardIt, class OutputIt > OutputIt rotate_copy( ForwardIt first, ForwardIt n_first, ForwardIt last, OutputIt d_first ); | (1) |
template< class ExecutionPolicy, class ForwardIt1, class ForwardIt2 > ForwardIt2 rotate_copy( ExecutionPolicy&& policy, ForwardIt1 first, ForwardIt1 n_first, ForwardIt1 last, ForwardIt2 d_first ); | (2) | (since C++17)

1) Copies the elements from the range `[first, last)`, to another range beginning at `d_first` in such a way, that the element `n_first` becomes the first element of the new range and `n_first - 1` becomes the last element.
2) Same as (1), but executed according to `policy`. This overload only participates in overload resolution if std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true

### [edit] Parameters

first, last | - | the range of elements to copy
n_first | - | an iterator to an element in `[first, last)` that should appear at the beginning of the new range
d_first | - | beginning of the destination range
policy | - | the execution policy to use. See execution policy for details.
Type requirements
- `ForwardIt, ForwardIt1, ForwardIt2` must meet the requirements of `ForwardIterator`.
- `OutputIt` must meet the requirements of `OutputIterator`.

### [edit] Return value

Output iterator to the element past the last element copied.

### [edit] 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 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

    template<class ForwardIt, class OutputIt>
    OutputIt rotate_copy(ForwardIt first, ForwardIt n_first,
                               ForwardIt last, OutputIt d_first)
    {
        d_first = std::copy(n_first, last, d_first);
        return std::copy(first, n_first, d_first);
    }

### [edit] Example

Run this code

    #include <algorithm>
    #include <vector>
    #include <iostream>

    int main()
    {
        std::vector<int> src = {1, 2, 3, 4, 5};
        auto pivot = std::find(src.begin(), src.end(), 3);
        std::vector<int> dest(src.size());

        std::rotate_copy(src.begin(), pivot, src.end(), dest.begin());

        for (const auto &i : dest) {
            std::cout << i << ' ';
        }
        std::cout << '\n';
    }

Output:

    3 4 5 1 2

### [edit] Complexity

linear in the distance between `first` and `last`

### [edit] See also

rotate | rotates the order of elements in a range (function template) [edit]

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