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Showing content from https://timsong-cpp.github.io/cppwp/n4659/input.output below:

[input.output]

#include <iosfwd>   
namespace std {
  using streamoff  = implementation-defined;
  using streamsize = implementation-defined;
  template <class stateT> class fpos;

  class ios_base;
  template <class charT, class traits = char_traits<charT>>
    class basic_ios;

    ios_base& boolalpha  (ios_base& str);
  ios_base& noboolalpha(ios_base& str);

  ios_base& showbase   (ios_base& str);
  ios_base& noshowbase (ios_base& str);

  ios_base& showpoint  (ios_base& str);
  ios_base& noshowpoint(ios_base& str);

  ios_base& showpos    (ios_base& str);
  ios_base& noshowpos  (ios_base& str);

  ios_base& skipws     (ios_base& str);
  ios_base& noskipws   (ios_base& str);

  ios_base& uppercase  (ios_base& str);
  ios_base& nouppercase(ios_base& str);

  ios_base& unitbuf    (ios_base& str);
  ios_base& nounitbuf  (ios_base& str);

    ios_base& internal   (ios_base& str);
  ios_base& left       (ios_base& str);
  ios_base& right      (ios_base& str);

    ios_base& dec        (ios_base& str);
  ios_base& hex        (ios_base& str);
  ios_base& oct        (ios_base& str);

    ios_base& fixed      (ios_base& str);
  ios_base& scientific (ios_base& str);
  ios_base& hexfloat   (ios_base& str);
  ios_base& defaultfloat(ios_base& str);

    enum class io_errc {
    stream = 1
  };

  template <> struct is_error_code_enum<io_errc> : public true_type { };
  error_code make_error_code(io_errc e) noexcept;
  error_condition make_error_condition(io_errc e) noexcept;
  const error_category& iostream_category() noexcept;
}

using streamoff = implementation-defined;

The type streamoff is a synonym for one of the signed basic integral types of sufficient size to represent the maximum possible file size for the operating system.290

using streamsize = implementation-defined;

The type streamsize is a synonym for one of the signed basic integral types. It is used to represent the number of characters transferred in an I/O operation, or the size of I/O buffers.291

namespace std {
  class ios_base {
  public:
    class failure; 
        using fmtflags = T1;
    static constexpr fmtflags boolalpha = unspecified;
    static constexpr fmtflags dec = unspecified;
    static constexpr fmtflags fixed = unspecified;
    static constexpr fmtflags hex = unspecified;
    static constexpr fmtflags internal = unspecified;
    static constexpr fmtflags left = unspecified;
    static constexpr fmtflags oct = unspecified;
    static constexpr fmtflags right = unspecified;
    static constexpr fmtflags scientific = unspecified;
    static constexpr fmtflags showbase = unspecified;
    static constexpr fmtflags showpoint = unspecified;
    static constexpr fmtflags showpos = unspecified;
    static constexpr fmtflags skipws = unspecified;
    static constexpr fmtflags unitbuf = unspecified;
    static constexpr fmtflags uppercase = unspecified;
    static constexpr fmtflags adjustfield = see below;
    static constexpr fmtflags basefield = see below;
    static constexpr fmtflags floatfield = see below;

        using iostate = T2;
    static constexpr iostate badbit = unspecified;
    static constexpr iostate eofbit = unspecified;
    static constexpr iostate failbit = unspecified;
    static constexpr iostate goodbit = see below;

        using openmode = T3;
    static constexpr openmode app = unspecified;
    static constexpr openmode ate = unspecified;
    static constexpr openmode binary = unspecified;
    static constexpr openmode in = unspecified;
    static constexpr openmode out = unspecified;
    static constexpr openmode trunc = unspecified;

        using seekdir = T4;
    static constexpr seekdir beg = unspecified;
    static constexpr seekdir cur = unspecified;
    static constexpr seekdir end = unspecified;

    class Init;

        fmtflags flags() const;
    fmtflags flags(fmtflags fmtfl);
    fmtflags setf(fmtflags fmtfl);
    fmtflags setf(fmtflags fmtfl, fmtflags mask);
    void unsetf(fmtflags mask);

    streamsize precision() const;
    streamsize precision(streamsize prec);
    streamsize width() const;
    streamsize width(streamsize wide);

        locale imbue(const locale& loc);
    locale getloc() const;

        static int xalloc();
    long&  iword(int index);
    void*& pword(int index);

        virtual ~ios_base();

        enum event { erase_event, imbue_event, copyfmt_event };
    using event_callback = void (*)(event, ios_base&, int index);
    void register_callback(event_callback fn, int index);

    ios_base(const ios_base&) = delete;
    ios_base& operator=(const ios_base&) = delete;

    static bool sync_with_stdio(bool sync = true);

  protected:
    ios_base();

  private:
    static int index;      long*  iarray;         void** parray;       };
}

ios_­base defines several member types:

• a type failure, defined as either a class derived from system_­error or a synonym for a class derived from system_­error;

• a class Init;

• three bitmask types, fmtflags, iostate, and openmode;

• an enumerated type, seekdir.

It maintains several kinds of data:

• state information that reflects the integrity of the stream buffer;

• control information that influences how to interpret (format) input sequences and how to generate (format) output sequences;

• additional information that is stored by the program for its private use.

[ Note: For the sake of exposition, the maintained data is presented here as:

• static int index, specifies the next available unique index for the integer or pointer arrays maintained for the private use of the program, initialized to an unspecified value;

• long* iarray, points to the first element of an arbitrary-length long array maintained for the private use of the program;

• void** parray, points to the first element of an arbitrary-length pointer array maintained for the private use of the program.

 — end note ]

namespace std {
  class ios_base::failure : public system_error {
  public:
    explicit failure(const string& msg, const error_code& ec = io_errc::stream);
    explicit failure(const char* msg, const error_code& ec = io_errc::stream);
  };
}

An implementation is permitted to define ios_­base​::​failure as a synonym for a class with equivalent functionality to class ios_­base​::​failure shown in this subclause. [ Note: When ios_­base​::​failure is a synonym for another type it shall provide a nested type failure, to emulate the injected class name.  — end note ] The class failure defines the base class for the types of all objects thrown as exceptions, by functions in the iostreams library, to report errors detected during stream buffer operations.

When throwing ios_­base​::​failure exceptions, implementations should provide values of ec that identify the specific reason for the failure. [ Note: Errors arising from the operating system would typically be reported as system_­category() errors with an error value of the error number reported by the operating system. Errors arising from within the stream library would typically be reported as error_­code(io_­errc​::​stream, iostream_­category()).  — end note ]

explicit failure(const string& msg, const error_code& ec = io_errc::stream);

Effects: Constructs an object of class failure by constructing the base class with msg and ec.

explicit failure(const char* msg, const error_code& ec = io_errc::stream);

Effects: Constructs an object of class failure by constructing the base class with msg and ec.

using fmtflags = T1;

The type fmtflags is a bitmask type. Setting its elements has the effects indicated in Table 107.

Table

—

effects

Type fmtflags also defines the constants indicated in Table 108.

Table

—

constants

using iostate = T2;

The type iostate is a bitmask type that contains the elements indicated in Table 109.

Table

—

effects

Type iostate also defines the constant:

• goodbit, the value zero.

using openmode = T3;

The type openmode is a bitmask type. It contains the elements indicated in Table 110.

Table

—

effects

using seekdir = T4;

The type seekdir is an enumerated type that contains the elements indicated in Table 111.

Table

—

effects

namespace std {
  class ios_base::Init {
  public:
    Init();
    ~Init();
  private:
    static int init_cnt;   };
}

The class Init describes an object whose construction ensures the construction of the eight objects declared in <iostream> ([iostream.objects]) that associate file stream buffers with the standard C streams provided for by the functions declared in <cstdio>.

For the sake of exposition, the maintained data is presented here as:

• static int init_­cnt, counts the number of constructor and destructor calls for class Init, initialized to zero.

Init();

Effects: Constructs an object of class Init. Constructs and initializes the objects cin, cout, cerr, clog, wcin, wcout, wcerr, and wclog if they have not already been constructed and initialized.

