std::iter_value_t, std::iter_reference_t, std::iter_difference_t, std::iter_rvalue_reference_t, std::iter_common_reference_t

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Iterator library

Iterator primitives
iterator_traits
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tag
iterator
Iterator adaptors
reverse_iterator move_iterator (C++11) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) back_inserter front_inserter inserter
Stream iterators
istream_iterator
ostream_iterator
istreambuf_iterator
ostreambuf_iterator
Iterator operations
advance
distance
prev (C++11)
next (C++11)
Range access
begincbegin (C++11)(C++14)
endcend (C++11)(C++14)
rbegincrbegin (C++14)(C++14)
rendcrend (C++14)(C++14)
Container access
sizessize (C++17)(C++20)
empty (C++17)
data (C++17)

 

Defined in header <iterator>
template< class T > concept /*dereferenceable*/ = /* see below */; // exposition only
template< class T > using iter_value_t = /* see below */;	(1)	(since C++20)
template< /*dereferenceable*/ T > using iter_reference_t = decltype(*std::declval<T&>());	(2)	(since C++20)
template< class T > using iter_difference_t = /* see below */;	(3)	(since C++20)
template< /*dereferenceable*/ T>     requires /* see below */ using iter_rvalue_reference_t = decltype(ranges::iter_move(std::declval<T&>()));	(4)	(since C++20)
template< Readable T > using iter_common_reference_t = std::common_reference_t<std::iter_reference_t<T>,                                                         std::iter_value_t<T>&>;	(5)	(since C++20)

Compute the associated types of an iterator. The exposition-only concept dereferenceable is satisfied if and only if the expression *std::declval<T&>() is valid and has a referenceable type (in particular, not void).

1) Computes the value type of T. If std::iterator_traits<T> is not specialized, then std::iter_value_t<T> is std::readable_traits<T>::value_type. Otherwise, it is std::iterator_traits<T>::value_type.

2) Computes the reference type of T.

3) Computes the difference type of T. If std::iterator_traits<T> is not specialized, then std::iter_difference_t<T> is std::incrementable_traits<T>::difference_type. Otherwise, it is std::iterator_traits<T>::difference_type.

4) Computes the rvalue reference type of T. The "see below" portion of the constraint on this alias template is satisfied if and only if the expression ranges::iter_move(std::declval<T&>()) is valid and has a referenceable type (in particular, not void).

5) Computes the common reference type of T. This is the common reference type between its reference type and an lvalue reference to its value type.

See also

Readable	specifies that a type is readable by applying operator * (concept)
WeaklyIncrementable	specifies that a Semiregular type can be incremented with pre- and post-increment operators (concept)
readable_traits	computes the value type of a Readable type (class template)
incrementable_traits	computes the difference type of a WeaklyIncrementable type (class template)
iterator_traits	provides uniform interface to the properties of an iterator (class template)