Input iterators

X (const X& a) Constructor on input iterators
== Operator on input iterators
!= Operator on input iterators
* Operator on input iterators
++ Operator on input iterators

A class or a built-in type X satisfies the requirements of an input iterator for the value type T if the following expressions are valid:


Table 2: Input iterator requirements

               
Expression Return type Operational semantics Assertion/note pre/post-condition
X(a)          X(a)is a copy of a.
note: a destructor is assumed.
X u(a);
X u = a; 		            post: u is a copy of a.
u = a X&        post: u is a copy of a
a == b convertible to bool         if a is a copy of b, then a == b returns true.
== is an equivalence relation over the domain of ==.
a != b convertible to bool !(a == b)
        
*a convertible to T            pre: a is dereferenceable.
if a is a copy of b, then *a is equivalent to *b.
++r X&      pre: r is dereferenceable.
post:  r is dereferenceable or r is past-the-end.
(void)r++ void (void)++r
      
*r++        
{ X tmp = r;
  ++r;
  return tmp; }
       

NOTE : For input iterators, there are no requirements on the type or value of r++ beyond the requirement that *r++ works appropriately. In particular, r == s does not imply ++r == ++s. (Equality does not guarantee the substitution property or referential transparency.) As for ++r, there are no more requirements on the values of any copies of r except that they can be safely destroyed or assigned to. After executing ++r, copies of (the previous) r are not required to be in the domain of ==. Algorithms on input iterators should never attempt to pass through the same iterator twice. They should be single pass algorithms. Value type T is not required to be an lvalue type. These algorithms can be used with istreams as the source of the input data through the istream_iterator class.