std::ranges::shift_left, std::ranges::shift_right
(on partitioned ranges)
std::ranges
<algorithm>
constexpr ranges::subrange <I>
requires std::permutable <ranges::iterator_t <R>>
constexpr ranges::borrowed_subrange_t <R>
constexpr ranges::subrange <I>
requires std::permutable <ranges::iterator_t <R>>
constexpr ranges::borrowed_subrange_t <R>
Shifts the elements in the range [
first,
last)
or r by n
positions. The behavior is undefined if [
first,
last)
is not a valid range.
i
in [
0,
last - first - n)
, moves the element originally at position first + n + i to position first + i. The moves are performed in increasing order of i
starting from 0.i
in [
0,
last - first - n)
, moves the element originally at position first + i to position first + n + i. If I
models bidirectional_iterator
, then the moves are performed in decreasing order of i
starting from last - first - n - 1.Elements that are in the original range but not the new range are left in a valid but unspecified state.
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
NEW_LAST
is the end of the resulting range and equivalent to:
n
is less than last - first;
NEW_FIRST
is the beginning of the resulting range and equivalent to:
n
is less than last - first;
ranges::shift_left
/ ranges::shift_right
has better efficiency on common implementations if I
models bidirectional_iterator
or (better) random_access_iterator
.
Implementations (e.g. MSVC STL) may enable vectorization when the iterator type models contiguous_iterator
and swapping its value type calls neither non-trivial special member function nor ADL-found swap
.
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_shift |
202202L |
(C++23) | std::ranges::shift_left and std::ranges::shift_right
|
#include <algorithm> #include <iostream> #include <string> #include <type_traits> #include <vector> struct S { int value{0}; bool specified_state{true}; S(int v = 0) : value{v} {} S(S const& rhs) = default; S(S&& rhs) { *this = std::move(rhs); } S& operator=(S const& rhs) = default; S& operator=(S&& rhs) { if (this != &rhs) { value = rhs.value; specified_state = rhs.specified_state; rhs.specified_state = false; } return *this; } }; template<typename T> std::ostream & operator<<(std::ostream & os, std::vector <T> const& v) { for (const auto& s : v) { if constexpr (std::is_same_v <T, S>) s.specified_state ? os << s.value << ' ' : os << ". "; else if constexpr (std::is_same_v <T, std::string >) os << (s.empty() ? "." : s) << ' '; else os << s << ' '; } return os; } int main() { std::cout << std::left ; std::vector <S> a{1, 2, 3, 4, 5, 6, 7}; std::vector <int> b{1, 2, 3, 4, 5, 6, 7}; std::vector <std::string > c{"α", "β", "γ", "δ", "ε", "ζ", "η"}; std::cout << "vector<S> \tvector<int> \tvector<string>\n"; std::cout << a << " " << b << " " << c << '\n'; std::ranges::shift_left(a, 3); std::ranges::shift_left(b, 3); std::ranges::shift_left(c, 3); std::cout << a << " " << b << " " << c << '\n'; std::ranges::shift_right(a, 2); std::ranges::shift_right(b, 2); std::ranges::shift_right(c, 2); std::cout << a << " " << b << " " << c << '\n'; std::ranges::shift_left(a, 8); // has no effect: n >= last - first std::ranges::shift_left(b, 8); // ditto std::ranges::shift_left(c, 8); // ditto std::cout << a << " " << b << " " << c << '\n'; // std::ranges::shift_left(a, -3); // UB }
Possible output:
vector<S> vector<int> vector<string> 1 2 3 4 5 6 7 1 2 3 4 5 6 7 α β γ δ ε ζ η 4 5 6 7 . . . 4 5 6 7 5 6 7 δ ε ζ η . . . . . 4 5 6 7 . 4 5 4 5 6 7 5 . . δ ε ζ η . . . 4 5 6 7 . 4 5 4 5 6 7 5 . . δ ε ζ η .