C++ concepts: Iterator
From cppreference.com
The Iterator concept describes types that can be used to identify and traverse the elements of a container.
Iterator is the base concept used by other iterator types: InputIterator, OutputIterator, ForwardIterator, BidirectionalIterator, and RandomAccessIterator. Iterators can be thought of as an abstraction of pointers.
[edit] Requirements
The type It satisfies Iterator if
- The type
ItsatisfiesCopyConstructible, and - The type
ItsatisfiesCopyAssignable, and - The type
ItsatisfiesDestructible, and - lvalues of type
ItsatisfySwappable, and - std::iterator_traits<It> has member typedefs
value_type,difference_type,reference,pointer, anditerator_category, and
Given
-
r, an lvalue of typeIt.
The following expressions must be valid and have their specified effects:
| Expression | Return Type | Precondition |
|---|---|---|
| *r | unspecified | r is dereferenceable (see below)
|
| ++r | It& | r is incrementable (the behavior of the expression ++r is defined)
|
[edit] Dereferenceable iterators
Iterators for which the behavior of the expression *i is defined are called dereferenceable.
Iterators are not dereferenceable if
- they are past-the-end iterators (including pointers past the end of an array) or before-begin iterators. Such iterators may be dereferenceable in a particular implementation, but the library never assumes that they are.
- they are singular iterators, that is, iterators that are not associated with any sequence. A null pointer, as well as a default-constructed pointer (holding an indeterminate value) is singular
- they were invalidated by one of the iterator-invalidating operations on the sequence to which they refer.