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                       Standard C++ Library
             Copyright 1998, Rogue Wave Software, Inc.


NAME
     istream_iterator

      - A stream iterator  that  has  iterator  capabilities  for
     istreams. This iterator allows generic algorithms to be used
     directly on streams.



SYNOPSIS
     #include <iterator>
     template   <class   T,   class   charT,   class   traits   =
     ios_traits<charT>,
              class Distance = ptrdiff_t>
     class istream_iterator : public iterator<input_iterator_tag,
                                   T,Distance>;



DESCRIPTION
     Stream iterators are the  standard  iterator  interface  for
     input and output streams.

     The class_istream_iterator  reads  elements  from  an  input
     stream using operator >>. A value of type T is retrieved and
     stored when the iterator is constructed and each time opera-
     tor++  is called. The iterator is equal to the end-of-stream
     iterator value if the end-of-file is reached.  You  can  use
     the constructor with no arguments to create an end-of-stream
     iterator. The only valid use of this iterator is to  compare
     to  other  iterators  when  checking for end of file. Do not
     attempt to dereference the end-of-stream iterator; it  plays
     the  same  role  as  the  past-the-end iterator of the end()
     function of containers.  Since  an  istream_iterator  is  an
     input  iterator,  you cannot assign to the value returned by
     dereferencing   the   iterator.   This   also   means   that
     istream_iterators  can  only  be  used for single pass algo-
     rithms.

     Since a new value is read every time the operator++ is  used
     on  an  istream_iterator,  that  operation  is not equality-
     preserving. This means that i == j does not mean that ++i ==
     ++j (although two end-of-stream iterators are always equal).



INTERFACE
     template   <class   T,   class   charT,   class   traits   =
     ios_traits<charT>
              class Distance = ptrdiff_t>
     class istream_iterator :
              public iterator<input_iterator_tag,T, Distance>
      {

     public:
        typedef T value_type;
        typedef charT char_type;
        typedef traits traits_type;
        typedef basic_istream<charT,traits> istream_type;

        istream_iterator();
        istream_iterator (istream_type&);
        istream_iterator
               (const stream_iterator<T,charT,traits,Distance>&);
         ~istream_itertor ();

        const T& operator*() const;
        const T* operator ->() const;
        istream_iterator <T,charT,traits,
                          Distance>& operator++();
        istream_iterator <T,charT,traits,Distance>
                          operator++ (int)
      };

     // Non-member Operators

     template <class T, class charT, class traits,class Distance>
     bool                                        operator==(const
     istream_iterator<T,charT,traits,Distance>&,
              const istream_iterator<T,charT,traits,Distance>&);

     template <class T, class charT, class traits,class Distance>
     bool                                        operator!=(const
     istream_iterator<T,charT,traits,Distance>&,
              const istream_iterator<T,charT,traits,Distance>&);



TYPES
     value_type;


        Type of value to stream in.



     char_type;
        Type of character the stream is built on.



     traits_type;


        Traits used to build the stream.



     istream_type;


        Type of stream this iterator is constructed on.



CONSTRUCTORS
     istream_iterator();


        Constructs an end-of-stream iterator. This  iterator  can
        be  used  to  compare against an end-of-stream condition.
        Use it to provide end iterators to algorithms.



     istream_iterator(istream& s);


        Constructs an istream_iterator on the given stream.



     istream_iterator(const istream_iterator& x);


        Copy constructor.



DESTRUCTORS
     ~istream_iterator();



OPERATORS
     const T&
     operator*() const;


        Returns the current value stored by the iterator.



     const T*
     operator->() const;


        Returns a pointer to the  current  value  stored  by  the
        iterator.



     istream_iterator& operator++()
     istream_iterator operator++(int)


        Retrieves the next element from the input stream.



NON-MEMBER OPERATORS
     bool
     operator==(const istream_iterator<T,charT,traits,
                Distance>& x,
                const
                istream_iterator<T,charT,traits,Distance>& y)


        Returns true if x is the same as y.



     bool
     operator!=(const istream_iterator<T,charT,traits,
                Distance>& x,
                const
                istream_iterator<T,charT,traits,Distance>& y)


        Returns true if x is not the same as y.



EXAMPLE
     //
     // io_iter.cpp
     //
      #include <iterator>
      #include <vector>
      #include <numeric>
      #include <iostream>
     using namespace std;

     int main ()
      {
       vector<int> d;
       int total = 0;
        //
        // Collect values from cin until end of file
        // Note use of default constructor to get ending iterator
        //
       cout << "Enter a sequence of integers (eof to quit): " ;
       copy(istream_iterator<int,char>(cin),
             istream_iterator<int,char>(),
            inserter(d,d.begin()));
        //
        // stream the whole vector and the sum to cout
        //
       copy(d.begin(),d.end()-1,
            ostream_iterator<int,char>(cout," + "));
       if (d.size())
         cout << *(d.end()-1) << " = " <<
              accumulate(d.begin(),d.end(),total) << endl;
       return 0;
      }



WARNINGS
     If your compiler does not support default  template  parame-
     ters,  then you always need to supply the Allocator template
     argument. You also have to include  all  parameters  to  the
     istream_iterator template. For instance, you have to write:

     vector<int, allocator<int> >

     instead of:

     vector<int>

     If your compiler does not support namespaces,  then  you  do
     not need the using declaration for std.


SEE ALSO
     Iterators, ostream_iterator

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