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template<classI>conceptinput_iterator=std::input_or_output_iterator<I>&&std::indirectly_readable<I>&&requires{typename/*ITER_CONCEPT*/<I>;}&&std::derived_from</*ITER_CONCEPT*/<I>,std::input_iterator_tag>;(since C++20)The input_iterator concept is a refinement of
, adding the requirement that the referenced values can be read (via
) and the requirement that the iterator concept tag be present.
Iterator concept determination
Definition of this concept is specified via an exposition-only alias template /*ITER_CONCEPT*/.
In order to determine /*ITER_CONCEPT*/<I>, let ITER_TRAITS<I> denote I if the specialization std::iterator_traits<I> is generated from the primary template, or std::iterator_traits<I> otherwise:
If ITER_TRAITS<I>::iterator_concept is valid and names a type, /*ITER_CONCEPT*/<I> denotes the type.
Otherwise, if ITER_TRAITS<I>::iterator_category is valid and names a type, /*ITER_CONCEPT*/<I> denotes the type.
Otherwise, if std::iterator_traits<I> is generated from the primary template, /*ITER_CONCEPT*/<I> denotes
std::random_access_iterator_tag
.
(That is, std::derived_from</*ITER_CONCEPT*/<I>,std::input_iterator_tag> is assumed to be true.)
Otherwise, /*ITER_CONCEPT*/<I> does not denote a type and results in a substitution failure.
Notes
Unlike the
requirements, the input_iterator concept does not require
, since input iterators are typically compared with sentinels.
Example
A minimum input iterator.
#include<cstddef>#include<iterator>structSimpleInputIterator{usingdifference_type=std::ptrdiff_t;usingvalue_type=int;intoperator*()const;SimpleInputIterator&operator++();voidoperator++(int){++*this;}};static_assert(std::input_iterator<SimpleInputIterator>);See also