[iterator.concept.forward] (original) (raw)

24 Iterators library [iterators]

24.3 Iterator requirements [iterator.requirements]

24.3.4 Iterator concepts [iterator.concepts]

24.3.4.11 Concept forward_iterator [iterator.concept.forward]

The forward_iterator concept adds copyability, equality comparison, and the multi-pass guarantee, specified below.

The domain of == for forward iterators is that of iterators over the same underlying sequence.

However, value-initialized iterators of the same type may be compared and shall compare equal to other value-initialized iterators of the same type.

[Note 1:

Value-initialized iterators behave as if they refer past the end of the same empty sequence.

— _end note_]

Pointers and references obtained from a forward iterator into a range [i, s) shall remain valid while [i, s) continues to denote a range.

Two dereferenceable iterators a and b of type Xoffer the multi-pass guarantee if

• a == b implies ++a == ++b and
• the expression((void)[](X x){++x;}(a), *a) is equivalent to the expression *a.

[Note 2:

The requirement thata == bimplies++a == ++band the removal of the restrictions on the number of assignments through a mutable iterator (which applies to output iterators) allow the use of multi-pass one-directional algorithms with forward iterators.

— _end note_]