| Filesystem Library
Version 4 |

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Reference Documentation

Introduction
Definitions
Conformance
Header <boost/filesystem.hpp> synopsis
Error reporting
Class path
path conversions
path conversions to native format
path conversions to generic format
path encoding conversions
path requirements
path constructors
path assignments
path appends
path concatenation
path modifiers
path native format observers
path generic format observers
path compare
path decomposition
path query
path iterators
path deprecated functions
path non-member functions
path inserters and extractors
Class filesystem_error
filesystem_error constructors
filesystem_error path1
filesystem_error path2
filesystem_error what

Enum file_type
Enum perms
Class file_status
file_statusconstructors
file_status-modifiersobservers
file_status-observersmodifiers
Class directory_entry
directory_entry constructors
directory_entry observers
directory_entry modifiers
Class directory_iterator
directory_iterator members
Class recursive_directory_iterator
Operational functions
absolute canonical copy copy_directory copy_file copy_symlink create_directories create_directory create_hard_link create_symlink creation_time current_path exists equivalent file_size hard_link_count initial_path is_directory is_empty

is_other is_regular_file is_symlink last_write_time permissions read_symlink relative remove remove_all rename resize_file space status status_known symlink_status system_complete temp_directory_path unique_path weakly_canonicalFile streams
Path decomposition table
Warning: Long paths on Windows and the extended-length *\?* prefix
Acknowledgements
References

Introduction

This reference documentation describes components that C++ programs may use to perform operations involving file systems, including paths, regular files, and directories.

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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.

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C++11 Feature

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Action if not supported by compiler

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noexcept

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Keyword omitted.

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constexpr

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Keyword omitted.

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R-value references

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Function signature omitted.

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New character types

|

The boost::filesystem interface doesn't use the new types directly. It does use u16string and u32string in namespace boost. These are typedefs to std::u16string and std::u32string for C++11, or to std::basic_string<boost::u16_t> and std::basic_string<boost::u32_t> for C++03.

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Defaulted and deleted functions

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Workaround replacement functions provided.

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Initializer lists

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Not currently used.

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Variadic templates

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Not currently used.

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Range-based for statements

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Supporting functions always provided; they do no harm even for C++03 compilers.

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Conformance [fs.conformance]

ISO/IEC 9945 conformance [fs.conform.9945]

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 #error directive, a static_assert, a filesystem_error exception, 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]

Operating system dependent conformance [fs.conform.os]

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.

Definitions [fs.definitions]

The following definitions shall apply throughout this reference documentation:

operating system dependent behavior [fs.def.osdep]

Behavior that is dependent upon the behavior and characteristics of an operating system. See [fs.conform.os].

file [fs.def.file]

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.

file system [fs.def.filesystem]

A collection of files and certain of their attributes.

filename [fs.def.filename]

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.

path [fs.def.path]

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]

absolute path [fs.def.absolute-path]

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.

relative path [fs.def.relative-path]

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]

canonical path [fs.def.canonical-path]

An absolute path that has no elements that are symbolic links, and no "." or ".." elements.

pathname [fs.def.pathname]

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.

native pathname format [fs.def.native]

The operating system dependent pathname format accepted by the host operating system.

normal form path [fs.def.normal]

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.]

link [fs.def.link]

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.

hard link [fs.def.hardlink]

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]

symbolic link [fs.def.symlink]

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]

file system race [fs.def.race]

The condition that occurs when multiple threads, processes, or computers interleave access and modification of the same object within a file system.

Generic pathname format [path.generic]

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.

Operating system dependent examples (Informative) [fs.os.examples]

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
POSIX ® API

Windows ® API

Notes

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path ::value_type

[class.path]

char

wchar_t

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path::preferred _separator

[class.path]

'/'

L'\\' (single backslash)

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path("/") .is_absolute() path("c:/") .is_absolute()

[path
.query]

` true

false`

` false

true`

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path argument disambiguation between generic format and native format

[path.arg
.fmt.cvt]

Not required

There is no need to distinguish between the generic format and native format for these operating systems.

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path argument format conversion

[path.arg
.fmt.cvt]

No conversion performed

The generic format is already acceptable to the native API of these operating systems.

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path ("/cats/jane") .c_str() path| ("/cats/jane/") .c_str()

[path.arg
.fmt.cvt]

"/cats/jane"

"/cats/jane/"`

L"/cats/jane"

L"/cats/jane/"`

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 path native format observers

[path.native
.obs]

No conversion performed

For efficiency, path objects are required to store pathnames in the native format regardless of operating system.

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Format conversion by path generic format observers

[path
.generic
.obs]

No conversion performed

Backslashes converted to slashes

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p. make_preferred()

[fs.path
.modifiers]

No change

Slashes converted to backslashes

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Characters prohibited in filenames

[fs.def
.filename]

0x00, '/'

0x00-0x1F, '"', '*', '*', '<', '>', '?', '\\' (single backslash), '/', '|'

Many operating systems prohibit the ASCII control characters (0x00-0x1F) in filenames.

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Initial imbued path locale

[path
.imbued
.locale]

std:: locale("") [footnote 2]

Implementation supplied locale using MultiByte ToWideChar and WideChar ToMultiByte with a codepage of CP_ACP if AreFileApisANSI is true, otherwise codepage CP_OEMCP.[footnote 3]

Apple OS X®: Implementation supplied locale providing UTF-8 codecvt facet.[footnote 4]

[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."

Header `<boost/filesystem.hpp>` synopsis [filesystem.synopsis]

namespace boost
{
  namespace filesystem
  {
    class[path](#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](#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-filesystem_error);
    class[directory\_entry](#Class-directory_entry);

    class[directory\_iterator](#Class-directory_iterator);

    // enable c++11 range-based for statements
    const directory_iterator&[begin](#directory_iterator-non-member-functions)(const directory_iterator& iter);
    directory_iterator[end](#directory_iterator-non-member-functions)(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](#Class-recursive_directory_iterator);

    // enable c++11 range-based for statements
    const recursive_directory_iterator&[begin](#recursive_directory_iterator-non-member-functions)(const recursive_directory_iterator& iter);
    recursive_directory_iterator[end](#recursive_directory_iterator-non-member-functions)(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](#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](#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](#file_status);

    structspace\_info// returned by[space](#space)function
    {
      uintmax_t capacity;
      uintmax_t free;
      uintmax_t available; // free space available to non-privileged process
    };

    enum classcopy\_options{
      none = 0u,
      //[copy\_file](#copy_file)options
      skip_existing,
      overwrite_existing,
      update_existing,
      synchronize_data,
      synchronize,
      //[copy](#copy)options
      recursive,
      copy_symlinks,
      skip_symlinks,
      directories_only,
      create_symlinks,
      create_hard_links
    };

    // Deprecated, use[copy\_options](#copy_options)instead
    enum classcopy\_option{
      none = copy_options::none,
      fail_if_exists = none,
      overwrite_if_exists = copy_options::overwrite_existing
    };

    enum classdirectory\_options{
      none = 0u,
      skip_permission_denied,
      follow_directory_symlink,
      pop_on_error
    };

    // Deprecated, use[directory\_options](#directory_options)instead
    enum classsymlink\_option{
      none = directory_options::none,
      no_recurse = none,
      recurse = directory_options::follow_directory_symlink
    };

    //[operational functions](#Operational-functions)path[absolute](#absolute)(const path& p, const path& base=current_path());
    path[absolute](#absolute)(const path& p, system::error_code& ec);
    path[absolute](#absolute)(const path& p, const path& base,
                   system::error_code& ec);

    path[canonical](#canonical)(const path& p, const path& base = current_path());
    path[canonical](#canonical)(const path& p, system::error_code& ec);
    path[canonical](#canonical)(const path& p, const path& base,
                   system::error_code& ec);

    void[copy](#copy)(const path& from, const path& to);
    void[copy](#copy)(const path& from, const path& to,
                   system::error_code& ec);
    void[copy](#copy)(const path& from, const path& to,[copy\_options](#copy_options)options);
    void[copy](#copy)(const path& from, const path& to,[copy\_options](#copy_options)options, system::error_code& ec);

