std::rotate_copy

 

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Defined in header <algorithm>
template< class ForwardIt, class OutputIt > OutputIt rotate_copy( ForwardIt first, ForwardIt middle,                       ForwardIt last, OutputIt d_first );	(1)	(constexpr since C++20)
template< class ExecutionPolicy,           class ForwardIt1, class ForwardIt2 > ForwardIt2 rotate_copy( ExecutionPolicy&& policy,                         ForwardIt1 first, ForwardIt1 middle,                         ForwardIt1 last, ForwardIt2 d_first );	(2)	(since C++17)

Copies the left rotation of [first, last) to d_first.

1) Copies the elements from the range [first, last), such that in the destination range beginning at d_first, the elements in [first, middle) are placed after the elements in [middle, last) while the orders of the elements in both ranges are preserved.

2) Same as (1), but executed according to policy.

This overload participates in overload resolution only if all following conditions are satisfied:

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)

If any of the following conditions is satisfied, the behavior is undefined:

• [first, middle) or [middle, last) is not a valid range.
• The source and destination ranges overlap.

Parameters

first, last	-	the pair of iterators defining the source range of elements to copy
middle	-	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
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

Exactly std::distance(first, last) assignments.

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 middle, ForwardIt last, OutputIt d_first) { d_first = std::copy(middle, last, d_first); return std::copy(first, middle, d_first); }

Example

Run this code

#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

See also

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