std::ranges::views::take,std::ranges::take_view

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Ranges library

Range access

begin
cbegin
end
cend

rbegin
crbegin
rend
crend

size
ssize
data
cdata

reserve_hint (C++26)
empty

Range conversions
std::from_range_t std::from_range (C++23)(C++23)
to (C++23)

Dangling iterator handling
dangling
borrowed_iterator_t
borrowed_subrange_t

Range primitives

range_size_trange_difference_trange_value_t
elements_of (C++23)

iterator_tconst_iterator_tsentinel_tconst_sentinel_t

(C++23)(C++23)

range_reference_trange_const_reference_trange_rvalue_reference_trange_common_reference_t

(C++23)

Range concepts

range
borrowed_range
common_range

sized_range
viewable_range
view

input_range
output_range
forward_range

bidirectional_range
random_access_range
contiguous_range

approximately_sized_range (C++26)
constant_range (C++23)

empty_viewviews::empty

single_viewviews::single

basic_istream_viewviews::istream

iota_viewviews::iota

repeat_viewviews::repeat

(C++23)(C++23)

Range adaptors

views::all_tviews::all
as_rvalue_viewviews::as_rvalue (C++23)(C++23)
filter_viewviews::filter
transform_viewviews::transform
take_viewviews::take
take_while_viewviews::take_while
common_viewviews::common
views::counted
to_input_viewviews::to_input (C++26)(C++26)

ref_view
drop_viewviews::drop
drop_while_viewviews::drop_while
lazy_split_viewviews::lazy_split
split_viewviews::split
join_viewviews::join
join_with_viewviews::join_with (C++23)(C++23)
concat_viewviews::concat (C++26)(C++26)
cache_latest_viewviews::cache_latest (C++26)(C++26)

owning_view
reverse_viewviews::reverse
as_const_viewviews::as_const (C++23)(C++23)
elements_viewviews::elements
keys_viewviews::keys
values_viewviews::values
enumerate_viewviews::enumerate (C++23)(C++23)
zip_viewviews::zip (C++23)(C++23)
zip_transform_viewviews::zip_transform (C++23)(C++23)

adjacent_viewviews::adjacent (C++23)(C++23)
views::pairwise (C++23)
adjacent_transform_viewviews::adjacent_transform (C++23)(C++23)
views::pairwise_transform (C++23)
chunk_viewviews::chunk (C++23)(C++23)
slide_viewviews::slide (C++23)(C++23)
chunk_by_viewviews::chunk_by (C++23)(C++23)
stride_viewviews::stride (C++23)(C++23)
cartesian_product_viewviews::cartesian_product (C++23)(C++23)

Range generators
std::generator (C++23)

Range adaptor closure objects
range_adaptor_closure (C++23)

Range adaptor objects

Helper items

copyable-box
movable-box

(until C++23) (C++23)

simple-view
non-propagating-cache

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std::ranges::take_view

Member functions
take_view::take_view
take_view::base
take_view::begin
take_view::end
take_view::size
take_view::reserve_hint (C++26)
Deduction guides
Sentinel
Member functions
take_view::sentinel::sentinel
Non-member functions
take_view::sentinel::base
operator==(std::counted_iterator,take_view::sentinel)

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Defined in header`<ranges>`
template<ranges::view V> class take_view :publicranges::view_interface<take_view<V>>	(1)	(since C++20)
namespace views{ inlineconstexpr/* unspecified / take=/ unspecified */; }	(2)	(since C++20)
Call signature
template<ranges::viewable_range R> requires/* see below */ constexprranges::viewauto take( R&& r,ranges::range_difference_t<R> count);		(since C++20)
template<class DifferenceType> constexpr/* range adaptor closure */ take( DifferenceType&& count);		(since C++20)

1) A range adaptor that representsview of the elements from an underlying sequence, starting at the beginning and ending at a given bound.

