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Filesystem Library Version 4 |
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This reference documentation describes components that C++ programs may use to perform operations involving file systems, including paths, regular files, and directories.
C++11 Support
This reference documentation is written as if all compilers supported C++11. Where possible, the implementation falls back to C++03 if a C++11 feature is not available.
C++11 Feature
Action if not supported by compiler
noexceptKeyword omitted.
constexprKeyword omitted.
R-value references
Function signature omitted.
Defaulted and deleted functions
Workaround replacement functions provided.
Initializer lists
Not currently used.
Variadic templates
Not currently used.
Range-based for statements
Supporting functions always provided; they do no harm even for C++03 compilers.
Some behavior in this reference documentation is specified by reference to ISO/IEC 9945. How such behavior is actually implemented is unspecified.
[Note: This constitutes an "as if" rule for implementation of operating system dependent behavior. In practice implementations will usually call native operating system API's. —end note]
Implementations are encouraged to provide such behavior as it is defined by ISO/IEC 9945. Implementations shall document any behavior that differs from the behavior defined by ISO/IEC 9945. Implementations that do not support exact ISO/IEC 9945 behavior are encouraged to provide behavior as close to ISO/IEC 9945 behavior as is reasonable given the limitations of actual operating systems and file systems. If an implementation cannot provide any reasonable behavior, the implementation shall report an error in an implementation-defined manner.
[Note: Such errors might be reported by an
#errordirective, astatic_assert, afilesystem_errorexception, a special return value, or some other manner. —end note]
Implementations are not required to provide behavior that is not supported by a particular file system.
[Example: The FAT file system used by some memory cards, camera memory, and floppy discs does not support hard links, symlinks, and many other features of more capable file systems. Implementations are only required to support the FAT features supported by the host operating system. —end example]
The behavior of functions described in this reference may differ from their specification in the presence of file system races. No diagnostic is required.
If the possibility of a file system race would make it unreliable for a program to test for a precondition before calling a function described in this reference documentation, Requires is not specified for the condition. Instead, the condition is specified as a Throws condition.
[Note: As a design practice, preconditions are not specified when it is unreasonable for a program to detect them prior to calling the function. —end note]
Some behavior is specified in this reference documentation as being operating system dependent ([fs.def.osdep]). The operation system an implementation is dependent upon is implementation defined.
It is permissible for an implementation to be dependent upon an operating system emulator rather than the actual operating system.
[Example: An implementation uses Cygwin, a Linux® API emulator for some Windows® operating system versions. The implementation would define Cygwin as its operating system. Users could refer to the Cygwin documentation to find details of the operating system dependent behavior. —end example]
It is user and conformance test detectable that such an implementation is running on Cygwin. Users would be misled and conformance tests would fail if the implementation defined Linux or Windows rather than Cygwin as the operating system, since real behavior is a blend of the two.
The following definitions shall apply throughout this reference documentation:
Behavior that is dependent upon the behavior and characteristics of an operating system. See [fs.conform.os].
An object that can be written to, or read from, or both. A file has certain attributes, including type. File types include regular files and directories. Other types of files, such as symbolic links, may be supported by the implementation.
A collection of files and certain of their attributes.
The name of a file. Filenames
"."
and ".." have special meaning. The follow characteristics of
filenames are operating system dependent:
The permitted characters. See [fs.os.examples].
Specific filenames that are not permitted.
Additional filenames that have special meaning.
Case awareness and sensitivity during path resolution.
Special rules that may apply to file types other than regular files, such as directories.
A sequence of elements that identify the location of a file within a filesystem. The elements are the root-nameopt, root-directoryopt, and an optional sequence of filenames. [Note: A pathname is the concrete representation of a path. —end note]
A path that unambiguously identifies the location of a file without reference to an additional starting location. The elements of a path that determine if it is absolute are operating system dependent.
A path that
is not absolute, and so only
unambiguously
identifies the location of a file when resolved relative to
an implied starting location. The elements of a path that determine if it is
relative are operating system dependent. [Note:
Paths "." and ".." are relative paths. —end note]
An absolute path that has
no elements that are symbolic links, and no "." or ".." elements.
A character string that represents the name of a path. Pathnames are formatted according to the generic pathname grammar or an operating system dependent native pathname format.
The operating system dependent pathname format accepted by the host operating system.
A path with no redundant directory separators, current directory (dot) or parent directory (dot-dot) elements. The normal form for an empty path is an empty path. [v3: The normal form for a path ending in a directory-separator that is not the root directory is the same path with a current directory (dot) element appended.]
A directory entry object that associates a filename with a file. On some file systems, several directory entries can associate names with the same file.
A link to an existing file. Some file systems support multiple hard links to a file. If the last hard link to a file is removed, the file itself is removed.
[Note: A hard link can be thought of as a shared-ownership smart pointer to a file. —end note]
A type of file with the property that when the file is encountered during pathname resolution, a string stored by the file is used to modify the pathname resolution.
[Note: A symbolic link can be thought of as a raw pointer to a file. If the file pointed to does not exist, the symbolic link is said to be a "dangling" symbolic link. —end note]
The condition that occurs when multiple threads, processes, or computers interleave access and modification of the same object within a file system.
pathname:
root-nameopt
root-directoryopt relative-pathopt
root-name:
An
operating system dependent name that identifies the starting location for
absolute paths.
[Note: Many operating systems define a name beginning with two directory-separator characters as a root-name that identifies network or other resource locations. Some operating systems define a single letter followed by a colon as a drive specifier - a root-name identifying a specific device such as a disc drive. —end note]
root-directory:
directory-separator
relative-path:
filename
relative-path
directory-separator
relative-path
directory-separator filename
filename:
name
"."
".."
preferred-separator:
An
operating system dependent directory separator character. May be a synonym for "/".
directory-separator:
"/" directory-separator
"/"
preferred-separator
preferred-separator directory-separator
Multiple successive directory-separator characters are considered to be the same as one directory-separator character.
The filename
"." is considered to be a reference to the current directory. The
filename ".." is considered to be a reference to the
parent
directory. Specific filenames may have special meanings for a particular
operating system.
Certain features are specified in this reference documentation as being operating system dependent. The following table shows the application of those specifications for operating systems that use the ISO/IEC 9945 or Windows® application program interfaces (APIs).[footnote1]
|
Feature |
Section |
ISO/IEC 9945 |
Windows® API |
Notes |
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Not required |
Not required |
There is no need to distinguish between the generic format and native format for these operating systems. |
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No conversion performed |
No conversion performed |
The generic format is already acceptable to the native API of these operating systems. |
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These operating systems accept the same native separator between directory names and a final file name, so no format conversion is performed. Other operating systems might require conversion. |
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Format conversion by |
No conversion performed |
No conversion performed |
For efficiency, |
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Format conversion by |
No conversion performed |
Backslashes converted to slashes |
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No change |
Slashes converted to backslashes |
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Characters prohibited in filenames |
0x00, |
0x00-0x1F, |
Many operating systems prohibit the ASCII control characters (0x00-0x1F) in filenames. |
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Initial imbued |
|
Implementation supplied locale using |
Apple OS X®: Implementation supplied locale providing UTF-8 |
[footnote1] OS X® and Windows® are examples of commercially available operating systems. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO or IEC of these products.
[footnote 2] Rationale: ISO C specifies std::locale("") as "the locale-specific native
environment", while ISO/IEC 9945 says it "Specifies an implementation-defined native
environment."
[footnote 3] Rationale: This is the current behavior of C and C++ standard library functions that perform file operations using narrow character strings to identify paths. Changing this behavior would be surprising and at variance with existing code, particularly where user input is involved.
[footnote 4] Rationale: Vendor's documentation states "All BSD system functions expect their string parameters to be in UTF-8 encoding and nothing else."
<boost/filesystem.hpp> synopsis
[filesystem.synopsis]namespace boost
{
namespace filesystem
{
class path;
bool lexicographical_compare(path::iterator first1, path::iterator last1,
path::iterator first2, path::iterator last2);
void swap(path& lhs, path& rhs) noexcept;
std::size_t hash_value(const path& p);
bool operator==(const path& lhs, const path& rhs);
bool operator!=(const path& lhs, const path& rhs);
bool operator< (const path& lhs, const path& rhs);
bool operator<=(const path& lhs, const path& rhs);
bool operator> (const path& lhs, const path& rhs);
bool operator>=(const path& lhs, const path& rhs);
path operator/ (const path& lhs, const path& rhs);
std::ostream& operator<<( std::ostream& os, const path& p );
std::wostream& operator<<( std::wostream& os, const path& p );
std::istream& operator>>( std::istream& is, path& p );
std::wistream& operator>>( std::wistream& is, path& p )
class filesystem_error;
class directory_entry;
class directory_iterator;
// enable c++11 range-based for statements
const directory_iterator& begin(const directory_iterator& iter);
directory_iterator end(const directory_iterator&);
// enable BOOST_FOREACH
directory_iterator& range_begin(directory_iterator& iter);
directory_iterator range_begin(const directory_iterator& iter);
directory_iterator range_end(const directory_iterator&);
class recursive_directory_iterator;
// enable c++11 range-based for statements
const recursive_directory_iterator&
begin(const recursive_directory_iterator& iter);
recursive_directory_iterator
end(const recursive_directory_iterator&);
// enable BOOST_FOREACH
recursive_directory_iterator&
range_begin(recursive_directory_iterator& iter);
recursive_directory_iterator
range_begin(const recursive_directory_iterator& iter);
recursive_directory_iterator
range_end(const recursive_directory_iterator&);
enum file_type
{
status_error, file_not_found, regular_file, directory_file,
symlink_file, block_file, character_file, fifo_file, socket_file,
reparse_file, type_unknown
};
enum perms
{
no_perms,
owner_read, owner_write, owner_exe, owner_all,
group_read, group_write, group_exe, group_all,
others_read, others_write, others_exe, others_all, all_all,
set_uid_on_exe, set_gid_on_exe, sticky_bit,
perms_mask, perms_not_known,
add_perms, remove_perms, symlink_perms
};
class file_status;
struct space_info // returned by space function
{
uintmax_t capacity;
uintmax_t free;
uintmax_t available; // free space available to non-privileged process
};
enum class copy_options
{
none = 0u,
// copy_file options
skip_existing,
overwrite_existing,
update_existing,
synchronize_data,
synchronize,
// copy options
recursive,
copy_symlinks,
skip_symlinks,
directories_only,
create_symlinks,
create_hard_links
};
// Deprecated, use copy_options instead
enum class copy_option
{
none = copy_options::none,
fail_if_exists = none,
overwrite_if_exists = copy_options::overwrite_existing
};
enum class directory_options
{
none = 0u,
skip_permission_denied,
follow_directory_symlink,
pop_on_error
};
// Deprecated, use directory_options instead
enum class symlink_option
{
none = directory_options::none,
no_recurse = none,
recurse = directory_options::follow_directory_symlink
};
// operational functions
path absolute(const path& p, const path& base=current_path());
path absolute(const path& p, system::error_code& ec);
path absolute(const path& p, const path& base,
system::error_code& ec);
path canonical(const path& p, const path& base = current_path());
path canonical(const path& p, system::error_code& ec);
path canonical(const path& p, const path& base,
system::error_code& ec);
void copy(const path& from, const path& to);
void copy(const path& from, const path& to,
system::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, system::error_code& ec);
// Deprecated, use create_directory instead
void copy_directory(const path& from, const path& to);
void copy_directory(const path& from, const path& to,
system::error_code& ec);
bool copy_file(const path& from, const path& to);
bool copy_file(const path& from, const path& to,
system::error_code& ec);
bool copy_file(const path& from, const path& to,
copy_options options);
bool copy_file(const path& from, const path& to,
copy_options options, system::error_code& ec);
// Deprecated, use overloads taking copy_options instead
bool copy_file(const path& from, const path& to,
copy_option options);
bool copy_file(const path& from, const path& to,
copy_option options, system::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, system::error_code& ec);
bool create_directories(const path& p);
bool create_directories(const path& p,
system::error_code& ec);
bool create_directory(const path& p);
bool create_directory(const path& p, system::error_code& ec);
bool create_directory(const path& p, const path& existing);
bool create_directory(const path& p, const path& existing, system::error_code& ec);
void create_directory_symlink(const path& to,
const path& new_symlink);
void create_directory_symlink(const path& to,
const path& new_symlink, system::error_code& ec);
void create_hard_link(const path& to, const path& new_hard_link);
void create_hard_link(const path& to, const path& new_hard_link,
system::error_code& ec);
void create_symlink(const path& to, const path& new_symlink);
void create_symlink(const path& to, const path& new_symlink,
system::error_code& ec);
std::time_t creation_time(const path& p);
std::time_t creation_time(const path& p, system::error_code& ec);
path current_path();
path current_path(system::error_code& ec);
void current_path(const path& p);
void current_path(const path& p, system::error_code& ec);
bool exists(file_status s) noexcept;
bool exists(const path& p);
bool exists(const path& p, system::error_code& ec) noexcept;
bool equivalent(const path& p1, const path& p2);
bool equivalent(const path& p1, const path& p2,
system::error_code& ec);
uintmax_t file_size(const path& p);
uintmax_t file_size(const path& p, system::error_code& ec);
uintmax_t hard_link_count(const path& p);
uintmax_t hard_link_count(const path& p, system::error_code& ec);
const path& initial_path();
const path& initial_path(system::error_code& ec);
bool is_directory(file_status s) noexcept;
bool is_directory(const path& p);
bool is_directory(const path& p,
system::error_code& ec) noexcept;
bool is_empty(const path& p);
bool is_empty(const path& p, system::error_code& ec);
bool is_other(file_status s) noexcept;
bool is_other(const path& p,);
bool is_other(const path& p, system::error_code& ec) noexcept;
bool is_regular_file(file_status s) noexcept;
bool is_regular_file(const path& p);
bool is_regular_file(const path& p,
system::error_code& ec) noexcept;
bool is_symlink(file_status s noexcept);
bool is_symlink(const path& p);
bool is_symlink(const path& p, system::error_code& ec) noexcept;
std::time_t last_write_time(const path& p);
std::time_t last_write_time(const path& p, system::error_code& ec);
void last_write_time(const path& p, const std::time_t new_time);
void last_write_time(const path& p, const std::time_t new_time,
system::error_code& ec);
path read_symlink(const path& p);
path read_symlink(const path& p, system::error_code& ec);
path relative(const path& p, system::error_code& ec);
path relative(const path& p, const path& base=current_path());
path relative(const path& p,
const path& base, system::error_code& ec);
bool remove(const path& p);
bool remove(const path& p, system::error_code& ec);
uintmax_t remove_all(const path& p);
uintmax_t remove_all(const path& p, system::error_code& ec);
void rename(const path& from, const path& to);
void rename(const path& from, const path& to,
system::error_code& ec);
void resize_file(const path& p, uintmax_t size);
void resize_file(const path& p, uintmax_t size,
system::error_code& ec);
space_info space(const path& p);
space_info space(const path& p, system::error_code& ec);
file_status status(const path& p);
file_status status(const path& p, system::error_code& ec) noexcept;
bool status_known(file_status s) noexcept;
file_status symlink_status(const path& p);
file_status symlink_status(const path& p,
system::error_code& ec) noexcept;
path system_complete(const path& p);
path system_complete(const path& p, system::error_code& ec);
path temp_directory_path();
path temp_directory_path(system::error_code& ec);
path unique_path(const path& model="%%%%-%%%%-%%%%-%%%%");
path unique_path(const path& model, system::error_code& ec);
path weakly_canonical(const path& p, const path& base=current_path());
path weakly_canonical(const path& p, system::error_code& ec);
path weakly_canonical(const path& p, const path& base,
system::error_code& ec);
} // namespace filesystem
} // namespace boost
Filesystem library functions often provide two overloads, one that
throws an exception to report file system errors, and another that sets an error_code.
