Standard Template Library Programmer's Guide

	Distance
Element operator	i[n]		Convertible to T
Element assignment	i[n] = t	X is mutable	Convertible to T

Expression semantics

Semantics of an expression is defined only where it differs from, or is not defined in, Bidirectional Iterator or LessThan Comparable.

Name	Expression	Precondition	Semantics	Postcondition
Forward motion	i += n	Including i itself, there must be n dereferenceable or past-the-end iterators following or preceding i, depending on whether n is positive or negative.	If n > 0, equivalent to executing ++i n times. If n < 0, equivalent to executing --i n times. If n == 0 , this is a null operation. [1]	i is dereferenceable or past-the-end.
Iterator addition	i + n or n + i	Same as for i += n	Equivalent to { X tmp = i; return tmp += n; } . The two forms i + n and n + i are identical.	Result is dereferenceable or past-the-end
Iterator subtraction	i –= n	Including i itself, there must be n dereferenceable or past-the-end iterators preceding or following i, depending on whether n is positive or negative.	Equivalent to i += (-n).	i is dereferenceable or past-the-end.
Iterator subtraction	i – n	Same as for i –= n	Equivalent to { X tmp = i; return tmp –= n; }.	Result is dereferenceable or past-the-end
Difference	i – j	Either i is reachable from j or j is reachable from i, or both.	Returns a number n such that i == j + n
Element operator	i[n]	i + n exists and is dereferenceable.	Equivalent to *(i + n) [2]
Element assignment	i[n] = t	i + n exists and is dereferenceable.	Equivalent to *(i + n) = t [2]	i[n] is a copy of t.
Less	i < j	Either i is reachable from j or j is reachable from i, or both. [3]	As described in LessThan Comparable [4]

Complexity guarantees

All operations on Random Access Iterators are amortized constant time. [5]

Invariants