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

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< size_t N >
    inline 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 ith element (a "window") is a tuple-like value that holds N references to the elements of the original view, from ith up to i + N - 1th 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 ranges adaptor object. 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​,
  • adjacent_view<views::all_t<decltype((e))>, N>(e) otherwise.

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

Expression-equivalent

Expression e is expression-equivalent to expression f, if.

  • e and f have the same effects, and
  • either both are constant subexpressions or else neither is a constant subexpression, and
  • either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Data members

Typical implementations of adjacent_view hold only one non-static data member base_ of type V. The name is for exposition only.

Member functions

(C++23)
 constructs a adjacent_view
(public member function)
(C++23)
 returns an iterator to the beginning
(public member function)
(C++23)
 returns an iterator or a sentinel to the end
(public member function)
(C++23)
 returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range.
(public member function)
Inherited from std::ranges::view_interface
(C++20)
 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++20)
 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>)
(C++20)
 Returns the first element in the derived view. Provided if it satisfies forward_range.
(public member function of std::ranges::view_interface<D>)
(C++20)
 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>)
(C++20)
 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

(C++23)
 the iterator type
(exposition-only member class template)
(C++23)
 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 >
    inline constexpr bool enable_borrowed_range<adjacent_view<V, N>> =
      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

There is a similarity between ranges::adjacent_view and ranges::slide_view — they both produce a "sliding window" of the size N, and, given a view of the size S, they both will have the same size: S - N + 1. The difference between these view adaptors are:

View adaptor value_type The window size N is
ranges::adjacent_view tuple-like object a template parameter
ranges::slide_view a range a runtime parameter
Feature-test macro Value Std
__cpp_lib_ranges_zip 202110L (C++23)

Example

#include <array>
#include <tuple>
#include <ranges>
#include <string>
#include <cstddef>
#include <iostream>
 
int main()
{
    constexpr std::size_t window{3};
 
    constexpr std::array v {1, 2, 3, 4, 5, 6};
    std::cout << "v = [1 2 3 4 5 6]\n";
 
    for (int i{}; auto const e: v | std::views::adjacent<window>(v))
    {
        std::cout << "e = " << std::string(2 * i++, ' ') << '['
                  << std::get<0>(e) << ' '
                  << std::get<1>(e) << ' '
                  << std::get<2>(e) << "]\n";
    }
}

Output:

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

See also

(C++23)
 a view consisting of tuples 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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