NAME¶

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

Synopsis¶

Defined in header <algorithm>
Call signature
template< std::bidirectional_iterator I, std::sentinel_for<I> S,

std::weakly_incrementable O > (since
requires std::indirectly_copyable<I, O> (1) C++20)
constexpr reverse_copy_result<I, O>

reverse_copy( I first, S last, O result );
template< ranges::bidirectional_range R, std::weakly_incrementable
O >
(since
requires std::indirectly_copyable<ranges::iterator_t<R>, O> (2) C++20)
constexpr reverse_copy_result<ranges::borrowed_iterator_t<R>, O>

reverse_copy( R&& r, O result );

Helper types¶

template< class I, class O > (3) (since
using reverse_copy_result = ranges::in_out_result<I, O>; C++20)

1) Copies the elements from the source range [first, last) to the destination range
[result, result + 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 [0, N).
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:

* Explicit template argument lists cannot be specified when calling any of them.
* None of them are visible to argument-dependent lookup.
* When any of them are found by normal unqualified lookup as the name to the left
of the function-call operator, argument-dependent lookup is inhibited.

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

Parameters¶

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

Return value¶

{last, result + N}.

Complexity¶

Exactly N assignments.

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.

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 {};

Example¶

// Run this code

#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';
}

Output:¶

12345 → 54321 → 12345

See also¶

ranges::reverse reverses the order of elements in a range
(C++20) (niebloid)
reverse_copy creates a copy of a range that is reversed
(function template)