cppreference.com

Namespaces

Variants

Actions

std::input_iterator

From cppreference.com

< cpp‎ | iterator

Compiler support

Freestanding and hosted

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

Memory management library

Metaprogramming library (C++11)

General utilities library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library (C++17)

Concurrency support library (C++11)

Execution control library (C++26)

Technical specifications

External libraries

Iterator library

Iterator concepts

indirectly_readable

(C++20)

indirectly_writable

(C++20)

weakly_incrementable

(C++20)

(C++20)

is-integer-like
is-signed-integer-like

(C++20)(C++20)

(C++20)

sized_sentinel_for

(C++20)

input_iterator

(C++20)

output_iterator

(C++20)

input_or_output_iterator

(C++20)

forward_iterator

(C++20)

bidirectional_iterator

(C++20)

random_access_iterator

(C++20)

contiguous_iterator

(C++20)

Iterator primitives

input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag

(C++20)

iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t

(C++20)(C++20)(C++20)(C++23)(C++20)(C++20)

(deprecated in C++17)

iterator_traits

incrementable_traits

(C++20)

indirectly_readable_traits

(C++20)

Algorithm concepts and utilities

Indirect callable concepts

indirectly_unary_invocableindirectly_regular_unary_invocable

(C++20)(C++20)

indirect_unary_predicate

(C++20)

indirect_binary_predicate

(C++20)

indirect_equivalence_relation

(C++20)

indirect_strict_weak_order

(C++20)

Common algorithm requirements

indirectly_movable

(C++20)

indirectly_movable_storable

(C++20)

indirectly_copyable

(C++20)

indirectly_copyable_storable

(C++20)

indirectly_swappable

(C++20)

indirectly_comparable

(C++20)

(C++20)

(C++20)

(C++20)

indirect_result_t

(C++20)

(C++20)

projected_value_t

(C++26)

Iterator adaptors

reverse_iterator

make_reverse_iterator

(C++14)

(C++11)

make_move_iterator

(C++11)

default_sentinel_tdefault_sentinel

(C++20)(C++20)

unreachable_sentinel_tunreachable_sentinel

(C++20)(C++20)

front_insert_iterator

back_insert_iterator

insert_iterator

(C++20)

common_iterator

(C++20)

counted_iterator

(C++20)

basic_const_iterator

(C++23)

(C++23)

(C++23)

make_const_iterator

(C++23)

make_const_sentinel

(C++23)

Stream iterators

istream_iterator

ostream_iterator

istreambuf_iterator

ostreambuf_iterator

Iterator customization points

ranges::iter_move

(C++20)

ranges::iter_swap

(C++20)

Iterator operations

(C++11)

(C++11)

ranges::advance

(C++20)

ranges::distance

(C++20)

(C++20)

(C++20)

(C++11)(C++14)

(C++14)(C++14)

(C++11)(C++14)

(C++14)(C++14)

(C++17)(C++20)

(C++17)

(C++17)

Defined in header <iterator>

template< class I >

concept input_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 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.

Contents

[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>, 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.

[edit] Notes

Unlike the LegacyInputIterator requirements, the input_iterator concept does not require equality_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

input_or_output_iterator

(C++20)

specifies that objects of a type can be incremented and dereferenced
(concept) [edit]

forward_iterator

(C++20)

specifies that an input_iterator is a forward iterator, supporting equality comparison and multi-pass
(concept) [edit]

Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/iterator/input_iterator&oldid=183121"