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. 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. 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. These overloads does not participate in overload resolution unless std::is_execution_policy_v<std::decay_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 positive and less than last - first, returns first + (last - first - n). Otherwise if n is positive, returns first. Otherwise, returns last.
3-4) The beginning of the resulting range. If n is positive and less than last - first, returns first + n. Otherwise if n is positive, returns last. Otherwise, returns first.

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 other ExecutionPolicy, the behavior is implementation-defined.
  • If the algorithm fails to allocate memory, std::bad_alloc is thrown.

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)

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