31 Input/output library [input.output]

31.12 File systems [filesystems]

31.12.13 Filesystem operation functions [fs.op.funcs]

31.12.13.1 General [fs.op.funcs.general]

1
#
Filesystem operation functions query or modify files, including directories, in external storage.
2
#
[Note 1: 
Because hardware failures, network failures, file system races ([fs.race.behavior]), and many other kinds of errors occur frequently in file system operations, any filesystem operation function, no matter how apparently innocuous, can encounter an error; see [fs.err.report].
— end note]

31.12.13.2 Absolute [fs.op.absolute]

🔗
path filesystem::absolute(const path& p); path filesystem::absolute(const path& p, error_code& ec);
1
#
Effects: Composes an absolute path referencing the same file system location as p according to the operating system ([fs.conform.os]).
2
#
Returns: The composed path.
The signature with argument ec returns path() if an error occurs.
3
#
[Note 1: 
For the returned path, rp, rp.is_absolute() is true unless an error occurs.
— end note]
4
#
Throws: As specified in [fs.err.report].
5
#
[Note 2: 
To resolve symlinks or perform other sanitization that can involve queries to secondary storage, such as hard disks, consider canonical ([fs.op.canonical]).
— end note]
6
#
[Note 3: 
Implementations are strongly encouraged to not query secondary storage, and not consider !exists(p) an error.
— end note]
7
#
[Example 1: 
For POSIX-based operating systems, absolute(p) is simply current_path()/p.
For Windows-based operating systems, absolute might have the same semantics as GetFullPathNameW.
— end example]

31.12.13.3 Canonical [fs.op.canonical]

🔗
path filesystem::canonical(const path& p); path filesystem::canonical(const path& p, error_code& ec);
1
#
Effects: Converts p to an absolute path that has no symbolic link, dot, or dot-dot elements in its pathname in the generic format.
2
#
Returns: A path that refers to the same file system object as absolute(p).
The signature with argument ec returns path() if an error occurs.
3
#
Throws: As specified in [fs.err.report].
4
#
Remarks: !exists(p) is an error.

