std::contiguous_iterator

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Metaprogramming library(C++11)
General utilities library
Containers library
Iterators library
Ranges library(C++20)
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Iterator library

Iterator concepts

indirectly_readable (C++20)
indirectly_writable (C++20)
weakly_incrementable (C++20)
incrementable (C++20)
is-integer-like is-signed-integer-like (C++20)(C++20)

sentinel_for (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)

iterator (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)

permutable (C++20)
mergeable (C++20)
sortable (C++20)

(C++20)

(C++20)

(C++26)

reverse_iterator
make_reverse_iterator (C++14)
move_iterator (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
inserter
insert_iterator
front_inserter
back_inserter
move_sentinel (C++20)

common_iterator (C++20)
counted_iterator (C++20)
basic_const_iterator (C++23)
const_iterator (C++23)
const_sentinel (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

advance
distance
prev (C++11)
next (C++11)

ranges::advance (C++20)
ranges::distance (C++20)
ranges::prev (C++20)
ranges::next (C++20)

Range access

begincbegin (C++11)(C++14)
rbegincrbegin (C++14)(C++14)

endcend (C++11)(C++14)
rendcrend (C++14)(C++14)

sizessize (C++17)(C++20)
empty (C++17)
data (C++17)

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Defined in header`<iterator>`
template<class I> concept contiguous_iterator= std::random_access_iterator<I>&& std::derived_from</ITER_CONCEPT/<I>,std::contiguous_iterator_tag>&& std::is_lvalue_reference_v<std::iter_reference_t<I>>&& std::same_as<std::iter_value_t<I>, std::remove_cvref_t<std::iter_reference_t<I>>>&& requires(const I& i){ {std::to_address(i)}-> std::same_as<std::add_pointer_t<std::iter_reference_t<I>>>; };		(since C++20)

Thecontiguous_iterator concept refinesrandom_access_iterator by providing a guarantee the denoted elements are stored contiguously in the memory.

Given an iteratori of a type that modelscontiguous_iterator, a sentinels and a non-negative integern:

For anyrange[i, s), standard library functions can replace it with[std::to_address(i), std::to_address(i+ranges::distance(i, s))).
For any rangei + [0, n), standard library functions can replace it withstd::to_address(i) + [0, std::to_address(i+ n)).

This means a program cannot rely on any side effects of dereferencing, incrementing or decrementing a contiguous iteratori, because standard library functions might operate on pointers obtained bystd::to_address(i) instead of operating oni directly.

(since C++26)

[edit]Iterator concept determination

Definition of this concept is specified via an exposition-only alias template/*ITER_CONCEPT*/.

In order to determine/*ITER_CONCEPT*/, letITER_TRAITS denoteI if the specializationstd::iterator_traits is generated from the primary template, orstd::iterator_traits otherwise:

IfITER_TRAITS::iterator_concept is valid and names a type,/*ITER_CONCEPT*/ denotes the type.
Otherwise, ifITER_TRAITS::iterator_category is valid and names a type,/*ITER_CONCEPT*/ denotes the type.
Otherwise, ifstd::iterator_traits is generated from the primary template,/*ITER_CONCEPT*/ denotesstd::random_access_iterator_tag.
(That is,std::derived_from</*ITER_CONCEPT*/,std::contiguous_iterator_tag> is assumed to befalse.)
Otherwise,/*ITER_CONCEPT*/ does not denote a type and results in a substitution failure.

[edit]Semantic requirements

Leta andb bedereferenceable iterators andc be a non-dereferenceable iterator of typeI such thatb isreachable froma andc is reachable fromb, the typeI modelscontiguous_iterator only if all the concepts it subsumes are modeled and all following conditions are satisfied:

std::to_address(a)==std::addressof(*a).
std::to_address(b)==std::to_address(a)+std::iter_difference_t(b- a).
std::to_address(c)==std::to_address(a)+std::iter_difference_t(c- a).
std::to_address(I{}) is well-defined.
ranges::iter_move(a) has the same type, value category, and effects asstd::move(*a).
Ifranges::iter_swap(a, b) is well-formed, it has effects equivalent toranges::swap(*a,*b).

[edit]Equality preservation

Expressions declared inrequires expressions of the standard library concepts are required to beequality-preserving (except where stated otherwise).

[edit]Implicit expression variations

Arequires expression that uses an expression that is non-modifying for some constant lvalue operand also requiresimplicit expression variations.

[edit]Notes

contiguous_iterator is modeled by every pointer type to complete object type.

Iterator types in the standard library that are required to satisfy theLegacyContiguousIterator requirements in C++17 are also required to modelcontiguous_iterator in C++20.

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3607	C++20	`contiguous_iterator` could have custom ranges::iter_move andranges::iter_swap behaviors	prohibited
LWG 4170	C++20	a pair of value-initialized`contiguous_iterator`s might not be able to represent an empty range	guaranteed