std::ranges::view_interface<D>::size

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Ranges library
Range access
Range conversions
(C++23)
Range primitives



Dangling iterator handling
Range concepts
Views

Range factories
Range adaptors
Range generators
Range adaptor objects
Range adaptor closure objects
Helper items
(until C++23)(C++23)


 
std::ranges::view_interface
Member functions
(C++20)
(C++23)
(C++23)
(C++20)
size
(C++20)
(C++20)
(C++20)
(C++20)
 
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 /*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():

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:

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)
returns an integer equal to the size of a range
(customization point object)
returns a signed integer equal to the size of a range
(customization point object)