29 Input/output library [input.output]

path(const path& p);
path(path&& p) noexcept;

Effects: Constructs an object of class path having the same pathname in the native and generic formats, respectively, as the original value of p.

In the second form, p is left in a valid but unspecified state.

path(string_type&& source, format fmt = auto_format);

Effects: Constructs an object of class path for which the pathname in the detected-format of source has the original value of source ([fs.path.fmt.cvt]), converting format if required ([fs.path.fmt.cvt]).

source is left in a valid but unspecified state.

template<class Source>
  path(const Source& source, format fmt = auto_format);
template<class InputIterator>
  path(InputIterator first, InputIterator last, format fmt = auto_format);

Effects: Let s be the effective range of source ([fs.path.req]) or the range [first, last), with the encoding converted if required ([fs.path.cvt]).

Finds the detected-format of s ([fs.path.fmt.cvt]) and constructs an object of class path for which the pathname in that format is s.

template<class Source>
  path(const Source& source, const locale& loc, format fmt = auto_format);
template<class InputIterator>
  path(InputIterator first, InputIterator last, const locale& loc, format fmt = auto_format);

Mandates: The value type of Source and InputIterator is char.

Effects: Let s be the effective range of source or the range [first, last), after converting the encoding as follows:

(6.1)
If value_type is wchar_t, converts to the native wide encoding ([fs.path.type.cvt]) using the codecvt<wchar_t, char, mbstate_t> facet of loc.
(6.2)
Otherwise a conversion is performed using the codecvt<wchar_t, char, mbstate_t> facet of loc, and then a second conversion to the current ordinary encoding.

Finds the detected-format of s ([fs.path.fmt.cvt]) and constructs an object of class path for which the pathname in that format is s.

A string is to be read from a database that is encoded in ISO/IEC 8859-1, and used to create a directory:

namespace fs = std::filesystem;
std::string latin1_string = read_latin1_data();
codecvt_8859_1<wchar_t> latin1_facet;
std::locale latin1_locale(std::locale(), latin1_facet);
fs::create_directory(fs::path(latin1_string, latin1_locale));

For POSIX-based operating systems, the path is constructed by first using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a wide character string in the native wide encoding ([fs.path.type.cvt]).

The resulting wide string is then converted to an ordinary character pathname string in the current native ordinary encoding.

If the native wide encoding is UTF-16 or UTF-32, and the current native ordinary encoding is UTF-8, all of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation, but for other native ordinary encodings some characters may have no representation.

For Windows-based operating systems, the path is constructed by using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a UTF-16 encoded wide character pathname string.

All of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation.

— end example

]

29.11.7.4.2 Assignments [fs.path.assign]

path& operator=(const path& p);

Effects: If *this and p are the same object, has no effect.

Otherwise, sets both respective pathnames of *this to the respective pathnames of p.

Returns: *this.

path& operator=(path&& p) noexcept;

Effects: If *this and p are the same object, has no effect.

Otherwise, sets both respective pathnames of *this to the respective pathnames of p.

p is left in a valid but unspecified state.

A valid implementation is swap(p).

— end note

]

Returns: *this.

path& operator=(string_type&& source);
path& assign(string_type&& source);

Effects: Sets the pathname in the detected-format of source to the original value of source.

source is left in a valid but unspecified state.

Returns: *this.

template<class Source>
  path& operator=(const Source& source);
template<class Source>
  path& assign(const Source& source);
template<class InputIterator>
  path& assign(InputIterator first, InputIterator last);

Effects: Let s be the effective range of source ([fs.path.req]) or the range [first, last), with the encoding converted if required ([fs.path.cvt]).

Finds the detected-format of s ([fs.path.fmt.cvt]) and sets the pathname in that format to s.

Returns: *this.

29.11.7.4.3 Appends [fs.path.append]

The append operations use operator/= to denote their semantic effect of appending preferred-separator when needed.

path& operator/=(const path& p);

Effects: If p.is_absolute() || (p.has_root_name() && p.root_name() != root_name()), then operator=(p).

