std::contiguous_iterator

 

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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)
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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)
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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)
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indirect_result_t (C++20)	projected (C++20)	projected_value_t (C++26)
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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)

 

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)

The contiguous_iterator concept refines random_access_iterator by providing a guarantee the denoted elements are stored contiguously in the memory.

Given an iterator i of a type that models contiguous_iterator, a sentinel s and a non-negative integer n: For any range[i, s), standard library functions can replace it with [std::to_address(i), std::to_address(i +ranges::distance(i, s))). For any range i + [​0​, n), standard library functions can replace it with std::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 iterator i, because standard library functions might operate on pointers obtained by std::to_address(i) instead of operating on i directly.

(since C++26)

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::contiguous_iterator_tag> is assumed to be false.)
• Otherwise, /*ITER_CONCEPT*/<I> does not denote a type and results in a substitution failure.

Semantic requirements

Let a and b be dereferenceable iterators and c be a non-dereferenceable iterator of type I such that b is reachable from a and c is reachable from b, the type I models contiguous_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<I>(b - a).
• std::to_address(c)==std::to_address(a)+std::iter_difference_t<I>(c - a).
• std::to_address(I{}) is well-defined.
• ranges::iter_move(a) has the same type, value category, and effects as std::move(*a).
• If ranges::iter_swap(a, b) is well-formed, it has effects equivalent to ranges::swap(*a, *b).

Equality preservation

Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).

Implicit expression variations

A requires expression that uses an expression that is non-modifying for some constant lvalue operand also requires implicit expression variations.

Notes

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

Iterator types in the standard library that are required to satisfy the LegacyContiguousIterator requirements in C++17 are also required to model contiguous_iterator in C++20.

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 and ranges::iter_swap behaviors	prohibited
LWG 4170	C++20	a pair of value-initialized contiguous_iterators might not be able to represent an empty range	guaranteed

See also

random_access_iterator (C++20)

specifies that a bidirectional_iterator is a random-access iterator, supporting advancement in constant time and subscripting (concept)