Standard library header <spanstream> (C++23)

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_spanbuf;
  using spanbuf = basic_spanbuf<char>;
  using wspanbuf = basic_spanbuf<wchar_t>;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ispanstream;
  using ispanstream = basic_ispanstream<char>;
  using wispanstream = basic_ispanstream<wchar_t>;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_ospanstream;
  using ospanstream = basic_ospanstream<char>;
  using wospanstream = basic_ospanstream<wchar_t>;
  template<class CharT, class Traits = char_traits<CharT>>
    class basic_spanstream;
  using spanstream = basic_spanstream<char>;
  using wspanstream = basic_spanstream<wchar_t>;
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_spanbuf
    : 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;
    // 构造函数
    basic_spanbuf() : basic_spanbuf(ios_base::in | ios_base::out) {}
    explicit basic_spanbuf(ios_base::openmode which)
      : basic_spanbuf(std::span<CharT>(), which) {}
    explicit basic_spanbuf(
      std::span<CharT> s,
      ios_base::openmode which = ios_base::in | ios_base::out);
    basic_spanbuf(const basic_spanbuf&) = delete;
    basic_spanbuf(basic_spanbuf&& rhs);
    // 赋值与交换
    basic_spanbuf& operator=(const basic_spanbuf&) = delete;
    basic_spanbuf& operator=(basic_spanbuf&& rhs);
    void swap(basic_spanbuf& rhs);
    // 获取与设置
    std::span<CharT> span() const noexcept;
    void span(std::span<CharT> s) noexcept;
    protected:
    // 重写的虚函数
    basic_streambuf<CharT, Traits>* setbuf(CharT*, streamsize) 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;
  private:
    ios_base::openmode mode; // 仅用于说明
    std::span<CharT> buf; // 仅用于说明
  };
  template<class CharT, class Traits>
    void swap(basic_spanbuf<CharT, Traits>& x,
              basic_spanbuf<CharT, Traits>& y);
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_ispanstream
    : public basic_istream<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_ispanstream(
      std::span<CharT> s,
      ios_base::openmode which = ios_base::in);
    basic_ispanstream(const basic_ispanstream&) = delete;
    basic_ispanstream(basic_ispanstream&& rhs);
    template<class ROS>
    explicit basic_ispanstream(ROS&& s);
    // 赋值与交换
    basic_ispanstream& operator=(const basic_ispanstream&) = delete;
    basic_ispanstream& operator=(basic_ispanstream&& rhs);
    void swap(basic_ispanstream& rhs);
    // 成员函数
    basic_spanbuf<CharT, Traits>* rdbuf() const noexcept;
    std::span<const CharT> span() const noexcept;
    void span(std::span<CharT> s) noexcept;
    template<class ROS>
    void span(ROS&& s) noexcept;
  private:
    basic_spanbuf<CharT, Traits> sb; // 仅用于说明
  };
  template<class CharT, class Traits>
    void swap(basic_ispanstream<CharT, Traits>& x,
              basic_ispanstream<CharT, Traits>& y);
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_ospanstream
    : 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_ospanstream(
      std::span<CharT> s,
      ios_base::openmode which = ios_base::out);
    basic_ospanstream(const basic_ospanstream&) = delete;
    basic_ospanstream(basic_ospanstream&& rhs);
    // 赋值与交换
    basic_ospanstream& operator=(const basic_ospanstream&) = delete;
    basic_ospanstream& operator=(basic_ospanstream&& rhs);
    void swap(basic_ospanstream& rhs);
    // 成员函数
    basic_spanbuf<CharT, Traits>* rdbuf() const noexcept;
    std::span<CharT> span() const noexcept;
    void span(std::span<CharT> s) noexcept;
  private:
    basic_spanbuf<CharT, Traits> sb; // 仅用于说明
  };
  template<class CharT, class Traits>
    void swap(basic_ospanstream<CharT, Traits>& x,
              basic_ospanstream<CharT, Traits>& y);
}

namespace std {
  template<class CharT, class Traits = char_traits<CharT>>
  class basic_spanstream
    : public basic_iostream<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_spanstream(
      std::span<CharT> s,
      ios_base::openmode which = ios_base::out | ios_base::in);
    basic_spanstream(const basic_spanstream&) = delete;
    basic_spanstream(basic_spanstream&& rhs);
    // 赋值与交换
    basic_spanstream& operator=(const basic_spanstream&) = delete;
    basic_spanstream& operator=(basic_spanstream&& rhs);
    void swap(basic_spanstream& rhs);
    // 成员函数
    basic_spanbuf<CharT, Traits>* rdbuf() const noexcept;
    std::span<CharT> span() const noexcept;
    void span(std::span<CharT> s) noexcept;
  private:
    basic_spanbuf<CharT, Traits> sb; // 仅用于说明
  };
  template<class CharT, class Traits>
    void swap(basic_spanstream<CharT, Traits>& x,
              basic_spanstream<CharT, Traits>& y);
}