31.12.13.4 Copy [fs.op.copy]

🔗
void filesystem::copy(const path& from, const path& to);
1
#
Effects: Equivalent to copy(from, to, copy_options​::​none).
🔗
void filesystem::copy(const path& from, const path& to, error_code& ec);
2
#
Effects: Equivalent to copy(from, to, copy_options​::​none, ec).
🔗
void filesystem::copy(const path& from, const path& to, copy_options options); void filesystem::copy(const path& from, const path& to, copy_options options, error_code& ec);
3
#
Preconditions: At most one element from each option group ([fs.enum.copy.opts]) is set in options.
4
#
Effects: Before the first use of f and t:
  • (4.1)
    If (options & copy_options::create_symlinks) != copy_options::none || (options & copy_options::skip_symlinks) != copy_options::none then auto f = symlink_status(from) and if needed auto t = symlink_status(to).
  • (4.2)
    Otherwise, if (options & copy_options::copy_symlinks) != copy_options::none then auto f = symlink_status(from) and if needed auto t = status(to).
  • (4.3)
    Otherwise, auto f = status(from) and if needed auto t = status(to).
Effects are then as follows:
  • (4.4)
    If f.type() or t.type() is an implementation-defined file type ([fs.enum.file.type]), then the effects are implementation-defined.
  • (4.5)
    Otherwise, an error is reported as specified in [fs.err.report] if:
    • (4.5.1)
      exists(f) is false, or
    • (4.5.2)
      equivalent(from, to) is true, or
    • (4.5.3)
      is_other(f) || is_other(t) is true, or
    • (4.5.4)
      is_directory(f) && is_regular_file(t) is true.
  • (4.6)
    Otherwise, if is_symlink(f), then:
    • (4.6.1)
      If (options & copy_options​::​skip_symlinks) != copy_options​::​none then return.
    • (4.6.2)
      Otherwise if !exists(t) && (options & copy_options::copy_symlinks) != copy_options::none then copy_symlink(from, to).
    • (4.6.3)
      Otherwise report an error as specified in [fs.err.report].
  • (4.7)
    Otherwise, if is_regular_file(f), then:
    • (4.7.1)
      If (options & copy_options​::​directories_only) != copy_options​::​none, then return.
    • (4.7.2)
      Otherwise, if (options & copy_options​::​create_symlinks) != copy_options​::​none, then create a symbolic link to the source file.
    • (4.7.3)
      Otherwise, if (options & copy_options​::​create_hard_links) != copy_options​::​none, then create a hard link to the source file.
    • (4.7.4)
      Otherwise, if is_directory(t), then copy_file(from, to/from.filename(), options).
    • (4.7.5)
      Otherwise, copy_file(from, to, options).
  • (4.8)
    Otherwise, if is_directory(f) && (options & copy_options::create_symlinks) != copy_options::none then report an error with an error_code argument equal to make_error_code(errc​::​is_a_directory).
  • (4.9)
    Otherwise, if is_directory(f) && ((options & copy_options::recursive) != copy_options::none || options == copy_options::none) then:
    • (4.9.1)
      If exists(t) is false, then create_directory(to, from).
    • (4.9.2)
      Then, iterate over the files in from, as if by for (const directory_entry& x : directory_iterator(from)) copy(x.path(), to/x.path().filename(), options | copy_options::in-recursive-copy); where in-recursive-copy is a bitmask element of copy_options that is not one of the elements in [fs.enum.copy.opts].
  • (4.10)
    Otherwise, for the signature with argument ec, ec.clear().
  • (4.11)
    Otherwise, no effects.
5
#
Throws: As specified in [fs.err.report].
6
#
Remarks: For the signature with argument ec, any library functions called by the implementation shall have an error_code argument if applicable.
7
#
[Example 1: 
Given this directory structure: 
/dir1
  file1
  file2
  dir2
    file3
Calling copy("/dir1", "/dir3") would result in: 
/dir1
  file1
  file2
  dir2
    file3
/dir3
  file1
  file2
Alternatively, calling copy("/dir1", "/dir3", copy_options​::​recursive) would result in: 
/dir1
  file1
  file2
  dir2
    file3
/dir3
  file1
  file2
  dir2
    file3
— end example]

31.12.13.5 Copy file [fs.op.copy.file]

🔗
bool filesystem::copy_file(const path& from, const path& to); bool filesystem::copy_file(const path& from, const path& to, error_code& ec);
1
#
Returns: copy_file(from, to, copy_options​::​none) or
copy_file(from, to, copy_options​::​none, ec), respectively.
2
#
Throws: As specified in [fs.err.report].
🔗
bool filesystem::copy_file(const path& from, const path& to, copy_options options); bool filesystem::copy_file(const path& from, const path& to, copy_options options, error_code& ec);
3
#
Preconditions: At most one element from each option group ([fs.enum.copy.opts]) is set in options.
4
#
Effects: As follows:
  • (4.1)
    Report an error as specified in [fs.err.report] if:
    • (4.1.1)
      is_regular_file(from) is false, or
    • (4.1.2)
      exists(to) is true and is_regular_file(to) is false, or
    • (4.1.3)
      exists(to) is true and equivalent(from, to) is true, or
    • (4.1.4)
      exists(to) is true and (options & (copy_options::skip_existing | copy_options::overwrite_existing | copy_options::update_existing)) == copy_options::none
  • (4.2)
    Otherwise, copy the contents and attributes of the file from resolves to, to the file to resolves to, if:
    • (4.2.1)
      exists(to) is false, or
    • (4.2.2)
      (options & copy_options​::​overwrite_existing) != copy_options​::​none, or
    • (4.2.3)
      (options & copy_options​::​update_existing) != copy_options​::​none and from is more recent than to, determined as if by use of the last_write_time function ([fs.op.last.write.time]).
  • (4.3)
    Otherwise, no effects.
5
#
Returns: true if the from file was copied, otherwise false.
The signature with argument ec returns false if an error occurs.
6
#
Throws: As specified in [fs.err.report].
7
#
Complexity: At most one direct or indirect invocation of status(to).

