23 Iterators library [iterators]

23.6 Stream iterators [stream.iterators]

23.6.2 Class template ostream_­iterator [ostream.iterator]

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ostream_­iterator writes (using operator<<) successive elements onto the output stream from which it was constructed.
If it was constructed with charT* as a constructor argument, this string, called a delimiter string, is written to the stream after every T is written.
namespace std {
  template<class T, class charT = char, class traits = char_traits<charT>>
  class ostream_iterator {
  public:
    using iterator_category = output_iterator_tag;
    using value_type        = void;
    using difference_type   = ptrdiff_t;
    using pointer           = void;
    using reference         = void;
    using char_type         = charT;
    using traits_type       = traits;
    using ostream_type      = basic_ostream<charT,traits>;

    constexpr ostream_iterator() noexcept = default;
    ostream_iterator(ostream_type& s);
    ostream_iterator(ostream_type& s, const charT* delimiter);
    ostream_iterator(const ostream_iterator& x);
    ~ostream_iterator();
    ostream_iterator& operator=(const ostream_iterator&) = default;
    ostream_iterator& operator=(const T& value);

    ostream_iterator& operator*();
    ostream_iterator& operator++();
    ostream_iterator& operator++(int);

  private:
    basic_ostream<charT,traits>* out_stream = nullptr;          // exposition only
    const charT* delim = nullptr;                               // exposition only
  };
}

23.6.2.1 Constructors and destructor [ostream.iterator.cons.des]

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ostream_iterator(ostream_type& s);
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Effects: Initializes out_­stream with addressof(s) and delim with nullptr.
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ostream_iterator(ostream_type& s, const charT* delimiter);
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Effects: Initializes out_­stream with addressof(s) and delim with delimiter.

23.6.2.2 Operations [ostream.iterator.ops]

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ostream_iterator& operator=(const T& value);
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Effects: As if by: 
*out_stream << value;
if (delim)
  *out_stream << delim;
return *this;
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ostream_iterator& operator*();
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Returns: *this.
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ostream_iterator& operator++(); ostream_iterator& operator++(int);
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Returns: *this.