std::ranges::copy_backward, std::ranges::copy_backward_result
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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template< std::bidirectional_iterator I1, std::sentinel_for<I1> S1,
std::bidirectional_iterator I2 >
requires std::indirectly_copyable<I1, I2>
constexpr copy_backward_result<I1, I2>
copy_backward( I1 first, S1 last, I2 d_last );
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(1) | (since C++20) |
template< ranges::bidirectional_range R, std::bidirectional_iterator I >
requires std::indirectly_copyable<ranges::iterator_t<R>, I>
constexpr copy_backward_result<ranges::borrowed_iterator_t<R>, I>
copy_backward( R&& r, I d_last );
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(2) | (since C++20) |
| Helper types |
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template< class I1, class I2 >
using copy_backward_result = ranges::in_out_result<I1, I2>;
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(3) | (since C++20) |
Copies all elements from the source range to the destination range ending at d_last, starting from the end and proceeding to the beginning (reverse order).
1) The source range is
[first, last).2) The source range is
r.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.
Parameters
| first, last | - | the iterator-sentinel pair defining the source range |
| r | - | the source range |
| d_last | - | the past-the-end iterator of the destination range |
Return value
A ranges::copy_backward_result object where:
- The data member
inholds the past-the-end iterator of the source range. - The data member
outholds and an iterator to the last copy-assigned element in the destination range, ord_lastif no element is copied.
Complexity
1) Exactly
ranges::distance(first, last) assignments.2) Exactly
ranges::distance(r) assignments.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).
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::next(ranges::begin(r), ranges::end(r)),
std::move(d_last));
}
};
inline constexpr copy_backward_fn copy_backward{};
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Example
Run this code
#include <algorithm>
#include <iostream>
#include <ranges>
#include <string_view>
#include <vector>
void print(std::string_view rem, const std::ranges::forward_range auto& r)
{
for (std::cout << rem << ": "; const auto& 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
See also
| copies a range of elements in backwards order (function template) | |
(C++20)(C++20) |
copies a range of elements to a new location (algorithm function object) |
(C++20) |
copies a number of elements to a new location (algorithm function object) |
(C++20)(C++20) |
copies a range of elements omitting those that satisfy specific criteria (algorithm function object) |
(C++20)(C++20) |
copies a range, replacing elements satisfying specific criteria with another value (algorithm function object) |
(C++20) |
creates a copy of a range that is reversed (algorithm function object) |
(C++20) |
copies and rotate a range of elements (algorithm function object) |
(C++20) |
creates a copy of some range of elements that contains no consecutive duplicates (algorithm function object) |
(C++20) |
moves a range of elements to a new location (algorithm function object) |
(C++20) |
moves a range of elements to a new location in backwards order (algorithm function object) |