31.12.13.7 Create directories [fs.op.create.directories]

🔗
bool filesystem::create_directories(const path& p); bool filesystem::create_directories(const path& p, error_code& ec);
1
#
Effects: Calls create_directory() for each element of p that does not exist.
2
#
Returns: true if a new directory was created for the directory p resolves to, otherwise false.
3
#
Throws: As specified in [fs.err.report].
4
#
Complexity: where n is the number of elements of p.

31.12.13.8 Create directory [fs.op.create.directory]

🔗
bool filesystem::create_directory(const path& p); bool filesystem::create_directory(const path& p, error_code& ec) noexcept;
1
#
Effects: Creates the directory p resolves to, as if by POSIX mkdir with a second argument of static_cast<int>(perms​::​all).
If mkdir fails because p resolves to an existing directory, no error is reported.
Otherwise on failure an error is reported.
2
#
Returns: true if a new directory was created, otherwise false.
3
#
Throws: As specified in [fs.err.report].
🔗
bool filesystem::create_directory(const path& p, const path& existing_p); bool filesystem::create_directory(const path& p, const path& existing_p, error_code& ec) noexcept;
4
#
Effects: Creates the directory p resolves to, with attributes copied from directory existing_p.
The set of attributes copied is operating system dependent.
If mkdir fails because p resolves to an existing directory, no error is reported.
Otherwise on failure an error is reported.
[Note 1: 
For POSIX-based operating systems, the attributes are those copied by native API stat(existing_p.c_str(), &attributes_stat) followed by mkdir(p.c_str(), attributes_stat.st_mode).
For Windows-based operating systems, the attributes are those copied by native API CreateDirectoryExW(existing_p.c_str(), p.c_str(), 0).
— end note]
5
#
Returns: true if a new directory was created with attributes copied from directory existing_p, otherwise false.
6
#
Throws: As specified in [fs.err.report].

31.12.13.9 Create directory symlink [fs.op.create.dir.symlk]

1
#
Effects: Establishes the postcondition, as if by POSIX symlink().
2
#
Postconditions: new_symlink resolves to a symbolic link file that contains an unspecified representation of to.
3
#
Throws: As specified in [fs.err.report].
4
#
[Note 1: 
Some operating systems require symlink creation to identify that the link is to a directory.
Thus, create_symlink() (instead of create_directory_symlink()) cannot be used reliably to create directory symlinks.
— end note]
5
#
[Note 2: 
Some operating systems do not support symbolic links at all or support them only for regular files.
Some file systems (such as the FAT file system) do not support symbolic links regardless of the operating system.
— end note]

31.12.13.10 Create hard link [fs.op.create.hard.lk]

1
#
Effects: Establishes the postcondition, as if by POSIX link().
2
#
Postconditions:
  • (2.1)
    exists(to) && exists(new_hard_link) && equivalent(to, new_hard_link)
  • (2.2)
    The contents of the file or directory to resolves to are unchanged.
3
#
Throws: As specified in [fs.err.report].
4
#
[Note 1: 
Some operating systems do not support hard links at all or support them only for regular files.
Some file systems (such as the FAT file system) do not support hard links regardless of the operating system.
Some file systems limit the number of links per file.
— end note]

