C++ named requirements: LegacyBidirectionalIterator

 

C++

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Technical Specifications

 

C++ named requirements

Basic
DefaultConstructible CopyAssignable CopyConstructible	MoveAssignable (C++11) MoveConstructible (C++11) Destructible
Layout
TrivialType (C++11) TriviallyCopyable (C++11)	StandardLayoutType (C++11) PODType
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EqualityComparable LessThanComparable Swappable (C++11) ValueSwappable (C++11) NullablePointer (C++11) Hash (C++11)	Allocator FunctionObject Callable Predicate BinaryPredicate Compare
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Container Elements
DefaultInsertable (C++11) CopyInsertable (C++11) MoveInsertable (C++11)	EmplaceConstructible (C++11) Erasable (C++11)
Iterator
LegacyIterator LegacyOutputIterator LegacyInputIterator LegacyForwardIterator	LegacyBidirectionalIterator LegacyRandomAccessIterator LegacyContiguousIterator (C++17) ConstexprIterator (C++20)
Stream I/O
FormattedInputFunction UnformattedInputFunction	FormattedOutputFunction UnformattedOutputFunction
Random Numbers
SeedSequence (C++11) RandomNumberEngine (C++11)	RandomNumberDistribution (C++11) UniformRandomBitGenerator (C++11) RandomNumberEngineAdaptor (C++11)
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Other
CharTraits RegexTraits (C++11) BitmaskType NumericType LiteralType (C++11)	UnaryTypeTrait (C++11) BinaryTypeTrait (C++11) TransformationTrait (C++11) Clock (C++11) TrivialClock (C++11)

 

A LegacyBidirectionalIterator is a LegacyForwardIterator that can be moved in both directions (i.e. incremented and decremented).

Requirements

The type It satisfies LegacyBidirectionalIterator if

• The type It satisfies LegacyForwardIterator

And, given

• a and b, iterators of type It
• reference, the type denoted by std::iterator_traits<It>::reference

The following expressions must be valid and have their specified effects

Expression	Return	Equivalent expression	Notes
--a	It&		Preconditions: a is decrementable (there exists such b that a == ++b) Postconditions: a is dereferenceable --(++a) == a If --a == --b then a == b a and --a designate the same iterator object
a--	convertible to const It&	It temp = a; --a; return temp;
*a--	reference

A mutable LegacyBidirectionalIterator is a LegacyBidirectionalIterator that additionally satisfies the LegacyOutputIterator requirements.

Notes

The begin iterator is not decrementable and the behavior is undefined if --container.begin() is evaluated.

A bidirectional iterator does not have to be dereferenceable to be decrementable (in particular, the end iterator is not dereferenceable but is decrementable)

Concept For the definition of std::iterator_traits, the following exposition-only concept is defined. template<class I> concept __LegacyBidirectionalIterator =   __LegacyForwardIterator<I> && requires(I i) {     {  --i } -> std::Same<I&>;     {  i-- } -> const I&;     { *i-- } -> std::Same<std::iter_reference_t<I>>;   }; where the exposition-only concept __LegacyForwardIterator is described in LegacyForwardIterator#Concept.

(since C++20)

See also

BidirectionalIterator

specifies that a ForwardIterator is a bidirectional iterator, supporting movement backwards (concept)

• Iterator library