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Showing content from https://timsong-cpp.github.io/cppwp/n4659/fs.class.path below:

[fs.class.path]

30 Input/output library [input.output] 30.10 File systems [filesystems] 30.10.27 Class path [fs.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.

[Note: Class path is used to support the differences between the string types used by different operating systems to represent pathnames, and to perform conversions between encodings when necessary. end note]

namespace std::filesystem {
  class path {
  public:
    using value_type  = see below;
    using string_type = basic_string<value_type>;
    static constexpr value_type preferred_separator = see below;

        enum format;

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

        path& operator=(const path& p);
    path& operator=(path&& p) noexcept;
    path& operator=(string_type&& source);
    path& assign(string_type&& source);
    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);

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

        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);
    path& operator+=(value_type x);
    template <class Source>
      path& operator+=(const Source& x);
    template <class EcharT>
      path& operator+=(EcharT x);
    template <class Source>
      path& concat(const Source& x);
    template <class InputIterator>
      path& concat(InputIterator first, InputIterator last);

        void  clear() noexcept;
    path& make_preferred();
    path& remove_filename();
    path& replace_filename(const path& replacement);
    path& replace_extension(const path& replacement = path());
    void  swap(path& rhs) noexcept;

        const string_type& native() const noexcept;
    const value_type*  c_str() const noexcept;
    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;
    std::string    string() const;
    std::wstring   wstring() const;
    std::string    u8string() const;
    std::u16string u16string() const;
    std::u32string u32string() const;

        template <class EcharT, class traits = char_traits<EcharT>,
              class Allocator = allocator<EcharT>>
      basic_string<EcharT, traits, Allocator>
        generic_string(const Allocator& a = Allocator()) const;
    std::string    generic_string() const;
    std::wstring   generic_wstring() const;
    std::string    generic_u8string() const;
    std::u16string generic_u16string() const;
    std::u32string generic_u32string() const;

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

        path root_name() const;
    path root_directory() const;
    path root_path() const;
    path relative_path() const;
    path parent_path() const;
    path filename() const;
    path stem() const;
    path extension() const;

        bool empty() const noexcept;
    bool has_root_name() const;
    bool has_root_directory() const;
    bool has_root_path() const;
    bool has_relative_path() const;
    bool has_parent_path() const;
    bool has_filename() const;
    bool has_stem() const;
    bool has_extension() const;
    bool is_absolute() const;
    bool is_relative() const;

        path lexically_normal() const;
    path lexically_relative(const path& base) const;
    path lexically_proximate(const path& base) const;

        class iterator;
    using const_iterator = iterator;

    iterator begin() const;
    iterator end() const;
  };
}

value_­type is a typedef for the operating system dependent encoded character type used to represent pathnames.

[Example: For POSIX-based operating systems, value_­type is char and preferred_­separator is the slash character ('/'). For Windows-based operating systems, value_­type is wchar_­t and preferred_­separator is the backslash character (L'\\'). end example]

30.10.27.2 path conversions [fs.path.cvt] 30.10.27.2.1 path argument format conversions [fs.path.fmt.cvt]

[Note: The format conversions described in this section are not applied on POSIX-based operating systems because on these systems:

end note]

Several functions are defined to accept detected-format arguments, which are character sequences. A detected-format argument represents a path using either a pathname in the generic format or a pathname in the native format. Such an argument is taken to be in the generic format if and only if it matches the generic format and is not acceptable to the operating system as a native path.

[Note: Some operating systems may have no unambiguous way 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. An implementation for an operating system where disambiguation is required is permitted to distinguish between the formats. end note]

Pathnames are converted as needed between the generic and native formats in an operating-system-dependent manner. Let G(n) and N(g) in a mathematical sense be the implementation's functions that convert native-to-generic and generic-to-native formats respectively. If g=G(n) for some n, then G(N(g))=g; if n=N(g) for some g, then N(G(n))=n. [Note: Neither G nor N need be invertible. 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 its last element is a directory-separator, otherwise it shall be treated as a path to a regular file.

[Note: A path stores a native format pathname ([fs.path.native.obs]) and acts as if it also stores a generic format pathname, related as given below. The implementation may generate the generic format pathname based on the native format pathname (and possibly other information) when requested. end note]

When a path is constructed from or is assigned a single representation separate from any path, the other representation is selected by the appropriate conversion function (G or N).