~Init();

Effects: Destroys an object of class Init. If there are no other instances of the class still in existence, calls cout.flush(), cerr.flush(), clog.flush(), wcout.flush(), wcerr.flush(), wclog.flush().

fmtflags flags() const;

Returns: The format control information for both input and output.

fmtflags flags(fmtflags fmtfl);

Postconditions: fmtfl == flags().

Returns: The previous value of flags().

fmtflags setf(fmtflags fmtfl);

Effects: Sets fmtfl in flags().

Returns: The previous value of flags().

fmtflags setf(fmtflags fmtfl, fmtflags mask);

Effects: Clears mask in flags(), sets fmtfl & mask in flags().

Returns: The previous value of flags().

void unsetf(fmtflags mask);

Effects: Clears mask in flags().

streamsize precision() const;

Returns: The precision to generate on certain output conversions.

streamsize precision(streamsize prec);

Postconditions: prec == precision().

Returns: The previous value of precision().

streamsize width() const;

Returns: The minimum field width (number of characters) to generate on certain output conversions.

streamsize width(streamsize wide);

Postconditions: wide == width().

Returns: The previous value of width().

locale imbue(const locale& loc);

Effects: Calls each registered callback pair (fn, index) ([ios.base.callback]) as (*fn)(imbue_­event, *this, index) at such a time that a call to ios_­base​::​getloc() from within fn returns the new locale value loc.

Returns: The previous value of getloc().

Postconditions: loc == getloc().

locale getloc() const;

Returns: If no locale has been imbued, a copy of the global C++ locale, locale(), in effect at the time of construction. Otherwise, returns the imbued locale, to be used to perform locale-dependent input and output operations.

bool sync_with_stdio(bool sync = true);

Returns: true if the previous state of the standard iostream objects was synchronized and otherwise returns false. The first time it is called, the function returns true.

Effects: If any input or output operation has occurred using the standard streams prior to the call, the effect is implementation-defined. Otherwise, called with a false argument, it allows the standard streams to operate independently of the standard C streams.

When a standard iostream object str is synchronized with a standard stdio stream f, the effect of inserting a character c by

fputc(f, c);

is the same as the effect of

str.rdbuf()->sputc(c);

for any sequences of characters; the effect of extracting a character c by

c = fgetc(f);

is the same as the effect of

c = str.rdbuf()->sbumpc();

for any sequences of characters; and the effect of pushing back a character c by

ungetc(c, f);

is the same as the effect of

str.rdbuf()->sputbackc(c);

for any sequence of characters.292

static int xalloc();

Remarks: Concurrent access to this function by multiple threads shall not result in a data race.

long& iword(int idx);

Effects: If iarray is a null pointer, allocates an array of long of unspecified size and stores a pointer to its first element in iarray. The function then extends the array pointed at by iarray as necessary to include the element iarray[idx]. Each newly allocated element of the array is initialized to zero. The reference returned is invalid after any other operations on the object.293 However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling iword with the same index yields another reference to the same value. If the function fails294 and *this is a base class subobject of a basic_­ios<> object or subobject, the effect is equivalent to calling basic_­ios<>​::​setstate(badbit) on the derived object (which may throw failure).

Returns: On success iarray[idx]. On failure, a valid long& initialized to 0.

void*& pword(int idx);

Effects: If parray is a null pointer, allocates an array of pointers to void of unspecified size and stores a pointer to its first element in parray. The function then extends the array pointed at by parray as necessary to include the element parray[idx]. Each newly allocated element of the array is initialized to a null pointer. The reference returned is invalid after any other operations on the object. However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling pword with the same index yields another reference to the same value. If the function fails295 and *this is a base class subobject of a basic_­ios<> object or subobject, the effect is equivalent to calling basic_­ios<>​::​setstate(badbit) on the derived object (which may throw failure).

Returns: On success parray[idx]. On failure a valid void*& initialized to 0.

Remarks: After a subsequent call to pword(int) for the same object, the earlier return value may no longer be valid.

void register_callback(event_callback fn, int index);

Effects: Registers the pair (fn, index) such that during calls to imbue() ([ios.base.locales]), copyfmt(), or ~ios_­base() ([ios.base.cons]), the function fn is called with argument index. Functions registered are called when an event occurs, in opposite order of registration. Functions registered while a callback function is active are not called until the next event.

Requires: The function fn shall not throw exceptions.

Remarks: Identical pairs are not merged. A function registered twice will be called twice.

ios_base();

Effects: Each ios_­base member has an indeterminate value after construction. The object's members shall be initialized by calling basic_­ios​::​init before the object's first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.

~ios_base();

Effects: Destroys an object of class ios_­base. Calls each registered callback pair (fn, index) ([ios.base.callback]) as (*fn)(​erase_­event, *this, index) at such time that any ios_­base member function called from within fn has well defined results.

namespace std {
  template <class stateT> class fpos {
  public:
        stateT state() const;
    void state(stateT);
  private;
    stateT st;   };
}

void state(stateT s);

Effects: Assigns s to st.

stateT state() const;

Returns: Current value of st.

Operations specified in Table 112 are permitted. In that table,

• P refers to an instance of fpos,

• p and q refer to values of type P,

• O refers to type streamoff,

• o refers to a value of type streamoff,

• sz refers to a value of type streamsize and

• i refers to a value of type int.

Table

— Position type requirements

[ Note: Every implementation is required to supply overloaded operators on fpos objects to satisfy the requirements of [fpos.operations]. It is unspecified whether these operators are members of fpos, global operators, or provided in some other way.  — end note ]

Stream operations that return a value of type traits​::​pos_­type return P(O(-1)) as an invalid value to signal an error. If this value is used as an argument to any istream, ostream, or streambuf member that accepts a value of type traits​::​pos_­type then the behavior of that function is undefined.

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_ios : public ios_base {
  public:
    using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        explicit operator bool() const;
    bool operator!() const;
    iostate rdstate() const;
    void clear(iostate state = goodbit);
    void setstate(iostate state);
    bool good() const;
    bool eof()  const;
    bool fail() const;
    bool bad()  const;

    iostate exceptions() const;
    void exceptions(iostate except);

        explicit basic_ios(basic_streambuf<charT, traits>* sb);
    virtual ~basic_ios();

        basic_ostream<charT, traits>* tie() const;
    basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);

    basic_streambuf<charT, traits>* rdbuf() const;
    basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);

    basic_ios& copyfmt(const basic_ios& rhs);

    char_type fill() const;
    char_type fill(char_type ch);

    locale imbue(const locale& loc);

    char      narrow(char_type c, char dfault) const;
    char_type widen(char c) const;

    basic_ios(const basic_ios&) = delete;
    basic_ios& operator=(const basic_ios&) = delete;

  protected:
    basic_ios();
    void init(basic_streambuf<charT, traits>* sb);
    void move(basic_ios& rhs);
    void move(basic_ios&& rhs);
    void swap(basic_ios& rhs) noexcept;
    void set_rdbuf(basic_streambuf<charT, traits>* sb);

  };
}

explicit basic_ios(basic_streambuf<charT, traits>* sb);

Effects: Constructs an object of class basic_­ios, assigning initial values to its member objects by calling init(sb).

basic_ios();

Effects: Constructs an object of class basic_­ios ([ios.base.cons]) leaving its member objects uninitialized. The object shall be initialized by calling basic_­ios​::​init before its first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.

~basic_ios();

Remarks: The destructor does not destroy rdbuf().

void init(basic_streambuf<charT, traits>* sb);

Postconditions: The postconditions of this function are indicated in Table 113.

Table

—

effects

basic_ostream<charT, traits>* tie() const;

Returns: An output sequence that is tied to (synchronized with) the sequence controlled by the stream buffer.

basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);

Requires: If tiestr is not null, tiestr must not be reachable by traversing the linked list of tied stream objects starting from tiestr->tie().

Postconditions: tiestr == tie().

Returns: The previous value of tie().

basic_streambuf<charT, traits>* rdbuf() const;

Returns: A pointer to the streambuf associated with the stream.

basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);

Postconditions: sb == rdbuf().