Otherwise, modifies *this as if by these steps:

(3.1)
If p.has_root_directory(), then removes any root directory and relative path from the generic format pathname. Otherwise, if !has_root_directory() && is_absolute() is true or if has_filename() is true, then appends path::preferred_separator to the generic format pathname.
(3.2)
Then appends the native format pathname of p, omitting any root-name from its generic format pathname, to the native format pathname.

Even if //host is interpreted as a root-name, both of the paths path("//host")/"foo" and path("//host/")/"foo" equal "//host/foo" (although the former might use backslash as the preferred separator).

Expression examples:

// On POSIX,
path("foo") /= path("");        // yields path("foo/")
path("foo") /= path("/bar");    // yields path("/bar")

// On Windows,
path("foo") /= path("");        // yields path("foo\\")
path("foo") /= path("/bar");    // yields path("/bar")
path("foo") /= path("c:/bar");  // yields path("c:/bar")
path("foo") /= path("c:");      // yields path("c:")
path("c:") /= path("");         // yields path("c:")
path("c:foo") /= path("/bar");  // yields path("c:/bar")
path("c:foo") /= path("c:bar"); // yields path("c:foo\\bar")

— end example

]

Returns: *this.

template<class Source>
  path& operator/=(const Source& source);
template<class Source>
  path& append(const Source& source);

Effects: Equivalent to: return operator/=(path(source));

template<class InputIterator>
  path& append(InputIterator first, InputIterator last);

Effects: Equivalent to: return operator/=(path(first, last));

29.11.7.4.4 Concatenation [fs.path.concat]

path& operator+=(const path& x);
path& operator+=(const string_type& x);
path& operator+=(basic_string_view<value_type> x);
path& operator+=(const value_type* x);
template<class Source>
  path& operator+=(const Source& x);
template<class Source>
  path& concat(const Source& x);

Effects: Appends path(x).native() to the pathname in the native format.

This directly manipulates the value of native() and may not be portable between operating systems.

— end note

]

Returns: *this.

path& operator+=(value_type x);
template<class EcharT>
  path& operator+=(EcharT x);

Effects: Equivalent to: return *this += basic_string_view(&x, 1);

template<class InputIterator>
  path& concat(InputIterator first, InputIterator last);

Effects: Equivalent to: return *this += path(first, last);

29.11.7.4.5 Modifiers [fs.path.modifiers]

void clear() noexcept;

Postconditions: empty() == true.

path& make_preferred();

Effects: Each directory-separator of the pathname in the generic format is converted to preferred-separator .

Returns: *this.

path p("foo/bar");
std::cout << p << '\n';
p.make_preferred();
std::cout << p << '\n';

On an operating system where preferred-separator is a slash, the output is:

"foo/bar"
"foo/bar"

On an operating system where preferred-separator is a backslash, the output is:

"foo/bar"
"foo\bar"

— end example

]

path& remove_filename();

Effects: Remove the generic format pathname of filename() from the generic format pathname.

Postconditions: !has_filename().

Returns: *this.

path("foo/bar").remove_filename();      // yields "foo/"
path("foo/").remove_filename();         // yields "foo/"
path("/foo").remove_filename();         // yields "/"
path("/").remove_filename();            // yields "/"

— end example

]

path& replace_filename(const path& replacement);

Effects: Equivalent to:

remove_filename();
operator/=(replacement);

Returns: *this.

path("/foo").replace_filename("bar");   // yields "/bar" on POSIX
path("/").replace_filename("bar");      // yields "/bar" on POSIX

— end example

]

path& replace_extension(const path& replacement = path());

Effects:

(12.1)
Any existing extension() ([fs.path.decompose]) is removed from the pathname in the generic format, then
(12.2)
If replacement is not empty and does not begin with a dot character, a dot character is appended to the pathname in the generic format, then
(12.3)
operator+=(replacement);.

Returns: *this.

void swap(path& rhs) noexcept;

Effects: Swaps the contents (in all formats) of the two paths.

Complexity: Constant time.

29.11.7.4.6 Native format observers [fs.path.native.obs]

The string returned by all native format observers is in the native pathname format ([fs.class.path]).

const string_type& native() const noexcept;

Returns: The pathname in the native format.

const value_type* c_str() const noexcept;

Effects: Equivalent to: return native().c_str();

operator string_type() const;

Returns: native().

