NAME¶

std::ranges::view_interface::size - std::ranges::view_interface::size

Synopsis¶

constexpr auto size() requires ranges::forward_range<D> &&

std::sized_sentinel_for<ranges::sentinel_t<D>, (1) (since C++20)

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

ranges::iterator_t<const D>>;

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 they return unsigned
functions returned a signed type type

See also¶

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