std::ranges::shift_left, std::ranges::shift_right

 

C++

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Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges(C++20)
Constrained algorithms, e.g. ranges::copy, 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 Batch operations for_each for_each_n (C++17) Search operations all_ofany_ofnone_of (C++11)                (C++11)(C++11) countcount_if mismatch equal findfind_iffind_if_not (C++11) find_end find_first_of adjacent_find search search_n Modifying sequence operations Copy operations copycopy_if (C++11) copy_backward copy_n (C++11) move (C++11) move_backward (C++11) Swap operations swap iter_swap swap_ranges Transformation operations replacereplace_if transform replace_copyreplace_copy_if Generation operations fill fill_n generate generate_n Removing operations removeremove_if unique remove_copyremove_copy_if unique_copy Order-changing operations reverse reverse_copy rotate rotate_copy random_shuffleshuffle (until C++17)(C++11) shift_leftshift_right (C++20)(C++20) Sampling operations sample (C++17)	Sorting and related operations Partitioning operations partition partition_copy (C++11)   stable_partition is_partitioned (C++11) partition_point (C++11) Sorting operations sort stable_sort partial_sort partial_sort_copy is_sorted (C++11) is_sorted_until (C++11) nth_element Binary search operations (on partitioned ranges) lower_bound upper_bound equal_range binary_search Set operations (on sorted ranges) includes set_union set_intersection set_difference set_symmetric_difference Merge operations (on sorted ranges) merge inplace_merge Heap operations push_heap pop_heap make_heap sort_heap is_heap (C++11) is_heap_until (C++11) Minimum/maximum operations max min minmax (C++11) clamp (C++17) max_element min_element minmax_element (C++11) Lexicographical comparison operations lexicographical_compare lexicographical_compare_three_way (C++20) Permutation operations next_permutation prev_permutation is_permutation (C++11) C library qsort bsearch
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)
Operations on uninitialized memory
uninitialized_copy uninitialized_move (C++17)    uninitialized_fill uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)       uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)

 

Constrained algorithms

All names in this menu belong to namespace std::ranges

Non-modifying sequence operations

all_ofany_ofnone_of for_each for_each_n    countcount_if adjacent_find mismatch equal lexicographical_compare    containscontains_subrange (C++23)(C++23) findfind_iffind_if_not find_lastfind_last_iffind_last_if_not (C++23)(C++23)(C++23)   find_end find_first_of search search_n starts_with (C++23) ends_with (C++23)

Modifying sequence operations

copycopy_if copy_n copy_backward    move move_backward shift_leftshift_right (C++23)(C++23)   fill fill_n generate generate_n    transform swap_ranges    shuffle sample removeremove_if replacereplace_if reverse rotate remove_copyremove_copy_if    unique replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy

Partitioning operations

is_partitioned    partition_point    partition    partition_copy    stable_partition

Sorting operations

is_sorted is_sorted_until     sort stable_sort         partial_sort       nth_element partial_sort_copy

Binary search operations (on sorted ranges)

lower_bound         upper_bound         binary_search      equal_range

Set operations (on sorted ranges)

merge inplace_merge       set_difference set_intersection    set_union          includes set_symmetric_difference

Heap operations

is_heap is_heap_until       make_heap           sort_heap push_heap pop_heap

Minimum/maximum operations

max max_element         min min_element         minmax minmax_element     clamp

Permutation operations

is_permutation      next_permutation    prev_permutation

Fold operations

fold_left (C++23) fold_left_first (C++23)   fold_right (C++23) fold_right_last (C++23)   fold_left_with_iter (C++23) fold_left_first_with_iter (C++23)

Numeric operations iota (C++23)             Random number generation generate_random (C++26)

Operations on uninitialized storage

construct_at    destroy destroy_n destroy_at uninitialized_copy    uninitialized_move uninitialized_fill uninitialized_copy_n    uninitialized_move_n uninitialized_fill_n uninitialized_default_construct uninitialized_default_construct_n uninitialized_value_construct uninitialized_value_construct_n

Return types

in_fun_result in_in_result in_found_result    in_out_result in_in_out_result    in_out_out_result    min_max_result out_value_result (C++23) in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
template<std::permutable I, std::sentinel_for<I> S > constexprranges::subrange<I>     shift_left( I first, S last, std::iter_difference_t<I> n );	(1)	(since C++23)
template<ranges::forward_range R > requires std::permutable<ranges::iterator_t<R>> constexprranges::borrowed_subrange_t<R>     shift_left( R&& r, ranges::range_difference_t<R> n );	(2)	(since C++23)
template<std::permutable I, std::sentinel_for<I> S > constexprranges::subrange<I>     shift_right( I first, S last, std::iter_difference_t<I> n );	(3)	(since C++23)
template<ranges::forward_range R > requires std::permutable<ranges::iterator_t<R>> constexprranges::borrowed_subrange_t<R>     shift_right( R&& r, ranges::range_difference_t<R> n );	(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 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 I models bidirectional_iterator, then the moves are performed in decreasing order of i starting 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 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 range of elements to shift
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 n is 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 n is 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	Feature
__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(constauto& s : v){ifconstexpr(std::is_same_v<T, S>) s.specified_state? os << s.value<<' ': os <<". ";elseifconstexpr(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);// dittostd::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

ranges::move (C++20)	moves a range of elements to a new location (algorithm function object)
ranges::move_backward (C++20)	moves a range of elements to a new location in backwards order (algorithm function object)
ranges::rotate (C++20)	rotates the order of elements in a range (algorithm function object)
shift_leftshift_right (C++20)	shifts elements in a range (function template)