Ranges library
Range access
Range conversions

Range primitives

Dangling iterator handling
Range concepts

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

constexpr auto size() requires ranges::forward_range<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).


[edit] Parameters


[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:

[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

returns the size of a container or array
(function template) [edit]
returns an integer equal to the size of a range
(customization point object)[edit]
returns a signed integer equal to the size of a range
(customization point object)[edit]