std::ranges::views::adjacent, std::ranges::adjacent_view, std::ranges::views::pairwise

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

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Filesystem library (C++17)

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Concurrency support library (C++11)

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Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata empty

Range conversions std::from_range_t std::from_range (C++23)(C++23)     to (C++23)

Dangling iterator handling dangling borrowed_iterator_t borrowed_subrange_t

Range primitives
range_size_trange_difference_trange_value_t elements_of (C++23)	iterator_tconst_iterator_tsentinel_tconst_sentinel_t (C++23)(C++23)	range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t (C++23)

Range concepts
range borrowed_range    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	constant_range (C++23)

Views
view_interface	subrange

Range factories
empty_viewviews::empty	single_viewviews::single	basic_istream_viewviews::istream	iota_viewviews::iota	repeat_viewviews::repeat (C++23)(C++23)

Range adaptors
views::all_tviews::all ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while concat_viewviews::concat (C++26)(C++26)	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) elements_viewviews::elements keys_viewviews::keys values_viewviews::values enumerate_viewviews::enumerate (C++23)(C++23) zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	adjacent_viewviews::adjacent (C++23)(C++23) views::pairwise (C++23) adjacent_transform_viewviews::adjacent_transform (C++23)(C++23) views::pairwise_transform (C++23) chunk_viewviews::chunk (C++23)(C++23) slide_viewviews::slide (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) stride_viewviews::stride (C++23)(C++23) cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators std::generator (C++23)

Range adaptor closure objects range_adaptor_closure (C++23)

Range adaptor objects

Helper items
copyable-box movable-box (until C++23)  (C++23)	simple-view non-propagating-cache

 

std::ranges::adjacent_view

Member functions

adjacent_view::adjacent_view

adjacent_view::begin

adjacent_view::end

adjacent_view::size

Iterator

Member functions

adjacent_view::iterator::iterator

adjacent_view::iterator::operator*

adjacent_view::iterator::operator[]

adjacent_view::iterator::operator++ adjacent_view::iterator::operator++(int) adjacent_view::iterator::operator-- adjacent_view::iterator::operator--(int) adjacent_view::iterator::operator+= adjacent_view::iterator::operator-=

Non-member functions

operator==(adjacent_view::iterator) operator<(adjacent_view::iterator) operator>(adjacent_view::iterator) operator<=(adjacent_view::iterator) operator>=(adjacent_view::iterator) operator<=>(adjacent_view::iterator)

operator+(adjacent_view::iterator) operator-(adjacent_view::iterator)

iter_move(adjacent_view::iterator)

iter_swap(adjacent_view::iterator)

Sentinel

Member functions

adjacent_view::sentinel::sentinel

Non-member functions

operator==(adjacent_view::iterator,adjacent_view::sentinel)

operator-(adjacent_view::iterator,adjacent_view::sentinel)

 

Defined in header <ranges>
template< ranges::forward_range V, std::size_t N >     requires ranges::view<V> && (N > 0) class adjacent_view     : public ranges::view_interface<adjacent_view<V, N>>	(1)	(since C++23)
namespace views {     template< std::size_t N >     constexpr /* unspecified */ adjacent = /* unspecified */ ; }	(2)	(since C++23)
namespace views {     inline constexpr auto pairwise = adjacent<2>; }	(3)	(since C++23)
Call signature
template< ranges::viewable_range R >     requires /* see below */ constexpr ranges::view auto adjacent<N>( R&& r );		(since C++23)

1) adjacent_view is a range adaptor that takes a view, and produces a view whose i^th element (a "window") is a std::tuple that holds N references to the elements of the original view, from i^th up to i + N - 1^th inclusively.

Let S be the size of the original view. Then the size of produced view is:

• S - N + 1, if S >= N,
• ​0​ otherwise, and the resulting view is empty.

2) The name views::adjacent<N> denotes a RangeAdaptorObject. Given a subexpression e and a constant expression N, the expression views::adjacent<N>(e) is expression-equivalent to

• ((void)e, auto(views::empty<tuple<>>)) if N is equal to ​0​ and decltype((e)) models forward_range,
• adjacent_view<views::all_t<decltype((e))>, N>(e) otherwise.

