std::shift_left, std::shift_right
Defined in header <algorithm> |
||
---|---|---|
template< class ForwardIt > constexpr ForwardIt shift_left( ForwardIt first, ForwardIt last, typename std::iterator_traits<ForwardIt>::difference_type n ); |
(1) | (since C++20) |
template< class ExecutionPolicy, class ForwardIt > ForwardIt shift_left( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, typename std::iterator_traits<ForwardIt>::difference_type n ); |
(2) | (since C++20) |
template< class ForwardIt > constexpr ForwardIt shift_right( ForwardIt first, ForwardIt last, typename std::iterator_traits<ForwardIt>::difference_type n ); |
(3) | (since C++20) |
template< class ExecutionPolicy, class ForwardIt > ForwardIt shift_right( ExecutionPolicy&& policy, ForwardIt first, ForwardIt last, typename std::iterator_traits<ForwardIt>::difference_type n ); |
(4) | (since C++20) |
Shifts the elements in the range [first, last)
by n
positions.
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
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
.
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
i
in
[0, last - first - n)
, moves the element originally at position
first + i
to position
first + n + i
. If
ForwardIt
meets the
LegacyBidirectionalIterator requirements, then the moves are performed in decreasing order of
i
starting from
last - first - n - 1
.
2,4) Same as
(1) and
(3), respectively, but executed according to
policy
and the moves may be performed in any order. This overload participates in overload resolution only if
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
is true
Elements that are in the original range but not the new range are left in a valid but unspecified state.
Parameters
first | - | the beginning of the original range |
last | - | the end of the original range |
n | - | the number of positions to shift |
policy | - | the execution policy to use. See execution policy for details. |
Type requirements | ||
-ForwardIt must meet the requirements of LegacyForwardIterator. |
||
-ForwardIt must meet either the requirements of LegacyBidirectionalIterator or the requirements of ValueSwappable for overloads (3-4). |
||
-The type of dereferenced ForwardIt must meet the requirements of MoveAssignable. |
Return value
1-2) The end of the resulting range. If
n
is less than
last - first
, returns
first + (last - first - n)
. Otherwise, returns
first
.
3-4) The beginning of the resulting range. If
n
is less than
last - first
, returns
first + n
. Otherwise, returns
last
.
Complexity
1-2) At most
std::distance(first, last) - n
assignments.
3-4) At most
std::distance(first, last) - n
assignment or swaps.
Exceptions
The overloads with a template parameter named ExecutionPolicy
report errors as follows:
- If execution of a function invoked as part of the algorithm throws an exception and
ExecutionPolicy
is one of the standard policies,std::terminate
is called. For any otherExecutionPolicy
, the behavior is implementation-defined. - If the algorithm fails to allocate memory,
std::bad_alloc
is thrown.
Notes
Feature testing macro: __cpp_lib_shift
.
Example
#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::shift_left(begin(a), end(a), 3); std::shift_left(begin(b), end(b), 3); std::shift_left(begin(c), end(c), 3); std::cout << a << " " << b << " " << c << '\n'; std::shift_right(begin(a), end(a), 2); std::shift_right(begin(b), end(b), 2); std::shift_right(begin(c), end(c), 2); std::cout << a << " " << b << " " << c << '\n'; std::shift_left(begin(a), end(a), 8); // has no effect: n >= last - first std::shift_left(begin(b), end(b), 8); // ditto std::shift_left(begin(c), end(c), 8); // ditto std::cout << a << " " << b << " " << c << '\n'; // std::shift_left(begin(a), end(a),-3); // UB, e.g. segfault.) }
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++11)
|
moves a range of elements to a new location (function template) |
(C++11)
|
moves a range of elements to a new location in backwards order (function template) |
rotates the order of elements in a range (function template) |
|
(C++23)
|
shifts elements in a range (niebloid) |
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