C++ concepts: Iterator

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.

Requirements

The type It satisfies Iterator if.

• The type It satisfies CopyConstructible, and
• The type It satisfies CopyAssignable, and
• The type It satisfies Destructible, and
• lvalues of type It satisfy Swappable, and
• std::iterator_traits<It> has member typedefs value_type, difference_type, reference, pointer, and iterator_category, and

Given.

• r, an lvalue of type It.

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)

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.

See also

• Iterator library