3) The name views::pairwise denotes a RangeAdaptorObject that behaves exactly as views::adjacent<2>.

adjacent_view always models forward_range, and models bidirectional_range, random_access_range, or sized_range if adapted view type models the corresponding concept.

Data members

Member name	Definition
base_ (private)	the underlying view of type V. (exposition-only member object*)

Member functions

(constructor)	constructs a adjacent_view (public member function)
begin	returns an iterator to the beginning (public member function)
end	returns an iterator or a sentinel to the end (public member function)
size	returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range. (public member function)
Inherited from std::ranges::view_interface
empty	returns whether the derived view is empty. Provided if it satisfies sized_range or forward_range. (public member function of std::ranges::view_interface<D>)
cbegin (C++23)	returns a constant iterator to the beginning of the range. (public member function of std::ranges::view_interface<D>)
cend (C++23)	returns a sentinel for the constant iterator of the range. (public member function of std::ranges::view_interface<D>)
operator bool	returns whether the derived view is not empty. Provided if ranges::empty is applicable to it. (public member function of std::ranges::view_interface<D>)
front	returns the first element in the derived view. Provided if it satisfies forward_range. (public member function of std::ranges::view_interface<D>)
back	returns the last element in the derived view. Provided if it satisfies bidirectional_range and common_range. (public member function of std::ranges::view_interface<D>)
operator[]	returns the nth element in the derived view. Provided if it satisfies random_access_range. (public member function of std::ranges::view_interface<D>)

Deduction guides

(none)

Nested classes

iterator	the iterator type (exposition-only member class template*)
sentinel	the sentinel type used when adjacent_view is not a common_range (exposition-only member class template*)

Helper templates

template< class V, size_t N > constexpr bool ranges::enable_borrowed_range<adjacent_view<V, N>> =     ranges::enable_borrowed_range<V>;		(since C++23)

This specialization of ranges::enable_borrowed_range makes adjacent_view satisfy borrowed_range when the underlying view satisfies it.

Notes

views::adjacent only accepts foward ranges even when N is 0.

There are similarities between ranges::adjacent_view and ranges::slide_view:

• Both create a "sliding window" of size N.
• Both have the same size S - N + 1, where S is the size of an adapted view such that S >= N > 0.

The following table shows the differences between these adaptors:

View adaptor	value_type	The window size N
ranges::adjacent_view	std::tuple	A template parameter
ranges::slide_view	ranges::range	A runtime argument

Feature-test macro	Value	Std	Feature
__cpp_lib_ranges_zip	202110L	(C++23)	ranges::zip_view, ranges::zip_transform_view, ranges::adjacent_view, ranges::adjacent_transform_view

Example

Run this code

#include <array>
#include <format>
#include <iostream>
#include <ranges>
#include <tuple>
 
int main()
{
    constexpr std::array v{1, 2, 3, 4, 5, 6};
    std::cout << "v = [1 2 3 4 5 6]\n";
 
    for (int i{}; std::tuple t : v | std::views::adjacent<3>)
    {
        auto [t0, t1, t2] = t;
        std::cout << std::format("e = {:<{}}[{} {} {}]\n", "", 2 * i++, t0, t1, t2);
    }
}

Output:

v = [1 2 3 4 5 6]
e = [1 2 3]
e =   [2 3 4]
e =     [3 4 5]
e =       [4 5 6]

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 4098	C++23	views::adjacent<0> used to accept input-only ranges	made rejected

References

• C++23 standard (ISO/IEC 14882:2024):

• 26.7.25 Adjacent view [range.adjacent]

See also

ranges::adjacent_transform_viewviews::adjacent_transform (C++23)	a view consisting of results of application of a transformation function to adjacent elements of the adapted view (class template) (range adaptor object)
ranges::slide_viewviews::slide (C++23)	a view whose Mth element is a view over the Mth through (M + N - 1)th elements of another view (class template) (range adaptor object)
ranges::chunk_viewviews::chunk (C++23)	a range of views that are N-sized non-overlapping successive chunks of the elements of another view (class template) (range adaptor object)
ranges::stride_viewviews::stride (C++23)	a view consisting of elements of another view, advancing over N elements at a time (class template) (range adaptor object)