    // Deprecated, use[create\_directory](#create_directory)instead
    void[copy\_directory](#copy_directory)(const path& from, const path& to);
    void[copy\_directory](#copy_directory)(const path& from, const path& to,
                   system::error_code& ec);

    bool[copy\_file](#copy_file)(const path& from, const path& to);
    bool[copy\_file](#copy_file)(const path& from, const path& to,
                   system::error_code& ec);
    bool[copy\_file](#copy_file)(const path& from, const path& to,[copy\_options](#copy_options)options);
    bool[copy\_file](#copy_file)(const path& from, const path& to,[copy\_options](#copy_options)options, system::error_code& ec);
    // Deprecated, use overloads taking[copy\_options](#copy_options)instead
    bool[copy\_file](#copy_file)(const path& from, const path& to,[copy\_option](#copy_option)options);
    bool[copy\_file](#copy_file)(const path& from, const path& to,[copy\_option](#copy_option)options, system::error_code& ec);

    void[copy\_symlink](#copy_symlink)(const path& existing_symlink,
                   const path& new_symlink);
    void[copy\_symlink](#copy_symlink)(const path& existing_symlink,
                   const path& new_symlink, system::error_code& ec);

    bool[create\_directories](#create_directories)(const path& p);
    bool[create\_directories](#create_directories)(const path& p,
                   system::error_code& ec);

    bool[create\_directory](#create_directory)(const path& p);
    bool[create\_directory](#create_directory)(const path& p, system::error_code& ec);
    bool[create\_directory](#create_directory)(const path& p, const path& existing);
    bool[create\_directory](#create_directory)(const path& p, const path& existing, system::error_code& ec);

    void[create\_directory\_symlink](#create_directory_symlink)(const path& to,
                   const path& new_symlink);
    void[create\_directory\_symlink](#create_directory_symlink)(const path& to,
                   const path& new_symlink, system::error_code& ec);

    void[create\_hard\_link](#create_hard_link)(const path& to, const path& new_hard_link);
    void[create\_hard\_link](#create_hard_link)(const path& to, const path& new_hard_link,
                                  system::error_code& ec);

    void[create\_symlink](#create_symlink)(const path& to, const path& new_symlink);
    void[create\_symlink](#create_symlink)(const path& to, const path& new_symlink,
                                system::error_code& ec);

    std::time_t[creation\_time](#creation_time)(const path& p);
    std::time_t[creation\_time](#creation_time)(const path& p, system::error_code& ec);

    path[current\_path](#current_path)();
    path[current\_path](#current_path)(system::error_code& ec);
    void[current\_path](#current_path)(const path& p);
    void[current\_path](#current_path)(const path& p, system::error_code& ec);

    bool[exists](#exists)(file_status s) noexcept;
    bool[exists](#exists)(const path& p);
    bool[exists](#exists)(const path& p, system::error_code& ec) noexcept;

    bool[equivalent](#equivalent)(const path& p1, const path& p2);
    bool[equivalent](#equivalent)(const path& p1, const path& p2,
                   system::error_code& ec);

    uintmax_t[file\_size](#file_size)(const path& p);
    uintmax_t[file\_size](#file_size)(const path& p, system::error_code& ec);

    uintmax_t[hard\_link\_count](#hard_link_count)(const path& p);
    uintmax_t[hard\_link\_count](#hard_link_count)(const path& p, system::error_code& ec);

    const path&[initial\_path](#initial_path)();
    const path&[initial\_path](#initial_path)(system::error_code& ec);

    bool[is\_directory](#is_directory)(file_status s) noexcept;
    bool[is\_directory](#is_directory2)(const path& p);
    bool[is\_directory](#is_directory2)(const path& p,
                   system::error_code& ec) noexcept;

    bool[is\_empty](#is_empty)(const path& p);
    bool[is\_empty](#is_empty)(const path& p, system::error_code& ec);

    bool[is\_other](#is_other)(file_status s) noexcept;
    bool[is\_other](#is_other2)(const path& p,);
    bool[is\_other](#is_other2)(const path& p, system::error_code& ec) noexcept;

    bool[is\_regular\_file](#is_regular_file)(file_status s) noexcept;
    bool[is\_regular\_file](#is_regular_file2)(const path& p);
    bool[is\_regular\_file](#is_regular_file2)(const path& p,
                   system::error_code& ec) noexcept;

    bool[is\_symlink](#is_symlink)(file_status s noexcept);
    bool[is\_symlink](#is_symlink2)(const path& p);
    bool[is\_symlink](#is_symlink2)(const path& p, system::error_code& ec) noexcept;

    std::time_t[last\_write\_time](#last_write_time)(const path& p);
    std::time_t[last\_write\_time](#last_write_time)(const path& p, system::error_code& ec);
    void[last\_write\_time](#last_write_time2)(const path& p, const std::time_t new_time);
    void[last\_write\_time](#last_write_time2)(const path& p, const std::time_t new_time,
                                 system::error_code& ec);

    path[read\_symlink](#read_symlink)(const path& p);
    path[read\_symlink](#read_symlink)(const path& p, system::error_code& ec);

    path[relative](#relative)(const path& p, system::error_code& ec);
    path[relative](#relative)(const path& p, const path& base=current_path());
    path[relative](#relative)(const path& p,
                     const path& base, system::error_code& ec);

    bool[remove](#remove)(const path& p);
    bool[remove](#remove)(const path& p, system::error_code& ec);

    uintmax_t[remove\_all](#remove_all)(const path& p);
    uintmax_t[remove\_all](#remove_all)(const path& p, system::error_code& ec);

    void[rename](#rename)(const path& from, const path& to);
    void[rename](#rename)(const path& from, const path& to,
                   system::error_code& ec);

    void[resize\_file](#resize_file)(const path& p, uintmax_t size);
    void[resize\_file](#resize_file2)(const path& p, uintmax_t size,
                   system::error_code& ec);[space\_info](#space_info)[space](#space)(const path& p);[space\_info](#space_info)[space](#space)(const path& p, system::error_code& ec);[file\_status](#file_status)[status](#status)(const path& p);[file\_status](#file_status)[status](#status)(const path& p, system::error_code& ec) noexcept;

    bool[status\_known](#status_known)(file_status s) noexcept;[file\_status](#file_status)[symlink\_status](#symlink_status)(const path& p);[file\_status](#file_status)[symlink\_status](#symlink_status)(const path& p,
                   system::error_code& ec) noexcept;

    path[system\_complete](#system_complete)(const path& p);
    path[system\_complete](#system_complete)(const path& p, system::error_code& ec);

    path[temp\_directory\_path](#temp_directory_path)();
    path[temp\_directory\_path](#temp_directory_path)(system::error_code& ec);

    path[unique\_path](#unique_path)(const path& model="%%%%-%%%%-%%%%-%%%%");
    path[unique\_path](#unique_path)(const path& model, system::error_code& ec);

    path[weakly\_canonical](#weakly_canonical)(const path& p, const path& base=current_path());
    path[weakly\_canonical](#weakly_canonical)(const path& p, system::error_code& ec);
    path[weakly\_canonical](#weakly_canonical)(const path& p, const path& base,
                   system::error_code& ec);

  } // namespace filesystem
} // namespace boost

Error reporting [fs.err.report]

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].