2)views::take is aRangeAdaptorObject. The expressionviews::take(e, f) results in a view that represents the firstf elements frome. The result is not necessarily atake_view.

views::take(e, f) isexpression-equivalent to (whereT isstd::remove_cvref_t<decltype((e))> andD isranges::range_difference_t<decltype((e))>):

((void)f, decay-copy(e)), ifT is aranges::empty_view, except that the evaluations ofe andf are indeterminately sequenced;
U(ranges::begin(e),ranges::begin(e)+std::min<D>(ranges::distance(e), f)), ifT is a specialization ofstd::span,std::basic_string_view, orranges::subrange that models bothrandom_access_range andsized_range, whereU is

std::span<typename T::element_type>, ifT is a specialization ofstd::span;
T, ifT is a specialization ofstd::basic_string_view;
ranges::subrange<ranges::iterator_t<T>>, ifT is a specialization ofranges::subrange;

ranges::iota_view(*ranges::begin(e),
*(ranges::begin(e)+std::min<D>(ranges::distance(e), f))), ifT is a specialization ofranges::iota_view that models bothrandom_access_range andsized_range;

otherwise, ifT is a specialization ofranges::repeat_view:

views::repeat(*e.value_,std::min<D>(ranges::distance(e), f)), ifT modelssized_range; is such casee is evaluated only once;
views::repeat(*e.value_,static_cast<D>(e)) otherwise;

(since C++23)

otherwise,take_view(e, f).

In all cases,decltype((f)) must modelstd::convertible_to<D>.

take_view models the conceptscontiguous_range,random_access_range,bidirectional_range,forward_range,input_range, andsized_range when the underlying viewV models respective concepts. It modelscommon_range when the underlying viewV models bothrandom_access_range andsized_range.

[edit]Data members

Member	Description
`Vbase_`	the underlying view (exposition-only member object*)
ranges::range_difference_t<V>`count_`	the number of elements to take (exposition-only member object*)

[edit]Member functions

(constructor)	constructs a`take_view` (public member function)[edit]
base	returns a copy of the underlying (adapted) view (public member function)[edit]
begin	returns an iterator to the beginning (public member function)[edit]
end	returns an iterator or a sentinel to the end (public member function)[edit]
size	returns the number of elements, provided only if the underlying (adapted) range satisfies`sized_range` (public member function)[edit]
reserve_hint (C++26)	returns the approximate size of the resulting`approximately_sized_range` (public member function)[edit]
Inherited fromstd::ranges::view_interface
empty	returns whether the derived view is empty, provided only if it satisfies`sized_range` or`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
cbegin (C++23)	returns a constant iterator to the beginning of the range (public member function of`std::ranges::view_interface<D>`)[edit]
cend (C++23)	returns a sentinel for the constant iterator of the range (public member function of`std::ranges::view_interface<D>`)[edit]
operator bool	returns whether the derived view is not empty, provided only ifranges::empty is applicable to it (public member function of`std::ranges::view_interface<D>`)[edit]
data	gets the address of derived view's data, provided only if its iterator type satisfies`contiguous_iterator` (public member function of`std::ranges::view_interface<D>`)[edit]
front	returns the first element in the derived view, provided if it satisfies`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
back	returns the last element in the derived view, provided only if it satisfies`bidirectional_range` and`common_range` (public member function of`std::ranges::view_interface<D>`)[edit]
operator[]	returns the`n`^th element in the derived view, provided only if it satisfies`random_access_range` (public member function of`std::ranges::view_interface<D>`)[edit]

[edit]Deduction guides

[edit]Nested classes

sentinel

(C++20)

the sentinel type
(exposition-only member class template*)

[edit]Helper templates

template<class T> constexprbool enable_borrowed_range<std::ranges::take_view<T>>= ranges::enable_borrowed_range<T>;		(since C++20)

This specialization ofranges::enable_borrowed_range makestake_view satisfyborrowed_range when the underlying view satisfies it.

[edit]Example

Run this code

#include <algorithm>#include <iostream>#include <ranges> int main(){namespace views= std::views;auto print=[](char x){std::cout<< x;}; for(constchar nums[]{'1','2','3'};int n:views::iota(0,5)){std::cout<<"take("<< n<<"): ";// safely takes only upto min(n, nums.size()) elements:        std::ranges::for_each(nums| views::take(n), print);std::cout<<'\n';}}

Output:

take(0): take(1): 1take(2): 12take(3): 123take(4): 123

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3407	C++20	`views::take` sometimes failed to construct a sized random access range	the result type is adjusted so that construction is always valid
LWG 3494	C++20	`take_view` was never a`borrowed_range`	it is a`borrowed_range` if its underlying view is

[edit]See also

views::counted (C++20)	creates a subrange from an iterator and a count (customization point object)[edit]
ranges::take_while_viewviews::take_while (C++20)	a`view` consisting of the initial elements of another`view`, until the first element on which a predicate returnsfalse (class template)(range adaptor object)[edit]
ranges::copy_n (C++20)	copies a number of elements to a new location (algorithm function object)[edit]