[Note: This supports two common use cases:
Uses where file system errors are truly exceptional and indicate a serious failure. Throwing an exception is the most appropriate response. This is the preferred default for most everyday programming.
Uses where file system errors are routine and do not necessarily represent failure. Returning an error code is the most appropriate response. This allows application specific error handling, including simply ignoring the error.
—end note]
Functions not having an argument of type system::error_code& report errors as follows, unless otherwise specified:
When a call by the
implementation to an operating system or other underlying API results in an
error that prevents the function from meeting its specifications, an exception
of type
filesystem_error is thrown.
Failure to allocate storage is reported by throwing an exception as described in the C++ standard,
17.6.4.10 [res.on.exception.handling].
Destructors throw nothing.
Functions having an argument of type system::error_code& report errors as follows, unless otherwise
specified:
If a call by the
implementation to an operating system or other underlying API results in an
error that prevents the function from meeting its specifications, the
system::error_code& argument is set as
appropriate for the specific error. Otherwise, clear()
is called on the
system::error_code& argument.
Failure to allocate storage is reported by throwing an exception as described in the C++ standard, 17.6.4.10 [res.on.exception.handling].
path [class.path]An object of class path represents a path,
and contains a pathname Such an object is concerned only with the lexical and syntactic aspects
of a path. The path does not necessarily exist in external storage, and the
pathname is not necessarily valid for the current operating
system or for a particular file system.
namespace boost
{
namespace filesystem
{
class path
{
public:
typedef see below value_type;
typedef std::basic_string<value_type> string_type;
typedef std::codecvt<wchar_t, char, std::mbstate_t> codecvt_type;
constexpr value_type dot;
constexpr value_type separator;
constexpr value_type preferred_separator;
// constructors and destructor
path();
path(const path& p);
path(path&& p) noexcept;
template <class Source>
path(Source const& source, const codecvt_type& cvt=codecvt());
template <class InputIterator>
path(InputIterator begin, InputIterator end,
const codecvt_type& cvt=codecvt());
~path();
// assignments
path& operator=(const path& p);
path& operator=(path&& p) noexcept;
template <class Source>
path& operator=(Source const& source);
path& assign(const path& p);
path& assign(path&& p) noexcept;
template <class Source>
path& assign(Source const& source,
const codecvt_type& cvt=codecvt())
template <class InputIterator>
path& assign(InputIterator begin, InputIterator end,
const codecvt_type& cvt=codecvt());
// appends
path& operator/=(const path& p);
template <class Source>
path& operator/=(Source const& source);
path& append(const path& x);
template <class Source>
path& append(Source const& source,
const codecvt_type& cvt=codecvt());
template <class InputIterator>
path& append(InputIterator begin, InputIterator end,
const codecvt_type& cvt=codecvt());
// concatenation
path& operator+=(const path& x);
template <class Source>
path& operator+=(Source const& source);
path& operator+=(value_type x);
template <class CharT>
path& operator+=(CharT x);
path& concat(const path& x);
template <class Source>
path& concat(Source const& x,
const codecvt_type& cvt=codecvt());
template <class InputIterator>
path& concat(InputIterator begin, InputIterator end,
const codecvt_type& cvt=codecvt());
// modifiers
void clear();
path& make_preferred();
path& remove_filename();
path& remove_filename_and_trailing_separators();
path& replace_filename(const path& replacement);
path& replace_extension(const path& new_extension = path());
void swap(path& rhs) noexcept;
// lexical operations
path lexically_normal() const;
path lexically_relative(const path& base) const;
path lexically_proximate(const path& base) const;
// native format observers
const string_type& native() const noexcept; // native format, encoding
const value_type* c_str() const noexcept; // native().c_str()
string_type::size_type size() const noexcept; // native().size()
template <class String>
String string(const codecvt_type& cvt=codecvt()) const;
string string(const codecvt_type& cvt=codecvt()) const;
wstring wstring(const codecvt_type& cvt=codecvt()) const;
// generic format observers
template <class String>
String generic_string() const;
string generic_string(const codecvt_type& cvt=codecvt()) const;
wstring generic_wstring(const codecvt_type& cvt=codecvt()) const;
// compare
int compare(const path& p) const noexcept;
int compare(const std::string& s) const;
int compare(const value_type* s) const;
// decomposition
path root_name() const;
path root_directory() const;
path root_path() const;
path relative_path() const;
path parent_path() const;
path filename() const;
path stem() const;
path extension() const;
// query
bool empty() const;
bool filename_is_dot() const;
bool filename_is_dot_dot() const;
bool has_root_name() const;
bool has_root_directory() const;
bool has_root_path() const;
bool has_relative_path() const;
bool has_parent_path() const;
bool has_filename() const;
bool has_stem() const;
bool has_extension() const;
bool is_absolute() const;
bool is_relative() const;
// iterators
class iterator;
typedef iterator const_iterator;
class reverse_iterator;
typedef reverse_iterator const_reverse_iterator;
iterator begin() const;
iterator end() const;
reverse_iterator rbegin() const;
reverse_iterator rend() const;
// imbued locale
static std::locale imbue(const std::locale& loc);
static const codecvt_type & codecvt();
private:
string_type pathname; // exposition only
};
} // namespace filesystem
} // namespace boost
value_type is a typedef for the
character type used by the operating system to represent pathnames.
path Usage concerns [path.usage]Filesystem library functions are not protected against data races. [Modifying an object of a Filesystem library type that is shared between threads risks undefined behavior unless objects of that type are explicitly specified as being sharable without data races or the user supplies a locking mechanism. —end note] [Note: Thus the Filesystem library behaves as if it were part of the standard library, and C++ standard 17.6.4.10 Shared objects and the library [res.on.objects] would thus apply. —end note]
Visual C++ at least through version 2012 does not employ C++11-style static
initialization locks, so the initialization of path::codecvt() can
race, either with itself or path::imbue() if they are called from
a different thread. A workaround is to call:
path::codecvt(); // ensure VC++ does not race during initialization.
in the main thread before launching any additional threads. [Note: The obvious fix of the Filesystem implementation doing the locking doesn't work because of unrelated problems with the Microsoft compiler; for static linking the runtime tries to do the initialization before main() starts, but doesn't permit operating system lock calls at that time. —end note]
Filesystem library initialization may throw an exception on POSIX
systems (e.g. Linux, but not Mac OS X) that use environmental variables to
determine the encoding of paths. This happens when std::locale("")
throws because an environmental variable such as LANG is set to an invalid
value, so it can affect any use of std::locale(""), not just
the Filesystem library. Filesystem uses lazy initialization so the exception is
only thrown if a valid std::locale("") is actually needed, and also
so that the exception is thrown after main() starts.
Rather than waiting until a call to some Filesystem library function
unexpectedly triggers the exception when it calls path::codecvt(),
a program that needs be highly robust against environmental variable problems
may want to preemptively call std::locale("") within a try block,
catch the exception, and diagnose or repair the invalid environmental variable.
path Conversions [path.cvt]path argument conversions [path.arg.cvt]path argument
format conversions [path.arg.fmt.cvt]Member function arguments that take character sequences representing paths may use the generic pathname format or the native pathname format. Iff such arguments are in the generic format and the generic format is not acceptable to the operating system as a native path, conversion to native format shall be performed during the processing of the argument. See [fs.os.examples].
[Note: Depending on the operating system, there may be no unambiguous way for an implementation to always be able to distinguish between native format and generic format arguments. This is by design as it simplifies use for operating systems that do not require disambiguation. Should an implementation encounter an operating system where disambiguation is required, an implementation can defined an extension to distinguish between the formats. —end note]
If the native format requires paths for regular files to be formatted differently from paths for directories, the path shall be treated as a directory path if last element is a separator, otherwise it shall be treated as a regular file path.
path argument encoding conversions
[path.arg.encoding.cvt]For member function arguments that take character sequences representing
paths, if the value type of the argument is not value_type and one
of the value types is char and the other is wchar_t, conversion to value_type
shall be performed by the path::codecvt() facet. ([path.imbued.locale]).
path Conversions
to generic format [fs.cvt.to.generic]Generic format observer functions shall return strings formatted according to the generic pathname format using preferred-separator. See [fs.os.examples].
path Requirements [path.req]Template parameters named InputIterator are required to meet the
requirements for a C++ standard library InputIterator compliant iterator. The iterator's value type is required
to be one of: char, wchar_t. Collectively, these types are referred to as supported path character types.
Template parameters named Source are required to be one of:
A std::basic_string, std::basic_string_view, boost::container::basic_string or boost::basic_string_view specialization with a value type of one of the supported path character types.
v3, deprecated: A container with a value type of one of the supported path character types.
A pointer into a null terminated string. The value type is required to be a supported path character type.
A C-array of supported path character type containing a null terminated string.
