std::shift_left, std::shift_right

 

C++

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Technical Specifications

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms: std::ranges::copy, std::ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)	execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)(C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	findfind_iffind_if_not (C++11) find_end find_first_of	search search_n lexicographical_compare lexicographical_compare_three_way (C++20)
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill destroy (C++17)	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n destroy_n (C++17)	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) destroy_at (C++17)	uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17) construct_at (C++20)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)
C library
qsort	bsearch

 

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. This overload only participates in overload resolution 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 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.

Example

Run this code

#include <iostream>
#include <algorithm>
#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;
    }
};
 
std::ostream& operator<< (std::ostream& os, std::vector<S> const& v) {
    for (const auto& s : v)
        s.specified_state ? os << s.value << ' ' : os << "? ";
    return os << '\n';
}
 
int main()
{
    std::vector<S> v{1,2,3,4,5,6,7};
    std::cout << v;
 
    std::shift_left(v.begin(), v.end(), 3);
    std::cout << v;
 
    std::shift_right(v.begin(), v.end(), 2);
    std::cout << v;
}

Output:

1 2 3 4 5 6 7 
4 5 6 7 ? ? ? 
? ? 4 5 6 7 ?

See also

move (C++11)	moves a range of elements to a new location (function template)
move_backward (C++11)	moves a range of elements to a new location in backwards order (function template)
rotate	rotates the order of elements in a range (function template)