C++ concepts: RandomAccessIterator

A RandomAccessIterator is a BidirectionalIterator that can be moved to point to any element in constant time.

A pointer to an element of an array satisfies all requirements of RandomAccessIterator.

Requirements

The type It satisfies RandomAccessIterator if.

• The type It satisfies BidirectionalIterator

And, given.

• value_type, the type denoted by std::iterator_traits<It>::value_type
• difference_type, the type denoted by std::iterator_traits<It>::difference_type
• reference, the type denoted by std::iterator_traits<It>::reference
• i, a, b, objects of type It or const It
• r, a value of type It&
• n, an integer of type difference_type

The following expressions must be valid and have their specified effects.

Expression	Return type	Operational semantics	Notes
r += n	It&	difference_type m = n; if (m >= 0) while (m--) ++r; else while (m++) --r; return r;	n can be both positive or negative The complexity is constant (that is, the implementation cannot actually execute the while loop shown in operational semantics)
a + n n + a.	It	It temp = a; return temp += n;	n can be both positive or negative a + n == n + a
r -= n	It&	return r += -n;	The absolute value of n must be within the range of representable values of difference_type.
i - n	It	It temp = i; return temp -= n;
b - a	difference_type	return n;	Precondition: there exists a value n of type difference_type such that a+n==b Postcondition: b == a + (b - a).
i[n]	convertible to reference	*(i + n)
a < b	contextually convertible to bool	b - a > 0	Strict total ordering relation: !(a < a) if a < b then !(b < a) if a < b and b < c then a < c a < b or b < a or a == b (exactly one of the expressions is true)
a > b	contextually convertible to bool	b < a	Total ordering relation opposite to a < b
a >= b	contextually convertible to bool	!(a < b)
a <= b	contextually convertible to bool	!(a > b)

The above rules imply that RandomAccessIterator also implements LessThanComparable.

A mutable RandomAccessIterator is a RandomAccessIterator that additionally satisfies the OutputIterator requirements.

See also

• Iterator library