Class `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)_**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](#path-constructors)and destructor
        path();
        path(const path& p);
        path(path&& p) noexcept;

        template <class[Source](#Source)>
          path(Source const& source, const codecvt_type& cvt=codecvt());

        template <class[InputIterator](#InputIterator)>
          path(InputIterator begin, InputIterator end,
            const codecvt_type& cvt=codecvt());

       ~path();

        //[assignments](#path-assignments)path& operator=(const path& p);
        path& operator=(path&& p) noexcept;

        template <class[Source](#Source)>
          path& operator=(Source const& source);

        path& assign(const path& p);
        path& assign(path&& p) noexcept;
        template <class[Source](#Source)>
          path& assign(Source const& source,
            const codecvt_type& cvt=codecvt())

        template <class[InputIterator](#InputIterator)>
          path& assign(InputIterator begin, InputIterator end,
            const codecvt_type& cvt=codecvt());

        //[appends](#path-appends)path& operator/=(const path& p);

        template <class[Source](#Source)>
          path& operator/=(Source const& source);

        path& append(const path& x);
        template <class[Source](#Source)>
          path& append(Source const& source,
            const codecvt_type& cvt=codecvt());

        template <class[InputIterator](#InputIterator)>
          path& append(InputIterator begin, InputIterator end,
            const codecvt_type& cvt=codecvt());

        //[concatenation](#path-concatenation)path& operator+=(const path& x);
        template <class[Source](#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](#Source)>
          path& concat(Source const& x,
            const codecvt_type& cvt=codecvt());
        template <class[InputIterator](#InputIterator)>
          path& concat(InputIterator begin, InputIterator end,
            const codecvt_type& cvt=codecvt());

        //[modifiers](#path-modifiers)void[clear](#path-clear)();
        path&[make\_preferred](#path-make_preferred)();
        path&[remove\_filename](#path-remove_filename)();
        path&[replace\_extension](#path-replace_extension)(const path& new_extension = path());
        void[swap](#path-swap)(path& rhs) noexcept;

        // lexical operations
        path[lexically\_normal](#lexically_normal)() const;
        path[lexically\_relative](#lexically_relative)(const path& base) const;
        path[lexically\_proximate](#lexically_proximate)(const path& base) const;

        //[native format observers](#path-native-format-observers)const string_type&[native](#native)() const noexcept; // native format, encoding
        const value_type*[c\_str](#c_str)() const noexcept; // native().c_str()
        string_type::size_type[size](#path-size)() const noexcept; // native().size()

        template <class String>
          String[string](#string-template)(const codecvt_type& cvt=codecvt()) const;
        string[string](#string)(const codecvt_type& cvt=codecvt()) const;
        wstring[wstring](#wstring)(const codecvt_type& cvt=codecvt()) const;
        u16string[u16string](#u16string)() const;
        u32string[u32string](#u32wstring)() const;

        //[generic format observers](#path-generic-format-observers)template <class String>
          String[generic\_string](#generic_string-template)() const;

        string[generic\_string](#generic_string)(const codecvt_type& cvt=codecvt()) const;
        wstring[generic\_wstring](#generic_wstring)(const codecvt_type& cvt=codecvt()) const;
        u16string[generic\_u16string](#generic_u16string)()
        u32string[generic\_u32string](#generic_u32wstring)()

        //[compare](#path-compare)int[compare](#path-compare)(const path& p) const noexcept;
        int[compare](#path-compare)(const std::string& s) const;
        int[compare](#path-compare)(const value_type* s) const;

        //[decomposition](#path-decomposition)path[root\_name](#path-root_name)() const;
        path[root\_directory](#path-root_directory)() const;
        path[root\_path](#path-root_path)() const;
        path[relative\_path](#path-relative_path)() const;
        path[parent\_path](#path-parent_path)() const;
        path[filename](#path-filename)() const;
        path[stem](#path-stem)() const;
        path[extension](#path-extension)() const;

        //[query](#path-query)bool[empty](#path-query)() const;
        bool[filename\_is\_dot](#filename_is_dot)() const;
        bool[filename\_is\_dot\_dot](#filename_is_dot_dot)() const;
        bool[has\_root\_name](#path-has_root_name)() const;
        bool[has\_root\_directory](#path-has_root_directory)() const;
        bool[has\_root\_path](#path-has_root_path)() const;
        bool[has\_relative\_path](#path-has_relative_path)() const;
        bool[has\_parent\_path](#path-has_parent_path)() const;
        bool[has\_filename](#path-has_filename)() const;
        bool[has\_stem](#path-has_stem)() const;
        bool[has\_extension](#path-has_extension)() const;
        bool[is\_absolute](#path-is_absolute)() const;
        bool[is\_relative](#path-is_relative)() const;

        //[iterators](#path-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](#path-imbued-locale)static std::locale[imbue](#path-imbue)(const std::locale& loc);
        static const codecvt_type &[codecvt](#path-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]

Multithreading concerns

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]

Windows concerns

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]

POSIX concerns

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 meet the requirements for a C++ standard library RandomIterator compliant iterator. The iterator's value type is required to be char, wchar_t, char16_t, or char32_t.

Template parameters named Source are required to be one of:

A container with a value type of char, wchar_t, char16_t, or char32_t.
An iterator for a null terminated byte-string. The value type is required to be char, wchar_t, char16_t, or char32_t.
A C-array. The value type is required to be char, wchar_t, char16_t, or char32_t.
A boost::filesystem::directory_entry.

`path` constructors [path.construct]

template <class[Source](#Source)>
path(Source const& source, const codecvt_type& cvt=codecvt());

template <class[InputIterator](#InputIterator)>
path(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());

Effects: Stores the contents [begin,end) or source in pathname, 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](#Source)>
path& operator=(Source const& source);
path& assign(const path& p);
path& assign(path&& p) noexcept;
template <class[Source](#Source)>
path& assign(Source const& source, const codecvt_type& cvt=codecvt());
template <class[InputIterator](#InputIterator)>
path& assign(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());

Effects: Stores the contents [begin,end) or source or p in pathname, 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_separator to pathname, 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() to pathname.

v4: If p.is_absolute() || (p.has_root_name() && p.root_name() != root_name()), assigns p to *this. Otherwise, modifies *this as if by these steps:

If p.has_root_directory(), removes root directory and relative path, if any.

Let x be a path with contents of p without a root name. If has_filename() is true and x does not start with a directory separator, appends path::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](#Source)>
path& operator/=(Source const & source);
template <class[Source](#Source)>
path& append(Source const & source, const codecvt_type& cvt=codecvt());
template <class[InputIterator](#InputIterator)>
path& append(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());

Effects:

As if append(path(args)), where args is 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](#Source)>
path& operator+=(Source const& source);
template <class CharT>
path& operator+=(CharT x);
path& concat(const path& p);
template <class[Source](#Source)>
path& concat(Source const& source, const codecvt_type& cvt=codecvt());
template <class[InputIterator](#InputIterator)>
path& concat(InputIterator begin, InputIterator end, const codecvt_type& cvt=codecvt());

Postcondition: native() == prior_native + effective-argument, where prior_native is native() prior to the call to operator+=, and effective-argument is:

p.native() if p is present and is const path&, otherwise

s, where s is std::basic_string<typename std::iterator_traits<InputIterator>::value_type>s(begin, end), if begin and end arguments are present, otherwise

x.

If the value type of effective-argument would not be path::value_type, the actual argument or argument range is first converted so that effective-argument has value type path::value_type.

Returns: *this

`path` modifiers [path.modifiers]

voidclear();

Postcondition: this->empty() is true.

path&make\_preferred();

Effects: _directory-separator_s are converted to _preferred-separator_s. See [fs.os.examples].

Returns: *this

path&remove\_filename();

Returns: 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]

path&replace\_extension(const path& new_extension = path());

Effects:

Any existing extension() is removed from the stored path, then

iff new_extension is not empty and does not begin with a dot character, a dot character is appended to the stored path, then

new_extension is 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]

pathlexically\_normal() const;

Overview: Returns *this with redundant current directory (dot), parent directory (dot-dot), and directory-separator elements removed.

Returns: *this in 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 path equality. —end example]

pathlexically\_relative(const path& base) const;

Overview: Returns *this made relative to base. Treats empty or identical paths as corner cases, not errors. Does not resolve symlinks. Does not first normalize *this or base.

Remarks: Uses std::mismatch(begin(), end(), base.begin(), base.end()), to determine the first mismatched element of *this and base. Uses operator== to determine if elements match.

Returns:

path() if the first mismatched element of *this is equal to begin() or the first mismatched element of base is equal to base.begin(), or

path(".") if the first mismatched element of *this is equal to end() and the first mismatched element of base is equal to base.end(), or

An object of class path composed via application of operator/= path("..") for each element in the half-open range [first mismatched element of base, base.end()), and then application of operator/= 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-separator_s will be backslashes rather than forward slashes, but that does not affect path equality. —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]
pathlexically\_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]

path native 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_typesize() const noexcept;
Returns: pathname.size().
template <class String>
Stringstring(const codecvt_type& cvt=codecvt()) const;
Returns: pathname.

