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
.The type
T shall meet the
DefaultConstructible,
CopyConstructible, and
CopyAssignable requirements
.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:
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();
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& operator++();
istream_iterator operator++(int);
private:
basic_istream<charT,traits>* in_stream; T value; };
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);
}constexpr istream_iterator();
Effects:
Constructs the end-of-stream iterator
. If
is_trivially_default_constructible_v<T> is
true,
then this constructor is a constexpr constructor
.Postconditions: in_stream == 0. istream_iterator(istream_type& s);
Effects:
Initializes
in_stream with
addressof(s). value may be initialized during
construction or the first time it is referenced
. Postconditions: in_stream == addressof(s). istream_iterator(const istream_iterator& x) = default;
Effects:
Constructs a copy of
x. If
is_trivially_copy_constructible_v<T> is
true,
then this constructor is a trivial copy constructor
.Postconditions: in_stream == x.in_stream. ~istream_iterator() = default;
Effects:
The iterator is destroyed
. If
is_trivially_destructible_v<T> is
true,
then this destructor is a trivial destructor
.const T& operator*() const;
const T* operator->() const;
Returns:
addressof(operator*()). istream_iterator& operator++();
Requires: in_stream != 0. Effects:
As if by: *in_stream >> value;
istream_iterator operator++(int);
Requires: in_stream != 0. Effects:
As if by:
istream_iterator 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);
Returns:
x.in_stream == y.in_stream. 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);