Returns: The previous value of rdbuf().

locale imbue(const locale& loc);

Returns: The prior value of ios_­base​::​imbue().

char narrow(char_type c, char dfault) const;

Returns: use_­facet<ctype<char_­type>>(getloc()).narrow(c, dfault)

char_type widen(char c) const;

Returns: use_­facet<ctype<char_­type>>(getloc()).widen(c)

char_type fill() const;

Returns: The character used to pad (fill) an output conversion to the specified field width.

char_type fill(char_type fillch);

Postconditions: traits​::​eq(fillch, fill()).

Returns: The previous value of fill().

basic_ios& copyfmt(const basic_ios& rhs);

Effects: If (this == &rhs) does nothing. Otherwise assigns to the member objects of *this the corresponding member objects of rhs as follows:

1. 1.calls each registered callback pair (fn, index) as (*fn)(erase_­event, *this, index);

2. 2.assigns to the member objects of *this the corresponding member objects of rhs, except that

   • rdstate(), rdbuf(), and exceptions() are left unchanged;

   • the contents of arrays pointed at by pword and iword are copied, not the pointers themselves;296 and

   • if any newly stored pointer values in *this point at objects stored outside the object rhs and those objects are destroyed when rhs is destroyed, the newly stored pointer values are altered to point at newly constructed copies of the objects;

3. 3.calls each callback pair that was copied from rhs as (*fn)(copyfmt_­event, *this, index);

4. 4.calls exceptions(rhs.exceptions()).

[ Note: The second pass through the callback pairs permits a copied pword value to be zeroed, or to have its referent deep copied or reference counted, or to have other special action taken.  — end note ]

Postconditions: The postconditions of this function are indicated in Table 114.

Table

—

effects

void move(basic_ios& rhs); void move(basic_ios&& rhs);

Postconditions: *this shall have the state that rhs had before the function call, except that rdbuf() shall return 0. rhs shall be in a valid but unspecified state, except that rhs.rdbuf() shall return the same value as it returned before the function call, and rhs.tie() shall return 0.

void swap(basic_ios& rhs) noexcept;

Effects: The states of *this and rhs shall be exchanged, except that rdbuf() shall return the same value as it returned before the function call, and rhs.rdbuf() shall return the same value as it returned before the function call.

void set_rdbuf(basic_streambuf<charT, traits>* sb);

Effects: Associates the basic_­streambuf object pointed to by sb with this stream without calling clear().

Postconditions: rdbuf() == sb.

explicit operator bool() const;

bool operator!() const;

iostate rdstate() const;

Returns: The error state of the stream buffer.

void clear(iostate state = goodbit);

Postconditions: If rdbuf() != 0 then state == rdstate(); otherwise rdstate() == (state | ios_­base​::​badbit).

Effects: If ((state | (rdbuf() ? goodbit : badbit)) & exceptions()) == 0, returns. Otherwise, the function throws an object of class basic_­ios​::​failure, constructed with implementation-defined argument values.

void setstate(iostate state);

bool good() const;

bool eof() const;

Returns: true if eofbit is set in rdstate().

bool fail() const;

Returns: true if failbit or badbit is set in rdstate().297

bool bad() const;

Returns: true if badbit is set in rdstate().

iostate exceptions() const;

Returns: A mask that determines what elements set in rdstate() cause exceptions to be thrown.

void exceptions(iostate except);

Postconditions: except == exceptions().

Effects: Calls clear(rdstate()).

ios_base& boolalpha(ios_base& str);

Effects: Calls str.setf(ios_­base​::​boolalpha).

ios_base& noboolalpha(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​boolalpha).

ios_base& showbase(ios_base& str);

Effects: Calls str.setf(ios_­base​::​showbase).

ios_base& noshowbase(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​showbase).

ios_base& showpoint(ios_base& str);

Effects: Calls str.setf(ios_­base​::​showpoint).

ios_base& noshowpoint(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​showpoint).

ios_base& showpos(ios_base& str);

Effects: Calls str.setf(ios_­base​::​showpos).

ios_base& noshowpos(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​showpos).

ios_base& skipws(ios_base& str);

Effects: Calls str.setf(ios_­base​::​skipws).

ios_base& noskipws(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​skipws).

ios_base& uppercase(ios_base& str);

Effects: Calls str.setf(ios_­base​::​uppercase).

ios_base& nouppercase(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​uppercase).

ios_base& unitbuf(ios_base& str);

Effects: Calls str.setf(ios_­base​::​unitbuf).

ios_base& nounitbuf(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​unitbuf).

ios_base& internal(ios_base& str);

Effects: Calls str.setf(ios_­base​::​internal, ios_­base​::​adjustfield).

ios_base& left(ios_base& str);

Effects: Calls str.setf(ios_­base​::​left, ios_­base​::​adjustfield).

ios_base& right(ios_base& str);

Effects: Calls str.setf(ios_­base​::​right, ios_­base​::​adjustfield).

ios_base& dec(ios_base& str);

Effects: Calls str.setf(ios_­base​::​dec, ios_­base​::​basefield).

ios_base& hex(ios_base& str);

Effects: Calls str.setf(ios_­base​::​hex, ios_­base​::​basefield).

ios_base& oct(ios_base& str);

Effects: Calls str.setf(ios_­base​::​oct, ios_­base​::​basefield).

ios_base& fixed(ios_base& str);

Effects: Calls str.setf(ios_­base​::​fixed, ios_­base​::​floatfield).

ios_base& scientific(ios_base& str);

Effects: Calls str.setf(ios_­base​::​scientific, ios_­base​::​floatfield).

ios_base& hexfloat(ios_base& str);

Effects: Calls str.setf(ios_­base​::​fixed | ios_­base​::​scientific, ios_­base​::​floatfield).

[ Note: The more obvious use of ios_­base​::​hex to specify hexadecimal floating-point format would change the meaning of existing well defined programs. C++ 2003 gives no meaning to the combination of fixed and scientific. — end note ]

ios_base& defaultfloat(ios_base& str);

Effects: Calls str.unsetf(ios_­base​::​floatfield).

error_code make_error_code(io_errc e) noexcept;

Returns: error_­code(static_­cast<int>(e), iostream_­category()).

error_condition make_error_condition(io_errc e) noexcept;

Returns: error_­condition(static_­cast<int>(e), iostream_­category()).

const error_category& iostream_category() noexcept;

Returns: A reference to an object of a type derived from class error_­category.

The object's default_­error_­condition and equivalent virtual functions shall behave as specified for the class error_­category. The object's name virtual function shall return a pointer to the string "iostream".

namespace std {
  template <class charT, class traits = char_traits<charT>>
    class basic_istream;

  using istream  = basic_istream<char>;
  using wistream = basic_istream<wchar_t>;

  template <class charT, class traits = char_traits<charT>>
    class basic_iostream;

  using iostream  = basic_iostream<char>;
  using wiostream = basic_iostream<wchar_t>;

  template <class charT, class traits>
    basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);

  template <class charT, class traits, class T>
    basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&& is, T&& x);
}

namespace std {
  template <class charT, class traits = char_traits<charT>>
    class basic_ostream;

  using ostream  = basic_ostream<char>;
  using wostream = basic_ostream<wchar_t>;

  template <class charT, class traits>
    basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);
  template <class charT, class traits>
    basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);
  template <class charT, class traits>
    basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);

  template <class charT, class traits, class T>
    basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&& os, const T& x);
}

namespace std {
    T1 resetiosflags(ios_base::fmtflags mask);
  T2 setiosflags  (ios_base::fmtflags mask);
  T3 setbase(int base);
  template<charT> T4 setfill(charT c);
  T5 setprecision(int n);
  T6 setw(int n);
  template <class moneyT> T7 get_money(moneyT& mon, bool intl = false);
  template <class moneyT> T8 put_money(const moneyT& mon, bool intl = false);
  template <class charT> T9 get_time(struct tm* tmb, const charT* fmt);
  template <class charT> T10 put_time(const struct tm* tmb, const charT* fmt);

  template <class charT>
    T11 quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\'));

  template <class charT, class traits, class Allocator>
    T12 quoted(const basic_string<charT, traits, Allocator>& s,
               charT delim = charT('"'), charT escape = charT('\\'));

  template <class charT, class traits, class Allocator>
    T13 quoted(basic_string<charT, traits, Allocator>& s,
               charT delim = charT('"'), charT escape = charT('\\'));

  template <class charT, class traits>
    T14 quoted(basic_string_view<charT, traits> s,
               charT delim = charT('"'), charT escape = charT('\\'));
}

The header <istream> defines two types and a function signature that control input from a stream buffer along with a function template that extracts from stream rvalues.

