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

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< cpp‎ | iterator‎ | istream iterator

constexpr istream_iterator(); | (1) |
istream_iterator( istream_type& stream ); | (2) |
istream_iterator( const istream_iterator& other ) = default; | (3) |

1) 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.
2) 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.
3) Constructs a copy of `other`. If std::is_trivially_copy_constructible_v<T> is `true` , this copy constructor is a trivial copy constructor.

### Parameters

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

### Defect reports

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

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
P0738R2 | C++98 | the first read may be deferred to the first dereferencing | the first read is performed in the constructor

### Examples

Run this code

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

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