31.12.13.12 Current path [fs.op.current.path]

🔗
path filesystem::current_path(); path filesystem::current_path(error_code& ec);
1
#
Returns: The absolute path of the current working directory, whose pathname in the native format is obtained as if by POSIX getcwd().
The signature with argument ec returns path() if an error occurs.
2
#
Throws: As specified in [fs.err.report].
3
#
Remarks: The current working directory is the directory, associated with the process, that is used as the starting location in pathname resolution for relative paths.
4
#
[Note 1: 
The current_path() name was chosen to emphasize that the returned value is a path, not just a single directory name.
— end note]
5
#
[Note 2: 
The current path as returned by many operating systems is a dangerous global variable and can be changed unexpectedly by third-party or system library functions, or by another thread.
— end note]
🔗
void filesystem::current_path(const path& p); void filesystem::current_path(const path& p, error_code& ec) noexcept;
6
#
Effects: Establishes the postcondition, as if by POSIX chdir().
7
#
Postconditions: equivalent(p, current_path()).
8
#
Throws: As specified in [fs.err.report].
9
#
[Note 3: 
The current path for many operating systems is a dangerous global state and can be changed unexpectedly by third-party or system library functions, or by another thread.
— end note]

31.12.13.13 Equivalent [fs.op.equivalent]

🔗
bool filesystem::equivalent(const path& p1, const path& p2); bool filesystem::equivalent(const path& p1, const path& p2, error_code& ec) noexcept;
1
#
Two paths are considered to resolve to the same file system entity if two candidate entities reside on the same device at the same location.
[Note 1: 
On POSIX platforms, this is determined as if by the values of the POSIX stat class, obtained as if by stat() for the two paths, having equal st_dev values and equal st_ino values.
— end note]
2
#
Returns: true, if p1 and p2 resolve to the same file system entity, otherwise false.
The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].
4
#
Remarks: !exists(p1) || !exists(p2) is an error.

31.12.13.14 Exists [fs.op.exists]

🔗
bool filesystem::exists(file_status s) noexcept;
1
#
Returns: status_known(s) && s.type() != file_type​::​not_found.
🔗
bool filesystem::exists(const path& p); bool filesystem::exists(const path& p, error_code& ec) noexcept;
2
#
Let s be a file_status, determined as if by status(p) or status(p, ec), respectively.
3
#
Effects: The signature with argument ec calls ec.clear() if status_known(s).
4
#
Returns: exists(s).
5
#
Throws: As specified in [fs.err.report].

31.12.13.15 File size [fs.op.file.size]

🔗
uintmax_t filesystem::file_size(const path& p); uintmax_t filesystem::file_size(const path& p, error_code& ec) noexcept;
1
#
Effects: If exists(p) is false, an error is reported ([fs.err.report]).
2
#
Returns:
  • (2.1)
    If is_regular_file(p), the size in bytes of the file p resolves to, determined as if by the value of the POSIX stat class member st_size obtained as if by POSIX stat().
  • (2.2)
    Otherwise, the result is implementation-defined.
The signature with argument ec returns static_cast<uintmax_t>(-1) if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.16 Hard link count [fs.op.hard.lk.ct]

1
#
Returns: The number of hard links for p.
The signature with argument ec returns static_cast<uintmax_t>(-1) if an error occurs.
2
#
Throws: As specified in [fs.err.report].

31.12.13.17 Is block file [fs.op.is.block.file]

🔗
bool filesystem::is_block_file(file_status s) noexcept;
1
#
Returns: s.type() == file_type​::​block.
🔗
bool filesystem::is_block_file(const path& p); bool filesystem::is_block_file(const path& p, error_code& ec) noexcept;
2
#
Returns: is_block_file(status(p)) or is_block_file(status(p, ec)), respectively.
The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.18 Is character file [fs.op.is.char.file]

🔗
bool filesystem::is_character_file(file_status s) noexcept;
1
#
Returns: s.type() == file_type​::​character.
🔗
bool filesystem::is_character_file(const path& p); bool filesystem::is_character_file(const path& p, error_code& ec) noexcept;
2
#
Returns: is_character_file(status(p)) or is_character_file(status(p, ec)), respectively.

