std::istream_iterator

Defined in header `<iterator>`
template< class T, class CharT = char, class Traits = std::char_traits<CharT>, class Distance = std::ptrdiff_t > class istream_iterator: public std::iterator<std::input_iterator_tag, T, Distance, const T*, const T&>

std::istream_iterator is a single-pass input iterator that reads successive objects of type T from the std::basic_istream object for which it was constructed, by calling the appropriate operator>>. The actual read operation is performed when the iterator is incremented, not when it is dereferenced. The first object may be read when the iterator is constructed or when the first dereferencing is done. Otherwise, dereferencing only returns a copy of the most recently read object.

The default-constructed std::istream_iterator is known as the end-of-stream iterator. When a valid std::istream_iterator reaches the end of the underlying stream, it becomes equal to the end-of-stream iterator. Dereferencing or incrementing it further invokes undefined behavior.

A typical implementation of std::istream_iterator holds two data members: a pointer to the associated std::basic_istream object and the most recently read value of type T.

(constructor)	constructs a new istream_iterator (public member function)
(destructor) (implicitly declared)	destructs an istream_iterator, including the cached value (public member function)
operator*operator->	returns the current element (public member function)
operator++operator++(int)	advances the iterator (public member function)

[edit] Non-member functions

operator==operator!=

compares two istream_iterators
(function template)

Inherited from std::iterator

Member types

Member type	Definition
`value_type`	T
`difference_type`	Distance
`pointer`	const T*
`reference`	const T&
`iterator_category`	std::input_iterator_tag

[edit] Notes

When reading characters, std::istream_iterator skips whitespace by default (unless disabled with std::noskipws or equivalent), while std::istreambuf_iterator does not. In addition, std::istreambuf_iterator is more efficient, since it avoids the overhead of constructing and destructing the sentry object once per character.

[edit] Example

Run this code

#include <iostream>
#include <sstream>
#include <iterator>
#include <numeric>
 
int main()
{
    std::istringstream str("0.1 0.2 0.3 0.4");
    std::partial_sum(std::istream_iterator<double>(str),
                     std::istream_iterator<double>(),
                     std::ostream_iterator<double>(std::cout, " "));
}

Output:

0.1 0.3 0.6 1

[edit] See also

ostream_iterator	output iterator that writes to std::basic_ostream (class template)
istreambuf_iterator	input iterator that reads from std::basic_streambuf (class template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

Member functions
istream_iterator::istream_iterator
istream_iterator::operator*istream_iterator::operator->
istream_iterator::operator++istream_iterator::operator++(int)
Non-member functions
operator==operator!=

Member type	Definition
`char_type`	`CharT`
`traits_type`	`Traits`
`istream_type`	std::basic_istream<CharT, Traits>