ForwardIterator

Category: iterators		Component type: concept

Description

A Forward Iterator is an iterator that corresponds to the usual intuitive notion of a linear sequence of values. It is possible to use Forward Iterators (unlike InputIterator and OutputIterator) in multipass algorithms. Forward Iterators do not, however, allow stepping backwards through a sequence, but only, as the name suggests, forward.

A type that is a model of Forward Iterator may be either mutable or immutable, as defined in the trivial requirements.

Refinement of

InputIterator, OutputIterator

Associated types

The same as for InputIterator

Notation

X	A type that is a model of Forward Iterator
T	The value type of X
i, j	Object of type X
t	Object of type T

Definitions

Valid expressions

Forward Iterator does not define any new expressions beyond those defined in InputIterator. However, some of the restrictions described in InputIterator are relaxed.

Name	Expression	Type requirements	Return type
Preincrement	++i		X&
Postincrement	i++		X

Expression semantics

Forward Iterator does not define any new expressions beyond those defined in InputIterator. However, some of the restrictions described in InputIterator are relaxed.

Name	Expression	Precondition	Semantics	Postcondition
Preincrement	++i	i is dereferenceable	i points to the next value	i is dereferenceable or past-the-end. &i == &++i. If i == j, then ++i == ++j. [1]
Postincrement	i++	i is dereferenceable	Equivalent to {X tmp = i; ++i; return tmp;}	i is dereferenceable or past-the-end. [1]

Complexity guarantees

The complexity of operations on Forward Iterators is guaranteed to be amortized constant time.

Invariants

Models

• T*
• hash_set<T>iterator

Notes

[1] The restrictions described in InputIterator have been removed. Incrementing a forward iterator does not invalidate copies of the old value and it is guaranteed that, if i and j are dereferenceable and i == j, then ++i == ++j. As a consequence of these two facts, it is possible to pass through the same Forward Iterator twice.

See also

InputIterator, OutputIterator, BidirectionalIterator, RandomAccessIterator, Iterators