Standard library header <filesystem> (C++17)

#include <compare>
namespace std::filesystem {
  // 路径
  class path;
  // 路径非成员函数
  void swap(path& lhs, path& rhs) noexcept;
  size_t hash_value(const path& p) noexcept;
  // 文件系统错误
  class filesystem_error;
  // 目录条目
  class directory_entry;
  // 目录迭代器
  class directory_iterator;
  // 目录迭代器的范围访问
  directory_iterator begin(directory_iterator iter) noexcept;
  directory_iterator end(directory_iterator) noexcept;
  // 递归目录迭代器
  class recursive_directory_iterator;
  // 递归目录迭代器的范围访问
  recursive_directory_iterator begin(recursive_directory_iterator iter) noexcept;
  recursive_directory_iterator end(recursive_directory_iterator) noexcept;
  // 文件状态
  class file_status;
  struct space_info {
    uintmax_t capacity;
    uintmax_t free;
    uintmax_t available;
    friend bool operator==(const space_info&, const space_info&) = default;
  };
  // 枚举
  enum class file_type;
  enum class perms;
  enum class perm_options;
  enum class copy_options;
  enum class directory_options;
  using file_time_type = chrono::time_point<chrono::file_clock>;
  // 文件系统操作
  path absolute(const path& p);
  path absolute(const path& p, error_code& ec);
  path canonical(const path& p);
  path canonical(const path& p, error_code& ec);
  void copy(const path& from, const path& to);
  void copy(const path& from, const path& to, error_code& ec);
  void copy(const path& from, const path& to, copy_options options);
  void copy(const path& from, const path& to, copy_options options,
            error_code& ec);
  bool copy_file(const path& from, const path& to);
  bool copy_file(const path& from, const path& to, error_code& ec);
  bool copy_file(const path& from, const path& to, copy_options option);
  bool copy_file(const path& from, const path& to, copy_options option,
                 error_code& ec);
  void copy_symlink(const path& existing_symlink, const path& new_symlink);
  void copy_symlink(const path& existing_symlink, const path& new_symlink,
                    error_code& ec) noexcept;
  bool create_directories(const path& p);
  bool create_directories(const path& p, error_code& ec);
  bool create_directory(const path& p);
  bool create_directory(const path& p, error_code& ec) noexcept;
  bool create_directory(const path& p, const path& attributes);
  bool create_directory(const path& p, const path& attributes,
                        error_code& ec) noexcept;
  void create_directory_symlink(const path& to, const path& new_symlink);
  void create_directory_symlink(const path& to, const path& new_symlink,
                                error_code& ec) noexcept;
  void create_hard_link(const path& to, const path& new_hard_link);
  void create_hard_link(const path& to, const path& new_hard_link,
                        error_code& ec) noexcept;
  void create_symlink(const path& to, const path& new_symlink);
  void create_symlink(const path& to, const path& new_symlink,
                      error_code& ec) noexcept;
  path current_path();
  path current_path(error_code& ec);
  void current_path(const path& p);
  void current_path(const path& p, error_code& ec) noexcept;
  bool equivalent(const path& p1, const path& p2);
  bool equivalent(const path& p1, const path& p2, error_code& ec) noexcept;
  bool exists(file_status

