C++ named requirements: InputIterator
An InputIterator is an Iterator that can read from the pointedto element. InputIterators only guarantee validity for single pass algorithms: once an InputIterator i has been incremented, all copies of its previous value may be invalidated.
Requirements
The type It
satisfies InputIterator if
 The type
It
satisfies Iterator  The type
It
satisfies EqualityComparable
And, given

i
andj
, values of type It or const It 
reference
, the type denoted by std::iterator_traits<It>::reference 
value_type
, the type denoted by std::iterator_traits<It>::value_type
The following expressions must be valid and have their specified effects
Expression  Return  Equivalent expression  Notes 

i != j  contextually convertible to bool  !(i == j)  Precondition: (i, j) is in the domain of ==. 
*i  reference, convertible to value_type  If i == j and (i, j) is in the domain of == then this is equivalent to *j. 
Precondition: i is dereferenceable. The expression (void)*i, *i is equivalent to *i. 
i>m  (*i).m  Precondition: i is dereferenceable.  
++i  It& 
Precondition: i is dereferenceable. Postcondition: i is dereferenceable or i is pasttheend. Postcondition: Any copies of the previous value of i are no longer required to be either dereferenceable or to be in the domain of ==.  
(void)i++  (void)++i  
*i++  convertible to value_type  value_type x = *i; ++i; 
Notes
"in the domain of ==
" means equality comparison is defined between the two iterator values. For input iterators, equality comparison does not need to be defined for all values, and the set of the values in the domain of ==
may change over time.
The reference type for an input iterator that is not also a ForwardIterator does not have to be a reference type: dereferencing an input iterator may return a proxy object or value_type itself by value (as in the case of std::istreambuf_iterator).
See also
specifies that a type is an input iterator, that is, its referenced values can be read and it can be both pre and postincremented (concept) 