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std::ranges::views::stride, std::ranges::stride_view

Defined in header <ranges> 
template< ranges::input_range V >
    requires ranges::view<V>
class stride_view :
    public ranges::view_interface<stride_view<V>>
 (1) (since C++23) 
namespace views {
    inline constexpr /* unspecified */ stride = /* unspecified */;
}
 (2) (since C++23)
Call signature 
template< ranges::viewable_range R >
constexpr ranges::view auto stride( R&& r, ranges::range_difference_t<R> n );
 (since C++23) 
template< class DifferenceType >
constexpr /*range adaptor closure*/ stride( DifferenceType&& n );
 (since C++23)
Helper templates
1) stride_view is a range adaptor that takes a view and a number n and produces a view, that consists of elements of the original view by advancing over n elements at a time. This means that each mth element of the produced view is (n * i)th element of the original view, for some non-negative index i. The elements of the original view, whose "index" is not a multiple of n, are not present in the produced view.
Let S be the size of the original view. Then the size of produced view is:
  • (S / n) + (S % n ? 1 : 0), if S >= n; otherwise,
  • 1, if S > 0; otherwise,
  • ​0​, and the resulting view is empty.
2) The name views::stride denotes a RangeAdaptorObject. Given subexpressions e and n, the expression views::stride(e, n) is expression-equivalent to stride_view(e, n).
The n must be greater than ​0​, otherwise the behavior is undefined.

stride_view always models input_range, and models forward_range, bidirectional_range, random_access_range, and/or sized_range, if adapted view type V models the corresponding concept. stride_view<V> models common_range whenever the underlying view V does.

Data members

Typical implementations of stride_view hold only two non-static data members:

  • the underlying view of type V (shown here as base_ for exposition only),
  • the size object (the "stride") of type ranges::range_difference_t<V> (shown here as stride_ for exposition only).

Member functions

(C++23)
 constructs a stride_view
(public member function)
(C++23)
 returns the stored stride value
(public member function)
(C++23)
 returns a copy of the underlying (adapted) 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++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>)
(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

Nested classes

(C++23)
 the iterator type
(exposition-only member class template)

Helper templates

template< class V >
inline constexpr bool ranges::enable_borrowed_range<stride_view<V>> =
    ranges::enable_borrowed_range<V>;
 (since C++23)

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

Notes

Feature-test macro Value Std Comment
__cpp_lib_ranges_stride 202207L (C++23) std::ranges::stride_view

Example

A link to test: Compiler Explorer.

#include <algorithm>
#include <iostream>
#include <ranges>
#include <string_view>
using namespace std::literals;
 
void print(std::ranges::viewable_range auto&& v, std::string_view separator = " ")
{
    for (auto const& x : v)
        std::cout << x << separator;
    std::cout << '\n';
}
 
int main()
{
    print(std::views::iota(1, 13) | std::views::stride(3));
    print(std::views::iota(1, 13) | std::views::stride(3) | std::views::reverse);
    print(std::views::iota(1, 13) | std::views::reverse | std::views::stride(3));
 
    print("0x0!133713337*x//42/A$"sv | std::views::stride(0B11) |
          std::views::transform([](char O) -> char { return 0100 + O; }),
          "");
}

Output:

1 4 7 10
10 7 4 1
12 9 6 3
password

References

  • C++23 standard (ISO/IEC 14882:2023):
    • 26.7.31 Stride view [range.stride]

See also

(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 tuples of references to adjacent elements of the adapted view
(class template) (range adaptor object)
(C++20)
 a view that consists of the elements of a range that satisfies a predicate
(class template) (range adaptor object)

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