std::ranges::reverse_copy, std::ranges::reverse_copy_result

< cpp‎ | algorithm‎ | ranges
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
Sampling operations

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Partitioning operations
Sorting operations
Binary search operations (on sorted ranges)
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutation operations
Numeric operations
Fold operations
Operations on uninitialized storage
Return types
Defined in header <algorithm>
Call signature
template< std::bidirectional_iterator I, std::sentinel_for<I> S,

          std::weakly_incrementable O >
requires std::indirectly_copyable<I, O>
constexpr reverse_copy_result<I, O>

    reverse_copy( I first, S last, O result );
(1) (since C++20)
template< ranges::bidirectional_range R, std::weakly_incrementable O >

requires std::indirectly_copyable<ranges::iterator_t<R>, O>
constexpr reverse_copy_result<ranges::borrowed_iterator_t<R>, O>

    reverse_copy( R&& r, O result );
(2) (since C++20)
Helper types
template< class I, class O >
using reverse_copy_result = ranges::in_out_result<I, O>;
(3) (since C++20)
1) Copies the elements from the source range [firstlast) to the destination range [resultresult + N), where N is ranges::distance(first, last), in such a way that the elements in the new range are in reverse order. Behaves as if by executing the assignment *(result + N - 1 - i) = *(first + i) once for each integer i in [0N). The behavior is undefined if the source and destination ranges overlap.
2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are niebloids, that is:

In practice, they may be implemented as function objects, or with special compiler extensions.


[edit] Parameters

first, last - the range of elements to copy
r - the range of elements to copy
result - the beginning of the destination range.

[edit] Return value

{last, result + N}.

[edit] Complexity

Exactly N assignments.

[edit] Notes

Implementations (e.g. MSVC STL) may enable vectorization when the both iterator types model contiguous_iterator and have the same value type, and the value type is TriviallyCopyable.

[edit] Possible implementation

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

struct reverse_copy_fn
    template<std::bidirectional_iterator I, std::sentinel_for<I> S,
             std::weakly_incrementable O>
    requires std::indirectly_copyable<I, O>
    constexpr ranges::reverse_copy_result<I, O>
        operator()(I first, S last, O result) const
        auto ret = ranges::next(first, last);
        for (; last != first; *result = *--last, ++result);
        return {std::move(ret), std::move(result)};
    template<ranges::bidirectional_range R, std::weakly_incrementable O>
    requires std::indirectly_copyable<ranges::iterator_t<R>, O>
    constexpr ranges::reverse_copy_result<ranges::borrowed_iterator_t<R>, O>
        operator()(R&& r, O result) const
        return (*this)(ranges::begin(r), ranges::end(r), std::move(result));
inline constexpr reverse_copy_fn reverse_copy {};

[edit] Example

#include <algorithm>
#include <iostream>
#include <string>
int main()
    std::string x {"12345"}, y(x.size(), ' ');
    std::cout << x << " → ";
    std::ranges::reverse_copy(x.begin(), x.end(), y.begin());
    std::cout << y << " → ";
    std::ranges::reverse_copy(y, x.begin());
    std::cout << x << '\n';


12345 → 54321 → 12345

[edit] See also

reverses the order of elements in a range
creates a copy of a range that is reversed
(function template) [edit]