Remarks: If string_type is a different type than String, conversion is performed by cvt.
stringstring(const codecvt_type& cvt=codecvt()) const;
wstringwstring(const codecvt_type& cvt=codecvt()) const;
u16stringu16string() const;
u32wstringu32wstring() const;
Returns: pathname.

Remarks: If string_type is a different type than function's return type, conversion is performed by cvt.

path generic format observers [path.generic.obs]

The string returned by all generic format observers is in the generic pathname format.
template <class String>
Stringgeneric\_string(const codecvt_type& cvt=codecvt()) const;
Returns: pathname.

Remarks: If string_type is a different type than String, conversion is performed by cvt.
stringgeneric\_string(const codecvt_type& cvt=codecvt()) const;
wstringgeneric\_wstring(const codecvt_type& cvt=codecvt()) const;
u16stringgeneric\_u16string() const;
u32wstringgeneric\_u32wstring() const;
Returns: pathname.

Remarks: If string_type is a different type than function's return type, conversion is performed by cvt.

path compare [path.compare]
int compare(const path& p) const noexcept;
Returns: A value less than 0 if the elements of *this are lexicographically less than the elements of p, otherwise a value greater than 0 if the elements of *this are lexicographically greater than the elements of p, otherwise 0.

Remark: The elements are determined as if by iteration over the half-open range [begin(), end()) for *this and p.
int compare(const std::string& s) const
Returns: compare(path(s)).
int compare(const value_type* s) const
Returns: compare(path(s)).

path decomposition [path.decompose]

See the Path decomposition table for examples for values returned by decomposition functions. The Tutorial may also be helpful.
pathroot\_name() const;
Returns: root-name, if pathname includes root-name, otherwise path().
pathroot\_directory() const;
Returns: root-directory, if pathname includes root-directory, otherwise path().

If root-directory is composed of slash name, slash is excluded from the returned string.
pathroot\_path() const;
Returns: root_name() / root_directory()
pathrelative\_path() const;
Returns: A path composed from pathname, if !empty(), beginning with the first filename after root-path. Otherwise, path().
pathparent\_path() const;
Returns: (empty() || begin() == --end()) ? path() : pp, where pp is constructed as if by starting with an empty path and successively applying operator/= for each element in the range begin(), --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]
pathfilename() 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]
pathstem() 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,] returns p.filename(). Otherwise returns the substring of p.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]
pathextension() const;
Returns: The substring of p.filename() that is not included in p.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]
path query [path.query]
boolempty() const;
Returns: m_pathname.empty().
boolfilename\_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 0
See the last bullet item in the forward traversal order list for why path("foo/").filename() is a dot filename in v3.

—end example]
boolfilename\_is\_dot\_dot() const;
Returns: filename() == path("..")
boolhas\_root\_path() const;
Returns: !root_path().empty()
boolhas\_root\_name() const;
Returns: !root_name().empty()
boolhas\_root\_directory() const;
Returns: !root_directory().empty()
boolhas\_relative\_path() const;
Returns: !relative_path().empty()
boolhas\_parent\_path() const;
Returns: !parent_path().empty()
boolhas\_filename() const;
Returns: !filename().empty()
boolhas\_stem() const;
Returns: !stem().empty()
boolhas\_extension() const;
Returns: !extension().empty()
boolis\_absolute() const;
Returns: true if the elements of root_path() uniquely identify a directory, else false.

[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]
boolis\_relative() const;
Returns: !is_absolute().

path iterators [path.itr]

Path iterators iterator, const_iterator, reverse_iterator, and const_reverse_iterator iterate 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_type of an iterator is path.

[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_iterator that 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 path object 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.

path imbued locale [path.imbued.locale]

path operations sometimes require encoding conversions between pathname and some other string object where one of the value types is char and the other is wchar_t. Such conversions shall be performed by the path::codecvt() facet.

[Example: ... —end example]
static std::localeimbue(const std::locale& loc);
Effects: Stores a copy of loc as the imbued path locale.

Returns: The previous imbued path locale.

Remarks: The initial value of the imbued path locale is operating system dependent. It shall be a locale with a codecvt facet for a char string encoding appropriate for the operating system. See ([fs.os.examples]).
static const codecvt_type&codecvt();
Returns: The codecvt facet for the imbued path locale .

path deprecated functions

Several member functions from previous versions of class path have 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_DEPRECATED is 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_DEPRECATED is 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(); }
path non-member functions [path.non-member]
bool lexicographical_compare(path::iterator first1, path::iterator last1,
path::iterator first2, path::iterator last2);
Returns: true if the sequence of native() strings for the elements defined by the half-open range [first1, last1) is lexicographically less than the sequence of native() strings for the elements defined by the half-open range [first2, last2). Returns false otherwise.

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 path aware lexicographical_compare algorithm is provided for historical reasons. —end note]
pathlexically\_normal(const path& p);
Overview: Returns p with redundant current directory (dot), parent directory (dot-dot), and directory-separator elements removed.

Returns: p in 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 path equality. —end example]
pathlexically\_relative(const path& p, const path& base);
Overview: Returns p made relative to base. Treats empty or identical paths as corner cases, not errors. Does not resolve symlinks. Does not first normalize p or base.

Remarks: Uses std::mismatch(p.begin(), p.end(), base.begin(), base.end()), to determine the first mismatched element of p and base. Uses operator== to determine if elements match.

Returns:

path() if the first mismatched element of p is equal to p.begin() or the first mismatched element of base is equal to base.begin(), or

path(".") if the first mismatched element of p is equal to p.end() and the first mismatched element of base is equal to base.end(), or

An object of class path composed via application of operator/= path("..") for each element in the half-open range [first mismatched element of base, base.end()), and then application of operator/= for each element in the half-open range [first mismatched element of p, 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-separator_s will be backslashes rather than forward slashes, but that does not affect path equality. —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 calls lexically_normal(). —end note]
void swap(path& lhs, path& rhs) noexcept;
Effects: lhs.swap(rhs).
std::size_thash\_value(const path& p);
Returns: A hash value for the path p. If for two paths, p1 == p2 then hash_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 path non-member operator==, which considers the two path's lexical representations only. Thus path("foo") == "bar" is never true.

Equivalence is determined by the equivalent() non-member function, which determines if two paths resolve to the same file system entity. Thus equivalent("foo", "bar") will be true when 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.

path inserter 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 by operator==, 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](../../io/doc/quoted_manip.html)(str, static_cast<Char>('&'));
—end note]

Returns: os
template <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 skipws flag.

p.clear()

Until an unescaped double-quote character is reached or is.not_good(), extract characters from is and append them to p, except that if an escape character is reached, ignore it and append the next character to p.

Discard the final double-quote character.

Restore the skipws flag to its original value.

Otherwise, is >> p.

[Note: Effects are similar to:
std::basic_string<Char> str;
is >>[boost::io::quoted](../../io/doc/quoted_manip.html)(str, static_cast<Char>('&'));
p = str;
—end note]

Returns: is
Class 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](#filesystem_error-2-arg)(const std::string& what_arg,
system::error_code ec);[filesystem\_error](#filesystem_error-3-arg)(const std::string& what_arg,
const path& p1, system::error_code ec);[filesystem\_error](#filesystem_error-4-arg)(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](#filesystem_error-path1)() const;
const path&[path2](#filesystem_error-path2)() const;

const char *[what](#filesystem_error-what)() const;
};
} // namespace filesystem
} // namespace boost
The class template filesystem_error defines the type of objects thrown as exceptions to report file system errors from functions described in this reference documentation.

