24 Iterators library [iterators]

24.2 Iterator requirements [iterator.requirements]

24.2.5 Forward iterators [forward.iterators]

A class or pointer type X satisfies the requirements of a forward iterator if

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

Two dereferenceable iterators a and b of type X offer the multi-pass guarantee if:

  • a == b implies ++a == ++b and

  • X is a pointer type or the expression (void)++X(a), *a is equivalent to the expression *a.

Note: The requirement that a == b implies ++a == ++b (which is not true for input and output iterators) and the removal of the restrictions on the number of the assignments through a mutable iterator (which applies to output iterators) allows the use of multi-pass one-directional algorithms with forward iterators.  — end note ]

Table 109 — Forward iterator requirements (in addition to input iterator)
ExpressionReturn typeOperationalAssertion/note
r++ convertible to const X& { X tmp = r;
return tmp; }
*r++ reference

If a and b are equal, then either a and b are both dereferenceable or else neither is dereferenceable.

If a and b are both dereferenceable, then a == b if and only if *a and *b are bound to the same object.