namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_streambuf;
  using streambuf  = basic_streambuf<char>;
  using wstreambuf = basic_streambuf<wchar_t>;
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_streambuf {
  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;
 
    virtual ~basic_streambuf();
 
    // 本地环境
    locale   pubimbue(const locale& loc);
    locale   getloc() const;
 
    // buffer and positioning
    basic_streambuf* pubsetbuf(char_type* s, streamsize n);
    pos_type pubseekoff(off_type off, ios_base::seekdir way,
                        ios_base::openmode which
                          = ios_base::in | ios_base::out);
    pos_type pubseekpos(pos_type sp,
                        ios_base::openmode which
                          = ios_base::in | ios_base::out);
    int      pubsync();
 
    // 获取与放置区
    // 获取区
    streamsize in_avail();
    int_type snextc();
    int_type sbumpc();
    int_type sgetc();
    streamsize sgetn(char_type* s, streamsize n);
 
    // 回放
    int_type sputbackc(char_type c);
    int_type sungetc();
 
    // 放置区
    int_type   sputc(char_type c);
    streamsize sputn(const char_type* s, streamsize n);
 
  protected:
    basic_streambuf();
    basic_streambuf(const basic_streambuf& rhs);
    basic_streambuf& operator=(const basic_streambuf& rhs);
 
    void swap(basic_streambuf& rhs);
 
    // 获取区访问
    char_type* eback() const;
    char_type* gptr()  const;
    char_type* egptr() const;
    void       gbump(int n);
    void       setg(char_type* gbeg, char_type* gnext, char_type* gend);
 
    // 放置区访问
    char_type* pbase() const;
    char_type* pptr() const;
    char_type* epptr() const;
    void       pbump(int n);
    void       setp(char_type* pbeg, char_type* pend);
 
    // 虚函数
    // 本地环境
    virtual void imbue(const locale& loc);
 
    // buffer management and positioning
    virtual basic_streambuf* setbuf(char_type* s, streamsize n);
    virtual pos_type seekoff(off_type off, ios_base::seekdir way,
                             ios_base::openmode which
                               = ios_base::in | ios_base::out);
    virtual pos_type seekpos(pos_type sp,
                             ios_base::openmode which
                               = ios_base::in | ios_base::out);
    virtual int      sync();
 
    // 获取区
    virtual streamsize showmanyc();
    virtual streamsize xsgetn(char_type* s, streamsize n);
    virtual int_type   underflow();
    virtual int_type   uflow();
 
    // 回放
    virtual int_type   pbackfail(int_type c = Traits::eof());
 
    // 放置区
    virtual streamsize xsputn(const char_type* s, streamsize n);
    virtual int_type   overflow(int_type c = Traits::eof());
  };
}