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#include <ostream>
 
namespace std {
 template<class CharT, class Traits = char_traits<CharT>,
 class Allocator = allocator<CharT>>
 class basic_syncbuf;
 
 using syncbuf = basic_syncbuf<char>;
 using wsyncbuf = basic_syncbuf<wchar_t>;
 
 template<class CharT, class Traits = char_traits<CharT>,
 class Allocator = allocator<CharT>>
 class basic_osyncstream;
 
 using osyncstream = basic_osyncstream<char>;
 using wosyncstream = basic_osyncstream<wchar_t>;
}

namespace std {
 template<class CharT, class Traits = char_traits<CharT>,
 class Allocator = allocator<CharT>>
 class basic_syncbuf : public basic_streambuf<CharT, Traits> {
 public:
 using char_type = CharT;
 using int_type = typename Traits::int_type;
 using pos_type = typename Traits::pos_type;
 using off_type = typename Traits::off_type;
 using traits_type = Traits;
 using allocator_type = Allocator;
 
 using streambuf_type = basic_streambuf<CharT, Traits>;
 
 // construction and destruction
 basic_syncbuf()
 : basic_syncbuf(nullptr) {}
 explicit basic_syncbuf(streambuf_type* obuf)
 : basic_syncbuf(obuf, Allocator()) {}
 basic_syncbuf(streambuf_type*, const Allocator&);
 basic_syncbuf(basic_syncbuf&&);
 ~basic_syncbuf();
 
 // assignment and swap
 basic_syncbuf& operator=(basic_syncbuf&&);
 void swap(basic_syncbuf&);
 
 // member functions
 bool emit();
 streambuf_type* get_wrapped() const noexcept;
 allocator_type get_allocator() const noexcept;
 void set_emit_on_sync(bool) noexcept;
 
 protected:
 // overridden virtual functions
 int sync() override;
 
 private:
 streambuf_type* wrapped; // exposition only
 bool emit_on_sync{}; // exposition only
 };
 
 // specialized algorithms
 template<class CharT, class Traits, class Allocator>
 void swap(basic_syncbuf<CharT, Traits, Allocator>&,
 basic_syncbuf<CharT, Traits, Allocator>&);
}

namespace std {
 template<class CharT, class Traits = char_traits<CharT>,
 class Allocator = allocator<CharT>>
 class basic_osyncstream : public basic_ostream<CharT, Traits> {
 public:
 using char_type = CharT;
 using int_type = typename Traits::int_type;
 using pos_type = typename Traits::pos_type;
 using off_type = typename Traits::off_type;
 using traits_type = Traits;
 
 using allocator_type = Allocator;
 using streambuf_type = basic_streambuf<CharT, Traits>;
 using syncbuf_type = basic_syncbuf<CharT, Traits, Allocator>;
 
 // construction and destruction
 basic_osyncstream(streambuf_type*, const Allocator&);
 explicit basic_osyncstream(streambuf_type* obuf)
 : basic_osyncstream(obuf, Allocator()) {}
 basic_osyncstream(basic_ostream<CharT, Traits>& os, const Allocator& allocator)
 : basic_osyncstream(os.rdbuf(), allocator) {}
 explicit basic_osyncstream(basic_ostream<CharT, Traits>& os)
 : basic_osyncstream(os, Allocator()) {}
 basic_osyncstream(basic_osyncstream&&) noexcept;
 ~basic_osyncstream();
 
 // assignment
 basic_osyncstream& operator=(basic_osyncstream&&) noexcept;
 
 // member functions
 void emit();
 streambuf_type* get_wrapped() const noexcept;
 syncbuf_type* rdbuf() const noexcept
 { return const_cast<syncbuf_type*>(addressof(sb)); }
 
 private:
 syncbuf_type sb; // exposition only
 };
}