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

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< cpp‎ | ranges
C++
Ranges library
Range adaptors
adjacent_viewviews::adjacent
(C++23)(C++23)
views::pairwise
(C++23)
(C++23)(C++23)
(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)
(C++23)(C++23)

std::ranges::adjacent_view
Member functions
Iterator
Member functions
Non-member functions
Sentinel
Member functions
Non-member functions
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
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
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

Data members

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

Member functions

 constructs a adjacent_view
(public member function)
returns an iterator to the beginning
(public member function)
returns an iterator or a sentinel to the end
(public member function)
returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range.
(public member function)
Inherited from std::ranges::view_interface
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>)
(C++23)
 returns a constant iterator to the beginning of the range.
(public member function of std::ranges::view_interface<D>)
(C++23)
 returns a sentinel for the constant iterator of the range.
(public member function of std::ranges::view_interface<D>)
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>)
returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>)
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>)
returns the n th 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

 the iterator type
(exposition-only member class template*
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

Notes

views::adjacent only accepts forward 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> made rejected

References

  • C++23 standard (ISO/IEC 14882:2024):
  • 26.7.25 Adjacent view [range.adjacent]

See also

(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)
(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)
(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)
(C++23)
 a view consisting of elements of another view, advancing over N elements at a time
(class template) (range adaptor object)
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