The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.19 Is directory [fs.op.is.directory]

🔗
bool filesystem::is_directory(file_status s) noexcept;
1
#
Returns: s.type() == file_type​::​directory.
🔗
bool filesystem::is_directory(const path& p); bool filesystem::is_directory(const path& p, error_code& ec) noexcept;
2
#
Returns: is_directory(status(p)) or is_directory(status(p, ec)), respectively.
The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.20 Is empty [fs.op.is.empty]

🔗
bool filesystem::is_empty(const path& p); bool filesystem::is_empty(const path& p, error_code& ec);
1
#
Effects:
  • (1.1)
    Determine file_status s, as if by status(p) or status(p, ec), respectively.
  • (1.2)
    For the signature with argument ec, return false if an error occurred.
  • (1.3)
    Otherwise, if is_directory(s):
    • (1.3.1)
      Create a variable itr, as if by directory_iterator itr(p) or directory_iterator itr(p, ec), respectively.
    • (1.3.2)
      For the signature with argument ec, return false if an error occurred.
    • (1.3.3)
      Otherwise, return itr == directory_iterator().
  • (1.4)
    Otherwise:
    • (1.4.1)
      Determine uintmax_t sz, as if by file_size(p) or file_size(p, ec), respectively.
    • (1.4.2)
      For the signature with argument ec, return false if an error occurred.
    • (1.4.3)
      Otherwise, return sz == 0.
2
#
Throws: As specified in [fs.err.report].

31.12.13.21 Is fifo [fs.op.is.fifo]

🔗
bool filesystem::is_fifo(file_status s) noexcept;
1
#
Returns: s.type() == file_type​::​fifo.
🔗
bool filesystem::is_fifo(const path& p); bool filesystem::is_fifo(const path& p, error_code& ec) noexcept;
2
#
Returns: is_fifo(status(p)) or is_fifo(status(p, ec)), respectively.
The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.22 Is other [fs.op.is.other]

🔗
bool filesystem::is_other(file_status s) noexcept;
1
#
Returns: exists(s) && !is_regular_file(s) && !is_directory(s) && !is_symlink(s).
🔗
bool filesystem::is_other(const path& p); bool filesystem::is_other(const path& p, error_code& ec) noexcept;
2
#
Returns: is_other(status(p)) or is_other(status(p, ec)), respectively.
The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.23 Is regular file [fs.op.is.regular.file]

🔗
bool filesystem::is_regular_file(file_status s) noexcept;
1
#
Returns: s.type() == file_type​::​regular.
🔗
bool filesystem::is_regular_file(const path& p);
2
#
Returns: is_regular_file(status(p)).
3
#
Throws: filesystem_error if status(p) would throw filesystem_error.
🔗
bool filesystem::is_regular_file(const path& p, error_code& ec) noexcept;
4
#
Effects: Sets ec as if by status(p, ec).
[Note 1: 
file_type​::​none, file_type​::​not_found and file_type​::​unknown cases set ec to error values.
To distinguish between cases, call the status function directly.
— end note]
5
#
Returns: is_regular_file(status(p, ec)).
Returns false if an error occurs.

31.12.13.24 Is socket [fs.op.is.socket]

🔗
bool filesystem::is_socket(file_status s) noexcept;
1
#
Returns: s.type() == file_type​::​socket.
🔗
bool filesystem::is_socket(const path& p); bool filesystem::is_socket(const path& p, error_code& ec) noexcept;
2
#
Returns: is_socket(status(p)) or is_socket(status(p, ec)), respectively.
The signature with argument ec returns false if an error occurs.
3
#
Throws: As specified in [fs.err.report].

31.12.13.26 Last write time [fs.op.last.write.time]

🔗
file_time_type filesystem::last_write_time(const path& p); file_time_type filesystem::last_write_time(const path& p, error_code& ec) noexcept;
1
#
Returns: The time of last data modification of p, determined as if by the value of the POSIX stat class member st_mtime obtained as if by POSIX stat().
The signature with argument ec returns file_time_type​::​min() if an error occurs.
2
#
Throws: As specified in [fs.err.report].
🔗
void filesystem::last_write_time(const path& p, file_time_type new_time); void filesystem::last_write_time(const path& p, file_time_type new_time, error_code& ec) noexcept;
3
#
Effects: Sets the time of last data modification of the file resolved to by p to new_time, as if by POSIX futimens().
4
#
Throws: As specified in [fs.err.report].
5
#
[Note 1: 
A postcondition of last_write_time(p) == new_time is not specified because it does not necessarily hold for file systems with coarse time granularity.
— end note]

