std::input_iterator(3)

NAME
std::input_iterator - std::input_iterator

Synopsis
   Defined in header <iterator>
   template<class I>
   concept input_iterator =
   std::input_or_output_iterator<I> && (since C++20)
   std::indirectly_readable<I> &&
   requires { typename /*ITER_CONCEPT*/<I>; } &&
   std::derived_from</*ITER_CONCEPT*/<I>, std::input_iterator_tag>;
   The input_iterator concept is a refinement of input_or_output_iterator, adding the
   requirement that the referenced values can be read (via indirectly_readable) 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.
     * Otherwise, /*ITER_CONCEPT*/<I> does not denote a type and results in a
       substitution failure.

Notes
   Unlike the LegacyInputIterator requirements, the input_iterator concept does not
   require equality_comparable, since input iterators are typically compared with
   sentinels.

See also
   input_or_output_iterator specifies that objects of a type can be incremented and
   (C++20) dereferenced
                        (concept)