filesystem_error members [filesystem_error.members]
filesystem\_error(const std::string& what_arg, error_code ec);
Postcondition:

| Expression | Value | | runtime_error::what() | what_arg.c_str() | | code() | ec | | path1().empty() | true | | path2().empty() | true |
filesystem\_error(const std::string& what_arg, const path& p1, error_code ec);
Postcondition:

| Expression | Value | | runtime_error::what() | what_arg.c_str() | | code() | ec | | path1() | Reference to stored copy of p1 | | path2().empty() | true |
filesystem\_error(const std::string& what_arg, const path& p1, const path& p2, error_code ec);
Postcondition:

| Expression | Value | | runtime_error::what() | w``hat_arg.c_str() | | code() | ec | | path1() | Reference to stored copy of p1 | | path2() | Reference to stored copy of p2 |
const path&path1() const;
Returns: Reference to copy of p1 stored by the constructor, or, if none, an empty path.
const path&path2() const;
Returns: Reference to copy of p2 stored 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 include path1.native_string()if not empty, path2.native_string()if not empty, and system_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_error | An 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_found | The file could not be found | | regular_file | Regular file | | directory_file | Directory file | | symlink_file | Symbolic link file | | block_file | Block special file | | character_file | Character special file | | fifo_file | FIFO or pipe file | | socket_file | Socket file | | type_unknown | The file exists, but it is of a system specific type not covered by any of the above cases. |

Enum perms [enum.perms]

This enum specifies 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
macro | Definition or notes | |

no_perms

| 0 | | There are no permissions set for the file. Note: file_not_found is no_perms rather than perms_not_known | | owner_read | 0400 | S_IRUSR | Read permission, owner | | owner_write | 0200 | S_IWUSR | Write permission, owner | | owner_exe | 0100 | S_IXUSR | Execute/search permission, owner | | owner_all | 0700 | S_IRWXU | Read, write, execute/search by owner; owner_read | owner_write | owner_exe | | group_read | 040 | S_IRGRP | Read permission, group | | group_write | 020 | S_IWGRP | Write permission, group | | group_exe | 010 | S_IXGRP | Execute/search permission, group | | group_all | 070 | S_IRWXG | Read, write, execute/search by group; group_read | group_write | group_exe | | others_read | 04 | S_IROTH | Read permission, others | | others_write | 02 | S_IWOTH | Write permission, others | | others_exe | 01 | S_IXOTH | Execute/search permission, others | | others_all | 07 | S_IRWXO | Read, write, execute/search by others; others_read | others_write | others_exe | | all_all | 0777 | | owner_all | group_all | others_all | | set_uid_on_exe | 04000 | S_ISUID | Set-user-ID on execution | | set_gid_on_exe | 02000 | S_ISGID | Set-group-ID on execution | | sticky_bit | 01000 | S_ISVTX | Operating system dependent. Inherently non-portable, even between ISO/IEC 9945 operating systems. | | perms_mask | 07777 | | all_all | set_uid_on_exe | set_gid_on_exe | sticky_bit | | perms_not_known | 0xFFFF | | The permissions are not known, such as when a file_status object is created without specifying the permissions | |

add_perms

| 0x1000 | |

permissions() adds the argument permission bits to the file's current bits

| | remove_perms | 0x2000 | | permissions() removes the argument permission bits from the file's current bits | | symlink_perms | 0x4000 | | On ISO/IEC 9945 permissions() resolves symlinks unless symlink_perms is specified. Meaningless on Windows as permissions() never resolves symlinks. Meaningless on Mac OS X and some other BSD systems as permissions() always resolves symlinks. Get over it. |

Class file_status [class.file_status]
namespace boost
{
namespace filesystem
{
class file_status
{
public:

//[constructors](#file_status-constructors)file_status() noexcept;
explicit file_status([file\_type](#file_type)ft,[perms](#Enum-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_status-observers)[file\_type](#file_type)type() const noexcept;[perms](#Enum-perms)permissions() const noexcept;

//[modifiers](#file_status-modifiers)void type([file\_type](#file_type)ft) noexcept;
void permissions([perms](#Enum-perms)prms) noexcept;
};
} // namespace filesystem
} // namespace boost
An object of type file_status stores information about the type and permissions of a file.

file_status constructors [file_status.cons]
explicit file_status() noexcept;
Postconditions: type() == status_error, permissions() == perms_not_known.
explicit file_status([file\_type](#file_type)ft,[perms](#Enum-perms)prms = perms_not_known) noexcept;
Postconditions: type() == ft, permissions() == prms.

file_status observers [file_status.obs]
[file\_type](#file_type)type() const noexcept;
Returns: The value of type() specified by the postconditions of the most recent call to a constructor, operator=, or type(file_type) function.
[perms](#Enum-perms)permissions() const noexcept;
Returns: The value of permissions() specified by the postconditions of the most recent call to a constructor, operator=, or permissions(perms) function.

file_status modifiers [file_status.mods]
void type([file\_type](#file_type)ft) noexcept;
Postconditions: type() == ft.
void permissions([perms](#Enum-perms)prms) noexcept;
Postconditions: permissions() == prms.

Class directory_entry [class.directory_entry]
namespace boost
{
namespace filesystem
{
class directory_entry
{
public:

//[constructors](#directory_entry-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-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](#directory_entry-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 boost
A directory_entry object stores a path object, a file_status object for non-symbolic link status, and a file_status object for symbolic link status. The file_status objects 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_entry constructors [directory_entry.cons]
directory_entry();
Postcondition:

| Expression | Value | | path().empty() | true | | status() | 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() | p | | status() | st | | symlink_status() | symlink_st |

directory_entry modifiers [directory_entry.mods]
void assign(const path& p, file_status st=file_status(), file_status symlink_st=file_status());
Postcondition:

| Expression | Value | | path() | p | | status() | st | | symlink_status() | symlink_st |
void replace_filename(const path& p, file_status st=file_status(), file_status symlink_st=file_status());
Postcondition:

| Expression | Value | | path() | path().branch() / s | | status() | st | | symlink_status() | symlink_st |

directory_entry observers [directory_entry.obs]
const path& path() const;
Returns: m_path
file_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_status

Throws: 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_status

Throws: 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_iterator provide standard library compliant iteration over the contents of a directory. Also see class recursive_directory_iterator.
namespace boost
{
namespace filesystem
{
class directory_iterator
{
public:
//[member functions](#directory_iterator-members)directory_iterator() noexcept; // creates the "end" iterator
directory_iterator(const directory_iterator&);
explicit directory_iterator(const path& p,[directory\_options](#directory_options)opts = directory_options::none);
directory_iterator(const path& p, system::error_code& ec);
directory_iterator(const path& p,[directory\_options](#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_iterator satisfies the requirements of an input iterator (C++ Std, 24.2.1, Input iterators [input.iterators]).

A directory_iterator reads successive elements from the directory for which it was constructed, as if by calling ISO/IEC 9945 readdir() or readdir_r(). After a directory_iterator is constructed, and every time operator++ is called, it reads a directory element and stores information about it in an object of type directory_entry. operator++ is not equality preserving; that is, i == j does 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 of operator* on an end iterator is not defined. For any other iterator value a const directory_entry& is returned. The result of operator-> on an end iterator is undefined behavior. For any other iterator value a const 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 the directory_entry object obtained by dereferencing a directory_iterator is a reference to a path object composed of the directory argument from which the iterator was constructed with filename of the directory entry appended as if by operator/=.

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_iterator is 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_iterator for 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 9945 readdir_r(). —end note]

directory_iterator members [directory_iterator.members]

directory_iterator() noexcept;

Effects: Constructs the end iterator.
explicit directory_iterator(const path& p,[directory\_options](#directory_options)opts = directory_options::none);
directory_iterator(const path& p, system::error_code& ec);
directory_iterator(const path& p,[directory\_options](#directory_options)opts, system::error_code& ec);
Effects: Constructs an iterator representing the first entry in the directory p resolves to, if any; otherwise, the end iterator. If opening the directory fails with a permission_denied error and (opts & directory_options::skip_permission_denied) != 0, constructs the end iterator and ignores the error (the operation completes successfully). If opts is not specified, it is assumed to be directory_options::none.

Throws: As specified in Error reporting.

[Note: To iterate over the current directory, use directory_iterator(".") rather than directory_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_iterator non-member functions
const 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_iterator provide 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](#directory_options)opts = directory_options::none);
recursive_directory_iterator(const path& p,[directory\_options](#directory_options)opts, system::error_code& ec);
// deprecated constructors, use overloads accepting directory_options instead
explicit recursive_directory_iterator(const path& p,[symlink\_option](#symlink_option)opts = symlink_option::none);
recursive_directory_iterator(const path& p,[symlink\_option](#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](#directory_options)m_options;_ **// for exposition only** _};

} // namespace filesystem
} // namespace boost
The behavior of a recursive_directory_iterator is the same as a directory_iterator unless otherwise specified.

