Concept RandomAccessIterator

RandomAccessIterator

Description

A random access iterator is an iterator that can read through a sequence of values. It can move in either direction through the sequence (by any amount in constant time), and can be either mutable (data pointed to by it can be changed) or not mutable.

An iterator represents a position in a sequence. Therefore, the iterator can point into the sequence (returning a value when dereferenced and being incrementable), or be off-the-end (and not dereferenceable or incrementable).

Refinement of

Associated types

value_type
```
std::iterator_traits<Iter>::value_type
```
The value type of the iterator

category

std::iterator_traits<Iter>::iterator_category

The category of the iterator

difference_type
```
std::iterator_traits<Iter>::difference_type
```
The difference type of the iterator (measure of the number of steps between two iterators)

Notation

Iter: A type playing the role of iterator-type in the RandomAccessIterator concept.
i, j: Objects of type Iter
x: Object of type value_type
n: Object of type difference_type
int_off: Object of type int

Type expressions

Category tag: category must be derived from std::random_access_iterator_tag.

Valid expressions

Name	Expression	Type	Semantics
Motion	i += n	Iter &	Equivalent to applying `i++` `n` times if `n` is positive, applying `i--` `-n` times if `n` is negative, and to a null operation if `n` is zero.
Motion (with integer offset)	i += int_off	Iter &	Equivalent to applying `i++` `n` times if `n` is positive, applying `i--` `-n` times if `n` is negative, and to a null operation if `n` is zero.
Subtractive motion	i -= n	Iter &	Equivalent to `i+=(-n)`
Subtractive motion (with integer offset)	i -= int_off	Iter &	Equivalent to `i+=(-n)`
Addition	i + n	Iter	Equivalent to `{Iter j = i; j += n; return j;}`
Addition with integer	i + int_off	Iter	Equivalent to `{Iter j = i; j += n; return j;}`
Addition (count first)	n + i	Iter	Equivalent to `i + n`
Addition with integer (count first)	int_off + i	Iter	Equivalent to `i + n`
Subtraction	i - n	Iter	Equivalent to `i + (-n)`
Subtraction with integer	i - int_off	Iter	Equivalent to `i + (-n)`
Distance	i - j	difference_type	The number of times `i` must be incremented (or decremented if the result is negative) to reach `j`. Not defined if `j` is not reachable from `i`.
Element access	i[n]	const-if-not-mutable value_type &	Equivalent to `*(i + n)`
Element access with integer index	i[int_off]	const-if-not-mutable value_type &	Equivalent to `*(i + n)`

Complexity

All iterator operations must take amortized constant time.

Models

T *
std::vector<T>::iterator
std::vector<T>::const_iterator
std::deque<T>::iterator
std::deque<T>::const_iterator