[fs.path.member] (original) (raw)

31 Input/output library [input.output]

31.12 File systems [filesystems]

31.12.6 Class path [fs.class.path]

31.12.6.5 Members [fs.path.member]

31.12.6.5.1 Constructors [fs.path.construct]

Postconditions: empty() is true.

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

Effects: Constructs an object of class pathhaving 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 pathfor which the pathname in the detected-format of sourcehas 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 pathfor 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 ischar.

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

• 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.
• Otherwise a conversion is performed using thecodecvt<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 pathfor which the pathname in that format is s.

[Example 1:

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 usinglatin1_facet to convert ISO/IEC 8859-1 encodedlatin1_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 encodedlatin1_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_]

31.12.6.5.2 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 *thisto the respective pathnames of p.

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

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

Otherwise, sets both respective pathnames of *thisto the respective pathnames of p.

p is left in a valid but unspecified state.

[Note 1:

A valid implementation is swap(p).

— _end note_]

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

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

source is left in a valid but unspecified state.

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.

31.12.6.5.3 Appends [fs.path.append]

The append operations use operator/= to denote their semantic effect of appendingpreferred-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:

• 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.
• Then appends the native format pathname of p, omitting any root-name from its generic format pathname, to the native format pathname.

[Example 1:

Even if 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:path("foo") /= path(""); path("foo") /= path("/bar"); path("foo") /= path(""); path("foo") /= path("/bar"); path("foo") /= path("c:/bar"); path("foo") /= path("c:"); path("c:") /= path(""); path("c:foo") /= path("/bar"); path("c:foo") /= path("c:bar");

— _end example_]

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));

31.12.6.5.4 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.

[Note 1:

This directly manipulates the value of native(), which is not necessarily portable between operating systems.

— _end note_]

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);

31.12.6.5.5 Modifiers [fs.path.modifiers]

Postconditions: empty() is true.

[Example 1: 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_]

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

Postconditions: !has_filename().

[Example 2: path("foo/bar").remove_filename(); path("foo/").remove_filename(); path("/foo").remove_filename(); path("/").remove_filename(); — _end example_]

path& replace_filename(const path& replacement);

Effects: Equivalent to:remove_filename();operator/=(replacement);

[Example 3: path("/foo").replace_filename("bar"); path("/").replace_filename("bar"); — _end example_]

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

Effects:

• Any existing extension() ([fs.path.decompose]) is removed from the pathname in the generic format, then
• 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
• operator+=(replacement);.

void swap(path& rhs) noexcept;

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

Complexity: Constant time.

31.12.6.5.6 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;

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

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

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

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

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

[Example 1:

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.

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.

31.12.6.5.8 Compare [fs.path.compare]

int compare(const path& p) const noexcept;

Returns:

• Let rootNameComparison be the result ofthis->root_name().native().compare(p.root_name().native()).
  If rootNameComparison is not 0,rootNameComparison.
• Otherwise, if!this->has_root_directory() and p.has_root_directory(), a value less than 0.
• Otherwise, ifthis->has_root_directory() and !p.has_root_directory(), a value greater than 0.
• Otherwise, ifnative() for the elements of this->relative_path() are lexicographically less thannative() for the elements of p.relative_path(), a value less than 0.
• Otherwise, ifnative() for the elements of this->relative_path() are lexicographically greater thannative() for the elements of p.relative_path(), a value greater than 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));

31.12.6.5.9 Decomposition [fs.path.decompose]

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

path root_directory() 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 *thisthat produces one fewer element in its iteration.

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

[Example 1: path("/foo/bar.txt").filename(); path("/foo/bar").filename(); path("/foo/bar/").filename(); path("/").filename(); path("//host").filename(); path(".").filename(); path("..").filename(); — _end example_]

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

Returns a path whose pathname in the generic format is

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

[Example 2: std::cout << path("/foo/bar.txt").stem(); path p = "foo.bar.baz.tar";for (; !p.extension().empty(); p = p.stem()) std::cout << p.extension() << '\n'; — _end example_]

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

[Example 3: path("/foo/bar.txt").extension(); path("/foo/bar").extension(); path("/foo/.profile").extension(); path(".bar").extension(); path("..bar").extension(); — _end example_]

[Note 1:

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

— _end note_]

[Note 2:

On non-POSIX operating systems, for a path p, it is possible that p.stem() + p.extension() == p.filename() is false, even though the generic format pathnames are the same.

— _end note_]

31.12.6.5.10 Query [fs.path.query]

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().

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.

[Example 1:

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

— _end example_]

bool is_relative() const;

31.12.6.5.11 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.

[Example 1: 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;

Effects: If:

• root_name() != base.root_name() is true, or
• is_absolute() != base.is_absolute() is true, or
• !has_root_directory() && base.has_root_directory() is true, or
• any filename inrelative_path() or base.relative_path()can be interpreted as a root-name,

returns path().

Determines the first mismatched element of *this and baseas if by:auto [a, b] = mismatch(begin(), end(), base.begin(), base.end());

Then,

• if a == end() and b == base.end(), returns path("."); otherwise
• 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
• if n == 0 and (a == end() || a->empty()), returns path("."); otherwise
• returns an object of class path that is default-constructed, followed by
  • application of operator/=(path("..")) n times, and then
  • application of operator/= for each element in [a, end()).

Returns: *this made relative to base.

[Example 2: 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_]

[Note 2:

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

— _end note_]

[Note 3:

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.

[Note 4:

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

— _end note_]

[Note 5:

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

— _end note_]