C++ concepts: InputIterator

An InputIterator is an Iterator that can read from the pointed-to 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 and j, 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 past-the-end. 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; return x;

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

• Iterator library