The class template istream_iterator is an input iterator ([input.iterators]) that reads (using operator>>) successive elements from the input stream for which it was constructed. After it is constructed, and every time ++ is used, the iterator reads and stores a value of T. If the iterator fails to read and store a value of T (fail() on the stream returns true), the iterator becomes equal to the end-of-stream iterator value. The constructor with no arguments istream_iterator() always constructs an end-of-stream input iterator object, which is the only legitimate iterator to be used for the end condition. The result of operator* on an end-of-stream iterator is not defined. For any other iterator value a const T& is returned. The result of operator-> on an end-of-stream iterator is not defined. For any other iterator value a const T* is returned. The behavior of a program that applies operator++() to an end-of-stream iterator is undefined. It is impossible to store things into istream iterators.
Two end-of-stream iterators are always equal. An end-of-stream iterator is not equal to a non-end-of-stream iterator. Two non-end-of-stream iterators are equal when they are constructed from the same stream.
namespace std { template <class T, class charT = char, class traits = char_traits<charT>, class Distance = ptrdiff_t> class istream_iterator: public iterator<input_iterator_tag, T, Distance, const T*, const T&> { public: typedef charT char_type; typedef traits traits_type; typedef basic_istream<charT,traits> istream_type; see below istream_iterator(); istream_iterator(istream_type& s); istream_iterator(const istream_iterator& x) = default; ~istream_iterator() = default; const T& operator*() const; const T* operator->() const; istream_iterator<T,charT,traits,Distance>& operator++(); istream_iterator<T,charT,traits,Distance> operator++(int); private: basic_istream<charT,traits>* in_stream; // exposition only T value; // exposition only }; template <class T, class charT, class traits, class Distance> bool operator==(const istream_iterator<T,charT,traits,Distance>& x, const istream_iterator<T,charT,traits,Distance>& y); template <class T, class charT, class traits, class Distance> bool operator!=(const istream_iterator<T,charT,traits,Distance>& x, const istream_iterator<T,charT,traits,Distance>& y); }
Effects: Constructs the end-of-stream iterator. If T is a literal type, then this constructor shall be a constexpr constructor.
Postcondition: in_stream == 0.
istream_iterator(istream_type& s);
Effects: Initializes in_stream with &s. value may be initialized during construction or the first time it is referenced.
Postcondition: in_stream == &s.
istream_iterator(const istream_iterator& x) = default;
Effects: Constructs a copy of x. If T is a literal type, then this constructor shall be a trivial copy constructor.
Postcondition: in_stream == x.in_stream.
~istream_iterator() = default;
Effects: The iterator is destroyed. If T is a literal type, then this destructor shall be a trivial destructor.
Returns: value.
Returns: &(operator*()).
istream_iterator<T,charT,traits,Distance>& operator++();
Requires: in_stream != 0.
Effects: *in_stream >> value.
Returns: *this.
istream_iterator<T,charT,traits,Distance> operator++(int);
Requires: in_stream != 0.
Effects:
istream_iterator<T,charT,traits,Distance> tmp = *this; *in_stream >> value; return (tmp);
template <class T, class charT, class traits, class Distance>
bool operator==(const istream_iterator<T,charT,traits,Distance> &x,
const istream_iterator<T,charT,traits,Distance> &y);
template <class T, class charT, class traits, class Distance>
bool operator!=(const istream_iterator<T,charT,traits,Distance> &x,
const istream_iterator<T,charT,traits,Distance> &y);
Returns: !(x == y)