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_istream : virtual public basic_ios<charT, traits> {
  public:
        using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        explicit basic_istream(basic_streambuf<charT, traits>* sb);
    virtual ~basic_istream();

        class sentry;

        basic_istream<charT, traits>&
      operator>>(basic_istream<charT, traits>& (*pf)(basic_istream<charT, traits>&));
    basic_istream<charT, traits>&
      operator>>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
    basic_istream<charT, traits>&
      operator>>(ios_base& (*pf)(ios_base&));

    basic_istream<charT, traits>& operator>>(bool& n);
    basic_istream<charT, traits>& operator>>(short& n);
    basic_istream<charT, traits>& operator>>(unsigned short& n);
    basic_istream<charT, traits>& operator>>(int& n);
    basic_istream<charT, traits>& operator>>(unsigned int& n);
    basic_istream<charT, traits>& operator>>(long& n);
    basic_istream<charT, traits>& operator>>(unsigned long& n);
    basic_istream<charT, traits>& operator>>(long long& n);
    basic_istream<charT, traits>& operator>>(unsigned long long& n);
    basic_istream<charT, traits>& operator>>(float& f);
    basic_istream<charT, traits>& operator>>(double& f);
    basic_istream<charT, traits>& operator>>(long double& f);

    basic_istream<charT, traits>& operator>>(void*& p);
    basic_istream<charT, traits>& operator>>(basic_streambuf<char_type, traits>* sb);

        streamsize gcount() const;
    int_type get();
    basic_istream<charT, traits>& get(char_type& c);
    basic_istream<charT, traits>& get(char_type* s, streamsize n);
    basic_istream<charT, traits>& get(char_type* s, streamsize n, char_type delim);
    basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb);
    basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb, char_type delim);

    basic_istream<charT, traits>& getline(char_type* s, streamsize n);
    basic_istream<charT, traits>& getline(char_type* s, streamsize n, char_type delim);

    basic_istream<charT, traits>& ignore(streamsize n = 1, int_type delim = traits::eof());
    int_type                      peek();
    basic_istream<charT, traits>& read    (char_type* s, streamsize n);
    streamsize                    readsome(char_type* s, streamsize n);

    basic_istream<charT, traits>& putback(char_type c);
    basic_istream<charT, traits>& unget();
    int sync();

    pos_type tellg();
    basic_istream<charT, traits>& seekg(pos_type);
    basic_istream<charT, traits>& seekg(off_type, ios_base::seekdir);

  protected:
        basic_istream(const basic_istream& rhs) = delete;
    basic_istream(basic_istream&& rhs);

        basic_istream& operator=(const basic_istream& rhs) = delete;
    basic_istream& operator=(basic_istream&& rhs);
    void swap(basic_istream& rhs);
  };

    template<class charT, class traits>
    basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT&);
  template<class traits>
    basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char&);
  template<class traits>
    basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char&);

  template<class charT, class traits>
    basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT*);
  template<class traits>
    basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char*);
  template<class traits>
    basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char*);
}

The class template basic_­istream defines a number of member function signatures that assist in reading and interpreting input from sequences controlled by a stream buffer.

Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc(). They may use other public members of istream.

If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), then the input function, except as explicitly noted otherwise, completes its actions and does setstate(eofbit), which may throw ios_­base​::​failure ([iostate.flags]), before returning.

If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in error state. If badbit is on in exceptions(), the input function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication.

explicit basic_istream(basic_streambuf<charT, traits>* sb);

Effects: Constructs an object of class basic_­istream, initializing the base class subobject with basic_­ios​::​init(sb) ([basic.ios.cons]).

Postconditions: gcount() == 0.

basic_istream(basic_istream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class, copying the gcount() from rhs, calling basic_­ios<charT, traits>​::​move(rhs) to initialize the base class, and setting the gcount() for rhs to 0.

virtual ~basic_istream();

Effects: Destroys an object of class basic_­istream.

Remarks: Does not perform any operations of rdbuf().

basic_istream& operator=(basic_istream&& rhs);

Effects: As if by swap(rhs).

void swap(basic_istream& rhs);

Effects: Calls basic_­ios<charT, traits>​::​swap(rhs). Exchanges the values returned by gcount() and rhs.gcount().

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_istream<charT, traits>::sentry {
    using traits_type = traits;
    bool ok_;   public:
    explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
    ~sentry();
    explicit operator bool() const { return ok_; }
    sentry(const sentry&) = delete;
    sentry& operator=(const sentry&) = delete;
  };
}

The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.

explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);

Effects: If is.good() is false, calls is.setstate(failbit). Otherwise, prepares for formatted or unformatted input. First, if is.tie() is not a null pointer, the function calls is.tie()->flush() to synchronize the output sequence with any associated external C stream. Except that this call can be suppressed if the put area of is.tie() is empty. Further an implementation is allowed to defer the call to flush until a call of is.rdbuf()->underflow() occurs. If no such call occurs before the sentry object is destroyed, the call to flush may be eliminated entirely.305 If noskipws is zero and is.flags() & ios_­base​::​skipws is nonzero, the function extracts and discards each character as long as the next available input character c is a whitespace character. If is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() returns traits​::​eof(), the function calls setstate(failbit | eofbit) (which may throw ios_­base​::​failure).

Remarks: The constructor

explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false)

uses the currently imbued locale in is, to determine whether the next input character is whitespace or not.

To decide if the character c is a whitespace character, the constructor performs as if it executes the following code fragment:

const ctype<charT>& ctype = use_facet<ctype<charT>>(is.getloc());
if (ctype.is(ctype.space, c) != 0)
  

If, after any preparation is completed, is.good() is true, ok_­ != false otherwise, ok_­ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_­base​::​​failure ([iostate.flags]))306

~sentry();

explicit operator bool() const;

Each formatted input function begins execution by constructing an object of class sentry with the noskipws (second) argument false. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. If an exception is thrown during input then ios​::​badbit is turned on307 in *this's error state. If (exceptions()&badbit) != 0 then the exception is rethrown. In any case, the formatted input function destroys the sentry object. If no exception has been thrown, it returns *this.

operator>>(unsigned short& val); operator>>(unsigned int& val); operator>>(long& val); operator>>(unsigned long& val); operator>>(long long& val); operator>>(unsigned long long& val); operator>>(float& val); operator>>(double& val); operator>>(long double& val); operator>>(bool& val); operator>>(void*& val);

As in the case of the inserters, these extractors depend on the locale's num_­get<> object to perform parsing the input stream data. These extractors behave as formatted input functions (as described in [istream.formatted.reqmts]). After a sentry object is constructed, the conversion occurs as if performed by the following code fragment:

using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = iostate::goodbit;
use_facet<numget>(loc).get(*this, 0, *this, err, val);
setstate(err);

In the above fragment, loc stands for the private member of the basic_­ios class. [ Note: The first argument provides an object of the istreambuf_­iterator class which is an iterator pointed to an input stream. It bypasses istreams and uses streambufs directly.  — end note ] Class locale relies on this type as its interface to istream, so that it does not need to depend directly on istream.

operator>>(short& val);

The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):

using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = ios_base::goodbit;
long lval;
use_facet<numget>(loc).get(*this, 0, *this, err, lval);
if (lval < numeric_limits<short>::min()) {
  err |= ios_base::failbit;
  val = numeric_limits<short>::min();
} else if (numeric_limits<short>::max() < lval) {
  err |= ios_base::failbit;
  val = numeric_limits<short>::max();
}  else
  val = static_cast<short>(lval);
setstate(err);

operator>>(int& val);

The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):

using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = ios_base::goodbit;
long lval;
use_facet<numget>(loc).get(*this, 0, *this, err, lval);
if (lval < numeric_limits<int>::min()) {
  err |= ios_base::failbit;
  val = numeric_limits<int>::min();
} else if (numeric_limits<int>::max() < lval) {
  err |= ios_base::failbit;
  val = numeric_limits<int>::max();
}  else
  val = static_cast<int>(lval);
setstate(err);

Each unformatted input function begins execution by constructing an object of class sentry with the default argument noskipws (second) argument true. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object returns false, when converted to a value of type bool, the function returns without attempting to obtain any input. In either case the number of extracted characters is set to 0; unformatted input functions taking a character array of nonzero size as an argument shall also store a null character (using charT()) in the first location of the array. If an exception is thrown during input then ios​::​badbit is turned on310 in *this's error state. (Exceptions thrown from basic_­ios<>​::​clear() are not caught or rethrown.) If (exceptions()&badbit) != 0 then the exception is rethrown. It also counts the number of characters extracted. If no exception has been thrown it ends by storing the count in a member object and returning the value specified. In any event the sentry object is destroyed before leaving the unformatted input function.

streamsize gcount() const;

Effects: None. This member function does not behave as an unformatted input function (as described above).

