std::ranges::copy_backward, std::ranges::copy_backward_result

 

C++

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Freestanding and hosted

Language

Standard library

Standard library headers

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::bidirectional_iterator I1, std::sentinel_for<I1> S1,           std::bidirectional_iterator I2 > requires std::indirectly_copyable<I1, I2> constexpr copy_backward_result<I1, I2>     copy_backward( I1 first, S1 last, I2 d_last );	(1)	(since C++20)
template<ranges::bidirectional_range R, std::bidirectional_iterator I > requires std::indirectly_copyable<ranges::iterator_t<R>, I> constexpr copy_backward_result<ranges::borrowed_iterator_t<R>, I>     copy_backward( R&& r, I d_last );	(2)	(since C++20)
Helper types
template<class I1, class I2 > using copy_backward_result =ranges::in_out_result<I1, I2>;	(3)	(since C++20)

1) Copies the elements from the range, defined by [first, last), to another range [d_last - N, d_last), where N =ranges::distance(first, last). The elements are copied in reverse order (the last element is copied first), but their relative order is preserved. The behavior is undefined if d_last is within (first, last]. In such a case std::ranges::copy can be used instead.

2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first, and ranges::end(r) as last.

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 copy from
r	-	the range of the elements to copy from
d_last	-	the end of the destination range

Return value

{last, d_last - N}

Complexity

Exactly N assignments.

Notes

When copying overlapping ranges, ranges::copy is appropriate when copying to the left (beginning of the destination range is outside the source range) while ranges::copy_backward is appropriate when copying to the right (end of the destination range is outside the source range).

Possible implementation

struct copy_backward_fn {template<std::bidirectional_iterator I1, std::sentinel_for<I1> S1, std::bidirectional_iterator I2> requires std::indirectly_copyable<I1, I2>constexpr ranges::copy_backward_result<I1, I2> operator()(I1 first, S1 last, I2 d_last)const{ I1 last1 {ranges::next(first, std::move(last))};for(I1 i {last1}; i != first;)*--d_last =*--i;return{std::move(last1), std::move(d_last)};}   template<ranges::bidirectional_range R, std::bidirectional_iterator I> requires std::indirectly_copyable<ranges::iterator_t<R>, I>constexpr ranges::copy_backward_result<ranges::borrowed_iterator_t<R>, I> operator()(R&& r, I d_last)const{return(*this)(ranges::begin(r), ranges::end(r), std::move(d_last));}};   inlineconstexpr copy_backward_fn copy_backward{};

Example

Run this code

#include <algorithm>#include <iostream>#include <ranges>#include <string_view>#include <vector>   void print(std::string_view rem, std::ranges::forward_rangeautoconst& r){for(std::cout<< rem <<": ";autoconst& elem : r)std::cout<< elem <<' ';std::cout<<'\n';}   int main(){constauto src ={1, 2, 3, 4}; print("src", src);   std::vector<int> dst(src.size()+2); std::ranges::copy_backward(src, dst.end()); print("dst", dst);   std::ranges::fill(dst, 0);constauto[in, out]= std::ranges::copy_backward(src.begin(), src.end()-2, dst.end()); print("dst", dst);   std::cout<<"(in - src.begin) == "<<std::distance(src.begin(), in)<<'\n'<<"(out - dst.begin) == "<<std::distance(dst.begin(), out)<<'\n';}

Output:

src: 1 2 3 4 dst: 0 0 1 2 3 4 dst: 0 0 0 0 1 2 (in - src.begin) == 2 (out - dst.begin) == 4

See also

ranges::copyranges::copy_if (C++20)(C++20)	copies a range of elements to a new location (algorithm function object)
ranges::copy_n (C++20)	copies a number of elements to a new location (algorithm function object)
ranges::remove_copyranges::remove_copy_if (C++20)(C++20)	copies a range of elements omitting those that satisfy specific criteria (algorithm function object)
ranges::replace_copyranges::replace_copy_if (C++20)(C++20)	copies a range, replacing elements satisfying specific criteria with another value (algorithm function object)
ranges::reverse_copy (C++20)	creates a copy of a range that is reversed (algorithm function object)
ranges::rotate_copy (C++20)	copies and rotate a range of elements (algorithm function object)
ranges::unique_copy (C++20)	creates a copy of some range of elements that contains no consecutive duplicates (algorithm function object)
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)
copy_backward	copies a range of elements in backwards order (function template)