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

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.

Return value

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

size ssize (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)