Conversion to string_type is provided so that an object of class path can be given as an argument to existing standard library file stream constructors and open functions.

— end note

]

template<class EcharT, class traits = char_traits<EcharT>,
         class Allocator = allocator<EcharT>>
  basic_string<EcharT, traits, Allocator>
    string(const Allocator& a = Allocator()) const;

Returns: native().

Remarks: All memory allocation, including for the return value, shall be performed by a.

Conversion, if any, is specified by [fs.path.cvt].

std::string string() const;
std::wstring wstring() const;
std::u8string u8string() const;
std::u16string u16string() const;
std::u32string u32string() const;

Returns: native().

Remarks: Conversion, if any, is performed as specified by [fs.path.cvt].

29.11.7.4.7 Generic format observers [fs.path.generic.obs]

Generic format observer functions return strings formatted according to the generic pathname format .

A single slash ('/') character is used as the directory-separator .

On an operating system that uses backslash as its preferred-separator,

path("foo\\bar").generic_string()

returns "foo/bar".

— end example

]

template<class EcharT, class traits = char_traits<EcharT>,
         class Allocator = allocator<EcharT>>
  basic_string<EcharT, traits, Allocator>
    generic_string(const Allocator& a = Allocator()) const;

Returns: The pathname in the generic format.

Remarks: All memory allocation, including for the return value, shall be performed by a.

Conversion, if any, is specified by [fs.path.cvt].

std::string generic_string() const;
std::wstring generic_wstring() const;
std::u8string generic_u8string() const;
std::u16string generic_u16string() const;
std::u32string generic_u32string() const;

Returns: The pathname in the generic format.

Remarks: Conversion, if any, is specified by [fs.path.cvt].

29.11.7.4.8 Compare [fs.path.compare]

int compare(const path& p) const noexcept;

Returns:

(1.1)
Let rootNameComparison be the result of this->root_name().native().compare(p.root_name().native()). If rootNameComparison is not 0, rootNameComparison.
(1.2)
Otherwise, if !this->has_root_directory() and p.has_root_directory(), a value less than 0.
(1.3)
Otherwise, if this->has_root_directory() and !p.has_root_directory(), a value greater than 0.
(1.4)
Otherwise, if native() for the elements of this->relative_path() are lexicographically less than native() for the elements of p.relative_path(), a value less than 0.
(1.5)
Otherwise, if native() for the elements of this->relative_path() are lexicographically greater than native() for the elements of p.relative_path(), a value greater than 0.
(1.6)
Otherwise, 0.

int compare(const string_type& s) const;
int compare(basic_string_view<value_type> s) const;
int compare(const value_type* s) const;

Effects: Equivalent to: return compare(path(s));

29.11.7.4.9 Decomposition [fs.path.decompose]

path root_name() const;

Returns: root-name, if the pathname in the generic format includes root-name, otherwise path().

path root_directory() const;

Returns: root-directory, if the pathname in the generic format includes root-directory, otherwise path().

path root_path() const;

Returns: root_name() / root_directory().

path relative_path() const;

Returns: A path composed from the pathname in the generic format, if empty() is false, beginning with the first filename after root_path().

Otherwise, path().

path parent_path() const;

Returns: *this if has_relative_path() is false, otherwise a path whose generic format pathname is the longest prefix of the generic format pathname of *this that produces one fewer element in its iteration.

path filename() const;

Returns: relative_path().empty() ? path() : *--end().

path("/foo/bar.txt").filename();        // yields "bar.txt"
path("/foo/bar").filename();            // yields "bar"
path("/foo/bar/").filename();           // yields ""
path("/").filename();                   // yields ""
path("//host").filename();              // yields ""
path(".").filename();                   // yields "."
path("..").filename();                  // yields ".."

— end example

]

path stem() const;

Returns: Let f be the generic format pathname of filename().

