std::ranges::move_backward, std::ranges::move_backward_result
From cppreference.com
| Defined in header <algorithm>
|
||
| Call signature |
||
template< std::bidirectional_iterator I1, std::sentinel_for<I1> S1, std::bidirectional_iterator I2 > requires std::indirectly_movable<I1, I2> constexpr move_backward_result<I1, I2> move_backward( I1 first, S1 last, I2 d_last ); |
(1) | (since C++20) |
template< ranges::bidirectional_range R, std::bidirectional_iterator I > requires std::indirectly_movable<ranges::iterator_t<R>, I> constexpr move_backward_result<ranges::borrowed_iterator_t<R>, I> move_backward( R&& r, I d_last ); |
(2) | (since C++20) |
| Helper types |
||
template< class I, class O > using move_backward_result = ranges::in_out_result<I, O>; |
(3) | (since C++20) |
1) Moves the elements in the range, defined by
[first, last), to another range [d_last - N, d_last), where N = ranges::distance(first, last). The elements are moved in reverse order (the last element is moved first), but their relative order is preserved. The behavior is undefined if d_last is within (first, last]. In such a case, ranges::move may 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 elements in the moved-from range will still contain valid values of the appropriate type, but not necessarily the same values as before the move, as if using *(d_last - n) = ranges::iter_move(last - n) for each integer n, where 0 ≤ n < N.
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 range of elements to move |
| r | - | the range of the elements to move |
| d_last | - | the end of the destination range |
Return value
{last, d_last - N}.
Complexity
1) Exactly
N move assignments.2) Exactly
ranges::distance(r) move assignments.Notes
When moving overlapping ranges, ranges::move is appropriate when moving to the left (beginning of the destination range is outside the source range) while ranges::move_backward is appropriate when moving to the right (end of the destination range is outside the source range).
Possible implementation
struct move_backward_fn
{
template<std::bidirectional_iterator I1, std::sentinel_for<I1> S1,
std::bidirectional_iterator I2>
requires std::indirectly_movable<I1, I2>
constexpr ranges::move_backward_result<I1, I2>
operator()(I1 first, S1 last, I2 d_last) const
{
auto i {last};
for (; i != first; *--d_last = ranges::iter_move(--i))
{}
return {std::move(last), std::move(d_last)};
}
template<ranges::bidirectional_range R, std::bidirectional_iterator I>
requires std::indirectly_movable<ranges::iterator_t<R>, I>
constexpr ranges::move_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 move_backward_fn move_backward {};
|
Example
Run this code
#include <algorithm>
#include <iostream>
#include <string>
#include <string_view>
#include <vector>
using Vec = std::vector<std::string>;
void print(std::string_view rem, Vec const& vec)
{
std::cout << rem << "[" << vec.size() << "]: ";
for (const std::string& s : vec)
std::cout << (s.size() ? s : std::string{"·"}) << ' ';
std::cout << '\n';
}
int main()
{
Vec a{"▁", "▂", "▃", "▄", "▅", "▆", "▇", "█"};
Vec b(a.size());
print("Before move:\n" "a", a);
print("b", b);
std::ranges::move_backward(a, b.end());
print("\n" "Move a >> b:\n" "a", a);
print("b", b);
std::ranges::move_backward(b.begin(), b.end(), a.end());
print("\n" "Move b >> a:\n" "a", a);
print("b", b);
std::ranges::move_backward(a.begin(), a.begin()+3, a.end());
print("\n" "Overlapping move a[0, 3) >> a[5, 8):\n" "a", a);
}
Possible output:
Before move:
a[8]: ▁ ▂ ▃ ▄ ▅ ▆ ▇ █
b[8]: · · · · · · · ·
Move a >> b:
a[8]: · · · · · · · ·
b[8]: ▁ ▂ ▃ ▄ ▅ ▆ ▇ █
Move b >> a:
a[8]: ▁ ▂ ▃ ▄ ▅ ▆ ▇ █
b[8]: · · · · · · · ·
Overlapping move a[0, 3) >> a[5, 8):
a[8]: · · · ▄ ▅ ▁ ▂ ▃
See also
(C++20) |
moves a range of elements to a new location (algorithm function object) |
(C++20)(C++20) |
copies a range of elements to a new location (algorithm function object) |
(C++20) |
copies a range of elements in backwards order (algorithm function object) |
(C++11) |
moves a range of elements to a new location (function template) |
(C++11) |
converts the argument to an xvalue (function template) |