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

template< ranges::view V >
    requires ranges::input_range<V>
class chunk_view :
    public ranges::view_interface<chunk_view<V>>

template< ranges::view V >
    requires ranges::forward_range<V>
class chunk_view<V> :
    public ranges::view_interface<chunk_view<V>>

namespace views {
    inline constexpr /* unspecified */ chunk = /* unspecified */;
}

template< ranges::viewable_range R >
constexpr ranges::view auto chunk( R&& r, ranges::range_difference_t<R> n );

template< class DifferenceType >
constexpr /*range adaptor closure*/ chunk( DifferenceType&& n );

template< class I > 
constexpr I __div_ceil( I num, I denom );    // 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.

I r = num / denom;
if (num % denom)
    ++r;
return r;

Data members

Typical implementations of chunk_view (1,2) hold two non-static data members:

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

In addition, if V models exactly the input_range, chunk_view (1) typically holds two more non-static data members:

• the number of elements left in the current chunk ranges::range_difference_t<V> (shown here as remainder_ for exposition only),
• the current cached underlying iterator __non_propagating_cache<ranges::iterator_t<V>> (shown here as current_ for exposition only).

Member functions

Deduction guides

Nested classes

Helper templates

template< class V >
inline constexpr bool ranges::enable_borrowed_range<chunk_view<V>> =
    ranges::forward_range<V> && ranges::enable_borrowed_range<V>;

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.

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';
    }
}

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