Incrementing a recursive_directory_iterator pointing to a directory causes that directory itself to be iterated over, as specified by the operator++ and increment functions.

When a recursive_directory_iterator reaches the end of the directory currently being iterated over, or when pop() is called, m_depth is 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](#directory_options)opts = directory_options::none);
recursive_directory_iterator(const path& p,[directory\_options](#directory_options)opts, system::error_code& ec);
explicit recursive_directory_iterator(const path& p,[symlink\_option](#symlink_option)opts = symlink_option::none);
recursive_directory_iterator(const path& p,[symlink\_option](#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 p resolves 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 the opts argument, opts is assumed to be directory_options::none.

Throws: As specified in Error reporting.

[Note: To iterate over the current directory, use recursive_directory_iterator(".") rather than recursive_directory_iterator(""). —end note]

[Note: By default, recursive_directory_iterator does not follow directory symlinks. To follow directory symlinks, specify directory_options::follow_directory_symlink in opts. —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:

if there are no more directory entries at this level then m_depth is 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 calling pop() until it succeeds or the iterator becomes equal to an end iterator; any pop() 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 *this to recursive_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 calling pop() until it succeeds or the iterator becomes equal to an end iterator; any pop() 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_iterator non-member functions
const 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 path to 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]
pathabsolute(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 p | return p.root_name() / absolute(base) .root_directory() / absolute(base) .relative_path() / p.relative_path() | | !p.has_root_name() | return absolute(base) .root_name() / p | return absolute(base) / p |

For the overload without a base argument, base is current_path().

[Note: For the returned path, rp, rp.is_absolute() is true. —end note]

Throws: As specified in Error reporting.
pathcanonical(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 a base argument, base is current_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.
voidcopy(const path& from, const path& to,[copy\_options](#copy_options)options);
void copy(const path& from, const path& to,[copy\_options](#copy_options)options, system::error_code& ec);
Precondition: options must contain at most one option from each of the following groups:

copy_options::skip_existing, copy_options::overwrite_existing or copy_options::update_existing;

copy_options::synchronize_data or copy_options::synchronize;

copy_options::recursive;

copy_options::copy_symlinks or copy_options::skip_symlinks;

copy_options::directories_only, copy_options::create_symlinks or copy_options::create_hard_links.

Effects: Let f and t be file_status objects obtained the following way:

If (options & (copy_options::create_symlinks | copy_options::skip_symlinks)) != copy_options::none then f = symlink_status(from) and t = symlink_status(to);

Otherwise, if (options & copy_options::copy_symlinks) != copy_options::none then f = symlink_status(from) and t = status(to);

Otherwise, f = status(from) and t = status(to).

Then, report an error if:

!exists(f), or

equivalent(from, to), or

is_other(f) || is_other(t), or

is_directory(f) && is_regular_file(t).

Otherwise, if is_symlink(f), then:

If (options & copy_options::skip_symlinks) != copy_options::none then return;

Otherwise if !exists(t) && (options & copy_options::copy_symlinks) != copy_options::none then copy_symlink(from, to);

Otherwise report error.

Otherwise, if is_regular_file(f), then:

If (options & copy_options::directories_only) != copy_options::none then return;

Otherwise if (options & copy_options::create_symlinks) != copy_options::none then create_symlink(link, to), where link is determined as follows:

If from.is_absolute() then link equals to from;

Otherwise, link is equivalent to relative(absolute(to.parent_path()), absolute(from.parent_path())) / from.filename().

Otherwise if (options & copy_options::create_hard_links) != copy_options::none then create_hard_link(from, to);

Otherwise if is_directory(t) then copy_file(from, to / from.filename(), options);

Otherwise copy_file(from, to, options).

Otherwise, if is_directory(f), then:

If (options & copy_options::create_symlinks) != copy_options::none then report error with error code equal to make_error_code(system::errc::is_a_directory);

Otherwise if

(options & copy_options::recursive) != copy_options::none, or

options == copy_options::none and this call to copy is not a recursive call from copy

then:

If !exists(t), then create_directory(to, from).

Then, iterate over files in from and for each directory_entry x obtained during iteration invoke copy(x.path(), to / x.path().filename(), options).

Otherwise, return.

Otherwise, for all unsupported file types of f report error.

Throws: As specified in Error reporting.
voidcopy\_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 directory from. 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 by mkdir(to.c_str(),from_stat.st_mode). For Windows based operating systems the attributes are those copied by native API CreateDirectoryExW(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.
boolcopy\_file(const path& from, const path& to,[copy\_options](#copy_options)options);
bool copy_file(const path& from, const path& to,[copy\_options](#copy_options)options, system::error_code& ec);
bool copy_file(const path& from, const path& to,[copy\_option](#copy_option)options);
bool copy_file(const path& from, const path& to,[copy\_option](#copy_option)options, system::error_code& ec);
Precondition: options must contain at most one option from each of the following groups:

copy_options::skip_existing, copy_options::overwrite_existing or copy_options::update_existing;

copy_options::synchronize_data or copy_options::synchronize.

Effects: Report an error if:

!is_regular_file(from), or

exists(to) && !is_regular_file(to), or

exists(to) && equivalent(from, to), or

exists(to) && (options & (copy_options::skip_existing | copy_options::overwrite_existing)) == copy_options::none.

Otherwise, return successfully with no effect if:

exists(to) && (options & copy_options::skip_existing) != copy_options::none, or

exists(to) && (options & copy_options::update_existing) != copy_options::none and last write time of from is more recent than that of to.

Otherwise:

The contents and attributes of the file from resolves to are copied to the file to resolves 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: true if the file was copied without error, otherwise false.

Throws: As specified in Error reporting.

[Note: The overloads taking copy_option are deprecated. Their effect is equivalent to the corresponding overloads taking copy_options after casting the options argument to copy_options.]

[Note: When copy_options::update_existing is specified, checking the write times of from and to may not be atomic with the copy operation. Another process may create or modify the file identified by to after 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_data and copy_options::synchronize options may have a significant performance impact. The copy_options::synchronize_data option may be less expensive than copy_options::synchronize. However, without these options, upon returning from copy_file it 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.]
voidcopy\_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.
boolcreate\_directories(const path& p);
boolcreate\_directories(const path& p, system::error_code& ec);
Effects: Establishes the postcondition by calling create_directory() for any element of p that does not exist.

Postcondition: is_directory(p)

Returns: true if a new directory was created, otherwise false.

Throws: As specified in Error reporting.

Complexity: O(n+1) where n is the number of elements of p that do not exist.
boolcreate\_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 p resolves to, as if by ISO/IEC 9945 mkdir(). For overloads without existing argument, the new directory is created with S_IRWXU|S_IRWXG|S_IRWXO mode. Overloads with existing argument obtain mode from existing, which must be a path to an existing directory. On Windows, CreateDirectoryW(p.c_str(), NULL) is used when existing is not specified and CreateDirectoryExW(existing.c_str(), p.c_str(), NULL) otherwise. Creation failure because p resolves to an existing directory shall not be treated as an error.

Postcondition: is_directory(p)

Returns: true if a new directory was created, otherwise false.

Throws: As specified in Error reporting.
voidcreate\_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_symlink resolves to a symbolic link file that contains an unspecified representation of to.

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 than create_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]
voidcreate\_hard\_link(const path& to, const path& new_hard_link);
voidcreate\_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 to resolves 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]
voidcreate\_symlink(const path& to, const path& new_symlink);
voidcreate\_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_symlink resolves to a symbolic link file that contains an unspecified representation of to.

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]
pathcurrent\_path();
pathcurrent\_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]
boolexists(file_status s) noexcept;
Returns: status_known(s) && s.type() != file_not_found
boolexists(const path& p);
boolexists(const path& p, system::error_code& ec) noexcept;
Returns: exists(status(p)) or exists(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 s1 and s2, as if by status(p1) and status(p2), respectively.

