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&> | (until C++17) | |
template< class T, class CharT = char, class Traits = std::char_traits<CharT>, class Distance = std::ptrdiff_t > class istream_iterator; | (since C++17) |
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
.
Member types
Member type | Definition |
---|---|
char_type | CharT |
traits_type | Traits |
istream_type | std::basic_istream<CharT, Traits> |
Member functions
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) |
advances the iterator (public member function) |
Non-member functions
compares two istream_iterator s (function template) |
Member types
Member type | Definition |
---|---|
value_type | T |
difference_type | Distance |
pointer | const T* |
reference | const T& |
iterator_category | std::input_iterator_tag |
Note: before C++17, these member types are required to be obtained by inheriting from std::iterator<std::input_iterator_tag,T,Distance,const T*,const T&>
.
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.
Example
#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
See also
output iterator that writes to std::basic_ostream (class template) | |
input iterator that reads from std::basic_streambuf (class template) |
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