Standard Template Library Programmer's Guide

Precondition	Semantics	Postcondition
Predecrement	--i	i is dereferenceable or past-the-end. There exists a dereferenceable iterator j such that i == ++j.	i is modified to point to the previous element.	i is dereferenceable. &i = &-- i . If i == j , then --i == --j . If j is dereferenceable and i == ++j , then --i == j.
Postdecrement	i--	i is dereferenceable or past-the-end. There exists a dereferenceable iterator j such that i == ++j.	Equivalent to { X tmp = i; --i; return tmp; }

Complexity guarantees

The complexity of operations on bidirectional iterators is guaranteed to be amortized constant time.

Invariants

Symmetry of increment and decrement

If i is dereferenceable, then ++i; -- i; is a null operation. Similarly, --i; ++i; is a null operation.

Models

• T*
• list<T>::iterator

See also

Input Iterator, Output Iterator, Forward Iterator, Random Access Iterator, Iterator overview

Random Access Iterator

Category: iterators

Component type: concept

Description

A Random Access Iterator is an iterator that provides both increment and decrement (just like a Bidirectional Iterator), and that also provides constant-time methods for moving forward and backward in arbitrary-sized steps. Random Access Iterators provide essentially all of the operations of ordinary C pointer arithmetic.

Refinement of

Bidirectional Iterator, LessThan Comparable

Associated types

The same as for Bidirectional Iterator

Notation

X A type that is a model of Random Access Iterator

T The value type of X

Distance The distance type of X

i, j Object of type X

t Object of type T

n Object of type Distance

Valid expressions

In addition to the expressions defined in Bidirectional Iterator, the following expressions must be valid.

Name	Expression	Type requirements	Return type
Iterator addition	i += n		X&
Iterator addition	i + n orn + i		X
Iterator subtraction	i –= n		X&
Iterator subtraction	i – n		X
Difference	i – j