When the (new) value p of one representation of a path is derived from the representation of that or another path, a value q is chosen for the other representation. The value q converts to p (by G or N as appropriate) if any such value does so; q is otherwise unspecified. [Note: If q is the result of converting any path at all, it is the result of converting p. end note]

30.10.27.2.2 path type and encoding conversions [fs.path.type.cvt]

For member function arguments that take character sequences representing paths and for member functions returning strings, value type and encoding conversion is performed if the value type of the argument or return value differs from path​::​value_­type. For the argument or return value, the method of conversion and the encoding to be converted to is determined by its value type:

If the encoding being converted to has no representation for source characters, the resulting converted characters, if any, are unspecified. Implementations should not modify member function arguments if already of type path​::​value_­type.

30.10.27.3 path requirements [fs.path.req]

In addition to the requirements ([fs.req]), function template parameters named Source shall be one of:

Functions taking template parameters named Source shall not participate in overload resolution unless either

[Note: See path conversions for how the value types above and their encodings convert to path​::​value_­type and its encoding. end note]

Arguments of type Source shall not be null pointers.

30.10.27.4 path members [fs.path.member] 30.10.27.4.1 path constructors [fs.path.construct]

path() noexcept;

Effects: Constructs an object of class path.

Postconditions: empty() == true.

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);

Requires: 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:

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.

[Example: 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.def.native.encode]). The resulting wide string is then converted to a narrow character pathname string in the current native narrow encoding. If the native wide encoding is UTF-16 or UTF-32, and the current native narrow 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 narrow 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]

30.10.27.4.2 path 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.

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. [Note: 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 source to 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.

30.10.27.4.3 path 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:

[Example: Even if //host is interpreted as a root-name, both of the paths path("//host")/"foo" and path("//host/")/"foo" equal "//host/foo".

Expression examples:

path("foo") / "";     path("foo") / "/bar"; 
path("foo") / "c:/bar";  path("foo") / "c:";      path("c:") / "";         path("c:foo") / "/bar";  path("c:foo") / "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));

30.10.27.4.4 path 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); path& operator+=(value_type x); template <class Source> path& operator+=(const Source& x); template <class EcharT> path& operator+=(EcharT x); template <class Source> path& concat(const Source& x);

Effects: Appends path(x).native() to the pathname in the native format. [Note: This directly manipulates the value of native() and may not be portable between operating systems. end note]

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

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

30.10.27.4.5 path modifiers [fs.path.modifiers]

void clear() noexcept;

Postconditions: empty() == true.

path& make_preferred();

[Example:

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();

Postconditions: !has_­filename().

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

[Example:

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:

path("/foo").replace_filename("bar");  path("/").replace_filename("bar");     

end example]

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

Effects:

void swap(path& rhs) noexcept;

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

Complexity: Constant time.

30.10.27.4.6 path native format observers [fs.path.native.obs]

const string_type& native() const noexcept;

Returns: The pathname in the native format.

const value_type* c_str() const noexcept;

Returns: Equivalent to native().c_­str().

operator string_type() const;

[Note: 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;

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

Remarks: Conversion, if any, is performed as specified by [fs.path.cvt]. The encoding of the string returned by u8string() is always UTF-8.

30.10.27.4.7 path generic format observers [fs.path.generic.obs]

[Example: 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::string 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]. The encoding of the string returned by generic_­u8string() is always UTF-8.

30.10.27.4.8 path compare [fs.path.compare]

int compare(const path& p) const noexcept;

Returns:

Remarks: The elements are determined as if by iteration over the half-open range [begin(), end()) for *this and p.

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

Returns: compare(path(s)).

int compare(const value_type* s) const

Returns: compare(path(s)).

30.10.27.4.9 path 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;

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(), beginning with the first filename after root-path. Otherwise, path().

path parent_path() const;

Returns: *this if !has_­relative_­path(), 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().