Returns: true, if sf1 == sf2 and p1 and p2 resolve to the same file system entity, else false.

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 stat structure, obtained as if by stat() for the two paths, having equal st_dev values and equal st_ino values.

[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_size and st_mtime values. Windows implementations may use GetFileInformationByHandle() as a surrogate for stat(), and consider "same" to be equal values for dwVolumeSerialNumber, nFileIndexHigh, nFileIndexLow, nFileSizeHigh, nFileSizeLow, ftLastWriteTime.dwLowDateTime, and ftLastWriteTime.dwHighDateTime. —end note]

Throws: filesystem_error if (!exists(s1) && !exists(s2)) || (is_other(s1) && is_other(s2)), otherwise as specified in Error reporting.
uintmax_tfile\_size(const path& p);
uintmax_tfile\_size(const path& p, system::error_code& ec);
Returns: If exists(p) && is_regular_file(p), the size in bytes of the file p resolves to, determined as if by the value of the ISO/IEC 9945 stat structure member st_size obtained as if by ISO/IEC 9945 stat(). Otherwise, static_cast<uintmax_t>(-1).

Throws: As specified in Error reporting.
uintmax_thard\_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 to initial_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 calling initial_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_file
bool is_directory(const path& p);
bool is_directory(const path& p, system::error_code& ec) noexcept;
Returns: is_directory(status(p)) or is_directory(status(p, ec)), respectively.

Throws: filesystem_error; overload with error_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 by status(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_file
bool is_regular_file(const path& p);
Returns: is_regular_file(status(p)).

Throws: filesystem_error if status(p) would throw filesystem_error.
bool is_regular_file(const path& p, system::error_code& ec) noexcept;
Effects: Sets ec as if by status(p, ec). [Note: status_error, file_not_found and type_unknown cases set ec to error values. To distinguish between cases, call the status function directly. —end note]

Returns: is_regular_file(status(p, ec)).
boolis\_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)) or is_other(status(p, ec)), respectively.

Throws: filesystem_error; overload with error_code& throws nothing.
boolis\_symlink(file_status s) noexcept;
Returns: s.type() == symlink_file
bool is_symlink(const path& p);
bool is_symlink(const path& p, system::error_code& ec) noexcept;
Returns: is_symlink(symlink_status(p)) or is_symlink(symlink_status(p, ec)), respectively.

Throws: filesystem_error; overload with error_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 p resolves.

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_supported error 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 9945 stat structure member st_mtime obtained as if by ISO/IEC 9945 stat().

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 p to new_time, as if by ISO/IEC 9945 stat() followed by ISO/IEC 9945 utime().

Throws: As specified in Error reporting.

[Note: A postcondition of last_write_time(p) == new_time is 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 prms to the file p resolves to, as if by ISO/IEC 9945 fchmodat(). The effective permission bits are determined as specified by the following table.

| bits present in prms | Effective bits applied | | Neither add_perms nor remove_perms | prms & perms_mask | | add_perms |

status(p).permissions() | (prms & perms_mask)

| | remove_perms | status(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.
pathread\_symlink(const path& p);
path read_symlink(const path& p, system::error_code& ec);
Returns: If p resolves to a symbolic link, a path object containing the contents of that symbolic link. Otherwise an empty path object.

Throws: As specified in Error reporting. [Note: It is an error if p does not resolve to a symbolic link. —end note]
pathrelative(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 p made relative to base. Treats empty or identical paths as corner cases, not errors. Resolves symlinks and normalizes both p and base before other processing.

Returns: weakly_canonical(p).lexically_relative(weakly_canonical(base)). The second form returns path() if an error occurs.

Throws: As specified in Error reporting.
boolremove(const path& p);
boolremove(const path& p, system::error_code& ec);
Effects: If exists(symlink_status(p,ec)), it is removed as if by ISO/IEC 9945 remove().

[Note: A symbolic link is itself removed, rather than the file it resolves to being removed. —end note]

Postcondition: !exists(symlink_status(p)).

Returns:false if p did not exist, otherwise true.

Throws: As specified in Error reporting.
uintmax_tremove\_all(const path& p);
uintmax_tremove\_all(const path& p, system::error_code& ec);
Effects: Recursively deletes the contents of p if it exists, then deletes file p itself, as if by ISO/IEC 9945 remove().

[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.
voidrename(const path& old_p, const path& new_p);
voidrename(const path& old_p, const path& new_p, system::error_code& ec);
Effects: Renames old_p to new_p, as if by ISO/IEC 9945 rename().

[Note: If old_p and new_p resolve to the same existing file, no action is taken. Otherwise, if new_p resolves to an existing non-directory file, it is removed, while if new_p resolves 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.
voidresize\_file(const path& p, uintmax_t new_size);
voidresize\_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_infospace(const path& p);
space_infospace(const path& p, system::error_code& ec);
Returns: An object of type space_info. The value of the space_info object is determined as if by using ISO/IEC 9945 statvfs() to obtain an ISO/IEC 9945 struct statvfs, and then multiplying its f_blocks, f_bfree, and f_bavail members by its f_frsize member, and assigning the results to the capacity, free, and available members respectively. Any members for which the value cannot be determined shall be set to -1.

Throws: As specified in Error reporting.
[file\_status](#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: result values of file_status(file_not_found)and file_status(type_unknown) are not considered failures and do not cause an exception to be thrown. —end note]
[file\_status](#file_status)status(const path& p, system::error_code& ec) noexcept;
Effects:

If possible, determines the attributes of the file p resolves to, as if by ISO/IEC 9945 stat().

If, during attribute determination, the underlying file system API reports an error, sets ec to indicate the specific error reported. Otherwise, ec.clear().

[Note: This allows users to inspect the specifics of underlying API errors even when the value returned by status() is not file_status(status_error). —end note]

Returns:

If ec != error_code():

If the specific error indicates that p cannot be resolved because some element of the path does not exist, return file_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 p can be resolved but the attributes cannot be determined, return file_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 p being known not to exist, p existing but not being able to determine its attributes, and there being an error that prevents even knowing if p exists. These distinctions are important to some use cases. —end note]

Otherwise,

If the attributes indicate a regular file, as if by ISO/IEC 9945 S_ISREG(), return file_status(regular_file). [Note: regular_file implies appropriate <fstream> operations would succeed, assuming no hardware, permission, access, or file system race errors. Lack of regular_file does 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_file implies directory_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.
boolstatus\_known(file_status s) noexcept;
Returns: s.type() != status_error
file_statussymlink\_status(const path& p);
file_statussymlink\_status(const path& p, system::error_code& ec) noexcept;
Effects: Same as status(), above, except that the attributes of p are determined as if by ISO/IEC 9945 lstat().

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 p names a symbolic link.

Throws: filesystem_error; overload with error_code& throws nothing.
pathsystem\_complete(const path& p);
pathsystem\_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 as absolute(p, current_path()).

For Windows, system_complete(p) has the same semantics as absolute(p, current_path()) if p.is_absolute() || !p.has_root_name() or p and base have the same root_name(). Otherwise it acts like absolute(p, kinky), where kinky is the current directory for the p.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.
pathtemp\_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), where p is 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 GetTempPath API 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]
pathunique\_path(const path& model="%%%%-%%%%-%%%%-%%%%");
path unique_path(const path& model, system::error_code& ec);
The unique_path function 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]
pathweakly\_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 p with symlinks resolved and the result normalized.

Effects: Let head be the path composed of the leading elements of p that exist and tail — from the rest of p. Where not specified, base is obtained from current_path() or current_path(ec) Calls canonical(head, base) or canonical(head, base, ec), appends tail to the returned path using operator/. The result is then normalized and returned.

Postcondition: The returned path is in normal form.

Remarks: Uses operator/= to compose the returned path. Uses the status function to determine existence.

Remarks: Implementations are encouraged to avoid unnecessary normalization such as when canonical has already been called on the entirety of p.

