std::ranges::view_interface<D>::size
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< cpp | ranges | view interface
| 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.
Return value
1)
to-unsigned-like (ranges::end(static_cast<D&>(this)) - ranges::begin(static_cast<D&>(this))).2)
to-unsigned-like (ranges::end(static_cast<const D&>(this)) - ranges::begin(static_cast<const D&>(this))).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
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
| (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) |