29 Input/output library [input.output]

29.11 File systems [filesystems]

29.11.10 Class directory_­entry [fs.class.directory.entry] General [fs.class.directory.entry.general]

namespace std::filesystem { class directory_entry { public: // [fs.dir.entry.cons], constructors and destructor 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(); // assignments directory_entry& operator=(const directory_entry&) = default; directory_entry& operator=(directory_entry&&) noexcept = default; // [fs.dir.entry.mods], modifiers 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; // [fs.dir.entry.obs], observers 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; // [fs.dir.entry.io], inserter template<class charT, class traits> friend basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const directory_entry& d); private: filesystem::path pathobject; // exposition only friend class directory_iterator; // exposition only }; }
A directory_­entry object stores a path object and may store additional objects for file attributes such as hard link count, status, symlink status, file size, and last write time.
Implementations should store such additional file attributes during directory iteration if their values are available and storing the values would allow the implementation to eliminate file system accesses by directory_­entry observer functions ([fs.op.funcs]).
Such stored file attribute values are said to be cached.
[Note 1:
For purposes of exposition, class directory_­iterator ([fs.class.directory.iterator]) is shown above as a friend of class directory_­entry.
Friendship allows the directory_­iterator implementation to cache already available attribute values directly into a directory_­entry object without the cost of an unneeded call to refresh().
— end note]
[Example 1: using namespace std::filesystem; // use possibly cached last write time to minimize disk accesses for (auto&& x : directory_iterator(".")) { std::cout << x.path() << " " << x.last_write_time() << std::endl; } // call refresh() to refresh a stale cache for (auto&& x : directory_iterator(".")) { lengthy_function(x.path()); // cache becomes stale x.refresh(); std::cout << x.path() << " " << x.last_write_time() << std::endl; }
On implementations that do not cache the last write time, both loops will result in a potentially expensive call to the std​::​filesystem​::​last_­write_­time function.
On implementations that do cache the last write time, the first loop will use the cached value and so will not result in a potentially expensive call to the std​::​filesystem​::​last_­write_­time function.
The code is portable to any implementation, regardless of whether or not it employs caching.
— end example]