Defined in header <ranges> | ||
|---|---|---|
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) |
| Call signature | ||
template< ranges::viewable_range R >
requires /* see below */
constexpr ranges::view auto
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) |
view of the elements from an underlying sequence, starting at the beginning and ending at a given bound.decltype((f))
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.
|
(C++20) | constructs a take_view (public member function) |
|
(C++20) | returns a copy of the underlying (adapted) view (public member function) |
|
(C++20) | returns an iterator to the beginning (public member function) |
|
(C++20) | returns an iterator or a sentinel to the end (public member function) |
|
(C++20) | returns the number of elements. Provided only if the underlying (adapted) range satisfies sized_range. (public member function) |
Inherited from |
|
|
(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) | gets the address of derived view's data. Provided if its iterator type satisfies contiguous_iterator. (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>) |
|
(C++20) | the sentinel type (exposition-only member class template) |
template<class T>
inline constexpr bool enable_borrowed_range<std::ranges::take_view<T>> =
std::ranges::enable_borrowed_range<T>;
| (since C++20) |
This specialization of std::ranges::enable_borrowed_range makes take_view satisfy borrowed_range when the underlying view satisfies it.
#include <algorithm>
#include <iostream>
#include <ranges>
auto print = [](char x){ std::cout << x; };
int main()
{
constexpr char pi[]{'3', '.', '1', '4', '1', '5', '9', '2'};
std::ranges::for_each(pi | std::ranges::views::take(6), print);
std::cout << '\n';
// safely takes 8 chars only, i.e. min(pi.size(), 42)
std::ranges::for_each(std::ranges::take_view{pi, 42}, print);
std::cout << '\n';
}Output:
3.1415 3.141592
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 toconstruct 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 |
|
(C++20) | creates a subrange from an iterator and a count (customization point object) |
|
(C++20) | a view consisting of the initial elements of another view, until the first element on which a predicate returns false (class template) (range adaptor object) |
|
(C++20) | copies a number of elements to a new location (niebloid) |
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