std::ranges::shift_left, std::ranges::shift_right
From cppreference.com
| Defined in header <algorithm>
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| Call signature |
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| template< std::permutable I, std::sentinel_for<I> S > constexpr ranges::subrange<I> |
(1) | (since C++23) |
| template< ranges::forward_range R > requires std::permutable<ranges::iterator_t<R>> |
(2) | (since C++23) |
| template< std::permutable I, std::sentinel_for<I> S > constexpr ranges::subrange<I> |
(3) | (since C++23) |
| template< ranges::forward_range R > requires std::permutable<ranges::iterator_t<R>> |
(4) | (since C++23) |
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.
1) Shifts the elements towards the beginning of the range:
- If n == 0 || n >= last - first, there are no effects.
- If n < 0, the behavior is undefined.
- Otherwise, for every integer
iin[0,last - first - n), moves the element originally at position first + n + i to position first + i. The moves are performed in increasing order ofistarting from 0.
3) Shifts the elements towards the end of the range:
- If n == 0 || n >= last - first, there are no effects.
- If n < 0, the behavior is undefined.
- Otherwise, for every integer
iin[0,last - first - n), moves the element originally at position first + i to position first + n + i. IfImodelsbidirectional_iterator, then the moves are performed in decreasing order ofistarting from last - first - n - 1.
2, 4) Same as (1) or (3) respectively, but uses r as the range, as if using ranges::begin(r) as first and ranges::end(r) as last.
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 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.
In practice, they may be implemented as function objects, or with special compiler extensions.
Parameters
| first | - | the beginning of the original range |
| last | - | the end of the original range |
| r | - | the range of elements to shift |
| n | - | the number of positions to shift |
Return value
1-2) {first, /*NEW_LAST*/}, where
NEW_LAST is the end of the resulting range and equivalent to:
- first + (last - first - n), if
nis less than last - first; - first otherwise.
3-4) {/*NEW_FIRST*/, last}, where
NEW_FIRST is the beginning of the resulting range and equivalent to:
- first + n, if
nis less than last - first; - last otherwise.
Complexity
1-2) At most ranges::distance(first, last) - n assignments.
3-4) At most ranges::distance(first, last) - n assignment or swaps.
Notes
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 | Comment |
|---|---|---|---|
__cpp_lib_shift |
202202L | (C++23) | std::ranges::shift_left and std::ranges::shift_right
|
Example
Run this code
#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 .
See also
| (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) |
| (C++20) |
rotates the order of elements in a range (niebloid) |
| (C++20) |
shifts elements in a range (function template) |