std::ranges::views::empty,std::ranges::empty_view

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Ranges library

Range access

begin
cbegin
end
cend

rbegin
crbegin
rend
crend

size
ssize
data
cdata

reserve_hint (C++26)
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
common_range

sized_range
viewable_range
view

input_range
output_range
forward_range

bidirectional_range
random_access_range
contiguous_range

approximately_sized_range (C++26)
constant_range (C++23)

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
as_rvalue_viewviews::as_rvalue (C++23)(C++23)
filter_viewviews::filter
transform_viewviews::transform
take_viewviews::take
take_while_viewviews::take_while
common_viewviews::common
views::counted
to_input_viewviews::to_input (C++26)(C++26)

ref_view
drop_viewviews::drop
drop_while_viewviews::drop_while
lazy_split_viewviews::lazy_split
split_viewviews::split
join_viewviews::join
join_with_viewviews::join_with (C++23)(C++23)
concat_viewviews::concat (C++26)(C++26)
cache_latest_viewviews::cache_latest (C++26)(C++26)

owning_view
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

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Defined in header`<ranges>`
template<class T> requiresstd::is_object_v<T> class empty_view:publicranges::view_interface<empty_view<T>>	(1)	(since C++20)
namespace views{ template<class T> constexpr empty_view<T> empty{}; }	(2)	(since C++20)

1) A range factory that produces aview of no elements of a particular type.

2) Variable template forempty_view.

[edit]Member functions

begin [static]	returnsnullptr (public static member function)
end [static]	returnsnullptr (public static member function)
data [static]	returnsnullptr (public static member function)
size [static]	returns0 (public static member function)
empty [static]	returnstrue (public static member function)
Inherited fromstd::ranges::view_interface
cbegin (C++23)	returns a constant iterator to the beginning of the range (public member function of`std::ranges::view_interface<D>`)[edit]
cend (C++23)	returns a sentinel for the constant iterator of the range (public member function of`std::ranges::view_interface<D>`)[edit]
operator bool	returns whether the derived view is not empty, provided only ifranges::empty is applicable to it (public member function of`std::ranges::view_interface<D>`)[edit]
front	returns the first element in the derived view, provided if it satisfies`forward_range` (public member function of`std::ranges::view_interface<D>`)[edit]
back	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]
operator[]	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

staticconstexpr T* begin()noexcept{return nullptr;}		(since C++20)

empty_view does not reference any element.

std::ranges::empty_view::end

staticconstexpr T* end()noexcept{return nullptr;}		(since C++20)

empty_view does not reference any element.

std::ranges::empty_view::data

staticconstexpr T* data()noexcept{return nullptr;}		(since C++20)

empty_view does not reference any element.

std::ranges::empty_view::size

staticconstexprstd::size_t size()noexcept{return0;}		(since C++20)

empty_view is always empty.

std::ranges::empty_view::empty

staticconstexprbool empty()noexcept{returntrue;}		(since C++20)

empty_view is always empty.

[edit]Helper templates

template<class T> constexprboolranges::enable_borrowed_range<ranges::empty_view<T>>=true;		(since C++20)

This specialization ofranges::enable_borrowed_range makesempty_view satisfyborrowed_range.

[edit]Notes

Althoughempty_view obtainsfront,back, andoperator[] member functions fromview_interface, calls to them always result in undefined behavior since anempty_view is always empty.

The inheritedoperatorbool conversion function always returnsfalse.

[edit]Example

Run this code

#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

optional (C++17)	a wrapper that may or may not hold an object (class template)[edit]
ranges::single_viewviews::single (C++20)	a`view` that contains a single element of a specified value (class template)(customization point object)[edit]
views::all_tviews::all (C++20)	a`view` that includes all elements of a`range` (alias template)(range adaptor object)[edit]
ranges::ref_view (C++20)	a`view` of the elements of some other`range` (class template)[edit]