Theinput_iterator concept is a refinement ofinput_or_output_iterator, adding the requirement that the referenced values can be read (viaindirectly_readable) and the requirement that the iterator concept tag be present.
[edit]Iterator concept determination
Definition of this concept is specified via an exposition-only alias template/*ITER_CONCEPT*/.
In order to determine/*ITER_CONCEPT*/<I>, letITER_TRAITS<I> denoteI if the specializationstd::iterator_traits<I> is generated from the primary template, orstd::iterator_traits<I> otherwise:
- IfITER_TRAITS<I>::iterator_concept is valid and names a type,/*ITER_CONCEPT*/<I> denotes the type.
- Otherwise, ifITER_TRAITS<I>::iterator_category is valid and names a type,/*ITER_CONCEPT*/<I> denotes the type.
- Otherwise, ifstd::iterator_traits<I> is generated from the primary template,/*ITER_CONCEPT*/<I> denotesstd::random_access_iterator_tag.
(That is,std::derived_from</*ITER_CONCEPT*/<I>,std::input_iterator_tag> is assumed to betrue.) - Otherwise,/*ITER_CONCEPT*/<I> does not denote a type and results in a substitution failure.
Unlike theLegacyInputIterator requirements, theinput_iterator concept does not requireequality_comparable, since input iterators are typically compared with sentinels.
[edit]Example
A minimum input iterator.
#include <cstddef>#include <iterator> class SimpleInputIterator{public:using difference_type=std::ptrdiff_t;using value_type=int; int operator*()const; SimpleInputIterator& operator++();void operator++(int){++*this;}}; static_assert(std::input_iterator<SimpleInputIterator>);[edit]See also
| specifies that objects of a type can be incremented and dereferenced
(concept)[edit] |
| specifies that aninput_iterator is a forward iterator, supporting equality comparison and multi-pass
(concept)[edit] |