Returns: The number of characters extracted by the last unformatted input member function called for the object.

int_type get();

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts a character c, if one is available. Otherwise, the function calls setstate(failbit), which may throw ios_­base​::​failure ([iostate.flags]),

Returns: c if available, otherwise traits​::​eof().

basic_istream<charT, traits>& get(char_type& c);

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts a character, if one is available, and assigns it to c.311 Otherwise, the function calls setstate(failbit) (which may throw ios_­base​::​failure ([iostate.flags])).

basic_istream<charT, traits>& get(char_type* s, streamsize n, char_type delim);

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.312 Characters are extracted and stored until any of the following occurs:

• n is less than one or n - 1 characters are stored;

• end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit));

• traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted).

If the function stores no characters, it calls setstate(failbit) (which may throw ios_­base​::​​failure ([iostate.flags])). In any case, if n is greater than zero it then stores a null character into the next successive location of the array.

basic_istream<charT, traits>& get(char_type* s, streamsize n);

Effects: Calls get(s, n, widen('\n')).

Returns: Value returned by the call.

basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb, char_type delim);

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and inserts them in the output sequence controlled by sb. Characters are extracted and inserted until any of the following occurs:

• end-of-file occurs on the input sequence;

• inserting in the output sequence fails (in which case the character to be inserted is not extracted);

• traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted);

• an exception occurs (in which case, the exception is caught but not rethrown).

If the function inserts no characters, it calls setstate(failbit), which may throw ios_­base​::​​failure ([iostate.flags]).

basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb);

Effects: Calls get(sb, widen('\n')).

Returns: Value returned by the call.

basic_istream<charT, traits>& getline(char_type* s, streamsize n, char_type delim);

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.313 Characters are extracted and stored until one of the following occurs:

1. 1.end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit));

2. 2.traits​::​eq(c, delim) for the next available input character c (in which case the input character is extracted but not stored);314

3. 3.n is less than one or n - 1 characters are stored (in which case the function calls setstate(​failbit)).

These conditions are tested in the order shown.315

If the function extracts no characters, it calls setstate(failbit) (which may throw ios_­base​::​​failure ([iostate.flags])).316

In any case, if n is greater than zero, it then stores a null character (using charT()) into the next successive location of the array.

[ Example:

#include <iostream>

int main() {
  using namespace std;
  const int line_buffer_size = 100;

  char buffer[line_buffer_size];
  int line_number = 0;
  while (cin.getline(buffer, line_buffer_size, '\n') || cin.gcount()) {
    int count = cin.gcount();
    if (cin.eof())
      cout << "Partial final line";       else if (cin.fail()) {
      cout << "Partial long line";
      cin.clear(cin.rdstate() & ~ios_base::failbit);
    } else {
      count--;                              cout << "Line " << ++line_number;
    }
    cout << " (" << count << " chars): " << buffer << endl;
  }
}

 — end example ]

basic_istream<charT, traits>& getline(char_type* s, streamsize n);

Returns: getline(s, n, widen('\n'))

basic_istream<charT, traits>& ignore(streamsize n = 1, int_type delim = traits::eof());

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and discards them. Characters are extracted until any of the following occurs:

• n != numeric_­limits<streamsize>​::​max() and n characters have been extracted so far

• end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), which may throw ios_­base​::​failure ([iostate.flags]));

• traits​::​eq_­int_­type(traits​::​to_­int_­type(c), delim) for the next available input character c (in which case c is extracted).

Remarks: The last condition will never occur if traits​::​eq_­int_­type(delim, traits​::​eof()).

int_type peek();

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, reads but does not extract the current input character.

Returns: traits​::​eof() if good() is false. Otherwise, returns rdbuf()->sgetc().

basic_istream<charT, traits>& read(char_type* s, streamsize n);

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s.317 Characters are extracted and stored until either of the following occurs:

• n characters are stored;

• end-of-file occurs on the input sequence (in which case the function calls setstate(failbit | eofbit), which may throw ios_­base​::​failure ([iostate.flags])).

streamsize readsome(char_type* s, streamsize n);

Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s. If rdbuf()->in_­avail() == -1, calls setstate(eofbit) (which may throw ios_­base​::​failure ([iostate.flags])), and extracts no characters;

• If rdbuf()->in_­avail() == 0, extracts no characters

• If rdbuf()->in_­avail() > 0, extracts min(rdbuf()->in_­avail(), n)).

Returns: The number of characters extracted.

basic_istream<charT, traits>& putback(char_type c);

Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit. After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. If rdbuf() is not null, calls rdbuf->sputbackc(). If rdbuf() is null, or if sputbackc() returns traits​::​eof(), calls setstate(badbit) (which may throw ios_­base​::​failure ([iostate.flags])). [ Note: This function extracts no characters, so the value returned by the next call to gcount() is 0.  — end note ]

basic_istream<charT, traits>& unget();

Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit. After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. If rdbuf() is not null, calls rdbuf()->sungetc(). If rdbuf() is null, or if sungetc() returns traits​::​eof(), calls setstate(badbit) (which may throw ios_­base​::​failure ([iostate.flags])). [ Note: This function extracts no characters, so the value returned by the next call to gcount() is 0.  — end note ]

int sync();

Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if rdbuf() is a null pointer, returns -1. Otherwise, calls rdbuf()->pubsync() and, if that function returns -1 calls setstate(badbit) (which may throw ios_­base​::​failure ([iostate.flags]), and returns -1. Otherwise, returns zero.

pos_type tellg();

Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount().

Returns: After constructing a sentry object, if fail() != false, returns pos_­type(-1) to indicate failure. Otherwise, returns rdbuf()->pubseekoff(0, cur, in).

basic_istream<charT, traits>& seekg(pos_type pos);

Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, it does not count the number of characters extracted, and it does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekpos(pos, ios_­base​::​in). In case of failure, the function calls setstate(failbit) (which may throw ios_­base​::​failure).

basic_istream<charT, traits>& seekg(off_type off, ios_base::seekdir dir);

Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, does not count the number of characters extracted, and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_­base​::​in). In case of failure, the function calls setstate(​failbit) (which may throw ios_­base​::​failure).

template <class charT, class traits> basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);

Effects: Behaves as an unformatted input function, except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to is.gcount(). After constructing a sentry object extracts characters as long as the next available character c is whitespace or until there are no more characters in the sequence. Whitespace characters are distinguished with the same criterion as used by sentry​::​sentry. If ws stops extracting characters because there are no more available it sets eofbit, but not failbit.

template <class charT, class traits, class T> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&& is, T&& x);

Effects: Equivalent to:

is >> std::forward<T>(x);
return is;

Remarks: This function shall not participate in overload resolution unless the expression is >> std​::​forward<T>(x) is well-formed.

