cpp / latest / ranges / view_interface / size.html /

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.

1) Let derived be static_cast<D&>(*this). Equivalent to return ranges::end(derived) - ranges::begin(derived);.
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.

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:

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)

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/ranges/view_interface/size