std::ranges::view_interface<D>::size

 

C++

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Named requirements

Feature test macros (C++20)

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Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

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Strings library

Containers library

Iterators library

Ranges library (C++20)

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Numerics library

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Filesystem library (C++17)

Regular expressions library (C++11)

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Technical specifications

Symbols index

External libraries

 

Ranges library

Range access
begin cbegin end cend	rbegin crbegin rend crend	size ssize data cdata	empty
Range conversions
to (C++23)
Range primitives
range_size_trange_difference_t range_value_t	range_reference_trange_const_reference_trange_rvalue_reference_t   (C++23)	iterator_tconst_iterator_tsentinel_t (C++23)
Dangling iterator handling
dangling	borrowed_iterator_t	borrowed_subrange_t
Range concepts
range borrowed_range    sized_range constant_range (C++23)	common_range view viewable_range	input_range output_range forward_range	bidirectional_range random_access_range contiguous_range
Views
view_interface	subrange
Factories
empty_viewviews::empty iota_viewviews::iota	single_viewviews::single cartesian_product_viewviews::cartesian_product (C++23)(C++23)	basic_istream_viewviews::istream repeat_viewviews::repeat (C++23)(C++23)
Adaptors
ref_view views::all_tviews::all common_viewviews::common reverse_viewviews::reverse as_const_viewviews::as_const (C++23)(C++23) as_rvalue_viewviews::as_rvalue (C++23)(C++23)   zip_viewviews::zip (C++23)(C++23) zip_transform_viewviews::zip_transform (C++23)(C++23)	owning_view take_viewviews::take take_while_viewviews::take_while drop_viewviews::drop drop_while_viewviews::drop_while 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)	views::counted elements_viewviews::elements keys_viewviews::keys values_viewviews::values transform_viewviews::transform chunk_viewviews::chunk (C++23)(C++23) chunk_by_viewviews::chunk_by (C++23)(C++23) slide_viewviews::slide (C++23)(C++23)	filter_viewviews::filter split_viewviews::split lazy_split_viewviews::lazy_split join_viewviews::join join_with_viewviews::join_with (C++23)(C++23) enumerate_viewviews::enumerate (C++23)(C++23) stride_viewviews::stride (C++23)(C++23)
Range generators
std::generator (C++23)
Range adaptor objects
Range adaptor closure objects
Helper items
movable-box	non-propagating-cache	simple-view

 

std::ranges::view_interface

Member functions

empty (C++20)

operator bool (C++20)

data (C++20)

size (C++20)

front (C++20)

back (C++20)

operator[] (C++20)

 

constexpr auto size() requires ranges::forward_range<D> &&     std::sized_sentinel_for<ranges::sentinel_t<D>,                             ranges::iterator_t<D>>;	(1)	(since C++20)
constexpr auto size() const requires ranges::forward_range<const D> &&     std::sized_sentinel_for<ranges::sentinel_t<const D>,                             ranges::iterator_t<const D>>;	(2)	(since C++20)

The default implementation of size() member function obtains the size of the range by calculating the difference between the sentinel and the beginning iterator.

1) Let derived be static_cast<D&>(*this). Equivalent to return /*to-unsigned-like*/(ranges::end(derived) - ranges::begin(derived));, where the exposition-only function template to-unsigned-like performs the explicit cast from the argument type to its corresponding unsigned type.

2) Same as (1), except that derived is static_cast<const D&>(*this).

Parameters

(none)

Return value

The difference between the sentinel and the beginning iterator of the value of the derived type, converted to its corresponding unsigned type.

Notes

Following derived types may use the default implementation of size():

• std::ranges::drop_while_view

Following types are derived from std::ranges::view_interface and do not declare their own size() member function, but they cannot use the default implementation, because their iterator and sentinel types never satisfy sized_sentinel_for:

• std::ranges::basic_istream_view
• std::ranges::filter_view
• std::ranges::join_view
• std::ranges::lazy_split_view
• std::ranges::split_view
• std::ranges::take_while_view

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 3646	C++20	the default implementations of size functions returned a signed type	they return unsigned type

See also

sizessize (C++17)(C++20)	returns the size of a container or array (function template)
ranges::size (C++20)	returns an integer equal to the size of a range (customization point object)
ranges::ssize (C++20)	returns a signed integer equal to the size of a range (customization point object)