namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_istream;
 
  using istream  = basic_istream<char>;
  using wistream = basic_istream<wchar_t>;
 
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_iostream;
 
  using iostream  = basic_iostream<char>;
  using wiostream = basic_iostream<wchar_t>;
 
  template<class CharT, class Traits>
    basic_istream<CharT, Traits>& ws(basic_istream<CharT, Traits>& is);
 
  template<class Istream, class T>
    Istream&& operator>>(Istream&& is, T&& x);
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_istream : virtual public basic_ios<CharT, Traits> {
  public:
    // 类型（继承自 basic_ios ）
    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;
 
    // 构造函数/析构函数
    explicit basic_istream(basic_streambuf<CharT, Traits>* sb);
    virtual ~basic_istream();
 
    // 前置工序/后置工序
    class sentry;
 
    // 有格式输出
    basic_istream<CharT, Traits>&
      operator>>(basic_istream<CharT, Traits>& (*pf)(basic_istream<CharT, Traits>&));
    basic_istream<CharT, Traits>&
      operator>>(basic_ios<CharT, Traits>& (*pf)(basic_ios<CharT, Traits>&));
    basic_istream<CharT, Traits>&
      operator>>(ios_base& (*pf)(ios_base&));
 
    basic_istream<CharT, Traits>& operator>>(bool& n);
    basic_istream<CharT, Traits>& operator>>(short& n);
    basic_istream<CharT, Traits>& operator>>(unsigned short& n);
    basic_istream<CharT, Traits>& operator>>(int& n);
    basic_istream<CharT, Traits>& operator>>(unsigned int& n);
    basic_istream<CharT, Traits>& operator>>(long& n);
    basic_istream<CharT, Traits>& operator>>(unsigned long& n);
    basic_istream<CharT, Traits>& operator>>(long long& n);
    basic_istream<CharT, Traits>& operator>>(unsigned long long& n);
    basic_istream<CharT, Traits>& operator>>(float& f);
    basic_istream<CharT, Traits>& operator>>(double& f);
    basic_istream<CharT, Traits>& operator>>(long double& f);
 
    basic_istream<CharT, Traits>& operator>>(void*& p);
    basic_istream<CharT, Traits>& operator>>(basic_streambuf<char_type, Traits>* sb);
 
    // 无格式输出
    streamsize gcount() const;
    int_type get();
    basic_istream<CharT, Traits>& get(char_type& c);
    basic_istream<CharT, Traits>& get(char_type* s, streamsize n);
    basic_istream<CharT, Traits>& get(char_type* s, streamsize n, char_type delim);
    basic_istream<CharT, Traits>& get(basic_streambuf<char_type, Traits>& sb);
    basic_istream<CharT, Traits>&
      get(basic_streambuf<char_type, Traits>& sb, char_type delim);
 
    basic_istream<CharT, Traits>& getline(char_type* s, streamsize n);
    basic_istream<CharT, Traits>& getline(char_type* s, streamsize n, char_type delim);
 
    basic_istream<CharT, Traits>& ignore(streamsize n = 1, int_type delim = Traits::eof());
    int_type                      peek();
    basic_istream<CharT, Traits>& read    (char_type* s, streamsize n);
    streamsize                    readsome(char_type* s, streamsize n);
 
    basic_istream<CharT, Traits>& putback(char_type c);
    basic_istream<CharT, Traits>& unget();
    int sync();
 
    pos_type tellg();
    basic_istream<CharT, Traits>& seekg(pos_type);
    basic_istream<CharT, Traits>& seekg(off_type, ios_base::seekdir);
 
  protected:
    // 复制/移动构造函数
    basic_istream(const basic_istream&) = delete;
    basic_istream(basic_istream&& rhs);
 
    // 赋值与交换
    basic_istream& operator=(const basic_istream&) = delete;
    basic_istream& operator=(basic_istream&& rhs);
    void swap(basic_istream& rhs);
  };
 
  // 字符提取模板
  template<class CharT, class Traits>
    basic_istream<CharT, Traits>& operator>>(basic_istream<CharT, Traits>&, CharT&);
  template<class Traits>
    basic_istream<char, Traits>& operator>>(basic_istream<char, Traits>&, unsigned char&);
  template<class Traits>
    basic_istream<char, Traits>& operator>>(basic_istream<char, Traits>&, signed char&);
 
  template<class CharT, class Traits, size_t N>
    basic_istream<CharT, Traits>&
      operator>>(basic_istream<CharT, Traits>&, CharT(&)[N]);
  template<class Traits, size_t N>
    basic_istream<char, Traits>&
      operator>>(basic_istream<char, Traits>&, unsigned char(&)[N]);
  template<class Traits, size_t N>
    basic_istream<char, Traits>&
      operator>>(basic_istream<char, Traits>&, signed char(&)[N]);
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_istream<CharT, Traits>::sentry {
    bool ok_;                   // 仅用于阐释
  public:
    explicit sentry(basic_istream<CharT, Traits>& is, bool noskipws = false);
    ~sentry();
    explicit operator bool() const { return ok_; }
    sentry(const sentry&) = delete;
    sentry& operator=(const sentry&) = delete;
  };
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_iostream
    : public basic_istream<CharT, Traits>,
      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;
 
    // 构造函数
    explicit basic_iostream(basic_streambuf<CharT, Traits>* sb);
 
    // 析构函数
    virtual ~basic_iostream();
 
  protected:
    // 构造函数
    basic_iostream(const basic_iostream&) = delete;
    basic_iostream(basic_iostream&& rhs);
 
    // 赋值与交换
    basic_iostream& operator=(const basic_iostream&) = delete;
    basic_iostream& operator=(basic_iostream&& rhs);
    void swap(basic_iostream& rhs);
  };
}