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 take const path& arguments instead of const 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 boost
Path 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
argument | Iteration
over
Elements | string() | 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 | .. | | foo | foo | foo | foo | empty | empty | empty | foo | empty | foo | | / | / | / | / | / | empty | / | empty | empty | / | | /foo | /,foo | /foo | /foo | / | empty | / | foo | / | foo | | foo/ | foo,. | foo/ | foo/ | empty | empty | empty | foo/ | foo | . | | /foo/ | /,foo,. | /foo/ | /foo/ | / | empty | / | foo/ | /foo | . | | foo/bar | foo,bar | foo/bar | foo/bar | empty | empty | empty | foo/bar | foo | bar | | /foo/bar | /,foo,bar | /foo/bar | /foo/bar | / | empty | / | foo/bar | /foo | bar | | //net | //net | //net | //net | //net | //net | empty | 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 | ///foo | bar | | /. | /,. | /. | /. | / | 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/./bar | foo,.,bar | foo/./bar | foo/./bar | empty | empty | empty | foo/./bar | foo/. | bar | | foo/.. | foo,.. | foo/.. | foo/.. | empty | empty | empty | foo/.. | foo | .. | | foo/../ | foo,..,. | foo/../ | foo/../ | empty | empty | empty | foo/../ | foo/.. | . | | foo/../bar | foo,..,bar | foo/../bar | foo/../bar | empty | empty | empty | foo/../bar | foo/.. | bar | | c: | c: | c: | c: | empty
c: | empty
c: | empty | c:
empty | empty | c: | | c:/ | c:,.
c:,/ | c:/ | c:/ | empty
c:/ | empty
c: | empty
/ | c:/
empty | c: | .
/ | | c:foo | c:foo
c:,foo | c:foo | c:foo | empty
c: | empty
c: | empty | c:foo
foo | empty
c: | c:foo
foo | | c:/foo | c:,foo
c:,/,foo | c:/foo | c:/foo | empty
c:/ | empty
c: | empty
/ | c:/foo
foo | c:
c:/ | foo | | c: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/bar | c:,foo,bar
c:,/,foo,bar | c:/foo/bar | c:/foo/bar | empty
c:/ | empty
c: | empty
/ | c:/foo/bar
foo/bar | c:/foo | bar | | prn: | prn: | prn: | prn: | empty
prn: | empty
prn: | empty | prn:
empty | empty | prn: | | c:\ | c:\
c:,/ | c:\ | c:\
c:/ | empty
c:\ | empty
c: | empty
\ | c:\
empty | empty
c: | c:\
\ | | c:foo | c:foo
c:,foo | c:foo | c:foo | empty
c: | empty
c: | empty | c:foo
foo | empty
c: | c:foo
foo | | c:\foo | c:\foo
c:,/,foo | c:\foo | c:\foo
c:/foo | empty
c:\ | empty
c: | empty
\ | c:\foo
foo | empty
c:\ | c:\foo
foo | | c:foo\ | c:foo\
c:,foo,. | c:foo\ | c:foo\
c:foo/ | empty
c: | empty
c: | empty | c:foo\
foo\ | empty
c:foo | c:foo\
. | | c:\foo\ | c:\foo\
c:,/,foo,. | c:\foo\ | c:\foo\
c:/foo/ | empty
c:\ | empty
c: | empty
\ | c:\foo\
foo\ | empty
c:\foo | c:\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\bar | c:,foo\bar
c:,/,foo,bar | c:/foo\bar | c:/foo\bar
c:/foo/bar | empty
c:/ | empty
c: | empty
/ | c:/foo\bar
foo\bar | c:
c:/foo | foo\bar
bar |

Warning: Long paths on Windows and the extended-length *\?* 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. Read the following cautions carefully!

Cautions for paths with extended-length 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 - relative paths are not allowed.

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 extended-length 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_iterator design. 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

Reference Documentation

Reference Documentation

Table of Contents

Introduction

Conformance [fs.conformance]

ISO/IEC 9945 conformance [fs.conform.9945]

Operating system dependent conformance [fs.conform.os]

Definitions [fs.definitions]

operating system dependent behavior [fs.def.osdep]

file [fs.def.file]

file system [fs.def.filesystem]

filename [fs.def.filename]

path [fs.def.path]

absolute path [fs.def.absolute-path]

relative path [fs.def.relative-path]

canonical path [fs.def.canonical-path]

pathname [fs.def.pathname]

native pathname format [fs.def.native]

normal form path [fs.def.normal]

link [fs.def.link]

hard link [fs.def.hardlink]

symbolic link [fs.def.symlink]

file system race [fs.def.race]

Generic pathname format [path.generic]

Operating system dependent examples (Informative) [fs.os.examples]

Header <boost/filesystem.hpp> synopsis [filesystem.synopsis]

Error reporting [fs.err.report]

Class path [class.path]

path Usage concerns [path.usage]

Multithreading concerns

Windows concerns

POSIX concerns

path Conversions [path.cvt]

path argument conversions [path.arg.cvt]

path argument format conversions [path.arg.fmt.cvt]

path argument encoding conversions [path.arg.encoding.cvt]

path Conversions to generic format [fs.cvt.to.generic]

path Requirements [path.req]

path constructors [path.construct]

path assignments [path.assign]

path appends [path.append]

path concatenation [path.concat]

path modifiers [path.modifiers]

path lexical operations [path.lex.ops]

path native format observers [path.native.obs]

path generic format observers [path.generic.obs]

path compare [path.compare]

path decomposition [path.decompose]

path query [path.query]

path iterators [path.itr]

path imbued locale [path.imbued.locale]

path deprecated functions

path non-member functions [path.non-member]

path inserter and extractor [path.io]

Class filesystem_error [class.filesystem_error]

filesystem_error members [filesystem_error.members]

Enum file_type [enum.file_type]

Enum perms [enum.perms]

Class file_status [class.file_status]

file_status constructors [file_status.cons]

file_status observers [file_status.obs]

file_status modifiers [file_status.mods]

Class directory_entry [class.directory_entry]

directory_entry constructors [directory_entry.cons]

directory_entry modifiers [directory_entry.mods]

directory_entry observers [directory_entry.obs]

Class directory_iterator [class.directory_iterator]

directory_iterator members [directory_iterator.members]

directory_iterator non-member functions

Class recursive_directory_iterator [class.rec.dir.itr]

recursive_directory_iterator non-member functions

Operational functions [fs.op.funcs]

File streams - <boost/filesystem/fstream.hpp>

Path decomposition table

Warning: Long paths on Windows and the extended-length *\?* prefix

Cautions for paths with extended-length prefixes

Acknowledgements

References

Header `<boost/filesystem.hpp>` synopsis [filesystem.synopsis]

Class `path` [class.path]

`path` Usage concerns [path.usage]

`path` Conversions [path.cvt]

`path` argument conversions [path.arg.cvt]

`path` argument format conversions [path.arg.fmt.cvt]

`path` argument encoding conversions [path.arg.encoding.cvt]

`path` Conversions to generic format [fs.cvt.to.generic]

`path` Requirements [path.req]

`path` constructors [path.construct]

`path` assignments [path.assign]

`path` appends [path.append]

`path` concatenation [path.concat]

`path` modifiers [path.modifiers]

`path` lexical operations [path.lex.ops]

`path` native format observers [path.native.obs]

`path` generic format observers [path.generic.obs]

`path` compare [path.compare]

`path` decomposition [path.decompose]

`path` query [path.query]

`path` iterators [path.itr]

`path` imbued locale [path.imbued.locale]

`path` deprecated functions

`path` non-member functions [path.non-member]

`path` inserter and extractor [path.io]

Class `filesystem_error` [class.filesystem_error]

`filesystem_error` members [filesystem_error.members]

`file_status` constructors [file_status.cons]

`file_status` observers [file_status.obs]

`file_status` modifiers [file_status.mods]

Class `directory_entry` [class.directory_entry]

`directory_entry` constructors [directory_entry.cons]

`directory_entry` modifiers [directory_entry.mods]

`directory_entry` observers [directory_entry.obs]

Class `directory_iterator` [class.directory_iterator]

`directory_iterator` members [directory_iterator.members]

`directory_iterator` non-member functions

Class `recursive_directory_iterator` [class.rec.dir.itr]

`recursive_directory_iterator` non-member functions

Warning: Long paths on Windows and the extended-length \? prefix