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std::ranges::take_view<V>::end

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< cpp‎ | ranges‎ | take view
 
 
Ranges library
Range access
Range conversions
(C++23)
Range primitives



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


 
 
constexpr auto end() requires (!__SimpleView<V>);
(1) (since C++20)
constexpr auto end() const requires ranges::range<const V>;
(2) (since C++20)

Returns a sentinel or an iterator representing the end of the take_view. The end of the take_view is either one past the count-th element in the underlying range, or the end of the underlying range if the latter has less than count elements.

1) Returns a take_view::/*sentinel*/<false>, a std::default_sentinel_t, or a ranges::iterator_t<V>.
2) Returns a take_view::/*sentinel*/<true>, a std::default_sentinel_t, or a ranges::iterator_t<const V>.

Overload (1) does not participate in overload resolution if V is a simple view (that is, if V and const V are views with the same iterator and sentinel types).

Contents

[edit] Parameters

(none)

[edit] Return value

The result depends on the concepts satisfied by possibly const-qualified underlying view type Base_, that is V (for overload (1)) or const V (for overload (2)).

Let base_ be the underlying view.

The underlying view satisfies ... random_access_range
yes no
sized_range yes ranges::begin(base_) +

ranges::range_difference_t<Base_>(this->size())

std::default_sentinel
no
1) /*sentinel*/<false>{ranges::end(base_)}
2) /*sentinel*/<true>{ranges::end(base_)}

[edit] Example

#include <list>
#include <ranges>
#include <iterator>
#include <iostream>
#include <type_traits>
 
int main()
{
    const auto list1 = { 3, 1, 4, 1, 5 };
    const auto seq1 = list1 | std::views::take(4);
    static_assert(std::ranges::sized_range<decltype(seq1)> and
                  std::ranges::random_access_range<decltype(seq1)> and
                  std::is_same_v<decltype(seq1.end()), decltype(list1.end())>);
    for (auto it = seq1.begin(); it != seq1.end(); ++it)
         std::cout << *it << ' ';
    std::cout << '\n';
 
    std::list list2 = { 2, 7, 1, 8, 2 };
    const auto seq2 = list2 | std::views::take(4);
    static_assert(std::ranges::sized_range<decltype(seq2)> and
                  not std::ranges::random_access_range<decltype(seq2)> and
                  std::is_same_v<decltype(seq2.end()), std::default_sentinel_t>);
    for (auto it = seq2.begin(); it != std::default_sentinel; ++it)
        std::cout << *it << ' ';
    std::cout << '\n';
}

Output:

3 1 4 1
2 7 1 8

[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
P2393R1 C++20 implicit conversions between signed and unsigned integer-class types might fail made explicit

[edit] See also

(C++20)
returns an iterator to the beginning
(public member function) [edit]
iterator adaptor that tracks the distance to the end of the range
(class template) [edit]
compares a sentinel with an iterator returned from take_view::begin
(function) [edit]