namespace std::filesystem {
  class path {
  public:
    using value_type  = /* 详见描述 */;
    using string_type = basic_string<value_type>;
    static constexpr value_type preferred_separator = /* 详见描述 */;
    // 枚举格式
    enum format;
    // 构造函数与析构函数
    path() noexcept;
    path(const path& p);
    path(path&& p) noexcept;
    path(string_type&& source, format fmt = auto_format);
    template<class Source>
      path(const Source& source, format fmt = auto_format);
    template<class InputIt>
      path(InputIt first, InputIt last, format fmt = auto_format);
    template<class Source>
      path(const Source& source, const locale& loc, format fmt = auto_format);
    template<class InputIt>
      path(InputIt first, InputIt last, const locale& loc, format fmt = auto_format);
    ~path();
    // 赋值操作
    path& operator=(const path& p);
    path& operator=(path&& p) noexcept;
    path& operator=(string_type&& source);
    path& assign(string_type&& source);
    template<class Source>
      path& operator=(const Source& source);
    template<class Source>
      path& assign(const Source& source);
    template<class InputIt>
      path& assign(InputIt first, InputIt last);
    // 追加操作
    path& operator/=(const path& p);
    template<class Source>
      path& operator/=(const Source& source);
    template<class Source>
      path& append(const Source& source);
    template<class InputIt>
      path& append(InputIt first, InputIt last);
    // 连接操作
    path& operator+=(const path& x);
    path& operator+=(const string_type& x);
    path& operator+=(basic_string_view<value_type> x);
    path& operator+=(const value_type* x);
    path& operator+=(value_type x);
    template<class Source>
      path& operator+=(const Source& x);
    template<class ECharT>
      path& operator+=(ECharT x);
    template<class Source>
      path& concat(const Source& x);
    template<class InputIt>
      path& concat(InputIt first, InputIt last);
    // 修改器
    void  clear() noexcept;
    path& make_preferred();
    path& remove_filename();
    path& replace_filename(const path& replacement);
    path& replace_extension(const path& replacement = path());
    void  swap(path& rhs) noexcept;
    // 非成员运算符
    friend bool operator==(const path& lhs, const path& rhs) noexcept;
    friend strong_ordering operator<=>(const path& lhs, const path& rhs) noexcept;
    friend path operator/ (const path& lhs, const path& rhs);
    // 原生格式观察器
    const string_type& native() const noexcept;
    const value_type*  c_str() const noexcept;
    operator string_type() const;
    template<class ECharT, class Traits = char_traits<ECharT>,
             class Allocator = allocator<ECharT>>
      basic_string<ECharT, Traits, Allocator>
        string(const Allocator& a <span

namespace std::filesystem {
  class filesystem_error : public system_error {
  public:
    filesystem_error(const string& what_arg, error_code ec);
    filesystem_error(const string& what_arg,
                     const path& p1, error_code ec);
    filesystem_error(const string& what_arg,
                     const path& p1, const path& p2, error_code ec);
    const path& path1() const noexcept;
    const path& path2() const noexcept;
    const char* what() const noexcept override;
  };
}

namespace std::filesystem {
  class directory_entry {
  public:
    // 构造函数与析构函数
    directory_entry() noexcept = default;
    directory_entry(const directory_entry&) = default;
    directory_entry(directory_entry&&) noexcept = default;
    explicit directory_entry(const filesystem::path& p);
    directory_entry(const filesystem::path& p, error_code& ec);
    ~directory_entry();
    // 赋值操作
    directory_entry& operator=(const directory_entry&) = default;
    directory_entry& operator=(directory_entry&&) noexcept = default;
    // 修改器
    void assign(const filesystem::path& p);
    void assign(const filesystem::path& p, error_code& ec);
    void replace_filename(const filesystem::path& p);
    void replace_filename(const filesystem::path& p, error_code& ec);
    void refresh();
    void refresh(error_code& ec) noexcept;
    // 观察器
    const filesystem::path& path() const noexcept;
    operator const filesystem::path&() const noexcept;
    bool exists() const;
    bool exists(error_code& ec) const noexcept;
    bool is_block_file() const;
    bool is_block_file(error_code& ec) const noexcept;
    bool is_character_file() const;
    bool is_character_file(error_code& ec) const noexcept;
    bool is_directory() const;
    bool is_directory(error_code& ec) const noexcept;
    bool is_fifo() const;
    bool is_fifo(error_code& ec) const noexcept;
    bool is_other() const;
    bool is_other(error_code& ec) const noexcept;
    bool is_regular_file() const;
    bool is_regular_file(error_code& ec) const noexcept;
    bool is_socket() const;
    bool is_socket(error_code& ec) const noexcept;
    bool is_symlink() const;
    bool is_symlink(error_code& ec) const noexcept;
    uintmax_t file_size() const;
    uintmax_t file_size(error_code& ec) const noexcept;
    uintmax_t hard_link_count() const;
    uintmax_t hard_link_count(error_code& ec) const noexcept;
    file_time_type last_write_time() const;
    file_time_type last_write_time(error_code& ec) const noexcept;
    file_status status() const;
    file_status status(error_code& ec) const noexcept;
    file_status symlink_status() const;
    file_status symlink_status(error_code& ec) const noexcept;
    bool operator==(const directory_entry& rhs) const noexcept;
    strong_ordering operator<=>(const directory_entry& rhs) const noexcept;
    // 插入器
    template<class CharT, class Traits>
      friend basic_ostream<CharT, Traits>&
        operator<<(basic_ostream<CharT, Traits>& os, const directory_entry& d);
  private:
    filesystem::path pathobject;        // 仅用于说明
    friend class directory_iterator;    // 仅用于说明
  };
}