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_iostream
    : public basic_istream<charT, traits>,
      public basic_ostream<charT, traits> {
  public:
    using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        explicit basic_iostream(basic_streambuf<charT, traits>* sb);

        virtual ~basic_iostream();

  protected:
        basic_iostream(const basic_iostream& rhs) = delete;
    basic_iostream(basic_iostream&& rhs);

        basic_iostream& operator=(const basic_iostream& rhs) = delete;
    basic_iostream& operator=(basic_iostream&& rhs);
    void swap(basic_iostream& rhs);
  };
}

The class template basic_­iostream inherits a number of functions that allow reading input and writing output to sequences controlled by a stream buffer.

explicit basic_iostream(basic_streambuf<charT, traits>* sb);

Postconditions: rdbuf() == sb and gcount() == 0.

basic_iostream(basic_iostream&& rhs);

Effects: Move constructs from the rvalue rhs by constructing the basic_­istream base class with move(rhs).

virtual ~basic_iostream();

Effects: Destroys an object of class basic_­iostream.

Remarks: Does not perform any operations on rdbuf().

basic_iostream& operator=(basic_iostream&& rhs);

Effects: As if by swap(rhs).

void swap(basic_iostream& rhs);

Effects: Calls basic_­istream<charT, traits>​::​swap(rhs).

The header <ostream> defines a type and several function signatures that control output to a stream buffer along with a function template that inserts into stream rvalues.

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_ostream : virtual public basic_ios<charT, traits> {
  public:
        using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        explicit basic_ostream(basic_streambuf<char_type, traits>* sb);
    virtual ~basic_ostream();

        class sentry;

        basic_ostream<charT, traits>&
      operator<<(basic_ostream<charT, traits>& (*pf)(basic_ostream<charT, traits>&));
    basic_ostream<charT, traits>&
      operator<<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
    basic_ostream<charT, traits>&
      operator<<(ios_base& (*pf)(ios_base&));

    basic_ostream<charT, traits>& operator<<(bool n);
    basic_ostream<charT, traits>& operator<<(short n);
    basic_ostream<charT, traits>& operator<<(unsigned short n);
    basic_ostream<charT, traits>& operator<<(int n);
    basic_ostream<charT, traits>& operator<<(unsigned int n);
    basic_ostream<charT, traits>& operator<<(long n);
    basic_ostream<charT, traits>& operator<<(unsigned long n);
    basic_ostream<charT, traits>& operator<<(long long n);
    basic_ostream<charT, traits>& operator<<(unsigned long long n);
    basic_ostream<charT, traits>& operator<<(float f);
    basic_ostream<charT, traits>& operator<<(double f);
    basic_ostream<charT, traits>& operator<<(long double f);

    basic_ostream<charT, traits>& operator<<(const void* p);
    basic_ostream<charT, traits>& operator<<(nullptr_t);
    basic_ostream<charT, traits>& operator<<(basic_streambuf<char_type, traits>* sb);

        basic_ostream<charT, traits>& put(char_type c);
    basic_ostream<charT, traits>& write(const char_type* s, streamsize n);

    basic_ostream<charT, traits>& flush();

        pos_type tellp();
    basic_ostream<charT, traits>& seekp(pos_type);
    basic_ostream<charT, traits>& seekp(off_type, ios_base::seekdir);

  protected:
        basic_ostream(const basic_ostream& rhs) = delete;
    basic_ostream(basic_ostream&& rhs);

        basic_ostream& operator=(const basic_ostream& rhs) = delete;
    basic_ostream& operator=(basic_ostream&& rhs);
    void swap(basic_ostream& rhs);
  };

    template<class charT, class traits>
    basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, charT);
  template<class charT, class traits>
    basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, char);
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char);

  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, signed char);
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, unsigned char);

  template<class charT, class traits>
    basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, const charT*);
  template<class charT, class traits>
    basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&, const char*);
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const char*);

  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const signed char*);
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, const unsigned char*);
}

The class template basic_­ostream defines a number of member function signatures that assist in formatting and writing output to output sequences controlled by a stream buffer.

Two groups of member function signatures share common properties: the formatted output functions (or inserters) and the unformatted output functions. Both groups of output functions generate (or insert) output characters by actions equivalent to calling rdbuf()->sputc(int_­type). They may use other public members of basic_­ostream except that they shall not invoke any virtual members of rdbuf() except overflow(), xsputn(), and sync().

If one of these called functions throws an exception, then unless explicitly noted otherwise the output function sets badbit in error state. If badbit is on in exceptions(), the output function rethrows the exception without completing its actions, otherwise it does not throw anything and treat as an error.

explicit basic_ostream(basic_streambuf<charT, traits>* sb);

Effects: Constructs an object of class basic_­ostream, initializing the base class subobject with basic_­ios<charT, traits>​::​init(sb) ([basic.ios.cons]).

Postconditions: rdbuf() == sb.

basic_ostream(basic_ostream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class and calling basic_­ios<charT, traits>​::​move(rhs) to initialize the base class.

virtual ~basic_ostream();

Effects: Destroys an object of class basic_­ostream.

Remarks: Does not perform any operations on rdbuf().

basic_ostream& operator=(basic_ostream&& rhs);

Effects: As if by swap(rhs).

void swap(basic_ostream& rhs);

Effects: Calls basic_­ios<charT, traits>​::​swap(rhs).

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_ostream<charT, traits>::sentry {
    bool ok_;   public:
    explicit sentry(basic_ostream<charT, traits>& os);
    ~sentry();
    explicit operator bool() const { return ok_; }

    sentry(const sentry&) = delete;
    sentry& operator=(const sentry&) = delete;
  };
}

The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.

explicit sentry(basic_ostream<charT, traits>& os);

If os.good() is nonzero, prepares for formatted or unformatted output. If os.tie() is not a null pointer, calls os.tie()->flush().318

If, after any preparation is completed, os.good() is true, ok_­ == true otherwise, ok_­ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_­base​::​​failure ([iostate.flags]))319

~sentry();

If (os.flags() & ios_­base​::​unitbuf) && !uncaught_­exceptions() && os.good() is true, calls os.rdbuf()->pubsync(). If that function returns -1, sets badbit in os.rdstate() without propagating an exception.

explicit operator bool() const;

Each seek member function begins execution by constructing an object of class sentry. It returns by destroying the sentry object.

pos_type tellp();

Returns: If fail() != false, returns pos_­type(-1) to indicate failure. Otherwise, returns rdbuf()->​pubseekoff(​0, cur, out).

basic_ostream<charT, traits>& seekp(pos_type pos);

Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_­base​::​out). In case of failure, the function calls setstate(failbit) (which may throw ios_­base​::​failure).

basic_ostream<charT, traits>& seekp(off_type off, ios_base::seekdir dir);

Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_­base​::​out). In case of failure, the function calls setstate(failbit) (which may throw ios_­base​::​failure).

Each formatted output function begins execution by constructing an object of class sentry. If this object returns true when converted to a value of type bool, the function endeavors to generate the requested output. If the generation fails, then the formatted output function does setstate(ios_­base​::​failbit), which might throw an exception. If an exception is thrown during output, then ios​::​badbit is turned on320 in *this's error state. If (exceptions()&badbit) != 0 then the exception is rethrown. Whether or not an exception is thrown, the sentry object is destroyed before leaving the formatted output function. If no exception is thrown, the result of the formatted output function is *this.

The descriptions of the individual formatted output functions describe how they perform output and do not mention the sentry object.

