std::ranges::copy_backward, std::ranges::copy_backward_result
Defined in header <algorithm> |
||
---|---|---|
Call signature | ||
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 result ); |
(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 result ); |
(2) | (since C++20) |
Helper types | ||
template< class I1, class I2 > using copy_backward_result = ranges::in_out_result<I1, I2>; |
(3) | (since C++20) |
1) Copies the elements from the range, defined by
[first, last)
, to another range
[result - N, result)
, 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
result
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 niebloids, that is:
- Explicit template argument lists may not be specified when calling any of them.
- None of them is visible to argument-dependent lookup.
- When one of them is found by normal unqualified lookup for the name to the left of the function-call operator, it inhibits argument-dependent lookup.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
first | - | the beginning of the range of elements to copy from |
last | - | the end of the range of elements to copy from |
r | - | the range of the elements to copy from |
result | - | the end of the destination range |
Return value
{last, result - N}
.
Complexity
Exactly N
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 result ) const { I1 last1{ ranges::next(first, std::move(last)) }; for (I1 i{ last1 }; i != first; *--result = *--i); return { std::move(last1), std::move(result) }; } 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 result ) const { return (*this)(ranges::begin(r), ranges::end(r), std::move(result)); } }; inline constexpr copy_backward_fn copy_backward{}; |
Example
#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
See also
(C++20)(C++20)
|
copies a range of elements to a new location (niebloid) |
(C++20)
|
copies a number of elements to a new location (niebloid) |
(C++20)(C++20)
|
copies a range of elements omitting those that satisfy specific criteria (niebloid) |
(C++20)(C++20)
|
copies a range, replacing elements satisfying specific criteria with another value (niebloid) |
(C++20)
|
creates a copy of a range that is reversed (niebloid) |
(C++20)
|
copies and rotate a range of elements (niebloid) |
(C++20)
|
creates a copy of some range of elements that contains no consecutive duplicates (niebloid) |
(C++20)
|
moves a range of elements to a new location (niebloid) |
(C++20)
|
moves a range of elements to a new location in backwards order (niebloid) |
copies a range of elements in backwards order (function template) |
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