A boost::filesystem::directory_entry.
path constructors [path.construct]template <class Source> path(Source const& source, const codecvt_type& cvt=codecvt());
template <class InputIterator> path(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());
Effects: Stores the contents [
begin,end) ofsourceinpathname, converting format and encoding if required ([path.arg.convert]).
path assignments [path.assign]path& operator=(const path& p); path& operator=(path&& p) noexcept; template <class Source> path& operator=(Source const& source); path& assign(const path& p); path& assign(path&& p) noexcept; template <class Source> path& assign(Source const& source, const codecvt_type& cvt=codecvt()); template <class InputIterator> path& assign(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());
Effects: Stores the contents [
begin,end) orsourceorpinpathname, converting format and encoding if required ([path.arg.convert]).Returns:
*this
path appends
[path.append]The append operations use
operator/= to denote their semantic effect of appending
preferred-separator when needed.
path& operator/=(const path& p); path& append(const path& p);
Effects:
v3: Appends
path::preferred_separatortopathname, converting format and encoding if required ([path.arg.convert]), unless:
an added separator would be redundant, or
would change a relative path to an absolute path, or
p.empty(), or
*p.native().cbegin()is a directory separator.Then appends
p.native()topathname.v4: If
p.is_absolute() || (p.has_root_name() && p.root_name() != root_name()), assignspto*this. Otherwise, modifies*thisas if by these steps:
- If
p.has_root_directory(), removes root directory and relative path, if any.- Let
xbe apathwith contents ofpwithout a root name. Ifhas_filename()istrueandxdoes not start with a directory separator, appendspath::preferred_separator.- Appends
x.native().[Note: Whether the path is absolute or not depends on the target OS conventions. Because of this, the result of append operation may be different for different operating systems for some paths. For example,
path("//net/foo") / "/bar"will result in"/bar"on POSIX systems and"//net/foo/bar"on Windows because"/bar"is an absolute path on POSIX systems but not on Windows. For portable behavior avoid appending paths with non-empty root path. —end note]Returns:
*this
template <class Source> path& operator/=(Source const & source); template <class Source> path& append(Source const & source, const codecvt_type& cvt=codecvt()); template <class InputIterator> path& append(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());
Effects:
As if
append(path(args)), whereargsis the list of arguments passed to the operation.Returns:
*this
path concatenation [path.concat]path& operator+=(const path& p); path& operator+=(value_type x); template <class Source> path& operator+=(Source const& source); template <class CharT> path& operator+=(CharT x); path& concat(const path& p); template <class Source> path& concat(Source const& source, const codecvt_type& cvt=codecvt()); template <class InputIterator> path& concat(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());
Postcondition:
native() == prior_native + effective-argument, whereprior_nativeisnative()prior to the call tooperator+=, andeffective-argumentis:
p.native()ifpis present and isconst path&, otherwise
s, wheresisstd::basic_string<typename std::iterator_traits<InputIterator>::value_type>, if
s(begin, end)beginandendarguments are present, otherwise
x.If the value type of
effective-argumentwould not bepath::value_type, the actual argument or argument range is first converted so thateffective-argumenthas value typepath::value_type.Returns:
*this
path modifiers [path.modifiers]void clear();
Postcondition:
this->empty()is true.
path& make_preferred();
Effects: directory-separators are converted to preferred-separators. See [fs.os.examples].
Returns:
*this
path& remove_filename();
Effects: v3: As if,
*this = parent_path();[Note: This function is needed to efficiently implement
directory_iterator. It is exposed to allow additional uses. The actual implementation may be much more efficient than*this = parent_path()—end note]v4: Removes the
filename()path element.[Note: Unlike v3, the trailing directory separator(s) are not removed.—end note]
Returns:
*this.
path& remove_filename_and_trailing_separators();
Effects: As if,
*this = parent_path();[Note: This function is similar to
path::remove_filenamefrom v3, but is also usable in v4.—end note]Returns:
*this.
path& replace_filename(const path& replacement);
Effects: As if,
remove_filename().append(replacement);Returns:
*this.
path& replace_extension(const path& new_extension = path());
Effects:
Any existing
extension()is removed from the stored path, theniff
new_extensionis not empty and does not begin with a dot character, a dot character is appended to the stored path, then
new_extensionis appended to the stored path.Returns:
*this
void swap(path& rhs) noexcept;
Effects: Swaps the contents of the two paths.
Complexity: constant time.
path lexical operations
[path.lex.ops]path lexically_normal() const;
Overview: Returns
*thiswith redundant current directory (dot), parent directory (dot-dot), and directory-separator elements removed.Returns:
*thisin normal form.Remarks: Uses
operator/=to compose the returned path.[Example:
std::cout << path("foo/./bar/..").lexically_normal() << std::endl; // outputs "foo" std::cout << path("foo/.///bar/../").lexically_normal() << std::endl; // v3: outputs "foo/." // v4: outputs "foo/"On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect
pathequality. —end example]
path lexically_relative(const path& base) const;
Overview: Returns
*thismade relative tobase. Treats empty or identical paths as corner cases, not errors. Does not resolve symlinks. Does not first normalize*thisorbase.Remarks: Uses
std::mismatch(begin(), end(), base.begin(), base.end()), to determine the first mismatched element of*thisandbase. Usesoperator==to determine if elements match.Returns:
path()if the first mismatched element of*thisis equal tobegin()or the first mismatched element ofbaseis equal tobase.begin(), or
path(".")if the first mismatched element of*thisis equal toend()and the first mismatched element ofbaseis equal tobase.end(), or
- An object of class
pathcomposed via application ofoperator/= path("..")for each element in the half-open range [first mismatched element ofbase,base.end()), and then application ofoperator/=for each element in the half-open range [first mismatched element of*this,end()).[Example:
assert(path("/a/d").lexically_relative("/a/b/c") == "../../d");
assert(path("/a/b/c").lexically_relative("/a/d") == "../b/c");
assert(path("a/b/c").lexically_relative("a") == "b/c");
assert(path("a/b/c").lexically_relative("a/b/c/x/y") == "../..");
assert(path("a/b/c").lexically_relative("a/b/c") == ".");
assert(path("a/b").lexically_relative("c/d") == "");The above assertions will succeed. On Windows, the returned path's directory-separators will be backslashes rather than forward slashes, but that does not affect
pathequality. —end example][Note: If symlink following semantics are desired, use the operational function
relative—end note][Note: If normalization is needed to ensure consistent matching of elements, apply
lexically_normal()to*this,base, or both. —end note]path lexically_proximate(const path& base) const;Returns: If
lexically_relative(base)returns a non-empty path, returns that path. Otherwise returns*this.[Note: If symlink following semantics are desired, use the operational function
relative—end note][Note: If normalization is needed to ensure consistent matching of elements, apply
lexically_normal()to*this,base, or both. —end note]
pathnative format observers [path.native.obs]The string returned by all native format observers is in the native pathname format.
const string_type& native() const noexcept;Returns:
pathname.const value_type* c_str() const noexcept;Returns:
pathname.c_str().string_type::size_type size() const noexcept;Returns:
pathname.size().template <class String> String string(const codecvt_type& cvt=codecvt()) const;Returns:
pathname.Remarks: If
string_typeis a different type thanString, conversion is performed bycvt.string string(const codecvt_type& cvt=codecvt()) const; wstring wstring(const codecvt_type& cvt=codecvt()) const;Returns:
pathname.Remarks: If
string_typeis a different type than function's return type, conversion is performed bycvt.
pathgeneric format observers [path.generic.obs]The string returned by all generic format observers is in the generic pathname format.
template <class String> String generic_string(const codecvt_type& cvt=codecvt()) const;Returns:
pathname.Remarks: If
string_typeis a different type thanString, conversion is performed bycvt.string generic_string(const codecvt_type& cvt=codecvt()) const; wstring generic_wstring(const codecvt_type& cvt=codecvt()) const;Returns:
pathname.Remarks: If
string_typeis a different type than function's return type, conversion is performed bycvt.
pathcompare [path.compare]int compare(const path& p) const noexcept;Returns: A value less than 0 if the elements of
*thisare lexicographically less than the elements ofp, otherwise a value greater than 0 if the elements of*thisare lexicographically greater than the elements ofp, otherwise 0.Remark: The elements are determined as if by iteration over the half-open range [
begin(),end()) for*thisandp.int compare(const std::string& s) constReturns:
compare(path(s)).int compare(const value_type* s) constReturns:
compare(path(s)).
pathdecomposition [path.decompose]See the Path decomposition table for examples for values returned by decomposition functions. The Tutorial may also be helpful.
path root_name() const;Returns: root-name, if
pathnameincludes root-name, otherwisepath().path root_directory() const;Returns: root-directory, if
pathnameincludes root-directory, otherwisepath().If root-directory is composed of slash name, slash is excluded from the returned string.
path root_path() const;Returns:
root_name() / root_directory()path relative_path() const;Returns: A
pathcomposed frompathname, if!empty(), beginning with the first filename after root-path. Otherwise,path().path parent_path() const;Returns:
(empty() || begin() == --end()) ? path() : pp, whereppis constructed as if by starting with an emptypathand successively applyingoperator/=for each element in the rangebegin(),--end().[Example:
std::cout << path("/foo/bar.txt").parent_path(); // outputs "/foo" std::cout << path("/foo/bar").parent_path(); // outputs "/foo" std::cout << path("/foo/bar/").parent_path(); // outputs "/foo/bar" std::cout << path("/").parent_path(); // outputs "" std::cout << path(".").parent_path(); // outputs "" std::cout << path("..").parent_path(); // outputs ""See the last bullet item in the forward traversal order list for why the
"/foo/bar/"example doesn't output"/foo".—end example]
path filename() const;Returns: v3:
empty() ? path() : *--end()
v4:*this == root_path() ? path() : *--end()[Example:
std::cout << path("/foo/bar.txt").filename(); // outputs "bar.txt" std::cout << path("/foo/bar").filename(); // outputs "bar" std::cout << path("/foo/bar/").filename(); // v3 outputs "." // v4 outputs "" std::cout << path("/").filename(); // v3 outputs "/" // v4 outputs "" std::cout << path(".").filename(); // outputs "." std::cout << path("..").filename(); // outputs ".."See the last bullet item in the forward traversal order list for why the
"/foo/bar/"example doesn't output"bar".—end example]
path stem() const;Returns: If
p.filename()does not contain dots, consist solely of one or to two dots, [Since v4: or contains exactly one dot as the initial character,] returnsp.filename(). Otherwise returns the substring ofp.filename()starting at its beginning and ending at the last dot (the dot is not included).[Example:
std::cout << path("/foo/bar.txt").stem() << '\n'; // outputs "bar" std::cout << path(".hidden").stem() << '\n'; // v3 outputs "" // v4 outputs ".hidden" path p = "foo.bar.baz.tar"; for (; !p.extension().empty(); p = p.stem()) std::cout << p.extension() << '\n'; // outputs: .tar // .baz // .bar—end example]
path extension() const;Returns: The substring of
p.filename()that is not included inp.stem().Remarks: Implementations are permitted but not required to define additional behavior for file systems which append additional elements to extensions, such as alternate data streams or partitioned dataset names.
[Example:
std::cout << path("/foo/bar.txt").extension(); // outputs ".txt"—end example]
[Note: The dot is included in the return value so that it is possible to distinguish between no extension and an empty extension. See https://lists.boost.org/Archives/boost/2010/02/162028.php for more extensive rationale. —end note]
pathquery [path.query]bool empty() const;Returns:
m_pathname.empty().bool filename_is_dot() const;Returns:
filename() == path(".")[Example:
std::cout << path(".").filename_is_dot(); // outputs 1 std::cout << path("/.").filename_is_dot(); // outputs 1 std::cout << path("foo/.").filename_is_dot(); // outputs 1 std::cout << path("foo/").filename_is_dot(); // v3 outputs 1, v4 outputs 0 std::cout << path("/").filename_is_dot(); // outputs 0 std::cout << path("/foo").filename_is_dot(); // outputs 0 std::cout << path("/foo.").filename_is_dot(); // outputs 0 std::cout << path("..").filename_is_dot(); // outputs 0See the last bullet item in the forward traversal order list for why
path("foo/").filename()is a dot filename in v3.—end example]
bool filename_is_dot_dot() const;Returns:
filename() == path("..")bool has_root_path() const;Returns:
!root_path().empty()bool has_root_name() const;Returns:
!root_name().empty()bool has_root_directory() const;Returns:
!root_directory().empty()bool has_relative_path() const;Returns:
!relative_path().empty()bool has_parent_path() const;Returns:
!parent_path().empty()bool has_filename() const;Returns:
!filename().empty()bool has_stem() const;Returns:
!stem().empty()bool has_extension() const;Returns:
!extension().empty()bool is_absolute() const;Returns:
trueif the elements ofroot_path()uniquely identify a directory, elsefalse.[Note: Path is considered absolute on POSIX systems if it has a root directory, and on Windows - if it has both root name and root directory. —end note]
bool is_relative() const;Returns:
!is_absolute().
pathiterators [path.itr]Path iterators
iterator,const_iterator,reverse_iterator, andconst_reverse_iteratoriterate over the elements of the stored pathname.Path iterators are constant iterators satisfying the requirements of a bidirectional iterator (C++ Std, 24.1.4 Bidirectional iterators [lib.bidirectional.iterators]). The
value_typeof an iterator ispath.[Note: Path iterators store their value objects internally and when dereferenced return references to those internal objects. They cannot be used with iterator adaptors such as
std::reverse_iteratorthat assume references obtained by dereferencing an iterator point to objects that out-live the iterator itself. —end note]Calling any non-const member function of a
pathobject invalidates all iterators referring to elements of that object.The forward traversal order is as follows:
- The root-name element, if present.
- The root-directory element, if present, in the generic format. [Note: the generic format is required to ensure lexicographical comparison works correctly. —end note]
- Each successive filename element, if present.
- [v3: Dot] [v4: Empty path], if one or more trailing non-root directory separators are present.