namespace std::filesystem {
  class directory_iterator {
  public:
    using iterator_category = input_iterator_tag;
    using value_type        = directory_entry;
    using difference_type   = ptrdiff_t;
    using pointer           = const directory_entry*;
    using reference         = const directory_entry&;
    // 成员函数
    directory_iterator() noexcept;
    explicit directory_iterator(const path& p);
    directory_iterator(const path& p, directory_options options);
    directory_iterator(const path& p, error_code& ec);
    directory_iterator(const path& p, directory_options options,
                       error_code& ec);
    directory_iterator(const directory_iterator& rhs);
    directory_iterator(directory_iterator&& rhs) noexcept;
    ~directory_iterator();
    directory_iterator& operator=(const directory_iterator& rhs);
    directory_iterator& operator=(directory_iterator&& rhs) noexcept;
    const directory_entry& operator*() const;
    const directory_entry* operator->() const;
    directory_iterator&    operator++();
    directory_iterator&    increment(error_code& ec);
    bool operator==(default_sentinel_t) const noexcept {
      return *this == directory_iterator();
    }
    // 输入迭代器所需的其他成员
  };
}

namespace std::filesystem {
  class recursive_directory_iterator {
  public:
    using iterator_category = input_iterator_tag;
    using value_type        = directory_entry;
    using difference_type   = ptrdiff_t;
    using pointer           = const directory_entry*;
    using reference         = const directory_entry&;
    // 构造函数与析构函数
    recursive_directory_iterator() noexcept;
    explicit recursive_directory_iterator(const path& p);
    recursive_directory_iterator(const path& p, directory_options options);
    recursive_directory_iterator(const path& p, directory_options options,
                                 error_code& ec);
    recursive_directory_iterator(const path& p, error_code& ec);
    recursive_directory_iterator(const recursive_directory_iterator& rhs);
    recursive_directory_iterator(recursive_directory_iterator&& rhs) noexcept;
    ~recursive_directory_iterator();
    // 观察器
    directory_options  options() const;
    int                depth() const;
    bool               recursion_pending() const;
    const directory_entry& operator*() const;
    const directory_entry* operator->() const;
    // 修改器
    recursive_directory_iterator&
      operator=(const recursive_directory_iterator& rhs);
    recursive_directory_iterator&
      operator=(recursive_directory_iterator&& rhs) noexcept;
    recursive_directory_iterator& operator++();
    recursive_directory_iterator& increment(error_code& ec);
    void pop();
    void pop(error_code& ec);
    void disable_recursion_pending();
    bool operator==(default_sentinel_t) const noexcept {
      return *this == recursive_directory_iterator();
    }
    // 输入迭代器所需的其他成员
  };
}

namespace std::filesystem {
  class file_status {
  public:
    // 构造函数与析构函数
    file_status() noexcept : file_status(file_type::none) {}
    explicit file_status(file_type ft,
                         perms prms = perms::unknown) noexcept;
    file_status(const file_status&) noexcept = default;
    file_status(file_status&&) noexcept = default;
    ~file_status();
    // 赋值操作
    file_status& operator=(const file_status&) noexcept = default;
    file_status& operator=(file_status&&) noexcept = default;
    // 修改器
    void       type(file_type ft) noexcept;
    void       permissions(perms prms) noexcept;
    // 观察器
    file_type  type() const noexcept;
    perms      permissions() const noexcept;
    friend bool operator==(const file_status& lhs, const file_status& rhs) noexcept
      { return lhs.type() == rhs.type() && lhs.permissions() == rhs.permissions(); }
  };
}