Returns a path whose pathname in the generic format is

(8.1)
f, if it contains no periods other than a leading period or consists solely of one or two periods;
(8.2)
otherwise, the prefix of f ending before its last period.

std::cout << path("/foo/bar.txt").stem();       // outputs "bar"
path p = "foo.bar.baz.tar";
for (; !p.extension().empty(); p = p.stem())
  std::cout << p.extension() << '\n';
  // outputs: .tar
  //          .baz
  //          .bar

— end example

]

path extension() const;

Returns: A path whose pathname in the generic format is the suffix of filename() not included in stem().

path("/foo/bar.txt").extension();       // yields ".txt" and stem() is "bar"
path("/foo/bar").extension();           // yields "" and stem() is "bar"
path("/foo/.profile").extension();      // yields "" and stem() is ".profile"
path(".bar").extension();               // yields "" and stem() is ".bar"
path("..bar").extension();              // yields ".bar" and stem() is "."

— end example

]

The period is included in the return value so that it is possible to distinguish between no extension and an empty extension.

— end note

]

On non-POSIX operating systems, for a path p, it may not be the case that p.stem() + p.extension() == p.filename(), even though the generic format pathnames are the same.

— end note

]

29.11.7.4.10 Query [fs.path.query]

[[nodiscard]] bool empty() const noexcept;

Returns: true if the pathname in the generic format is empty, otherwise false.

bool has_root_path() const;

Returns: !root_path().empty().

bool has_root_name() const;

Returns: !root_name().empty().

bool has_root_directory() const;

Returns: !root_directory().empty().

bool has_relative_path() const;

Returns: !relative_path().empty().

bool has_parent_path() const;

Returns: !parent_path().empty().

bool has_filename() const;

Returns: !filename().empty().

bool has_stem() const;

Returns: !stem().empty().

bool has_extension() const;

Returns: !extension().empty().

bool is_absolute() const;

Returns: true if the pathname in the native format contains an absolute path ([fs.class.path]), otherwise false.

path("/").is_absolute() is true for POSIX-based operating systems, and false for Windows-based operating systems.

— end example

]

bool is_relative() const;

Returns: !is_absolute().

29.11.7.4.11 Generation [fs.path.gen]

path lexically_normal() const;

Returns: A path whose pathname in the generic format is the normal form ([fs.path.generic]) of the pathname in the generic format of *this.

assert(path("foo/./bar/..").lexically_normal() == "foo/");
assert(path("foo/.///bar/../").lexically_normal() == "foo/");

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

]

path lexically_relative(const path& base) const;

Returns: *this made relative to base.

Does not resolve ([fs.class.path]) symlinks.

Does not first normalize ([fs.path.generic]) *this or base.

Effects: If:

(4.1)
root_name() != base.root_name() is true, or
(4.2)
is_absolute() != base.is_absolute() is true, or
(4.3)
!has_root_directory() && base.has_root_directory() is true, or
(4.4)
any filename in relative_path() or base.relative_path() can be interpreted as a root-name,

returns path().

On a POSIX implementation, no filename in a relative-path is acceptable as a root-name .

— end note

]

Determines the first mismatched element of *this and base as if by:

auto [a, b] = mismatch(begin(), end(), base.begin(), base.end());

Then,

(4.5)
if a == end() and b == base.end(), returns path("."); otherwise
(4.6)
let n be the number of filename elements in [b, base.end()) that are not dot or dot-dot or empty, minus the number that are dot-dot. If n<0, returns path(); otherwise
(4.7)
if n == 0 and (a == end() || a->empty()), returns path("."); otherwise
(4.8)
returns an object of class path that is default-constructed, followed by
- (4.8.1)
  application of operator/=(path("..")) n times, and then
- (4.8.2)
  application of operator/= for each element in [a, end()).

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") == "../../a/b");

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

]

If symlink following semantics are desired, use the operational function relative().

— end note

]

If normalization ([fs.path.generic]) is needed to ensure consistent matching of elements, apply lexically_normal() to *this, base, or both.

— end note

]

path lexically_proximate(const path& base) const;

Returns: If the value of lexically_relative(base) is not an empty path, return it.

Otherwise return *this.

If symlink following semantics are desired, use the operational function proximate().

— end note

]