std:: input_iterator

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

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>);

See also