31.12.13.27 Permissions [fs.op.permissions]

🔗
void filesystem::permissions(const path& p, perms prms, perm_options opts=perm_options::replace); void filesystem::permissions(const path& p, perms prms, error_code& ec) noexcept; void filesystem::permissions(const path& p, perms prms, perm_options opts, error_code& ec);
1
#
Preconditions: Exactly one of the perm_options constants replace, add, or remove is present in opts.
2
#
Effects: Applies the action specified by opts to the file p resolves to, or to file p itself if p is a symbolic link and perm_options​::​nofollow is set in opts.
The action is applied as if by POSIX fchmodat().
3
#
[Note 1: 
Conceptually permissions are viewed as bits, but the actual implementation can use some other mechanism.
— end note]
4
#
Throws: As specified in [fs.err.report].
5
#
Remarks: The second signature behaves as if it had an additional parameter perm_options opts with an argument of perm_options​::​replace.

31.12.13.28 Proximate [fs.op.proximate]

🔗
path filesystem::proximate(const path& p, error_code& ec);
1
#
Returns: proximate(p, current_path(), ec).
2
#
Throws: As specified in [fs.err.report].
🔗
path filesystem::proximate(const path& p, const path& base = current_path()); path filesystem::proximate(const path& p, const path& base, error_code& ec);
3
#
Returns: For the first form: weakly_canonical(p).lexically_proximate(weakly_canonical(base));
For the second form: weakly_canonical(p, ec).lexically_proximate(weakly_canonical(base, ec)); or path() at the first error occurrence, if any.
4
#
Throws: As specified in [fs.err.report].

31.12.13.30 Relative [fs.op.relative]

🔗
path filesystem::relative(const path& p, error_code& ec);
1
#
Returns: relative(p, current_path(), ec).
2
#
Throws: As specified in [fs.err.report].
🔗
path filesystem::relative(const path& p, const path& base = current_path()); path filesystem::relative(const path& p, const path& base, error_code& ec);
3
#
Returns: For the first form: weakly_canonical(p).lexically_relative(weakly_canonical(base));
For the second form: weakly_canonical(p, ec).lexically_relative(weakly_canonical(base, ec)); or path() at the first error occurrence, if any.
4
#
Throws: As specified in [fs.err.report].

31.12.13.31 Remove [fs.op.remove]

🔗
bool filesystem::remove(const path& p); bool filesystem::remove(const path& p, error_code& ec) noexcept;
1
#
Effects: If exists(symlink_status(p, ec)), the file p is removed as if by POSIX remove().
[Note 1: 
A symbolic link is itself removed, rather than the file it resolves to.
— end note]
2
#
Postconditions: exists(symlink_status(p)) is false.
3
#
Returns: false if p did not exist, otherwise true.
The signature with argument ec returns false if an error occurs.
4
#
Throws: As specified in [fs.err.report].

31.12.13.32 Remove all [fs.op.remove.all]

🔗
uintmax_t filesystem::remove_all(const path& p); uintmax_t filesystem::remove_all(const path& p, error_code& ec);
1
#
Effects: Recursively deletes the contents of p if it exists, then deletes file p itself, as if by POSIX remove().
[Note 1: 
A symbolic link is itself removed, rather than the file it resolves to.
— end note]
2
#
Postconditions: exists(symlink_status(p)) is false.
3
#
Returns: The number of files removed.
The signature with argument ec returns static_cast< uintmax_t>(-1) if an error occurs.
4
#
Throws: As specified in [fs.err.report].

