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>
shift_left( I first, S last, std::iter_difference_t<I> count );
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(1) | (since C++23) |
template< ranges::forward_range R >
requires std::permutable<ranges::iterator_t<R>>
constexpr ranges::borrowed_subrange_t<R>
shift_left( R&& r, ranges::range_difference_t<R> count );
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(2) | (since C++23) |
template< std::permutable I, std::sentinel_for<I> S >
constexpr ranges::subrange<I>
shift_right( I first, S last, std::iter_difference_t<I> count );
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(3) | (since C++23) |
template< ranges::forward_range R >
requires std::permutable<ranges::iterator_t<R>>
constexpr ranges::borrowed_subrange_t<R>
shift_right( R&& r, ranges::range_difference_t<R> count );
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(4) | (since C++23) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S >
requires std::permutable<I>
ranges::subrange<I>
shift_left( Ep&& policy, I first, S last,
std::iter_difference_t<I> count );
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(5) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R >
requires std::permutable<ranges::iterator_t<R>>
ranges::borrowed_subrange_t<R>
shift_left( Ep&& policy, R&& r, ranges::range_difference_t<R> count );
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(6) | (since C++26) |
template< /*execution-policy*/ Ep,
std::random_access_iterator I, std::sized_sentinel_for<I> S >
requires std::permutable<I>
ranges::subrange<I>
shift_right( Ep&& policy, I first, S last,
std::iter_difference_t<I> count );
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(7) | (since C++26) |
template< /*execution-policy*/ Ep, /*sized-random-access-range*/ R >
requires std::permutable<ranges::iterator_t<R>>
ranges::borrowed_subrange_t<R>
shift_right( Ep&& policy, R&& r, ranges::range_difference_t<R> count );
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(8) | (since C++26) |
For the definition of /*execution-policy*/, see this page; for the definition of /*sized-random-access-range*/, see this page.
Shifts the elements in the target range [first, last) or r by count positions. If count is not less than ranges::distance(first, last) or ranges::distance(r), does nothing.
1,2)
shift_left shifts the elements towards the beginning of the target range. For every integer
i starting from 0 to ranges::distance(first, last) - count - 1, moves the element originally at position ranges::next(first, count + i) to position ranges::next(first, i).3,4)
shift_right shifts the elements towards the end of the target range. For every integer
i starting from ranges::distance(first, last) - count - 1 to 0, moves the element originally at position ranges::next(first, i) to position ranges::next(first, count + i). If
I or ranges::iterator_t<R> does not model bidirectional_iterator, the shifting process is performed by swapping elements instead, the swap order is unspecified.5-8) Same as (1-4), but the move order is determined by
policy.If count >= 0 is not true, the behavior is undefined.
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 target range |
| r | - | the target range |
| count | - | the shift offset |
| policy | - | the execution policy to use |
Return value
A subrange containing all elements that are not shifted away from the target range, or an empty range if count is not less than ranges::distance(first, last) or ranges::distance(r).
Complexity
Given \(\scriptsize N\)N as ranges::distance(first, last) or ranges::distance(r):
1,2,5,6) At most \(\scriptsize \max(N-\mathtt{count},0)\)max(N-
count,0) assignments.3,4,7,8) At most \(\scriptsize \max(N-\mathtt{count},0)\)max(N-
count,0) assignment or swaps.Exceptions
5-8) During the execution process:
- If the temporary memory resources required for parallelization are not available, std::bad_alloc is thrown.
- If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).
Notes
ranges::shift_left / ranges::shift_right has better efficiency on common implementations if I or ranges::iterator_t<R> 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
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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(const S& rhs) = default;
S(S&& rhs) { *this = std::move(rhs); }
S& operator=(const S& 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, const std::vector<T>& 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{"", "", "", "", "", "", ""};
std::cout << "vector<S> \t\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
4 5 6 7 . . . 4 5 6 7 5 6 7 . . .
. . 4 5 6 7 . 4 5 4 5 6 7 5 . . .
. . 4 5 6 7 . 4 5 4 5 6 7 5 . . .
See also
(C++20)(C++20) |
shifts elements in a range (function template) |
(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) |
(C++20) |
rotates the order of elements in a range (algorithm function object) |