[Note: Treating the last element during iteration as [v3: dot] [v4: an empty path] when there is a trailing directory separator enables lexical (i.e. syntactic) distinction between paths to directories versus paths to regular files. Such a distinction is usually irrelevant on POSIX and Windows based operating systems, but may be a requirement on other operating systems. —end note]
The backward traversal order is the reverse of forward traversal.
iterator begin() const;Returns: An iterator for the first element in forward traversal order. If no elements are present, the end iterator.
iterator end() const;Returns: The end iterator.
reverse_iterator rbegin() const;Returns: An iterator for the first element in backward traversal order. If no elements are present, the end iterator.
reverse_iterator rend() const;Returns: The end iterator.
pathimbued locale [path.imbued.locale]
pathoperations sometimes require encoding conversions betweenpathnameand some other string object where one of the value types ischarand the other iswchar_t. Such conversions shall be performed by thepath::codecvt()facet.[Example: ... —end example]
static std::locale imbue(const std::locale& loc);Effects: Stores a copy of
locas the imbuedpathlocale.Returns: The previous imbued
pathlocale.Remarks: The initial value of the imbued
pathlocale is operating system dependent. It shall be a locale with acodecvtfacet for acharstring encoding appropriate for the operating system. See ([fs.os.examples]).static const codecvt_type& codecvt();Returns: The
codecvtfacet for the imbuedpathlocale .
pathdeprecated functionsSeveral member functions from previous versions of
class pathhave been deprecated, either because they have been renamed or because the functionality is no longer desirable or has become obsolete.Deprecated functions available by default; will be suppressed if
BOOST_FILESYSTEM_NO_DEPRECATEDis defined:path& remove_leaf() { return remove_filename(); } path leaf() const { return filename(); } path branch_path() const { return parent_path(); } bool has_leaf() const { return !m_path.empty(); } bool has_branch_path() const { return !parent_path().empty(); }Deprecated functions not available by default; will be supplied if
BOOST_FILESYSTEM_DEPRECATEDis defined:const std::string file_string() const { return native_string(); } const std::string directory_string() const { return native_string(); } const std::string native_file_string() const { return native_string(); } const std::string native_directory_string() const { return native_string(); } const string_type external_file_string() const { return native(); } const string_type external_directory_string() const { return native(); }
pathnon-member functions [path.non-member]bool lexicographical_compare(path::iterator first1, path::iterator last1, path::iterator first2, path::iterator last2);Returns:
trueif the sequence ofnative()strings for the elements defined by the half-open range[first1, last1)is lexicographically less than the sequence ofnative()strings for the elements defined by the half-open range[first2, last2). Returnsfalseotherwise.Remarks: If two sequences have the same number of elements and their corresponding elements are equivalent, then neither sequence is lexicographically less than the other. If one sequence is a prefix of the other, then the shorter sequence is lexicographically less than the longer sequence. Otherwise, the lexicographical comparison of the sequences yields the same result as the comparison of the first corresponding pair of elements that are not equivalent.
[Note: A
pathawarelexicographical_comparealgorithm is provided for historical reasons. —end note]path lexically_normal(const path& p);Overview: Returns
pwith redundant current directory (dot), parent directory (dot-dot), and directory-separator elements removed.Returns:
pin normal form.Remarks: Uses
operator/=to compose the returned path.[Example:
assert(lexically_normal("foo/./bar/..") == "foo");
assert(lexically_normal("foo/.///bar/../") == "foo/.");All of the above assertions will succeed. On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect
pathequality. —end example]path lexically_relative(const path& p, const path& base);Overview: Returns
pmade relative tobase. Treats empty or identical paths as corner cases, not errors. Does not resolve symlinks. Does not first normalizeporbase.Remarks: Uses
std::mismatch(p.begin(), p.end(), base.begin(), base.end()), to determine the first mismatched element ofpandbase. Usesoperator==to determine if elements match.Returns:
path()if the first mismatched element ofpis equal top.begin()or the first mismatched element ofbaseis equal tobase.begin(), or
path(".")if the first mismatched element ofpis equal top.end()and the first mismatched element ofbaseis equal tobase.end(), or
An object of class
pathcomposed via application ofoperator/= path("..")for each element in the half-open range [first mismatched element ofbase,base.end()), and then application ofoperator/=for each element in the half-open range [first mismatched element ofp,p.end()).[Example:
assert(lexically_relative("/a/d", "/a/b/c") == "../../d");
assert(lexically_relative("/a/b/c", "/a/d") == "../b/c");
assert(lexically_relative("a/b/c", "a") == "b/c");
assert(lexically_relative("a/b/c", "a/b/c/x/y") == "../..");
assert(lexically_relative("a/b/c", "a/b/c") == ".");
assert(lexically_relative("a/b", "c/d") == "");All of the above assertions will succeed. On Windows, the returned path's directory-separators will be backslashes rather than forward slashes, but that does not affect
pathequality. —end example][Note: If symlink following semantics are desired, use the operational function
relative—end note][Note: If normalization is needed to ensure consistent matching of elements, wrap
p,base, or both in callslexically_normal(). —end note]void swap(path& lhs, path& rhs) noexcept;Effects:
lhs.swap(rhs).std::size_t hash_value(const path& p);Returns: A hash value for the path
p. If for two paths,p1 == p2thenhash_value(p1) == hash_value(p2).This allows paths to be used with Boost.Hash.
bool operator< (const path& lhs, const path& rhs);Returns:
return lhs.compare(rhs.begin) < 0.bool operator<=(const path& lhs, const path& rhs);Returns:
!(rhs < lhs).bool operator> (const path& lhs, const path& rhs);Returns:
rhs < lhs.bool operator>=(const path& lhs, const path& rhs);Returns:
!(lhs < rhs).bool operator==(const path& lhs, const path& rhs);Returns:
!(lhs < rhs) && !(rhs < lhs).[Note: Path equality and path equivalence have different semantics.
Equality is determined by the
pathnon-memberoperator==, which considers the two path's lexical representations only. Thuspath("foo") == "bar"is nevertrue.Equivalence is determined by the
equivalent()non-member function, which determines if two paths resolve to the same file system entity. Thusequivalent("foo", "bar")will betruewhen both paths resolve to the same file.Programmers wishing to determine if two paths are "the same" must decide if "the same" means "the same representation" or "resolve to the same actual file", and choose the appropriate function accordingly. —end note]
bool operator!=(const path& lhs, const path& rhs);Returns:
!(lhs == rhs).path operator/ (const path& lhs, const path& rhs);Returns:
path(lhs) /= rhs.
pathinserter and extractor [path.io]The inserter and extractor delimit the string with double-quotes (
") so that paths with embedded spaces will round trip correctly. Ampersand (&) is as an escape character, so the path can itself contain double quotes.template <class Char, class Traits> std::basic_ostream<Char, Traits>& operator<<(std::basic_ostream<Char, Traits>& os, const path& p);Effects: Insert characters into
os:
A double-quote.
Each character in
p.string<std::basic_string<Char>>(). If the character to be inserted is equal to the escape character or a double-quote, as determined byoperator==, first insert the escape character.A double-quote.
[Note: Effects are similar to:
std::basic_string<Char> str(p.string<std::basic_string<Char>>()); os << boost::io::quoted(str, static_cast<Char>('&'));—end note]Returns:
ostemplate <class Char, class Traits> std::basic_istream<Char, Traits>& operator>>(std::basic_istream<Char, Traits>& is, path& p);Effects: Extract characters from
is:
- If the first character that would be extracted is equal to double-quote, as determined by
operator==, then:
- Discard the initial double-quote.
- Save the value and then turn off the
skipwsflag.p.clear()- Until an unescaped double-quote character is reached or
is.not_good(), extract characters fromisand append them top, except that if an escape character is reached, ignore it and append the next character top.- Discard the final double-quote character.
- Restore the
skipwsflag to its original value.- Otherwise,
is >> p.[Note: Effects are similar to:
std::basic_string<Char> str; is >> boost::io::quoted(str, static_cast<Char>('&')); p = str;—end note]Returns:
isClass
filesystem_error[class.filesystem_error]namespace boost { namespace filesystem { class filesystem_error : public system_error { public: filesystem_error(); filesystem_error(const filesystem_error&); filesystem_error(const std::string& what_arg, system::error_code ec); filesystem_error(const std::string& what_arg, const path& p1, system::error_code ec); filesystem_error(const std::string& what_arg, const path& p1, const path& p2, system::error_code ec); filesystem_error& filesystem_error(const filesystem_error&); ~filesystem_error(); filesystem_error& operator=(const filesystem_error&); const path& path1() const; const path& path2() const; const char * what() const; }; } // namespace filesystem } // namespace boostThe class template
filesystem_errordefines the type of objects thrown as exceptions to report file system errors from functions described in this reference documentation.
filesystem_errormembers [filesystem_error.members]filesystem_error(const std::string& what_arg, error_code ec);Postcondition:
Expression Value runtime_error::what()what_arg.c_str()code()ecpath1().empty()truepath2().empty()truefilesystem_error(const std::string& what_arg, const path& p1, error_code ec);Postcondition:
Expression Value runtime_error::what()what_arg.c_str()code()ecpath1()Reference to stored copy of p1path2().empty()truefilesystem_error(const std::string& what_arg, const path& p1, const path& p2, error_code ec);Postcondition:
Expression Value runtime_error::what()what_arg.c_str()code()ecpath1()Reference to stored copy of p1path2()Reference to stored copy of p2const path& path1() const;Returns: Reference to copy of
p1stored by the constructor, or, if none, an empty path.const path& path2() const;Returns: Reference to copy of
p2stored by the constructor, or, if none, an empty path.const char* what() const;Returns: A string containing
runtime_error::what(). The exact format is unspecified. Implementations are encouraged but not required to includepath1.native_string()if not empty,path2.native_string()if not empty, andsystem_error::what()strings in the returned string.Enum file_type [enum.file_type]
This enum specifies constants uses to identify file types.
Constant Name Meaning status_errorAn error occurred while trying to obtain the status of the file. The file simply not being found is not considered a status error. file_not_foundThe file could not be found regular_fileRegular file directory_fileDirectory file symlink_fileSymbolic link file block_fileBlock special file character_fileCharacter special file fifo_fileFIFO or pipe file socket_fileSocket file type_unknownThe file exists, but it is of a system specific type not covered by any of the above cases. Enum perms [enum.perms]
This
enumspecifies bitmask constants uses to identify file permissions. ISO/IEC 9945 (POSIX) specifies actual values, and those values have been adopted here because they are very familiar and ingrained for many POSIX users.Windows: All permissions except write are currently ignored. There is only a single write permission; setting write permission for owner, group, or others sets write permission for all, and removing write permission for owner, group, or others removes write permission for all.
Name Value
(octal)ISO/IEC 9945
macroDefinition or notes
no_perms0There are no permissions set for the file. Note: file_not_foundisno_permsrather thanperms_not_knownowner_read0400S_IRUSRRead permission, owner owner_write0200S_IWUSRWrite permission, owner owner_exe0100S_IXUSRExecute/search permission, owner owner_all0700S_IRWXURead, write, execute/search by owner; owner_read | owner_write | owner_exegroup_read040S_IRGRPRead permission, group group_write020S_IWGRPWrite permission, group group_exe010S_IXGRPExecute/search permission, group group_all070S_IRWXGRead, write, execute/search by group; group_read | group_write | group_exeothers_read04S_IROTHRead permission, others others_write02S_IWOTHWrite permission, others others_exe01S_IXOTHExecute/search permission, others others_all07S_IRWXORead, write, execute/search by others; others_read | others_write | others_exeall_all0777owner_all | group_all | others_allset_uid_on_exe04000S_ISUIDSet-user-ID on execution set_gid_on_exe02000S_ISGIDSet-group-ID on execution sticky_bit01000S_ISVTXOperating system dependent. Inherently non-portable, even between ISO/IEC 9945 operating systems. perms_mask07777all_all | set_uid_on_exe | set_gid_on_exe | sticky_bitperms_not_known0xFFFFThe permissions are not known, such as when a file_statusobject is created without specifying the permissions
add_perms0x1000
permissions()adds the argument permission bits to the file's current bitsremove_perms0x2000permissions()removes the argument permission bits from the file's current bitssymlink_perms0x4000On ISO/IEC 9945 permissions()resolves symlinks unlesssymlink_permsis specified. Meaningless on Windows aspermissions()never resolves symlinks. Meaningless on Mac OS X and some other BSD systems aspermissions()always resolves symlinks. Get over it.Class file_status [class.file_status]
namespace boost { namespace filesystem { class file_status { public: // constructors file_status() noexcept; explicit file_status(file_type ft, perms prms = perms_not_known) noexcept; // compiler generated file_status(const file_status&) noexcept; file_status& operator=(const file_status&) noexcept; ~file_status() noexcept; // observers file_type type() const noexcept; perms permissions() const noexcept; // modifiers void type(file_type ft) noexcept; void permissions(perms prms) noexcept; }; } // namespace filesystem } // namespace boostAn object of type
file_statusstores information about the type and permissions of a file.