31.12.13.33 Rename [fs.op.rename]

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void filesystem::rename(const path& old_p, const path& new_p); void filesystem::rename(const path& old_p, const path& new_p, error_code& ec) noexcept;
1
#
Effects: Renames old_p to new_p, as if by POSIX rename().
[Note 1: 
  • (1.1)
    If old_p and new_p resolve to the same existing file, no action is taken.
  • (1.2)
    Otherwise, the rename can include the following effects:
    • (1.2.1)
      if new_p resolves to an existing non-directory file, new_p is removed; otherwise,
    • (1.2.2)
      if new_p resolves to an existing directory, new_p is removed if empty on POSIX compliant operating systems but might be an error on other operating systems.
A symbolic link is itself renamed, rather than the file it resolves to.
— end note]
2
#
Throws: As specified in [fs.err.report].

31.12.13.34 Resize file [fs.op.resize.file]

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void filesystem::resize_file(const path& p, uintmax_t new_size); void filesystem::resize_file(const path& p, uintmax_t new_size, error_code& ec) noexcept;
1
#
Effects: Causes the size that would be returned by file_size(p) to be equal to new_size, as if by POSIX truncate().
2
#
Throws: As specified in [fs.err.report].

31.12.13.35 Space [fs.op.space]

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space_info filesystem::space(const path& p); space_info filesystem::space(const path& p, error_code& ec) noexcept;
1
#
Returns: An object of type space_info.
The value of the space_info object is determined as if by using POSIX statvfs to obtain a POSIX struct statvfs, and then multiplying its f_blocks, f_bfree, and f_bavail members by its f_frsize member, and assigning the results to the capacity, free, and available members respectively.
Any members for which the value cannot be determined shall be set to static_cast<uintmax_t>(-1).
For the signature with argument ec, all members are set to static_cast<uintmax_t>(-1) if an error occurs.
2
#
Throws: As specified in [fs.err.report].
3
#
Remarks: The value of member space_info​::​available is operating system dependent.
[Note 1: 
available might be less than free.
— end note]

31.12.13.36 Status [fs.op.status]

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file_status filesystem::status(const path& p);
1
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Effects: As if: error_code ec; file_status result = status(p, ec); if (result.type() == file_type::none) throw filesystem_error(implementation-supplied-message, p, ec); return result;
2
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Returns: See above.
3
#
Throws: filesystem_error.
[Note 1: 
result values of file_status(file_type​::​not_found) and file_status(file_type​::​unknown) are not considered failures and do not cause an exception to be thrown.
— end note]
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file_status filesystem::status(const path& p, error_code& ec) noexcept;
4
#
Effects: If possible, determines the attributes of the file p resolves to, as if by using POSIX stat() to obtain a POSIX struct stat.
If, during attribute determination, the underlying file system API reports an error, sets ec to indicate the specific error reported.
Otherwise, ec.clear().
[Note 2: 
This allows users to inspect the specifics of underlying API errors even when the value returned by status() is not file_status(file_type​::​none).
— end note]
5
#
Let prms denote the result of (m & perms​::​mask), where m is determined as if by converting the st_mode member of the obtained struct stat to the type perms.
6
#
Returns:
  • (6.1)
    If ec != error_code():
    • (6.1.1)
      If the specific error indicates that p cannot be resolved because some element of the path does not exist, returns file_status(file_type​::​not_found).
    • (6.1.2)
      Otherwise, if the specific error indicates that p can be resolved but the attributes cannot be determined, returns file_status(file_type​::​unknown).
    • (6.1.3)
      Otherwise, returns file_status(file_type​::​none).
    [Note 3: 
    These semantics distinguish between p being known not to exist, p existing but not being able to determine its attributes, and there being an error that prevents even knowing if p exists.
    These distinctions are important to some use cases.
    — end note]
  • (6.2)
    Otherwise,
    • (6.2.1)
      If the attributes indicate a regular file, as if by POSIX S_ISREG, returns file_status(file_type​::​regular, prms).
      [Note 4: 
      file_type​::​regular implies appropriate <fstream> operations would succeed, assuming no hardware, permission, access, or file system race errors.
      Lack of file_type​::​regular does not necessarily imply <fstream> operations would fail on a directory.
      — end note]
    • (6.2.2)
      Otherwise, if the attributes indicate a directory, as if by POSIX S_ISDIR, returns file_status(file_type​::​directory, prms).
      [Note 5: 
      file_type​::​directory implies that calling directory_iterator(p) would succeed.
      — end note]
    • (6.2.3)
      Otherwise, if the attributes indicate a block special file, as if by POSIX S_ISBLK, returns file_status(file_type​::​block, prms).
    • (6.2.4)
      Otherwise, if the attributes indicate a character special file, as if by POSIX S_ISCHR, returns file_status(file_type​::​character, prms).
    • (6.2.5)
      Otherwise, if the attributes indicate a fifo or pipe file, as if by POSIX S_ISFIFO, returns file_status(file_type​::​fifo, prms).
    • (6.2.6)
      Otherwise, if the attributes indicate a socket, as if by POSIX S_ISSOCK, returns file_status(file_type​::​socket, prms).
    • (6.2.7)
      Otherwise, if the attributes indicate an implementation-defined file type ([fs.enum.file.type]), returns file_status(file_type​::​A, prms), where A is the constant for the implementation-defined file type.
    • (6.2.8)
      Otherwise, returns file_status(file_type​::​unknown, prms).
7
#
Remarks: If a symbolic link is encountered during pathname resolution, pathname resolution continues using the contents of the symbolic link.

