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std::rotate_copy

Defined in header `<algorithm>`
	(1)
template< class ForwardIt, class OutputIt > OutputIt rotate_copy( ForwardIt first, ForwardIt n_first, ForwardIt last, OutputIt d_first );		(until C++20)
template< class ForwardIt, class OutputIt > constexpr OutputIt rotate_copy( ForwardIt first, ForwardIt n_first, ForwardIt last, OutputIt d_first );		(since C++20)
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.

The behavior is undefined if either [first, n_first) or [n_first, last) is not a valid range, or the source and destination ranges overlap.

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`.	(until C++20)
`std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>` is `true`.	(since C++20)

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 LegacyForwardIterator.
-`OutputIt` must meet the requirements of LegacyOutputIterator.

Return value

Output iterator to the element past the last element copied.

Complexity

linear in the distance between first and last.

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

See also the implementations in libstdc++, libc++, and MSVC STL.

template<class ForwardIt, class OutputIt>
constexpr // since C++20
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);
}

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> src {1, 2, 3, 4, 5};
    std::vector<int> dest(src.size());
    auto pivot = std::find(src.begin(), src.end(), 3);
 
    std::rotate_copy(src.begin(), pivot, src.end(), dest.begin());
    for (int i : dest)
        std::cout << i << ' ';
    std::cout << '\n';
 
    // copy the rotation result directly to the std::cout
    pivot = std::find(dest.begin(), dest.end(), 1);
    std::rotate_copy(dest.begin(), pivot, dest.end(),
                     std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
}

Output:

3 4 5 1 2
1 2 3 4 5

rotate	rotates the order of elements in a range (function template)
ranges::rotate_copy (C++20)	copies and rotate a range of elements (niebloid)