file_statusconstructors [file_status.cons]explicit file_status() noexcept;Postconditions:
type() == status_error,permissions() == perms_not_known.explicit file_status(file_type ft, perms prms = perms_not_known) noexcept;Postconditions:
type() == ft,permissions() == prms.
file_statusobservers [file_status.obs]file_type type() const noexcept;Returns: The value of
type()specified by the postconditions of the most recent call to a constructor, operator=, ortype(file_type)function.perms permissions() const noexcept;Returns: The value of
permissions()specified by the postconditions of the most recent call to a constructor, operator=, orpermissions(perms)function.
file_statusmodifiers [file_status.mods]void type(file_type ft) noexcept;Postconditions:
type() == ft.void permissions(perms prms) noexcept;Postconditions:
permissions() == prms.Class
directory_entry[class.directory_entry]namespace boost { namespace filesystem { class directory_entry { public: // constructors and destructor directory_entry(); directory_entry(const directory_entry&); explicit directory_entry(const path& p, file_status st=file_status(), file_status symlink_st=file_status()); ~directory_entry(); // modifiers directory_entry& operator=(const directory_entry&); void assign(const path& p, file_status st=file_status(), file_status symlink_st=file_status()); void replace_filename(const path& p, file_status st=file_status(), file_status symlink_st=file_status()); // observers const path& path() const; file_status status() const; file_status status(system::error_code& ec) const; file_status symlink_status() const; file_status symlink_status(system::error_code& ec) const; bool operator< (const directory_entry& rhs); bool operator==(const directory_entry& rhs); bool operator!=(const directory_entry& rhs); bool operator< (const directory_entry& rhs); bool operator<=(const directory_entry& rhs); bool operator> (const directory_entry& rhs); bool operator>=(const directory_entry& rhs); private: path m_path; // for exposition only mutable file_status m_status; // for exposition only; stat()-like mutable file_status m_symlink_status; // for exposition only; lstat()-like }; } // namespace filesystem } // namespace boostA
directory_entryobject stores apath object, afile_statusobject for non-symbolic link status, and afile_statusobject for symbolic link status. Thefile_statusobjects act as value caches.[Note: Because
status()on a pathname may be a relatively expensive operation, some operating systems provide status information as a byproduct of directory iteration. Caching such status information can result is significant time savings. Cached and non-cached results may differ in the presence of file system races. —end note]Actual cold-boot timing of iteration over a directory with 15,047 entries was six seconds for non-cached status queries versus one second for cached status queries. Windows XP, 3.0 GHz processor, with a moderately fast hard-drive. Similar speedups are expected on Linux and BSD-derived systems that provide status as a by-product of directory iteration.
directory_entryconstructors [directory_entry.cons]directory_entry();Postcondition:
Expression Value path().empty()truestatus()file_status()symlink_status()file_status()explicit directory_entry(const path& p, file_status st=file_status(), file_status symlink_st=file_status());Postcondition:
Expression Value path()pstatus()stsymlink_status()symlink_st
directory_entrymodifiers [directory_entry.mods]void assign(const path& p, file_status st=file_status(), file_status symlink_st=file_status());Postcondition:
Expression Value path()pstatus()stsymlink_status()symlink_stvoid replace_filename(const path& p, file_status st=file_status(), file_status symlink_st=file_status());Postcondition:
Expression Value path()path().branch() / sstatus()stsymlink_status()symlink_st
directory_entryobservers [directory_entry.obs]const path& path() const;Returns:
m_pathfile_status status() const; file_status status(system::error_code& ec) const;Effects: As if,
if ( !status_known( m_status ) ) { if ( status_known(m_symlink_status) && !is_symlink(m_symlink_status) ) { m_status = m_symlink_status; } else { m_status = status(m_path[, ec]); } }Returns:
m_statusThrows: As specified in Error reporting.
file_status symlink_status() const; file_status symlink_status(system::error_code& ec) const;Effects: As if,
if ( !status_known( m_symlink_status ) ) { m_symlink_status = symlink_status(m_path[, ec]); }Returns:
m_symlink_statusThrows: As specified in Error reporting.
bool operator==(const directory_entry& rhs);Returns:
m_path == rhs.m_path.bool operator!=(const directory_entry& rhs);Returns:
m_path != rhs.m_path.bool operator< (const directory_entry& rhs);Returns:
m_path < rhs.m_path.bool operator<=(const directory_entry& rhs);Returns:
m_path <= rhs.m_path.bool operator> (const directory_entry& rhs);Returns:
m_path > rhs.m_path.bool operator>=(const directory_entry& rhs);Returns:
m_path >= rhs.m_path.Class
directory_iterator[class.directory_iterator]Objects of type
directory_iteratorprovide standard library compliant iteration over the contents of a directory. Also see classrecursive_directory_iterator.namespace boost { namespace filesystem { class directory_iterator { public: // member functions directory_iterator() noexcept; // creates the "end" iterator directory_iterator(const directory_iterator&); explicit directory_iterator(const path& p, directory_options opts = directory_options::none); directory_iterator(const path& p, system::error_code& ec); directory_iterator(const path& p, directory_options opts, system::error_code& ec); ~directory_iterator(); directory_iterator& operator=(const directory_iterator&); directory_iterator& operator++(); directory_iterator& increment(system::error_code& ec); // other members as required by // C++ Std, 24.1.1 Input iterators [input.iterators] }; } // namespace filesystem } // namespace boost
directory_iteratorsatisfies the requirements of an input iterator (C++ Std, 24.2.1, Input iterators [input.iterators]).A
directory_iteratorreads successive elements from the directory for which it was constructed, as if by calling ISO/IEC 9945readdir() or readdir_r(). After adirectory_iteratoris constructed, and every timeoperator++is called, it reads a directory element and stores information about it in an object of typedirectory_entry.operator++is not equality preserving; that is,i == jdoes not imply that++i == ++j.[Note: The practical consequence of not preserving equality is that directory iterators can only be used for single-pass algorithms. —end note]
If the end of the directory elements is reached, the iterator shall become equal to the end iterator value. The constructor
directory_iterator()with no arguments always constructs an end iterator object, which shall be the only valid iterator for the end condition. The result ofoperator*on an end iterator is not defined. For any other iterator value aconst directory_entry&is returned. The result ofoperator->on an end iterator is undefined behavior. For any other iterator value aconst directory_entry*is returned.Two end iterators are always equal. An end iterator shall not be equal to a non-end iterator.
The above wording is based on the Standard Library's istream_iterator wording.
The result of calling the
path()member of thedirectory_entryobject obtained by dereferencing adirectory_iteratoris a reference to apathobject composed of the directory argument from which the iterator was constructed with filename of the directory entry appended as if byoperator/=.Directory iteration shall not yield directory entries for the current (dot) and parent (dot dot) directories.
The order of directory entries obtained by dereferencing successive increments of a
directory_iteratoris unspecified.[Note: Programs performing directory iteration may wish to test if the path obtained by dereferencing a directory iterator actually exists. It could be a symbolic link to a non-existent file. Programs recursively walking directory trees for purposes of removing and renaming entries may wish to avoid following symbolic links.
If a file is removed from or added to a directory after the construction of a
directory_iteratorfor the directory, it is unspecified whether or not subsequent incrementing of the iterator will ever result in an iterator whose value is the removed or added directory entry. See ISO/IEC 9945readdir_r(). —end note]
directory_iteratormembers [directory_iterator.members]
directory_iterator() noexcept;Effects: Constructs the end iterator.
explicit directory_iterator(const path& p, directory_options opts = directory_options::none); directory_iterator(const path& p, system::error_code& ec); directory_iterator(const path& p, directory_options opts, system::error_code& ec);Effects: Constructs an iterator representing the first entry in the directory
presolves to, if any; otherwise, the end iterator. If opening the directory fails with apermission_deniederror and(opts & directory_options::skip_permission_denied) != 0, constructs the end iterator and ignores the error (the operation completes successfully). Ifoptsis not specified, it is assumed to bedirectory_options::none.Throws: As specified in Error reporting.
[Note: To iterate over the current directory, use
directory_iterator(".")rather thandirectory_iterator(""). —end note]directory_iterator& operator++(); directory_iterator& increment(system::error_code& ec);Effects: As specified by the C++ Standard, 24.1.1 Input iterators [input.iterators]. In case of error the iterator is left in the end state.
Returns:
*this.Throws: As specified in Error reporting.
directory_iteratornon-member functionsconst directory_iterator& begin(const directory_iterator& iter);Returns:
iter.directory_iterator end(const directory_iterator&);Returns:
directory_iterator().Class
recursive_directory_iterator[class.rec.dir.itr]Objects of type
recursive_directory_iteratorprovide standard library compliant iteration over the contents of a directory, including recursion into its sub-directories.namespace boost { namespace filesystem { class recursive_directory_iterator : public iterator<input_iterator_tag, directory_entry> { public: // constructors and destructor recursive_directory_iterator() noexcept; recursive_directory_iterator(const recursive_directory_iterator&); explicit recursive_directory_iterator(const path& p, directory_options opts = directory_options::none); recursive_directory_iterator(const path& p, directory_options opts, system::error_code& ec); // deprecated constructors, use overloads accepting directory_options instead explicit recursive_directory_iterator(const path& p, symlink_option opts = symlink_option::none); recursive_directory_iterator(const path& p, symlink_option opts, system::error_code& ec); recursive_directory_iterator(const path& p, system::error_code& ec); ~recursive_directory_iterator(); // observers int depth() const noexcept; bool recursion_pending() const noexcept; // deprecated observers int level() const noexcept; bool no_push_pending() const noexcept; // modifiers recursive_directory_iterator& operator=(const recursive_directory_iterator&); recursive_directory_iterator& operator++(); recursive_directory_iterator& increment(system::error_code& ec); void pop(); void pop(system::error_code& ec); void disable_recursion_pending(bool value = true) noexcept; // deprecated modifiers void no_push(bool value = true); // other members as required by // C++ Std, Input iterators [input.iterators] private: // actual data members will probably be stored in a shared object, // or some similar mechanism, to achieve the required input iterator // copy semantics int m_depth; // for exposition only bool m_recursion_pending; // for exposition only directory_options m_options; // for exposition only }; } // namespace filesystem } // namespace boostThe behavior of a
recursive_directory_iteratoris the same as adirectory_iteratorunless otherwise specified.
- Incrementing a
recursive_directory_iteratorpointing to a directory causes that directory itself to be iterated over, as specified by theoperator++andincrementfunctions.
- When a
recursive_directory_iteratorreaches the end of the directory currently being iterated over, or whenpop()is called,m_depthis decremented, and iteration of the parent directory continues.recursive_directory_iterator() noexcept;Effects: Constructs the end iterator.
explicit recursive_directory_iterator(const path& p, directory_options opts = directory_options::none); recursive_directory_iterator(const path& p, directory_options opts, system::error_code& ec); explicit recursive_directory_iterator(const path& p, symlink_option opts = symlink_option::none); recursive_directory_iterator(const path& p, symlink_option opts, system::error_code& ec); recursive_directory_iterator(const path& p, system::error_code& ec);Effects: Constructs an iterator representing the first entry in the directory
presolves to, if any; otherwise, the end iterator.Postcondition: Unless the end iterator was constructed,
depth() == 0 && recursion_pending() == true && m_options == opts. For the signature without theoptsargument,optsis assumed to bedirectory_options::none.Throws: As specified in Error reporting.
[Note: To iterate over the current directory, use
recursive_directory_iterator(".")rather thanrecursive_directory_iterator(""). —end note][Note: By default,
recursive_directory_iteratordoes not follow directory symlinks. To follow directory symlinks, specifydirectory_options::follow_directory_symlinkinopts. —end note]int depth() const noexcept; int level() const noexcept;Requires:
*this != recursive_directory_iterator().Returns:
m_depth.bool recursion_pending() const noexcept;Requires:
*this != recursive_directory_iterator().Returns:
m_recursion_pending.bool no_push_pending() const noexcept;Requires:
*this != recursive_directory_iterator().Returns:
!recursion_pending().recursive_directory_iterator& operator++(); recursive_directory_iterator& increment(system::error_code& ec);Effects: As specified by the C++ Standard, 24.1.1 Input iterators [input.iterators], except:
if
recursion_pending() && is_directory(this->status()) && (!is_symlink(this->symlink_status()) || (m_options & directory_options::follow_directory_symlink) != 0)then:
directory
(*this)->path()is opened and recursively iterated into andm_depthis incremented;if opening the directory fails with a
permission_deniederror and(m_options & directory_options::skip_permission_denied) != 0, increment the iterator on the current level and ignore the error (the operation completes successfully).- if there are no more directory entries at this level then
m_depthis decremented and iteration of the parent directory resumes.If the operation completes with an error, then
- if
(m_options & directory_options::pop_on_error) != 0, the iterator is left in a state as if after repeatedly callingpop()until it succeeds or the iterator becomes equal to an end iterator; anypop()failures are not reported to the caller;- otherwise, the iterator is left equal to an end iterator.
