std::ranges::copy_backward, std::ranges::copy_backward_result
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Constrained algorithms
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std::ranges
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Defined in header
<algorithm>
Call signature
template< std::bidirectional_iterator I1, std::sentinel_for <I1> S1,
(1)
(since C++20)
std::bidirectional_iterator I2 >
requires std::indirectly_copyable <I1, I2>
constexpr copy_backward_result<I1, I2>
template< ranges::bidirectional_range R, std::bidirectional_iterator I >
(2)
(since C++20)
requires std::indirectly_copyable <ranges::iterator_t <R>, I>
constexpr copy_backward_result<ranges::borrowed_iterator_t <R>, I>
Helper types
template< class I1, class I2 >
using copy_backward_result = ranges::in_out_result <I1, I2>;
(3)
(since C++20)
using copy_backward_result = ranges::in_out_result <I1, I2>;
1) Copies the elements from the range, defined by
[first, last), to another range [d_last - N, d_last), where N = ranges::distance (first, last). The elements are copied in reverse order (the last element is copied first), but their relative order is preserved. The behavior is undefined if d_last is within (first, last]. In such a case std::ranges::copy can be used instead.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
[edit] Parameters
first, last
-
the iterator-sentinel pair defining the range of elements to copy from
r
-
the range of the elements to copy from
d_last
-
the end of the destination range
[edit] Return value
{last, d_last - N}
[edit] Complexity
Exactly N assignments.
[edit] Notes
When copying overlapping ranges, ranges::copy is appropriate when copying to the left (beginning of the destination range is outside the source range) while ranges::copy_backward is appropriate when copying to the right (end of the destination range is outside the source range).
[edit] Possible implementation
struct copy_backward_fn { template<std::bidirectional_iterator I1, std::sentinel_for <I1> S1, std::bidirectional_iterator I2> requires std::indirectly_copyable <I1, I2> constexpr ranges::copy_backward_result<I1, I2> operator()(I1 first, S1 last, I2 d_last) const { I1 last1 {ranges::next (first, std::move(last))}; for (I1 i {last1}; i != first;) *--d_last = *--i; return {std::move(last1), std::move(d_last)}; } template<ranges::bidirectional_range R, std::bidirectional_iterator I> requires std::indirectly_copyable <ranges::iterator_t <R>, I> constexpr ranges::copy_backward_result<ranges::borrowed_iterator_t <R>, I> operator()(R&& r, I d_last) const { return (*this)(ranges::begin (r), ranges::end (r), std::move(d_last)); } }; inline constexpr copy_backward_fn copy_backward{};
[edit] Example
Run this code
#include <algorithm> #include <iostream> #include <ranges> #include <string_view> #include <vector> void print(std::string_view rem, std::ranges::forward_range auto const& r) { for (std::cout << rem << ": "; auto const& elem : r) std::cout << elem << ' '; std::cout << '\n'; } int main() { const auto src = {1, 2, 3, 4}; print("src", src); std::vector <int> dst(src.size() + 2); std::ranges::copy_backward(src, dst.end()); print("dst", dst); std::ranges::fill (dst, 0); const auto [in, out] = std::ranges::copy_backward(src.begin(), src.end() - 2, dst.end()); print("dst", dst); std::cout << "(in - src.begin) == " << std::distance (src.begin(), in) << '\n' << "(out - dst.begin) == " << std::distance (dst.begin(), out) << '\n'; }
Output:
src: 1 2 3 4 dst: 0 0 1 2 3 4 dst: 0 0 0 0 1 2 (in - src.begin) == 2 (out - dst.begin) == 4
[edit] See also
(C++20)(C++20)
(algorithm function object)[edit]
(C++20)(C++20)
(algorithm function object)[edit]
(C++20)
(algorithm function object)[edit]
(C++20)
(algorithm function object)[edit]