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

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

Technical specifications

Symbols index

External libraries

 

Ranges library

Range access begin cbegin   end cend rbegin crbegin   rend crend size ssize   data cdata 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    sized_range	common_range view viewable_range	input_range output_range forward_range	bidirectional_range    random_access_range contiguous_range	constant_range (C++23)

Views
view_interface	subrange

Range factories
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 ref_view owning_view as_rvalue_viewviews::as_rvalue (C++23)(C++23)   filter_viewviews::filter transform_viewviews::transform take_viewviews::take take_while_viewviews::take_while concat_viewviews::concat (C++26)(C++26)	drop_viewviews::drop drop_while_viewviews::drop_while join_viewviews::join join_with_viewviews::join_with (C++23)(C++23)   lazy_split_viewviews::lazy_split split_viewviews::split views::counted common_viewviews::common	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

 

std::ranges::take_view

Member functions

take_view::take_view

take_view::base

take_view::begin

take_view::end

take_view::size

Deduction guides

Sentinel

Member functions

take_view::sentinel::sentinel

Non-member functions

take_view::sentinel::base

operator==(std::counted_iterator,take_view::sentinel)

 

template< ranges::view V > class take_view : public ranges::view_interface<take_view<V>>	(1)	(since C++20)
namespace views {     inline constexpr /*unspecified*/ take = /*unspecified*/; }	(2)	(since C++20)

1) A range adaptor that represents view of the first N elements from an underlying sequence, or all elements if the underlying sequence contains fewer than N.

2) The expression views::take(E, F) results in a view that represents the first F elements from E. The result is not necessarily a take_view.

It is expression-equivalent to (where T is std::remove_cvref_t<decltype((E))> and D is ranges::range_difference_t<decltype((E))>):

• ((void)F, static_cast<T>(E)), if T is a ranges::empty_view;
• T{ranges::begin(E), ranges::begin(E) + std::min<D>(ranges::size(E), F)}, if T models both random_access_range and sized_range, and T is a specialization of

• std::span where T::extent == std::dynamic_extent,
• std::basic_string_view,
• ranges::iota_view, or
• ranges::subrange;

• otherwise, take_view{E, F}.

In all cases, decltype((F)) must model std::convertible_to<D>.

take_view models the concepts contiguous_range, random_access_range, bidirectional_range, forward_range, input_range, and sized_range when the underlying view V models respective concepts. It models common_range when the underlying view V models both random_access_range and sized_range.

Expression-equivalent

Expression e is expression-equivalent to expression f, if

• e and f have the same effects, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

Member functions

(constructor)	constructs a take_view (public member function)
base	returns a copy of the underlying (adapted) view (public member function)
begin	returns an iterator to the beginning (public member function)
end	returns an iterator or a sentinel to the end (public member function)
size	returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range. (public member function)

Nested classes

sentinel

the sentinel type (public member class)

Example

Run this code

#include <ranges>
#include <algorithm> // for std::ranges::for_each
#include <iostream>
 
auto print = [](char x) { std::cout << x; };
 
int main()
{
    constexpr char pi[] { '3', '.', '1', '4', '1', '5', '9', '2', '6', '5' };
 
    std::ranges::for_each(pi | std::ranges::views::take(8), print);
    std::cout << '\n';
 
    std::ranges::for_each(std::ranges::take_view{pi, 8}, print);
    std::cout << '\n';
}

Output:

3.141592
3.141592