Postcondition:
recursion_pending() == true.Returns:
*this.Throws: As specified in Error reporting.
void pop(); void pop(system::error_code& ec);Requires:
*this != recursive_directory_iterator().Effects: If
depth() == 0, set*thistorecursive_directory_iterator(). Otherwise,--m_depth, cease iteration of the directory currently being iterated over, and continue iteration over the parent directory.If the operation completes with an error, then
- if
(m_options & directory_options::pop_on_error) != 0, the iterator is left in a state as if after repeatedly callingpop()until it succeeds or the iterator becomes equal to an end iterator; anypop()failures are not reported to the caller;- otherwise, the iterator is left equal to an end iterator.
void disable_recursion_pending(bool value = true) noexcept; void no_push(bool value = true) noexcept;Requires:
*this != recursive_directory_iterator().Postcondition:
recursion_pending() == !value.[Note: These functions are used to prevent unwanted recursion into a directory. —end note]
recursive_directory_iteratornon-member functionsconst recursive_directory_iterator& begin(const recursive_directory_iterator& iter);Returns:
iter.recursive_directory_iterator end(const recursive_directory_iterator&);Returns:
recursive_directory_iterator().Operational functions [fs.op.funcs]
Operational functions query or modify files, including directories, in external storage.
Operational functions access a file by resolving an object of class
pathto a particular file in a file hierarchy. The path is resolved as if by the ISO/IEC 9945 Pathname Resolution mechanism.[Note: Because hardware failures, network failures, file system races, and many other kinds of errors occur frequently in file system operations, users should be aware that any filesystem operational function, no matter how apparently innocuous, may encounter an error. See Error reporting. —end note]
path absolute(const path& p, const path& base=current_path()); path absolute(const path& p, system::error_code& ec); path absolute(const path& p, const path& base, system::error_code& ec);Returns: A absolute path composed according to the following table
p.
has_root_directory()!p.has_root_directory()p.has_root_name()return preturn
p.root_name()
/ absolute(base)
.root_directory()
/ absolute(base)
.relative_path()
/ p.relative_path()!p.has_root_name()return
absolute(base)
.root_name()
/ preturn absolute(base)
/ pFor the overload without a
baseargument,baseiscurrent_path().[Note: For the returned path,
rp,rp.is_absolute()istrue. —end note]Throws: As specified in Error reporting.
path canonical(const path& p, const path& base = current_path()); path canonical(const path& p, system::error_code& ec); path canonical(const path& p, const path& base, system::error_code& ec);Overview: Converts
p, which must exist, to an absolute path that has no symbolic link, dot, or dot-dot elements.Returns: A canonical path that refers to the same file system object as
absolute(p, base). For the overload without abaseargument,baseiscurrent_path().Throws: As specified in Error reporting.
Remarks:
!exists(p)is an error.[Note: Canonical pathnames allow security checking of a path (eg. does this path live in /home/goodguy or /home/badguy?) —end note]
void copy(const path& from, const path& to); void copy(const path& from, const path& to, system::error_code& ec);Effects:
copy(from, to, copy_options::none[, ec]).Throws: As specified in Error reporting.
void copy(const path& from, const path& to, copy_options options); void copy(const path& from, const path& to, copy_options options, system::error_code& ec);Precondition:
optionsmust contain at most one option from each of the following groups:
copy_options::skip_existing,copy_options::overwrite_existingorcopy_options::update_existing;copy_options::synchronize_dataorcopy_options::synchronize;copy_options::recursive;copy_options::copy_symlinksorcopy_options::skip_symlinks;copy_options::directories_only,copy_options::create_symlinksorcopy_options::create_hard_links.Effects: Let
fandtbefile_statusobjects obtained the following way:Then, report an error if:
- If
(options & (copy_options::create_symlinks | copy_options::skip_symlinks)) != copy_options::nonethenf = symlink_status(from)andt = symlink_status(to);- Otherwise, if
(options & copy_options::copy_symlinks) != copy_options::nonethenf = symlink_status(from)andt = status(to);- Otherwise,
f = status(from)andt = status(to).Otherwise, if
!exists(f), orequivalent(from, to), oris_other(f) || is_other(t), oris_directory(f) && is_regular_file(t).is_symlink(f), then:Otherwise, if
- If
(options & copy_options::skip_symlinks) != copy_options::nonethen return;- Otherwise if
!exists(t) && (options & copy_options::copy_symlinks) != copy_options::nonethencopy_symlink(from, to);- Otherwise report error.
is_regular_file(f), then:Otherwise, if
- If
(options & copy_options::directories_only) != copy_options::nonethen return;- Otherwise if
(options & copy_options::create_symlinks) != copy_options::nonethencreate_symlink(link, to), wherelinkis determined as follows:- Otherwise if
(options & copy_options::create_hard_links) != copy_options::nonethencreate_hard_link(from, to);- Otherwise if
is_directory(t)thencopy_file(from, to / from.filename(), options);- Otherwise
copy_file(from, to, options).is_directory(f), then:Otherwise, for all unsupported file types of
- If
(options & copy_options::create_symlinks) != copy_options::nonethen report error with error code equal tomake_error_code(system::errc::is_a_directory);- Otherwise if
then:
(options & copy_options::recursive) != copy_options::none, oroptions == copy_options::noneand this call tocopyis not a recursive call fromcopy
- If
!exists(t), thencreate_directory(to, from).- Then, iterate over files in
fromand for eachdirectory_entry xobtained during iteration invokecopy(x.path(), to / x.path().filename(), options).- Otherwise, return.
freport error.Throws: As specified in Error reporting.
void copy_directory(const path& from, const path& to); void copy_directory(const path& from, const path& to, system::error_code& ec);Effects: Creates directory
to, with attributes copied from directoryfrom. The set of attributes copied is operating system dependent.[Note: For ISO 9945/POSIX based operating systems the attributes are those copied by native API
stat(from.c_str(), &from_stat)followed bymkdir(to.c_str(),from_stat.st_mode). For Windows based operating systems the attributes are those copied by native APICreateDirectoryExW(from.c_str(), to.c_str(), 0). —end note]Throws: As specified in Error reporting.
[Note: This operation is deprecated, use create_directory instead. —end note]
bool copy_file(const path& from, const path& to); bool copy_file(const path& from, const path& to, system::error_code& ec);Effects:
return copy_file(from, to, copy_options::none[, ec]).Throws: As specified in Error reporting.
bool copy_file(const path& from, const path& to, copy_options options); bool copy_file(const path& from, const path& to, copy_options options, system::error_code& ec); bool copy_file(const path& from, const path& to, copy_option options); bool copy_file(const path& from, const path& to, copy_option options, system::error_code& ec);Precondition:
optionsmust contain at most one option from each of the following groups:
copy_options::skip_existing,copy_options::overwrite_existingorcopy_options::update_existing;copy_options::synchronize_dataorcopy_options::synchronize.Effects: Report an error if:
Otherwise, return successfully with no effect if:
!is_regular_file(from), orexists(to) && !is_regular_file(to), orexists(to) && equivalent(from, to), orexists(to) && (options & (copy_options::skip_existing | copy_options::overwrite_existing)) == copy_options::none.Otherwise:
exists(to) && (options & copy_options::skip_existing) != copy_options::none, orexists(to) && (options & copy_options::update_existing) != copy_options::noneand last write time offromis more recent than that ofto.
- The contents and attributes of the file
fromresolves to are copied to the filetoresolves to; then- If
(options & copy_options::synchronize) != copy_options::none, the written data and attributes are synchronized with the permanent storage; otherwise- If
(options & copy_options::synchronize_data) != copy_options::none, the written data is synchronized with the permanent storage.Returns:
trueif the file was copied without error, otherwisefalse.Throws: As specified in Error reporting.
[Note: The overloads taking
copy_optionare deprecated. Their effect is equivalent to the corresponding overloads takingcopy_optionsafter casting theoptionsargument tocopy_options.][Note: When
copy_options::update_existingis specified, checking the write times offromandtomay not be atomic with the copy operation. Another process may create or modify the file identified bytoafter the file modification times have been checked but before copying starts. In this case the target file will be overwritten.][Note: The
copy_options::synchronize_dataandcopy_options::synchronizeoptions may have a significant performance impact. Thecopy_options::synchronize_dataoption may be less expensive thancopy_options::synchronize. However, without these options, upon returning fromcopy_fileit is not guaranteed that the copied file is completely written and preserved in case of a system failure. Any delayed write operations may fail after the function returns, at the point of physically writing the data to the underlying media, and this error will not be reported to the caller.]void copy_symlink(const path& existing_symlink, const path& new_symlink); void copy_symlink(const path& existing_symlink, const path& new_symlink, system::error_code& ec);Effects:
create_symlink(read_symlink(existing_symlink[, ec]), new_symlink[, ec]).Throws: As specified in Error reporting.
bool create_directories(const path& p); bool create_directories(const path& p, system::error_code& ec);Effects: Establishes the postcondition by calling
create_directory()for any element ofpthat does not exist.Postcondition:
is_directory(p)Returns:
trueif a new directory was created, otherwisefalse.Throws: As specified in Error reporting.
Complexity: O(n+1) where n is the number of elements of
pthat do not exist.bool create_directory(const path& p); bool create_directory(const path& p, system::error_code& ec); bool create_directory(const path& p, const path& existing); bool create_directory(const path& p, const path& existing, system::error_code& ec);Effects: Establishes the postcondition by attempting to create the directory
presolves to, as if by ISO/IEC 9945mkdir(). For overloads withoutexistingargument, the new directory is created withS_IRWXU|S_IRWXG|S_IRWXOmode. Overloads withexistingargument obtain mode fromexisting, which must be a path to an existing directory. On Windows,CreateDirectoryW(p.c_str(), NULL)is used whenexistingis not specified andCreateDirectoryExW(existing.c_str(), p.c_str(), NULL)otherwise. Creation failure becausepresolves to an existing directory shall not be treated as an error.Postcondition:
is_directory(p)Returns:
trueif a new directory was created, otherwisefalse.Throws: As specified in Error reporting.
void create_directory_symlink(const path& to, const path& new_symlink); void create_directory_symlink(const path& to, const path& new_symlink, system::error_code& ec);Effects: Establishes the postcondition, as if by ISO/IEC 9945
symlink().Postcondition:
new_symlinkresolves to a symbolic link file that contains an unspecified representation ofto.Throws: As specified in Error reporting.
[Note: Some operating systems, such as Windows, require symlink creation to identify that the link is to a directory. Portable code should use
create_directory_symlink()to create directory symlinks rather thancreate_symlink()—end note][Note: Some operating systems do not support symbolic links at all or support them only for regular files. Some file systems do not support symbolic links regardless of the operating system - the FAT file system used on memory cards and flash drives, for example. —end note]
void create_hard_link(const path& to, const path& new_hard_link); void create_hard_link(const path& to, const path& new_hard_link, system::error_code& ec);Effects: Establishes the postcondition, as if by ISO/IEC 9945
link().Postcondition:
exists(to) && exists(new_hard_link) && equivalent(to,new_hard_link)- The contents of the file or directory
toresolves to are unchanged.Throws: As specified in Error reporting.
[Note: Some operating systems do not support hard links at all or support them only for regular files. Some file systems do not support hard links regardless of the operating system - the FAT file system used on memory cards and flash drives, for example. Some file systems limit the number of links per file. —end note]
void create_symlink(const path& to, const path& new_symlink); void create_symlink(const path& to, const path& new_symlink, system::error_code& ec);Effects: Establishes the postcondition, as if by ISO/IEC 9945
symlink().Postcondition:
new_symlinkresolves to a symbolic link file that contains an unspecified representation ofto.Throws: As specified in Error reporting.
[Note: Some operating systems do not support symbolic links at all or support them only for regular files. Some file systems do not support symbolic links regardless of the operating system - the FAT system used on memory cards and flash drives, for example. —end note]
path current_path(); path current_path(system::error_code& ec);Returns: The current working directory path, as if by ISO/IEC 9945
getcwd().is_absolute()is true for the returned path.Throws: As specified in Error reporting.
[Note: The
current_path()name was chosen to emphasize that the return is a path, not just a single directory name.The current path as returned by many operating systems is a dangerous global variable. It may be changed unexpectedly by a third-party or system library functions, or by another thread. —end note]
void current_path(const path& p); void current_path(const path& p, system::error_code& ec);Effects: Establishes the postcondition, as if by ISO/IEC 9945
chdir().Postcondition:
equivalent(p, current_path()).Throws: As specified in Error reporting.