If a formatted output function of a stream os determines padding, it does so as follows. Given a charT character sequence seq where charT is the character type of the stream, if the length of seq is less than os.width(), then enough copies of os.fill() are added to this sequence as necessary to pad to a width of os.width() characters. If (os.flags() & ios_­base​::​adjustfield) == ios_­base​::​left is true, the fill characters are placed after the character sequence; otherwise, they are placed before the character sequence.

operator<<(bool val); operator<<(short val); operator<<(unsigned short val); operator<<(int val); operator<<(unsigned int val); operator<<(long val); operator<<(unsigned long val); operator<<(long long val); operator<<(unsigned long long val); operator<<(float val); operator<<(double val); operator<<(long double val); operator<<(const void* val);

Effects: The classes num_­get<> and num_­put<> handle locale-dependent numeric formatting and parsing. These inserter functions use the imbued locale value to perform numeric formatting. When val is of type bool, long, unsigned long, long long, unsigned long long, double, long double, or const void*, the formatting conversion occurs as if it performed the following code fragment:

bool failed = use_facet<
  num_put<charT, ostreambuf_iterator<charT, traits>>
    >(getloc()).put(*this, *this, fill(), val).failed();

When val is of type short the formatting conversion occurs as if it performed the following code fragment:

ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
bool failed = use_facet<
  num_put<charT, ostreambuf_iterator<charT, traits>>
    >(getloc()).put(*this, *this, fill(),
    baseflags == ios_base::oct || baseflags == ios_base::hex
      ? static_cast<long>(static_cast<unsigned short>(val))
      : static_cast<long>(val)).failed();

When val is of type int the formatting conversion occurs as if it performed the following code fragment:

ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
bool failed = use_facet<
  num_put<charT, ostreambuf_iterator<charT, traits>>
    >(getloc()).put(*this, *this, fill(),
    baseflags == ios_base::oct || baseflags == ios_base::hex
      ? static_cast<long>(static_cast<unsigned int>(val))
      : static_cast<long>(val)).failed();

When val is of type unsigned short or unsigned int the formatting conversion occurs as if it performed the following code fragment:

bool failed = use_facet<
  num_put<charT, ostreambuf_iterator<charT, traits>>
    >(getloc()).put(*this, *this, fill(),
      static_cast<unsigned long>(val)).failed();

When val is of type float the formatting conversion occurs as if it performed the following code fragment:

bool failed = use_facet<
  num_put<charT, ostreambuf_iterator<charT, traits>>
    >(getloc()).put(*this, *this, fill(),
      static_cast<double>(val)).failed();

The first argument provides an object of the ostreambuf_­iterator<> class which is an iterator for class basic_­ostream<>. It bypasses ostreams and uses streambufs directly. Class locale relies on these types as its interface to iostreams, since for flexibility it has been abstracted away from direct dependence on ostream. The second parameter is a reference to the base class subobject of type ios_­base. It provides formatting specifications such as field width, and a locale from which to obtain other facets. If failed is true then does setstate(badbit), which may throw an exception, and returns.

basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& (*pf)(basic_ostream<charT, traits>&));

basic_ostream<charT, traits>& operator<<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));

Effects: Calls pf(*this). This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).

basic_ostream<charT, traits>& operator<<(ios_base& (*pf)(ios_base&));

Effects: Calls pf(*this). This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).

basic_ostream<charT, traits>& operator<<(basic_streambuf<charT, traits>* sb);

Effects: Behaves as an unformatted output function. After the sentry object is constructed, if sb is null calls setstate(badbit) (which may throw ios_­base​::​failure).

Gets characters from sb and inserts them in *this. Characters are read from sb and inserted until any of the following occurs:

• end-of-file occurs on the input sequence;

• inserting in the output sequence fails (in which case the character to be inserted is not extracted);

• an exception occurs while getting a character from sb.

If the function inserts no characters, it calls setstate(failbit) (which may throw ios_­base​::​​failure ([iostate.flags])). If an exception was thrown while extracting a character, the function sets failbit in error state, and if failbit is on in exceptions() the caught exception is rethrown.

basic_ostream<charT, traits>& operator<<(nullptr_t);

Effects: Equivalent to:

return *this << s;

where s is an implementation-defined NTCTS.

template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, charT c); template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, char c); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, char c); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, signed char c); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, unsigned char c);

Effects: Behaves as a formatted output function of out. Constructs a character sequence seq. If c has type char and the character type of the stream is not char, then seq consists of out.widen(c); otherwise seq consists of c. Determines padding for seq as described in [ostream.formatted.reqmts]. Inserts seq into out. Calls os.width(0).

template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, const charT* s); template<class charT, class traits> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out, const char* s); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, const char* s); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, const signed char* s); template<class traits> basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out, const unsigned char* s);

Requires: s shall not be a null pointer.

Effects: Behaves like a formatted inserter (as described in [ostream.formatted.reqmts]) of out. Creates a character sequence seq of n characters starting at s, each widened using out.widen() ([basic.ios.members]), where n is the number that would be computed as if by:

• traits​::​length(s) for the overload where the first argument is of type basic_­ostream<charT, traits>& and the second is of type const charT*, and also for the overload where the first argument is of type basic_­ostream<char, traits>& and the second is of type const char*,

• char_­traits<char>​::​length(s) for the overload where the first argument is of type basic_­ostream<charT, traits>& and the second is of type const char*,

• traits​::​length(reinterpret_­cast<const char*>(s)) for the other two overloads.

Determines padding for seq as described in [ostream.formatted.reqmts]. Inserts seq into out. Calls width(0).

Each unformatted output function begins execution by constructing an object of class sentry. If this object returns true, while converting to a value of type bool, the function endeavors to generate the requested output. If an exception is thrown during output, then ios​::​badbit is turned on323 in *this's error state. If (exceptions() & badbit) != 0 then the exception is rethrown. In any case, the unformatted output function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified for the unformatted output function.

basic_ostream<charT, traits>& put(char_type c);

Effects: Behaves as an unformatted output function (as described above). After constructing a sentry object, inserts the character c, if possible.324

Otherwise, calls setstate(badbit) (which may throw ios_­base​::​failure ([iostate.flags])).

basic_ostream& write(const char_type* s, streamsize n);

Effects: Behaves as an unformatted output function (as described above). After constructing a sentry object, obtains characters to insert from successive locations of an array whose first element is designated by s.325 Characters are inserted until either of the following occurs:

• n characters are inserted;

• inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_­base​::​failure ([iostate.flags])).

basic_ostream& flush();

Effects: Behaves as an unformatted output function (as described above). If rdbuf() is not a null pointer, constructs a sentry object. If this object returns true when converted to a value of type bool the function calls rdbuf()->pubsync(). If that function returns -1 calls setstate(badbit) (which may throw ios_­base​::​failure ([iostate.flags])). Otherwise, if the sentry object returns false, does nothing.

template <class charT, class traits> basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);

Effects: Calls os.put(os.widen('\n')), then os.flush().

template <class charT, class traits> basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);

Effects: Inserts a null character into the output sequence: calls os.put(charT()).

template <class charT, class traits> basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);

Effects: Calls os.flush().

template <class charT, class traits, class T> basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&& os, const T& x);

Effects: As if by: os << x;

Remarks: This function shall not participate in overload resolution unless the expression os << x is well-formed.

The header <iomanip> defines several functions that support extractors and inserters that alter information maintained by class ios_­base and its derived classes.

unspecified resetiosflags(ios_base::fmtflags mask);

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> then the expression out << resetiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_­istream<charT, traits> then the expression in >> resetiosflags(​mask) behaves as if it called f(in, mask), where the function f is defined as:326

void f(ios_base& str, ios_base::fmtflags mask) {
    str.setf(ios_base::fmtflags(0), mask);
}

The expression out << resetiosflags(mask) shall have type basic_­ostream<charT, traits>& and value out. The expression in >> resetiosflags(mask) shall have type basic_­istream<charT, traits>& and value in.

unspecified setiosflags(ios_base::fmtflags mask);

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> then the expression out << setiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_­istream<charT, traits> then the expression in >> setiosflags(mask) behaves as if it called f(in, mask), where the function f is defined as:

void f(ios_base& str, ios_base::fmtflags mask) {
    str.setf(mask);
}

The expression out << setiosflags(mask) shall have type basic_­ostream<charT, traits>& and value out. The expression in >> setiosflags(mask) shall have type basic_­istream<charT,
traits>& and value in.

unspecified setbase(int base);

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> then the expression out << setbase(base) behaves as if it called f(out, base), or if in is an object of type basic_­istream<charT, traits> then the expression in >> setbase(base) behaves as if it called f(in, base), where the function f is defined as:

void f(ios_base& str, int base) {
    str.setf(base ==  8 ? ios_base::oct :
      base == 10 ? ios_base::dec :
      base == 16 ? ios_base::hex :
      ios_base::fmtflags(0), ios_base::basefield);
}

The expression out << setbase(base) shall have type basic_­ostream<charT, traits>& and value out. The expression in >> setbase(base) shall have type basic_­istream<charT, traits>& and value in.

unspecified setfill(char_type c);

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> and c has type charT then the expression out << setfill(c) behaves as if it called f(out, c), where the function f is defined as:

template<class charT, class traits>
void f(basic_ios<charT, traits>& str, charT c) {
    str.fill(c);
}

The expression out << setfill(c) shall have type basic_­ostream<charT, traits>& and value out.

unspecified setprecision(int n);

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> then the expression out << setprecision(n) behaves as if it called f(out, n), or if in is an object of type basic_­istream<charT, traits> then the expression in >> setprecision(n) behaves as if it called f(in, n), where the function f is defined as:

void f(ios_base& str, int n) {
    str.precision(n);
}

The expression out << setprecision(n) shall have type basic_­ostream<charT, traits>& and value out. The expression in >> setprecision(n) shall have type basic_­istream<charT, traits>& and value in.

unspecified setw(int n);

Returns: An object of unspecified type such that if out is an instance of basic_­ostream<charT, traits> then the expression out << setw(n) behaves as if it called f(out, n), or if in is an object of type basic_­istream<charT, traits> then the expression in >> setw(n) behaves as if it called f(in, n), where the function f is defined as:

void f(ios_base& str, int n) {
    str.width(n);
}

The expression out << setw(n) shall have type basic_­ostream<charT, traits>& and value out. The expression in >> setw(n) shall have type basic_­istream<charT, traits>& and value in.

