Boost Concept RandomAccessIterator

Concept RandomAccessIterator

RandomAccessIterator

Description（描述）

一 个 random access iterator 是一个能够读取一个值序列的 iterator 。它可以沿着 sequence 的两个方向运动（一次移动任意距离都可以保证在 constant time 内），而且可以是 mutable （它所指向的数据可以被改变）或者是 not mutable 。

一个 iterator 表示一个 sequence 中的一个 position 。也就是说， iterator 能够指向 sequence 的内部（当 dereferenced 及被 incrementable 时，返回一个 value ），或者 off-the-end （不能 dereferenceable 或 incrementable ）。

Refinement of（强化自）

• BidirectionalIterator

• LessThanComparable

Associated types（相关型别）

• value_type

  std::iterator_traits::value_type

  The value type of the iterator

• category

  std::iterator_traits::iterator_category

  The category of the iterator

• difference_type

  std::iterator_traits::difference_type

  The difference type of the iterator (measure of the number of steps between two iterators)

Notation（符号）

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（有效表达式）

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（复杂度）

所有 iterator operations 必须是 amortized constant time 。

Models

• T *
• std::vector::iterator
• std::vector::const_iterator
• std::deque::iterator
• std::deque::const_iterator

See also

• LessThanComparable