std::ranges::reverse_copy, std::ranges::reverse_copy_result - cppreference.com (original) (raw)

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 algorithm function objects (informally known as 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.

Contents

• 1 Parameters
• 2 Return value
• 3 Complexity
• 4 Notes
• 5 Possible implementation
• 6 Example
• 7 See also

[edit] Parameters

[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 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, O> constexpr ranges::reverse_copy_result<ranges::borrowed_iterator_t, 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 #include #include   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:

[edit] See also