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>>;

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

1) to-unsigned-like (ranges::end(static_cast<D&>(this))-
                     ranges::begin(static_cast<D&>(this))). 2) to-unsigned-like (ranges::end(static_cast<constD&>(this))-
                     ranges::begin(static_cast<constD&>(this))).

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)