23 Iterators library [iterators]

23.6 Stream iterators [stream.iterators]

23.6.2 Class template istream_­iterator [istream.iterator] General [istream.iterator.general]

The class template istream_­iterator is an input iterator ([input.iterators]) that reads successive elements from the input stream for which it was constructed.
namespace std { template<class T, class charT = char, class traits = char_traits<charT>, class Distance = ptrdiff_t> class istream_iterator { public: using iterator_category = input_iterator_tag; using value_type = T; using difference_type = Distance; using pointer = const T*; using reference = const T&; using char_type = charT; using traits_type = traits; using istream_type = basic_istream<charT,traits>; constexpr istream_iterator(); constexpr istream_iterator(default_sentinel_t); istream_iterator(istream_type& s); istream_iterator(const istream_iterator& x) = default; ~istream_iterator() = default; istream_iterator& operator=(const istream_iterator&) = default; const T& operator*() const; const T* operator->() const; istream_iterator& operator++(); istream_iterator operator++(int); friend bool operator==(const istream_iterator& i, default_sentinel_t); private: basic_istream<charT,traits>* in_stream; // exposition only T value; // exposition only }; }
The type T shall meet the Cpp17DefaultConstructible, Cpp17CopyConstructible, and Cpp17CopyAssignable requirements. Constructors and destructor [istream.iterator.cons]

constexpr istream_iterator(); constexpr istream_iterator(default_sentinel_t);
Effects: Constructs the end-of-stream iterator, value-initializing value.
Postconditions: in_­stream == nullptr is true.
Remarks: If the initializer T() in the declaration auto x = T(); is a constant initializer ([expr.const]), then these constructors are constexpr constructors.
istream_iterator(istream_type& s);
Effects: Initializes in_­stream with addressof(s), value-initializes value, and then calls operator++().
istream_iterator(const istream_iterator& x) = default;
Postconditions: in_­stream == x.in_­stream is true.
Remarks: If is_­trivially_­copy_­constructible_­v<T> is true, then this constructor is trivial.
~istream_iterator() = default;
Remarks: If is_­trivially_­destructible_­v<T> is true, then this destructor is trivial. Operations [istream.iterator.ops]

const T& operator*() const;
Preconditions: in_­stream != nullptr is true.
Returns: value.
const T* operator->() const;
Preconditions: in_­stream != nullptr is true.
Returns: addressof(value).
istream_iterator& operator++();
Preconditions: in_­stream != nullptr is true.
Effects: Equivalent to: if (!(*in_stream >> value)) in_stream = nullptr;
Returns: *this.
istream_iterator operator++(int);
Preconditions: in_­stream != nullptr is true.
Effects: Equivalent to: istream_iterator tmp = *this; ++*this; 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);
Returns: x.in_­stream == y.in_­stream.
friend bool operator==(const istream_iterator& i, default_sentinel_t);
Returns: !i.in_­stream.