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std::ranges::views::chunk, std::ranges::chunk_view

Defined in header <ranges> 
template< ranges::view V >
    requires ranges::input_range<V>
class chunk_view
    : public ranges::view_interface<chunk_view<V>>
 (1) (since C++23) 
template< ranges::view V >
    requires ranges::forward_range<V>
class chunk_view<V>
    : public ranges::view_interface<chunk_view<V>>
 (2) (since C++23) 
namespace views {
    inline constexpr /* unspecified */ chunk = /* unspecified */;
}
 (3) (since C++23)
Call signature 
template< ranges::viewable_range R >
constexpr ranges::view auto chunk( R&& r, ranges::range_difference_t<R> n );
 (since C++23) 
template< class DifferenceType >
constexpr /*range adaptor closure*/ chunk( DifferenceType&& n );
 (since C++23)
Helper templates 
template< class I > 
constexpr I __div_ceil( I num, I denom );
 (4) (exposition only*)

chunk_view takes a view and a number n and produces a range of views (the chunks) of the original view, such that each chunk, except maybe the last one, has the size n. These chunks are non-overlapping, successive sub-ranges of the elements of the original view, in order.

Let s be the size of the original view. If s is not the multiple of n, the size of the last produced view is exactly s % n (the remainder). Otherwise, the size of each chunk, including the last one, is n.

The size of produced view is __div_ceil(s).

If the n is not greater than ​0​ the behavior is undefined.

1) An implementation that supports the underlying view V that models only input_range.
2) A partial specialization that supports the underlying view V that models forward_range or stronger. Models common_range if the underlying view V is forward_range, common_range, and either sized_range or non bidirectional_range.
3) The name views::chunk denotes a RangeAdaptorObject. Given subexpressions e and n, the expression views::chunk(e, n) is expression-equivalent to chunk_view(e, n).
4) Computes the smallest integer value that is not less than the quotient of dividing num by denom. Equivalent to: 
I r = num / denom;
if (num % denom)
    ++r;
return r;

Data members

Member object Definition
base_ (private) The underlying view of type V.
(exposition-only member object*)
n_ (private) The "chunk size" of type ranges::range_difference_t<V>.
(exposition-only member object*)
If V models exactly input_range (1)
remainder_ (private)
(optional)		 The number of elements left in the current chunk, of type ranges::range_difference_t<V>.
(exposition-only member object*)
current_ (private)
(optional)		 An optional-like object of type /*non-propagating-cache*/<ranges::iterator_t<V>> that caches current underlying iterator.
(exposition-only member object*)

Member functions

(C++23)
constructs a chunk_view
(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 output ("chunk-wise") iterator type when V models input_range (1)
(exposition-only member class*)
(C++23)
the inner ("element-wise") iterator type when V models input_range (1)
(exposition-only member class*)
(C++23)
the iterator type when V models forward_range (2)
(exposition-only member class template*)

Helper templates

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

This specialization of ranges::enable_borrowed_range makes chunk_view satisfy borrowed_range when the underlying view V satisfies both, the forward_range and the borrowed_range.

Notes

If V models input_range (1), chunk_view's iterator has a dedicated type: outer_iterator::value_type that is itself an input view.

If V models forward_range or stronger (2), chunk_view defers to views::take for its value_type.

If V models bidirectional_range or stronger ranges (2), the need to calculate size the last chunk correctly (from the end iterator) requires the underlying range type V to be sized_range.

Feature-test macro Value Std Feature
__cpp_lib_ranges_chunk 202202L (C++23) std::ranges::chunk_view

Example

#include <algorithm>
#include <iostream>
#include <ranges>
 
auto print_subrange = [](std::ranges::viewable_range auto&& r)
{
    std::cout << '[';
    for (int pos{}; auto elem : r)
        std::cout << (pos++ ? " " : "") << elem;
    std::cout << "] ";
};
 
int main()
{
    const auto v = {1, 2, 3, 4, 5, 6};
 
    for (const unsigned width : std::views::iota(1U, 2U + v.size()))
    {
        auto const chunks = v | std::views::chunk(width);
        std::cout << "chunk(" << width << "): ";
        std::ranges::for_each(chunks, print_subrange);
        std::cout << '\n';
    }
}

Output:

chunk(1): [1] [2] [3] [4] [5] [6]
chunk(2): [1 2] [3 4] [5 6]
chunk(3): [1 2 3] [4 5 6]
chunk(4): [1 2 3 4] [5 6]
chunk(5): [1 2 3 4 5] [6]
chunk(6): [1 2 3 4 5 6]
chunk(7): [1 2 3 4 5 6]

References

  • C++23 standard (ISO/IEC 14882:2023):
    • 26.7.28 Chunk view [range.chunk]

See also

(C++23)
splits the view into subranges between each pair of adjacent elements for which the given predicate returns false
(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++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)

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