31.12.13.37 Status known [fs.op.status.known]

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bool filesystem::status_known(file_status s) noexcept;
1
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Returns: s.type() != file_type​::​none.

31.12.13.38 Symlink status [fs.op.symlink.status]

1
#
Effects: Same as status(), above, except that the attributes of p are determined as if by using POSIX lstat() to obtain a POSIX struct stat.
2
#
Let prms denote the result of (m & perms​::​mask), where m is determined as if by converting the st_mode member of the obtained struct stat to the type perms.
3
#
Returns: Same as status(), above, except that if the attributes indicate a symbolic link, as if by POSIX S_ISLNK, returns file_status(file_type​::​symlink, prms).
The signature with argument ec returns file_status(file_type​::​none) if an error occurs.
4
#
Throws: As specified in [fs.err.report].
5
#
Remarks: Pathname resolution terminates if p names a symbolic link.

31.12.13.39 Temporary directory path [fs.op.temp.dir.path]

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path filesystem::temp_directory_path(); path filesystem::temp_directory_path(error_code& ec);
1
#
Let p be an unspecified directory path suitable for temporary files.
2
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Effects: If exists(p) is false or is_directory(p) is false, an error is reported ([fs.err.report]).
3
#
Returns: The path p.
The signature with argument ec returns path() if an error occurs.
4
#
Throws: As specified in [fs.err.report].
5
#
[Example 1: 
For POSIX-based operating systems, an implementation might return the path supplied by the first environment variable found in the list TMPDIR, TMP, TEMP, TEMPDIR, or if none of these are found, "/tmp".
For Windows-based operating systems, an implementation might return the path reported by the Windows GetTempPath API function.
— end example]

31.12.13.40 Weakly canonical [fs.op.weakly.canonical]

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path filesystem::weakly_canonical(const path& p); path filesystem::weakly_canonical(const path& p, error_code& ec);
1
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Effects: Using status(p) or status(p, ec), respectively, to determine existence, return a path composed by operator/= from the result of calling canonical() with a path argument composed of the leading elements of p that exist, if any, followed by the elements of p that do not exist, if any.
For the first form, canonical() is called without an error_code argument.
For the second form, canonical() is called with ec as an error_code argument, and path() is returned at the first error occurrence, if any.
2
#
Postconditions: The returned path is in normal form ([fs.path.generic]).
3
#
Returns: p with symlinks resolved and the result normalized ([fs.path.generic]).
4
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Throws: As specified in [fs.err.report].