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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/ranges/../../ranges/take_view.html below:

std::ranges::views::take, std::ranges::take_view - cppreference.com

(1) (since C++20) namespace views { inline constexpr /* unspecified */ take = /* unspecified */; } (2) (since C++20)

Call signature

(since C++20)

template< class DifferenceType > constexpr /* range adaptor closure */ take( DifferenceType&& count );

(since C++20) 1)

A range adaptor that represents

view

of the elements from an underlying sequence, starting at the beginning and ending at a given bound.

2) views::take

is a

RangeAdaptorObject

. 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

views::take(e, f) is expression-equivalent to (where T is std::remove_cvref_t<decltype((e))> and D is ranges::range_difference_t<decltype((e))>):

((void)f, decay-copy(e)), if T is a ranges::empty_view, except that the evaluations of e and f are indeterminately sequenced;
U(ranges::begin(e), ranges::begin(e) + std::min<D>(ranges::distance(e), f)), if T is a specialization of std::span, std::basic_string_view, or ranges::subrange that models both random_access_range and sized_range, where U is

std::span<typename T::element_type>, if T is a specialization of std::span;
T, if T is a specialization of std::basic_string_view;
ranges::subrange<ranges::iterator_t<T>>, if T is a specialization of ranges::subrange;

ranges::iota_view(*ranges::begin(e), *(ranges::begin(e) + std::min<D>(ranges::distance(e), f))), if T is a specialization of ranges::iota_view that models both random_access_range and sized_range;

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.

[edit] Data members Member Description V base_ 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 constructs a take_view
(public member function) [edit] returns a copy of the underlying (adapted) view
(public member function) [edit] returns an iterator to the beginning
(public member function) [edit] returns an iterator or a sentinel to the end
(public member function) [edit] returns the number of elements, provided only if the underlying (adapted) range satisfies sized_range
(public member function) [edit] returns the approximate size of the resulting approximately_sized_range
(public member function) [edit] Inherited from std::ranges::view_interface 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] returns a constant iterator to the beginning of the range
(public member function of std::ranges::view_interface<D>) [edit] returns a sentinel for the constant iterator of the range
(public member function of std::ranges::view_interface<D>) [edit] returns whether the derived view is not empty, provided only if ranges::empty is applicable to it
(public member function of std::ranges::view_interface<D>) [edit] 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] returns the first element in the derived view, provided if it satisfies forward_range
(public member function of std::ranges::view_interface<D>) [edit] 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] 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 the sentinel type
(exposition-only member class template*) [edit] Helper templates

This specialization of ranges::enable_borrowed_range makes take_view satisfy borrowed_range when the underlying view satisfies it.

[edit] Example

#include <algorithm>
#include <iostream>
#include <ranges>
 
int main()
{
    namespace views = std::views;
    auto print = [](char x){ std::cout << x; };
 
    for (const char 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): 1
take(2): 12
take(3): 123
take(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

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