31 Input/output library [input.output]

31.12 File systems [filesystems]

31.12.10 Class directory_entry [fs.class.directory.entry]

31.12.10.1 General [fs.class.directory.entry.general]

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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 path-object; // exposition only }; }
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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.
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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.
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[Note 1: 
directory_iterator can cache already available attribute values directly into a directory_entry object without the cost of a call to refresh().
— end note]
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[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]

31.12.10.2 Constructors [fs.dir.entry.cons]

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explicit directory_entry(const filesystem::path& p); directory_entry(const filesystem::path& p, error_code& ec);
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Effects: Calls refresh() or refresh(ec), respectively.
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Postconditions: path() == p if no error occurs, otherwise path() == filesystem​::​path().
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Throws: As specified in [fs.err.report].

31.12.10.3 Modifiers [fs.dir.entry.mods]

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void assign(const filesystem::path& p); void assign(const filesystem::path& p, error_code& ec);
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Effects: Equivalent to path-object = p, then refresh() or refresh(ec), respectively.
If an error occurs, the values of any cached attributes are unspecified.
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Throws: As specified in [fs.err.report].
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void replace_filename(const filesystem::path& p); void replace_filename(const filesystem::path& p, error_code& ec);
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Effects: Equivalent to path-object.replace_filename(p), then refresh() or refresh(ec), respectively.
If an error occurs, the values of any cached attributes are unspecified.
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Throws: As specified in [fs.err.report].
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void refresh(); void refresh(error_code& ec) noexcept;
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Effects: Stores the current values of any cached attributes of the file p resolves to.
If an error occurs, an error is reported ([fs.err.report]) and the values of any cached attributes are unspecified.
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Throws: As specified in [fs.err.report].
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[Note 1: 
Implementations of directory_iterator ([fs.class.directory.iterator]) are prohibited from directly or indirectly calling the refresh function as described in [fs.class.directory.iterator.general].
— end note]

31.12.10.4 Observers [fs.dir.entry.obs]

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Unqualified function names in the Returns: elements of the directory_entry observers described below refer to members of the std​::​filesystem namespace.
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const filesystem::path& path() const noexcept; operator const filesystem::path&() const noexcept;
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Returns: path-object.
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bool exists() const; bool exists(error_code& ec) const noexcept;
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Returns: exists(this->status()) or exists(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_block_file() const; bool is_block_file(error_code& ec) const noexcept;
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Returns: is_block_file(this->status()) or is_block_file(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_character_file() const; bool is_character_file(error_code& ec) const noexcept;
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Returns: is_character_file(this->status()) or is_character_file(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_directory() const; bool is_directory(error_code& ec) const noexcept;
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Returns: is_directory(this->status()) or is_directory(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_fifo() const; bool is_fifo(error_code& ec) const noexcept;
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Returns: is_fifo(this->status()) or is_fifo(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_other() const; bool is_other(error_code& ec) const noexcept;
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Returns: is_other(this->status()) or is_other(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_regular_file() const; bool is_regular_file(error_code& ec) const noexcept;
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Returns: is_regular_file(this->status()) or is_regular_file(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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bool is_socket() const; bool is_socket(error_code& ec) const noexcept;
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Returns: is_socket(this->status()) or is_socket(this->status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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Returns: is_symlink(this->symlink_status()) or is_symlink(this->symlink_status(ec)), respectively.
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Throws: As specified in [fs.err.report].
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uintmax_t file_size() const; uintmax_t file_size(error_code& ec) const noexcept;
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Returns: If cached, the file size attribute value.
Otherwise, file_size(path()) or file_size(path(), ec), respectively.
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Throws: As specified in [fs.err.report].
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Returns: If cached, the hard link count attribute value.
Otherwise, hard_link_count(path()) or hard_link_count(path(), ec), respectively.
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Throws: As specified in [fs.err.report].
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file_time_type last_write_time() const; file_time_type last_write_time(error_code& ec) const noexcept;
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Returns: If cached, the last write time attribute value.
Otherwise, last_write_time(path()) or last_write_time(path(), ec), respectively.
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Throws: As specified in [fs.err.report].
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file_status status() const; file_status status(error_code& ec) const noexcept;
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Returns: If cached, the status attribute value.
Otherwise, status(path()) or status(path(), ec), respectively.
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Throws: As specified in [fs.err.report].
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Returns: If cached, the symlink status attribute value.
Otherwise, symlink_status(path()) or symlink_status(path(), ec), respectively.
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Throws: As specified in [fs.err.report].
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bool operator==(const directory_entry& rhs) const noexcept;
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Returns: path-object == rhs.path-object.
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strong_ordering operator<=>(const directory_entry& rhs) const noexcept;
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Returns: path-object <=> rhs.path-object.

31.12.10.5 Inserter [fs.dir.entry.io]

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template<class charT, class traits> friend basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const directory_entry& d);
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Effects: Equivalent to: return os << d.path();