namespace std {
  class strstreambuf;
  class istrstream;
  class ostrstream;
  class strstream;
}

namespace std {
  class strstreambuf : public basic_streambuf<char> {
  public:
    strstreambuf() : strstreambuf(0) {}
    explicit strstreambuf(streamsize alsize_arg);
    strstreambuf(void* (*palloc_arg)(size_t), void (*pfree_arg)(void*));
    strstreambuf(char* gnext_arg, streamsize n, char* pbeg_arg = nullptr);
    strstreambuf(const char* gnext_arg, streamsize n);
 
    strstreambuf(signed char* gnext_arg, streamsize n,
                 signed char* pbeg_arg = nullptr);
    strstreambuf(const signed char* gnext_arg, streamsize n);
    strstreambuf(unsigned char* gnext_arg, streamsize n,
                 unsigned char* pbeg_arg = nullptr);
    strstreambuf(const unsigned char* gnext_arg, streamsize n);
 
    virtual ~strstreambuf();
 
    void  freeze(bool freezefl = true);
    char* str();
    int   pcount();
 
  protected:
    int_type overflow (int_type c = EOF) override;
    int_type pbackfail(int_type c = EOF) override;
    int_type underflow() override;
    pos_type seekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which = ios_base::in | ios_base::out) override;
    pos_type seekpos(pos_type sp,
                     ios_base::openmode which = ios_base::in | ios_base::out) override;
    streambuf* setbuf(char* s, streamsize n) override;
 
  private:
    using strstate = /*位掩码类型*/;      // 仅用于阐释
    static const strstate allocated;    // 仅用于阐释
    static const strstate constant;     // 仅用于阐释
    static const strstate dynamic;      // 仅用于阐释
    static const strstate frozen;       // 仅用于阐释
    strstate strmode;                   // 仅用于阐释
    streamsize alsize;                  // 仅用于阐释
    void* (*palloc)(size_t);            // 仅用于阐释
    void (*pfree)(void*);               // 仅用于阐释
  };
}

namespace std {
  class istrstream : public basic_istream<char> {
  public:
    explicit istrstream(const char* s);
    explicit istrstream(char* s);
    istrstream(const char* s, streamsize n);
    istrstream(char* s, streamsize n);
    virtual ~istrstream();
 
    strstreambuf* rdbuf() const;
    char* str();
  private:
    strstreambuf sb;            // 仅用于阐释
  };
}

namespace std {
  class ostrstream : public basic_ostream<char> {
  public:
    ostrstream();
    ostrstream(char* s, int n, ios_base::openmode mode = ios_base::out);
    virtual ~ostrstream();
 
    strstreambuf* rdbuf() const;
    void freeze(bool freezefl = true);
    char* str();
    int pcount() const;
  private:
    strstreambuf sb;            // 仅用于阐释
  };
}

namespace std {
  class strstream
    : public basic_iostream<char> {
  public:
    // 类型
    using char_type = char;
    using int_type  = char_traits<char>::int_type;
    using pos_type  = char_traits<char>::pos_type;
    using off_type  = char_traits<char>::off_type;
 
    // 构造函数/析构函数
    strstream();
    strstream(char* s, int n,
              ios_base::openmode mode = ios_base::in | ios_base::out);
    virtual ~strstream();
 
    // 成员
    strstreambuf* rdbuf() const;
    void freeze(bool freezefl = true);
    int pcount() const;
    char* str();
 
  private:
    strstreambuf sb;            // 仅用于阐释
  };
}