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

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< cpp‎ | ranges

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 `m`th 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

(constructor) (C++23) | constructs a `stride_view` (public member function)
stride (C++23) | returns the stored stride value (public member function)
base (C++23) | returns a copy of the underlying (adapted) view (public member function)
begin (C++23) | returns an iterator to the beginning (public member function)
end (C++23) | returns an iterator or a sentinel to the end (public member function)
size (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
empty (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>`)
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 (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>`)
front (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>`)
back (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>`)
operator[] (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

iterator (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.

Run this code

    #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

ranges::slide_view views::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_view views::chunk (C++23) | a range of `view`s that are `N`-sized non-overlapping successive chunks of the elements of another `view` (class template) (range adaptor object)
ranges::adjacent_view views::adjacent (C++23) | a `view` consisting of tuples of references to adjacent elements of the adapted view (class template) (range adaptor object)
ranges::filter_view views::filter (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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