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

std::ranges::views::empty, std::ranges::empty_view - cppreference.com

(1) (since C++20) namespace views { template<class T> constexpr empty_view<T> empty{}; } (2) (since C++20) 1)

A range factory that produces a

view

of no elements of a particular type.

2) Variable template for empty_view.

[edit] Member functions returns nullptr
(public static member function) returns nullptr
(public static member function) returns nullptr
(public static member function) returns â0â
(public static member function) returns true
(public static member function) Inherited from std::ranges::view_interface 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] 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] std::ranges::empty_view::begin

static constexpr T* begin() noexcept { return nullptr; }

(since C++20)

empty_view does not reference any element.

std::ranges::empty_view::end

static constexpr T* end() noexcept { return nullptr; }

(since C++20)

empty_view does not reference any element.

std::ranges::empty_view::data

static constexpr T* data() noexcept { return nullptr; }

(since C++20)

empty_view does not reference any element.

std::ranges::empty_view::size static constexpr std::size_t size() noexcept { return 0; } (since C++20)

empty_view is always empty.

std::ranges::empty_view::empty

static constexpr bool empty() noexcept { return true; }

(since C++20)

empty_view is always empty.

[edit] Helper templates

This specialization of ranges::enable_borrowed_range makes empty_view satisfy borrowed_range.

[edit] Notes

Although empty_view obtains front, back, and operator[] member functions from view_interface, calls to them always result in undefined behavior since an empty_view is always empty.

The inherited operator bool conversion function always returns false.

[edit] Example

#include <ranges>
 
int main()
{
    namespace ranges = std::ranges;
 
    ranges::empty_view<long> e;
    static_assert(ranges::empty(e)); // uses operator bool
    static_assert(0 == e.size());
    static_assert(nullptr == e.data());
    static_assert(nullptr == e.begin());
    static_assert(nullptr == e.end());
    static_assert(nullptr == e.cbegin());
    static_assert(nullptr == e.cend());
}

[edit] See also

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