[Note: The current path for many operating systems is a dangerous global state. It may be changed unexpectedly by a third-party or system library functions, or by another thread. —end note]
bool exists(file_status s) noexcept;Returns:
status_known(s) && s.type() != file_not_foundbool exists(const path& p); bool exists(const path& p, system::error_code& ec) noexcept;Returns:
exists(status(p))orexists(status(p, ec)), respectively.Throws: As specified in Error reporting.
bool equivalent(const path& p1, const path& p2); bool equivalent(const path& p1, const path& p2, system::error_code& ec);Effects: Determines
file_status s1ands2, as if bystatus(p1)andstatus(p2), respectively.Returns:
true, ifsf1 == sf2andp1andp2resolve to the same file system entity, elsefalse.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. This is determined as if by the values of the ISO/IEC 9945
statstructure,obtained as if bystat()for the two paths, having equalst_devvalues and equalst_inovalues.[Note: ISO/IEC 9945 requires that "st_dev must be unique within a Local Area Network". Conservative ISO/IEC 9945 implementations may also wish to check for equal
st_sizeandst_mtimevalues. Windows implementations may useGetFileInformationByHandle()as a surrogate forstat(), and consider "same" to be equal values fordwVolumeSerialNumber,nFileIndexHigh,nFileIndexLow,nFileSizeHigh,nFileSizeLow,ftLastWriteTime.dwLowDateTime, andftLastWriteTime.dwHighDateTime. —end note]Throws:
filesystem_errorif(!exists(s1) && !exists(s2)) || (is_other(s1) && is_other(s2)), otherwise as specified in Error reporting.uintmax_t file_size(const path& p); uintmax_t file_size(const path& p, system::error_code& ec);Returns: If
exists(p) && is_regular_file(p), the size in bytes of the filepresolves to, determined as if by the value of the ISO/IEC 9945statstructure memberst_sizeobtained as if by ISO/IEC 9945stat(). Otherwise,static_cast<uintmax_t>(-1).Throws: As specified in Error reporting.
uintmax_t hard_link_count(const path& p); uintmax_t hard_link_count(const path& p, system::error_code& ec);Returns: The number of hard links for
p.Throws: As specified in Error reporting.
const path& initial_path(); const path& initial_path(system::error_code& ec);Returns:
current_path()as of the first call toinitial_path().[Note:
initial_path()is not thread safe, and may return an undesirable result if called subsequent to a change to the current directory. These problems can be avoided by callinginitial_path()immediately on entry to main(). —end note]Throws: For the first call, as specified in Error reporting. Subsequent calls throw nothing.
boolis_directory(file_status s) noexcept;Returns:
s.type() == directory_filebool is_directory(const path& p); bool is_directory(const path& p, system::error_code& ec) noexcept;Returns:
is_directory(status(p))oris_directory(status(p, ec)), respectively.Throws:
filesystem_error; overload witherror_code&throws nothing.bool is_empty(const path& p); bool is_empty(const path& p, system::error_code& ec);Effects: Determines
file_status s, as if bystatus(p, ec).Returns:
is_directory(s)
? directory_iterator(p) == directory_iterator()
: file_size(p) == 0;boolis_regular_file(file_status s) noexcept;Returns:
s.type() == regular_filebool is_regular_file(const path& p);Returns:
is_regular_file(status(p)).Throws:
filesystem_errorifstatus(p)would throwfilesystem_error.bool is_regular_file(const path& p, system::error_code& ec) noexcept;Effects: Sets
ecas if bystatus(p, ec). [Note:status_error,file_not_foundandtype_unknowncases setecto error values. To distinguish between cases, call thestatusfunction directly. —end note]Returns:
is_regular_file(status(p, ec)).bool is_other(file_status s) noexcept;Returns:
return exists(s) && !is_regular_file(s) && !is_directory(s) && !is_symlink(s)bool is_other(const path& p); bool is_other(const path& p, system::error_code& ec) noexcept;Returns:
is_other(status(p))oris_other(status(p, ec)), respectively.Throws:
filesystem_error; overload witherror_code&throws nothing.bool is_symlink(file_status s) noexcept;Returns:
s.type() == symlink_filebool is_symlink(const path& p); bool is_symlink(const path& p, system::error_code& ec) noexcept;Returns:
is_symlink(symlink_status(p))oris_symlink(symlink_status(p, ec)), respectively.Throws:
filesystem_error; overload witherror_code&throws nothing.std::time_t creation_time(const path& p); std::time_t creation_time(const path& p, system::error_code& ec);Returns: The time of creation of the file to which
presolves.Throws: As specified in Error reporting.
[Note: Not all platforms support querying file creation time. Where not supported, the operation will fail with
errc::function_not_supportederror code. —end note]std::time_t last_write_time(const path& p); std::time_t last_write_time(const path& p, system::error_code& ec);Returns: The time of last data modification of
p, determined as if by the value of the ISO/IEC 9945statstructure memberst_mtimeobtained as if by ISO/IEC 9945stat().Throws: As specified in Error reporting.
void last_write_time(const path& p, const std::time_t new_time); void last_write_time(const path& p, const std::time_t new_time, system::error_code& ec);Effects: Sets the time of last data modification of the file resolved to by
ptonew_time, as if by ISO/IEC 9945stat()followed by ISO/IEC 9945utime().Throws: As specified in Error reporting.
[Note: A postcondition of
last_write_time(p) == new_timeis not specified since it might not hold for file systems with coarse time granularity. —end note]void permissions(const path& p, perms prms); void permissions(const path& p, perms prms, system::error_code& ec);Requires:
!((prms & add_perms) && (prms & remove_perms)).Effects: Applies the effective permissions bits from
prmsto the filepresolves to, as if by ISO/IEC 9945fchmodat(). The effective permission bits are determined as specified by the following table.
bits present in prmsEffective bits applied Neither add_permsnorremove_permsprms & perms_maskadd_perms
status(p).permissions() | (prms & perms_mask)remove_permsstatus(p).permissions() & ~(prms & perms_mask)[Note: Conceptually permissions are viewed as bits, but the actual implementation may use some other mechanism. —end note]
Throws: As specified in Error reporting.
path read_symlink(const path& p); path read_symlink(const path& p, system::error_code& ec);Returns: If
presolves to a symbolic link, apathobject containing the contents of that symbolic link. Otherwise an emptypathobject.Throws: As specified in Error reporting. [Note: It is an error if
pdoes not resolve to a symbolic link. —end note]path relative(const path& p, system::error_code& ec);Returns:
relative(p, current_path(), ec).Throws: As specified in Error reporting.
path relative(const path& p, const path& base=current_path()); path relative(const path& p, const path& base, system::error_code& ec);Overview: Returns
pmade relative tobase. Treats empty or identical paths as corner cases, not errors. Resolves symlinks and normalizes bothpandbasebefore other processing.Returns:
weakly_canonical(p).lexically_relative(weakly_canonical(base)). The second form returnspath()if an error occurs.Throws: As specified in Error reporting.
bool remove(const path& p); bool remove(const path& p, system::error_code& ec);Effects: If
exists(symlink_status(p,ec)), it is removed as if by ISO/IEC 9945remove().[Note: A symbolic link is itself removed, rather than the file it resolves to being removed. —end note]
Postcondition:
!exists(symlink_status(p)).Returns:
falseifpdid not exist, otherwisetrue.Throws: As specified in Error reporting.
uintmax_t remove_all(const path& p); uintmax_t remove_all(const path& p, system::error_code& ec);Effects: Recursively deletes the contents of
pif it exists, then deletes filepitself, as if by ISO/IEC 9945remove().[Note: A symbolic link is itself removed, rather than the file it resolves to being removed. —end note]
Postcondition:
!exists(p)Returns: The number of files removed.
Throws: As specified in Error reporting.
void rename(const path& old_p, const path& new_p); void rename(const path& old_p, const path& new_p, system::error_code& ec);Effects: Renames
old_ptonew_p, as if by ISO/IEC 9945rename().[Note: If
old_pandnew_presolve to the same existing file, no action is taken. Otherwise, ifnew_presolves to an existing non-directory file, it is removed, while ifnew_presolves to an existing directory, it is removed if empty on ISO/IEC 9945 but is an error on Windows. A symbolic link is itself renamed, rather than the file it resolves to being renamed. —end note]Throws: As specified in Error reporting.
void resize_file(const path& p, uintmax_t new_size); void resize_file(const path& p, uintmax_t new_size, system::error_code& ec);Postcondition:
file_size() == new_size.Throws: As specified in Error reporting.
Remarks: Achieves its postconditions as if by ISO/IEC 9945
truncate().space_info space(const path& p); space_info space(const path& p, system::error_code& ec);Returns: An object of type
space_info. The value of thespace_infoobject is determined as if by using ISO/IEC 9945statvfs()to obtain an ISO/IEC 9945 structstatvfs, and then multiplying itsf_blocks,f_bfree, andf_bavailmembers by itsf_frsizemember, and assigning the results to thecapacity,free, andavailablemembers respectively. Any members for which the value cannot be determined shall be set to -1.Throws: As specified in Error reporting.
file_status status(const path& p);Effects: As if:
system::error_code ec; file_status result = status(p, ec); if (result == status_error) throw filesystem_error(implementation-supplied-message, p, ec); return result;Returns: See above.
Throws:
filesystem_error. [Note:resultvalues offile_status(file_not_found)andfile_status(type_unknown)are not considered failures and do not cause an exception to be thrown. —end note]file_status status(const path& p, system::error_code& ec) noexcept;Effects:
If possible, determines the attributes of the file
If, during attribute determination, the underlying file system API reports an error, setspresolves to, as if by ISO/IEC 9945stat().ecto indicate the specific error reported. Otherwise,ec.clear().[Note: This allows users to inspect the specifics of underlying API errors even when the value returned by
status()is notfile_status(status_error). —end note]Returns:
If
ec != error_code():
- If the specific error indicates that
pcannot be resolved because some element of the path does not exist, returnfile_status(file_not_found). [Note: ISO/IEC 9945 errors that indicate this are ENOENT or ENOTDIR. Windows equivalents include ERROR_FILE_NOT_FOUND, ERROR_PATH_NOT_FOUND, ERROR_INVALID_NAME, ERROR_INVALID_PARAMETER, ERROR_BAD_PATHNAME, and ERROR_BAD_NETPATH. -- end note]
- Otherwise, if the specific error indicates that
pcan be resolved but the attributes cannot be determined, returnfile_status(type_unknown). [Note: For example, Windows ERROR_SHARING_VIOLATION errors. For ISO/IEC 9945, the case never arises. —end note]
- Otherwise, return
file_status(status_error).[Note: These semantics distinguish between
pbeing known not to exist,pexisting but not being able to determine its attributes, and there being an error that prevents even knowing ifpexists. These distinctions are important to some use cases. —end note]Otherwise,
- If the attributes indicate a regular file, as if by ISO/IEC 9945 S_ISREG(), return
file_status(regular_file). [Note:regular_fileimplies appropriate<fstream>operations would succeed, assuming no hardware, permission, access, or file system race errors. Lack ofregular_filedoes not necessarily imply<fstream>operations would fail on a directory. —end note]
- Otherwise, if the attributes indicate a directory, as if by ISO/IEC 9945 S_ISDIR(), return
file_status(directory_file). [Note:directory_fileimpliesdirectory_iterator(p)would succeed. —end note]
- Otherwise, if the attributes indicate a block special file, as if by ISO/IEC 9945 S_ISBLK(), return
file_status(block_file).
- Otherwise, if the attributes indicate a character special file, as if by ISO/IEC 9945 S_ISCHR(), return
file_status(character_file).
- Otherwise, if the attributes indicate a fifo or pipe file, as if by ISO/IEC 9945 S_ISFIFO(), return
file_status(fifo_file).
- Otherwise, if the attributes indicate a socket, as if by ISO/IEC 9945 S_ISSOCK(), return
file_status(socket_file).
- Otherwise, return
file_status(type_unknown).Remarks: If a symbolic link is encountered during pathname resolution, pathname resolution continues using the contents of the symbolic link.
bool status_known(file_status s) noexcept;Returns:
s.type() != status_errorfile_status symlink_status(const path& p); file_status symlink_status(const path& p, system::error_code& ec) noexcept;Effects: Same as status(), above, except that the attributes of
pare determined as if by ISO/IEC 9945lstat().Returns: Same as status(), above, except that if the attributes indicate a symbolic link, as if by ISO/IEC 9945 S_ISLNK(), return
file_status(symlink_file).Remarks: Pathname resolution terminates if
pnames a symbolic link.Throws:
filesystem_error; overload witherror_code&throws nothing.path system_complete(const path& p); path system_complete(const path& p, system::error_code& ec);Effects: Composes an absolute path from
p, using the same rules used by the operating system to resolve a path passed as the filename argument to standard library open functions.Returns: The composed path.
