std::ranges::view_interface<D>::size
constexpr auto size() requires ranges::forward_range<D> && std::sized_sentinel_for<ranges::sentinel_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>, |
(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.
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.derived
is static_cast<const D&>(*this).Contents |
[edit] Parameters
(none)
[edit] Return value
The difference between the sentinel and the beginning iterator of the value of the derived type, converted to its corresponding unsigned type.
[edit] Notes
Following derived types may use the default implementation of size()
:
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
[edit] 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 |
[edit] See also
(C++17)(C++20) |
returns the size of a container or array (function template) |
(C++20) |
returns an integer equal to the size of a range (customization point object) |
(C++20) |
returns a signed integer equal to the size of a range (customization point object) |