[Example:

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

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

[Example:

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]

path extension() const;

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

[Example:

path("/foo/bar.txt").extension();  path("/foo/bar").extension();      path("/foo/.profile").extension(); path(".bar").extension();          path("..bar").extension();         

end example]

[Note: 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: 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]

30.10.27.4.10 path query [fs.path.query]

bool empty() const noexcept;

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

[Example: path("/").is_­absolute() is true for POSIX-based operating systems, and false for Windows-based operating systems. end example]

bool is_relative() const;

30.10.27.4.11 path generation [fs.path.gen]

path lexically_normal() const;

Returns: A path whose pathname in the generic format is the normal form of the pathname in the generic format of *this.

[Example:

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 symlinks. Does not first normalize *this or base.

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, returns path(). Determines the first mismatched element of *this and base as if by:

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

Then,

[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") == "../../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: If symlink following semantics are desired, use the operational function relative(). end note]

[Note: If normalization is needed to ensure consistent matching of elements, apply lexically_­normal() to *this, base, or both. end note]

path lexically_proximate(const path& base) const;

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

[Note: If symlink following semantics are desired, use the operational function proximate(). end note]

[Note: If normalization is needed to ensure consistent matching of elements, apply lexically_­normal() to *this, base, or both. end note]

30.10.27.5 path iterators [fs.path.itr]

Path iterators iterate over the elements of the pathname in the generic format.

A path​::​iterator is a constant iterator satisfying all the requirements of a bidirectional iterator except that, for dereferenceable iterators a and b of type path​::​iterator with a == b, there is no requirement that *a and *b are bound to the same object. Its value_­type is path.

Calling any non-const member function of a path object invalidates all iterators referring to elements of that object.

For the elements of the pathname in the generic format, the forward traversal order is as follows:

The backward traversal order is the reverse of forward traversal.

iterator begin() const;

Returns: An iterator for the first present element in the traversal list above. If no elements are present, the end iterator.

iterator end() const;

Returns: The end iterator.

30.10.27.6 path non-member functions [fs.path.nonmember]

void swap(path& lhs, path& rhs) noexcept;

Effects: Equivalent to: lhs.swap(rhs);

size_t hash_value (const path& p) noexcept;

Returns: A hash value for the path p. If for two paths, p1 == p2 then hash_­value(p1) == hash_­value(p2).

bool operator< (const path& lhs, const path& rhs) noexcept;

Returns: lhs.compare(rhs) < 0.

bool operator<=(const path& lhs, const path& rhs) noexcept;

bool operator> (const path& lhs, const path& rhs) noexcept;

bool operator>=(const path& lhs, const path& rhs) noexcept;

bool operator==(const path& lhs, const path& rhs) noexcept;

Returns: !(lhs < rhs) && !(rhs < lhs).

[Note: Path equality and path equivalence have different semantics.

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) noexcept;

path operator/ (const path& lhs, const path& rhs);

Effects: Equivalent to: return path(lhs) /= rhs;

30.10.27.6.1 path inserter and extractor [fs.path.io]

template <class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& os, const path& p);

Effects: Equivalent to: os << quoted(p.string<charT, traits>()); [Note: The quoted function is described in [quoted.manip]. end note]

template <class charT, class traits> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& is, path& p);

Effects: Equivalent to:

basic_string<charT, traits> tmp;
is >> quoted(tmp);
p = tmp;
30.10.27.6.2 path factory functions [fs.path.factory]

template <class Source> path u8path(const Source& source); template <class InputIterator> path u8path(InputIterator first, InputIterator last);

Requires: The source and [first, last) sequences are UTF-8 encoded. The value type of Source and InputIterator is char.

Returns:

Remarks: Argument format conversion applies to the arguments for these functions. How Unicode encoding conversions are performed is unspecified.

[Example: A string is to be read from a database that is encoded in UTF-8, and used to create a directory using the native encoding for filenames:

namespace fs = std::filesystem;
std::string utf8_string = read_utf8_data();
fs::create_directory(fs::u8path(utf8_string));

For POSIX-based operating systems with the native narrow encoding set to UTF-8, no encoding or type conversion occurs.

For POSIX-based operating systems with the native narrow encoding not set to UTF-8, a conversion to UTF-32 occurs, followed by a conversion to the current native narrow encoding. Some Unicode characters may have no native character set representation.

For Windows-based operating systems a conversion from UTF-8 to UTF-16 occurs. end example]


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