Postcondition: For the returned path,
rp,rp.is_absolute()is true.Throws: As specified in Error reporting.
[Note: For ISO/IEC 9945,
system_complete(p)has the same semantics asabsolute(p, current_path()).For Windows,
system_complete(p)has the same semantics asabsolute(p, current_path())ifp.is_absolute() || !p.has_root_name()orpandbasehave the sameroot_name(). Otherwise it acts likeabsolute(p, kinky), wherekinkyis the current directory for thep.root_name()drive. This will be the current directory of that drive the last time it was set, and thus may be residue left over from a prior program run by the command processor! Although these semantics are often useful, they are also very error-prone.path temp_directory_path(); path temp_directory_path(system::error_code& ec);Returns: A directory path suitable for temporary files under the conventions of the operating system. The specifics of how this path is determined are implementation defined. An error shall be reported if
!exists(p) || !is_directory(p), wherepis the path to be returned.ISO/IEC 9945: The path supplied by the first environment variable found in the list TMPDIR, TMP, TEMP, TEMPDIR. If none of these are found,
"/tmp", or, if macro__ANDROID__is defined,"/data/local/tmp".Windows: The path reported by the Windows
GetTempPathAPI function.Throws: As specified in Error reporting.
[Note: The
temp_directory_path()name was chosen to emphasize that the return is a path, not just a single directory name. —end note]path unique_path(const path& model="%%%%-%%%%-%%%%-%%%%"); path unique_path(const path& model, system::error_code& ec);The
unique_pathfunction generates a path name suitable for creating temporary files, including directories. The name is based on a model that uses the percent sign character to specify replacement by a random hexadecimal digit. [Note: The more bits of randomness in the generated path name, the less likelihood of prior existence or being guessed. Each replacement hexadecimal digit in the model adds four bits of randomness. The default model thus provides 64 bits of randomness. This is sufficient for most applications. —end note]Returns: A path identical to
model, except that each occurrence of a percent sign character is replaced by a random hexadecimal digit character in the range 0-9, a-f.Throws: As specified in Error reporting.
Remarks: Implementations are encouraged to obtain the required randomness via a cryptographically secure pseudo-random number generator, such as one provided by the operating system. [Note: Such generators may block until sufficient entropy develops. —end note]
path weakly_canonical(const path& p, const path& base=current_path()); path weakly_canonical(const path& p, system::error_code& ec); path weakly_canonical(const path& p, const path& base, system::error_code& ec);Overview: Returns
pwith symlinks resolved and the result normalized.Effects: Let
headbe the path composed of the leading elements ofpthat exist andtail— from the rest ofp. Where not specified,baseis obtained fromcurrent_path()orcurrent_path(ec)Callscanonical(head, base)orcanonical(head, base, ec), appendstailto the returned path usingoperator/. The result is then normalized and returned.Postcondition: The returned path is in normal form.
Remarks: Uses
operator/=to compose the returned path. Uses thestatusfunction to determine existence.Remarks: Implementations are encouraged to avoid unnecessary normalization such as when
canonicalhas already been called on the entirety ofp.Throws: As specified in Error reporting.
File streams - <boost/filesystem/fstream.hpp>
Replacements are provided for the file stream classes from the C++ standard library's
<fstream>header. These replacement classes publicly inherit from the standard library classes. In the Boost.Filesystem version, constructors and open functions takeconst path&arguments instead ofconst char*arguments. There are no other differences in syntax or semantics.namespace boost { namespace filesystem { template < class charT, class traits = std::char_traits<charT> > class basic_filebuf : public std::basic_filebuf<charT,traits> { public: basic_filebuf<charT,traits>* open(const path& p, std::ios_base::openmode mode); }; template < class charT, class traits = std::char_traits<charT> > class basic_ifstream : public std::basic_ifstream<charT,traits> { public: explicit basic_ifstream(const path& p, std::ios_base::openmode mode=std::ios_base::in) void open(const path& p, std::ios_base::openmode mode=std::ios_base::in); }; template < class charT, class traits = std::char_traits<charT> > class basic_ofstream : public std::basic_ofstream<charT,traits> { public: explicit basic_ofstream(const path& p, std::ios_base::openmode mode=std::ios_base::out); void open(const path& p, std::ios_base::openmode mode=std::ios_base::out); }; template < class charT, class traits = std::char_traits<charT> > class basic_fstream : public std::basic_fstream<charT,traits> { public: explicit basic_fstream(const path& p, std::ios_base::openmode mode=std::ios_base::in | std::ios_base::out); void open(const path& p, std::ios_base::openmode mode=std::ios_base::in | std::ios_base::out); }; typedef basic_filebuf<char> filebuf; typedef basic_ifstream<char> ifstream; typedef basic_ofstream<char> ofstream; typedef basic_fstream<char> fstream; typedef basic_filebuf<wchar_t> wfilebuf; typedef basic_ifstream<wchar_t> wifstream; typedef basic_fstream<wchar_t> wfstream; typedef basic_ofstream<wchar_t> wofstream; } // namespace filesystem } // namespace boostPath decomposition table
The table is generated by a program compiled with the Boost implementation.
Shaded entries indicate cases where ISO/IEC 9945 (POSIX) and Windows implementations yield different results. The top value is the ISO/IEC 9945 result and the bottom value is the Windows result.
Constructor
argumentIteration
over
Elementsstring()generic_
string()root_
path()root_
name()root_
directory()relative_
path()parent_
path()filename()empty empty empty empty empty empty empty empty empty empty ....empty empty empty .empty .........empty empty empty ..empty ..foofoofoofooempty empty empty fooempty foo/////empty /empty empty //foo/,foo/foo/foo/empty /foo/foofoo/foo,.foo/foo/empty empty empty foo/foo./foo//,foo,./foo//foo//empty /foo//foo.foo/barfoo,barfoo/barfoo/barempty empty empty foo/barfoobar/foo/bar/,foo,bar/foo/bar/foo/bar/empty /foo/bar/foobar//net//net//net//net//net//netempty empty empty //net//net/foo//net,/,foo//net/foo//net/foo//net///net/foo//net/foo///foo////,foo,.///foo//////foo////empty /foo//////foo.///foo///bar/,foo,bar///foo///bar///foo///bar/empty /foo///bar///foobar/./,./././empty /./../.,.././empty empty empty ./../../,../../../empty /../..../..,.../../empty empty empty ../...foo/.foo,.foo/.foo/.empty empty empty foo/.foo.foo/..foo,..foo/..foo/..empty empty empty foo/..foo..foo/./foo,.,.foo/./foo/./empty empty empty foo/./foo/..foo/./barfoo,.,barfoo/./barfoo/./barempty empty empty foo/./barfoo/.barfoo/..foo,..foo/..foo/..empty empty empty foo/..foo..foo/../foo,..,.foo/../foo/../empty empty empty foo/../foo/...foo/../barfoo,..,barfoo/../barfoo/../barempty empty empty foo/../barfoo/..barc:c:c:c:empty c:empty c:empty c:
emptyempty c:c:/c:,.c:,/c:/c:/empty c:/empty c:empty /c:/
emptyc:./c:fooc:fooc:,fooc:fooc:fooempty c:empty c:empty c:foofooempty c:c:foofooc:/fooc:,fooc:,/,fooc:/fooc:/fooempty c:/empty c:empty /c:/foofooc:c:/fooc:foo/c:foo,.c:,foo,.c:foo/c:foo/empty c:empty c:empty c:foo/foo/c:foo.c:/foo/c:,foo,.c:,/,foo,.c:/foo/c:/foo/empty c:/empty c:empty /c:/foo/foo/c:/foo.c:/foo/barc:,foo,barc:,/,foo,barc:/foo/barc:/foo/barempty c:/empty c:empty /c:/foo/barfoo/barc:/foobarprn:prn:prn:prn:empty prn:empty prn:empty prn:
emptyempty prn:c:\c:\c:,/c:\c:\c:/empty c:\empty c:empty \c:\
emptyempty c:c:\\c:fooc:fooc:,fooc:fooc:fooempty c:empty c:empty c:foofooempty c:c:foofooc:\fooc:\fooc:,/,fooc:\fooc:\fooc:/fooempty c:\empty c:empty \c:\foofooempty c:\c:\foofooc:foo\c:foo\c:,foo,.c:foo\c:foo\c:foo/empty c:empty c:empty c:foo\foo\empty c:fooc:foo\.c:\foo\c:\foo\c:,/,foo,.c:\foo\c:\foo\c:/foo/empty c:\empty c:empty \c:\foo\foo\empty c:\fooc:\foo\.c:\foo/c:\foo,.c:,/,foo,.c:\foo/c:\foo/c:/foo/empty c:\empty c:empty \c:\foo/foo/c:\foo.c:/foo\barc:,foo\barc:,/,foo,barc:/foo\barc:/foo\barc:/foo/barempty c:/empty c:empty /c:/foo\barfoo\barc:c:/foofoo\barbarLong paths on Windows and the \\?\ namespace prefix
The Microsoft Windows "Maximum Path Length Limitation" specifies:
In the Windows API (with some exceptions ...), the maximum length for a path is
MAX_PATH, which is defined as 260 characters.The Windows API has many functions that also have Unicode versions to permit an extended-length path for a maximum total path length of 32,767 characters. ... To specify an extended-length path, use the "\\?\" prefix. For example, "\\?\D:\very long path". [C++ string literals require backslashes be doubled, of course.]
Because most Boost.Filesystem operational functions just pass the contents of a class path object to the Windows API, they do work with the extended-length prefixes. But some won't work, because to the limitations imposed by Windows.
Effectively, the "\\?\" prefix informs the underlying Windows API that the path identifies an object in the Win32 filesystem namespace and disables most of the internal path processing, including normalization, by the Windows API. While it lifts the length limitation, this imposes a number of other restrictions on the acceptable paths that are listed in the section below. There are a number of other prefixes that have different special meanings, such as "\\.\" (a local device namespace prefix) and "\??\" (NT object namespace prefix). Note that UNC paths can be extended with the prefixes by referring to a special "UNC" device. For example, "\\server\share" can be extended as "\\?\UNC\server\share".
In terms of Boost.Filesystem, the namespace prefixes are considered as parts of the path's root name. For example, the root name of "\\?\c:\foo" is "\\?\c:". This interpretation is chosen to allow root paths to be iterable, that is you can list the contents of the "\\?\c:\" directory, provided that drive C: exists and you have the necessary permissions. [Note: You can't list the contents of "\\?\" as such path does not exist.]
Cautions for paths with namespace prefixes
- Individual components of a path are still are limited to whatever is supported for the particular filesystem, commonly 255 characters.
- Only backslashes are acceptable as directory separators. Slashes are not treated as separators.
- All paths must be absolute and must not contain "." or ".." components.
- Once an absolute path grows beyond 260 characters, it is essentially poisoned and all operations must use extended-length prefixes. So even a simple operation like
create_directory("a")will fail if the absolute path of the resulting directory would exceed 260 characters.- Certain Boost.Filesystem functions that decompose their argument path and then work on individual relative directories or files will not work properly with namespace prefix paths.
Acknowledgements
This Filesystem Library is dedicated to my wife, Sonda, who provided the support necessary to see both a trial implementation and the proposal itself through to completion. She gave me the strength to continue after a difficult year of cancer treatment in the middle of it all.
Many people contributed technical comments, ideas, and suggestions to the Boost Filesystem Library. See http://www.boost.org/libs/filesystem/doc/index.htm#Acknowledgements.
Dietmar Kühl contributed the original Boost Filesystem Library
directory_iteratordesign. Peter Dimov, Walter Landry, Rob Stewart, and Thomas Witt were particularly helpful in refining the library.The create_directories, extension, basename, and replace_extension functions were developed by Vladimir Prus. The temp_directory_path function was contributed by Jeff Flinn. David Svoboda suggested the canonical function and provided pseudo-code.
Howard Hinnant and John Maddock reviewed a draft of the version 2 proposal, and identified a number of mistakes or weaknesses, resulting in a more polished final document.
Peter Dimov suggested a single class path, with member templates to adapt to multiple string types. His idea became the basis for the version 3 path design.
References
[ISO/IEC 9945] ISO/IEC 9945:2003, IEEE Std 1003.1-2001, and The Open Group Base Specifications, Issue 6. Also known as The Single UNIX® Specification, Version 3. Available from each of the organizations involved in its creation. For example, read online or download from www.unix.org/single_unix_specification/. The ISO JTC1/SC22/WG15 - POSIX homepage is www.open-std.org/jtc1/sc22/WG15/ [Abrahams] Dave Abrahams, Error and Exception Handling, www.boost.org/more/error_handling.html
© Copyright Beman Dawes, 2002, 2006, 2007, 2009, 2010, 2011
© Copyright Andrey Semashev, 2019-2021
Distributed under the Boost Software License, Version 1.0. See www.boost.org/LICENSE_1_0.txt