# std::istream_iterator<T,CharT,Traits,Distance>::istream_iterator

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< cpp‎ | iterator‎ | istream iterator

| (1) |
istream_iterator(); |  | (until C++11)
constexpr istream_iterator(); |  | (since C++11)
constexpr istream_iterator( std::default_sentinel_t ); | (2) | (since C++20)
istream_iterator( istream_type& stream ); | (3) |
| (4) |
istream_iterator( const istream_iterator& other ); |  | (until C++11)
istream_iterator( const istream_iterator& other ) = default; |  | (since C++11)

1,2) Constructs the end-of-stream iterator, value-initializes the stored value. This constructor is constexpr if the initializer in the definition auto x = T(); is a constant initializer(since C++11).
3) Initializes the iterator, stores the address of stream in a data member, and performs the first read from the input stream to initialize the cached value data member.
4) Constructs a copy of other. If std::is_trivially_copy_constructible <T>::value is true, this copy constructor is a trivial copy constructor.(since C++11)

### Parameters

stream | - | stream to initialize the `istream_iterator` with
other | - | another `istream_iterator` of the same type

### Example

Run this code

    #include <algorithm>
    #include <iostream>
    #include <iterator>
    #include <sstream>

    int main()
    {
        std::istringstream stream("1 2 3 4 5");
        std::copy(
            std::istream_iterator<int>(stream),
            std::istream_iterator<int>(),
            std::ostream_iterator<int>(std::cout, " ")
        );
    }

Output:

    1 2 3 4 5

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 1280 | C++98 | overload (3) stored stream directly | stores its address instead
P0738R2 | C++98 | the first read might be deferred to the first dereference | always performed in the constructor

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