NAME¶

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

Synopsis¶

Defined in header <ranges>
template< ranges::view V >

requires ranges::input_range<V> (1) (since C++23)
class chunk_view

: public ranges::view_interface<chunk_view<V>>
template< ranges::view V >

requires ranges::forward_range<V> (2) (since C++23)
class chunk_view<V>

: public ranges::view_interface<chunk_view<V>>
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, (since C++23)
ranges::range_difference_t<R> n );
template< class DifferenceType >
constexpr /*range adaptor closure*/ chunk( DifferenceType&& n (since C++23)
);
Helper templates
template< class I > (4) (exposition only*)
constexpr I __div_ceil( I num, I denom );

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;

Member functions¶

constructor constructs a chunk_view
(C++23) (public member function)
base returns a copy of the underlying (adapted) view
(C++23) (public member function)
begin returns an iterator to the beginning
(C++23) (public member function)
end returns an iterator or a sentinel to the end
(C++23) (public member function)
size returns the number of elements. Provided only if the underlying
(C++23) (adapted) range satisfies sized_range.
(public member function)
Inherited from std::ranges::view_interface
empty returns whether the derived view is empty. Provided if it satisfies
(C++20) sized_range or forward_range.
(public member function of std::ranges::view_interface<D>)
cbegin returns a constant iterator to the beginning of the range.
(C++23) (public member function of std::ranges::view_interface<D>)
cend returns a sentinel for the constant iterator of the range.
(C++23) (public member function of std::ranges::view_interface<D>)
operator bool returns whether the derived view is not empty. Provided if
(C++20) ranges::empty is applicable to it.
(public member function of std::ranges::view_interface<D>)
front returns the first element in the derived view. Provided if it
(C++20) satisfies forward_range.
(public member function of std::ranges::view_interface<D>)
back returns the last element in the derived view. Provided if it satisfies
(C++20) bidirectional_range and common_range.
(public member function of std::ranges::view_interface<D>)
operator[] returns the n^th element in the derived view. Provided if it satisfies
(C++20) random_access_range.
(public member function of std::ranges::view_interface<D>)

Deduction guides

Nested classes

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

Helper templates

template< class V >

inline constexpr bool ranges::enable_borrowed_range<chunk_view<V>> = (since C++23)

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.

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

Example¶

// Run this code

#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¶

ranges::chunk_by_view splits the view into subranges between each pair of adjacent
views::chunk_by elements for which the given predicate returns false
(C++23) (class template) (range adaptor object)
ranges::adjacent_view a view consisting of tuples of references to adjacent elements
views::adjacent of the adapted view
(C++23) (class template) (range adaptor object)
ranges::slide_view a view whose M^th element is a view over the M^th through (M +
views::slide N - 1)^th elements of another view
(C++23) (class template) (range adaptor object)