The header <iomanip> defines several functions that support extractors and inserters that allow for the parsing and formatting of sequences and values for money and time.

template <class moneyT> unspecified get_money(moneyT& mon, bool intl = false);

Requires: The type moneyT shall be either long double or a specialization of the basic_­string template (Clause [strings]).

Returns: An object of unspecified type such that if in is an object of type basic_­istream<charT, traits> then the expression in >> get_­money(mon, intl) behaves as if it called f(in, mon, intl), where the function f is defined as:

template <class charT, class traits, class moneyT>
void f(basic_ios<charT, traits>& str, moneyT& mon, bool intl) {
  using Iter     = istreambuf_iterator<charT, traits>;
  using MoneyGet = money_get<charT, Iter>;

  ios_base::iostate err = ios_base::goodbit;
  const MoneyGet& mg = use_facet<MoneyGet>(str.getloc());

  mg.get(Iter(str.rdbuf()), Iter(), intl, str, err, mon);

  if (ios_base::goodbit != err)
    str.setstate(err);
}

The expression in >> get_­money(mon, intl) shall have type basic_­istream<charT, traits>& and value in.

template <class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);

Requires: The type moneyT shall be either long double or a specialization of the basic_­string template (Clause [strings]).

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> then the expression out << put_­money(mon, intl) behaves as a formatted output function that calls f(out, mon, intl), where the function f is defined as:

template <class charT, class traits, class moneyT>
void f(basic_ios<charT, traits>& str, const moneyT& mon, bool intl) {
  using Iter     = ostreambuf_iterator<charT, traits>;
  using MoneyPut = money_put<charT, Iter>;

  const MoneyPut& mp = use_facet<MoneyPut>(str.getloc());
  const Iter end = mp.put(Iter(str.rdbuf()), intl, str, str.fill(), mon);

  if (end.failed())
    str.setstate(ios::badbit);
}

The expression out << put_­money(mon, intl) shall have type basic_­ostream<charT, traits>& and value out.

template <class charT> unspecified get_time(struct tm* tmb, const charT* fmt);

Requires: The argument tmb shall be a valid pointer to an object of type struct tm. The argument fmt shall be a valid pointer to an array of objects of type charT with char_­traits<charT>​::​length(fmt) elements.

Returns: An object of unspecified type such that if in is an object of type basic_­istream<charT, traits> then the expression in >> get_­time(tmb, fmt) behaves as if it called f(in, tmb, fmt), where the function f is defined as:

template <class charT, class traits>
void f(basic_ios<charT, traits>& str, struct tm* tmb, const charT* fmt) {
  using Iter    = istreambuf_iterator<charT, traits>;
  using TimeGet = time_get<charT, Iter>;

  ios_base::iostate err = ios_base::goodbit;
  const TimeGet& tg = use_facet<TimeGet>(str.getloc());

  tg.get(Iter(str.rdbuf()), Iter(), str, err, tmb,
    fmt, fmt + traits::length(fmt));

  if (err != ios_base::goodbit)
    str.setstate(err);
}

The expression in >> get_­time(tmb, fmt) shall have type basic_­istream<charT, traits>& and value in.

template <class charT> unspecified put_time(const struct tm* tmb, const charT* fmt);

Requires: The argument tmb shall be a valid pointer to an object of type struct tm, and the argument fmt shall be a valid pointer to an array of objects of type charT with char_­traits<charT>​::​length(​fmt) elements.

Returns: An object of unspecified type such that if out is an object of type basic_­ostream<charT, traits> then the expression out << put_­time(tmb, fmt) behaves as if it called f(out, tmb, fmt), where the function f is defined as:

template <class charT, class traits>
void f(basic_ios<charT, traits>& str, const struct tm* tmb, const charT* fmt) {
  using Iter    = ostreambuf_iterator<charT, traits>;
  using TimePut = time_put<charT, Iter>;

  const TimePut& tp = use_facet<TimePut>(str.getloc());
  const Iter end = tp.put(Iter(str.rdbuf()), str, str.fill(), tmb,
    fmt, fmt + traits::length(fmt));

  if (end.failed())
    str.setstate(ios_base::badbit);
}

The expression out << put_­time(tmb, fmt) shall have type basic_­ostream<charT, traits>& and value out.

[ Note: Quoted manipulators provide string insertion and extraction of quoted strings (for example, XML and CSV formats). Quoted manipulators are useful in ensuring that the content of a string with embedded spaces remains unchanged if inserted and then extracted via stream I/O.  — end note ]

template <class charT> unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\')); template <class charT, class traits, class Allocator> unspecified quoted(const basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\')); template <class charT, class traits> unspecified quoted(basic_string_view<charT, traits> s, charT delim = charT('"'), charT escape = charT('\\'));

Returns: An object of unspecified type such that if out is an instance of basic_­ostream with member type char_­type the same as charT and with member type traits_­type, which in the second and third forms is the same as traits, then the expression out << quoted(s, delim, escape) behaves as a formatted output function of out. This forms a character sequence seq, initially consisting of the following elements:

• delim.

• Each character in s. If the character to be output is equal to escape or delim, as determined by traits_­type​::​eq, first output escape.

• delim.

Let x be the number of elements initially in seq. Then padding is determined for seq as described in [ostream.formatted.reqmts], seq is inserted as if by calling out.rdbuf()->sputn(seq, n), where n is the larger of out.width() and x, and out.width(0) is called. The expression out << quoted(s, delim, escape) shall have type basic_­ostream<charT, traits>& and value out.

template <class charT, class traits, class Allocator> unspecified quoted(basic_string<charT, traits, Allocator>& s, charT delim = charT('"'), charT escape = charT('\\'));

Returns: An object of unspecified type such that:

• If in is an instance of basic_­istream with member types char_­type and traits_­type the same as charT and traits, respectively, then the expression in >> quoted(s, delim, escape) behaves as if it extracts the following characters from in using operator>>(basic_­istream<charT, traits>&, charT&) ([istream.extractors]) which may throw ios_­base​::​failure ([ios::failure]):

  • If the first character extracted is equal to delim, as determined by traits_­type​::​eq, then:

    • Turn off the skipws flag.

    • s.clear()

    • Until an unescaped delim character is reached or !in, extract characters from in and append them to s, except that if an escape is reached, ignore it and append the next character to s.

    • Discard the final delim character.

    • Restore the skipws flag to its original value.

  • Otherwise, in >> s.

• If out is an instance of basic_­ostream with member types char_­type and traits_­type the same as charT and traits, respectively, then the expression out << quoted(s, delim, escape) behaves as specified for the const basic_­string<charT, traits, Allocator>& overload of the quoted function.

The expression in >> quoted(s, delim, escape) shall have type basic_­istream<charT, traits>& and value in. The expression out << quoted(s, delim, escape) shall have type basic_­ostream​<charT, traits>& and value out.

namespace std {
  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
    class basic_stringbuf;

  using stringbuf  = basic_stringbuf<char>;
  using wstringbuf = basic_stringbuf<wchar_t>;

  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
    class basic_istringstream;

  using istringstream  = basic_istringstream<char>;
  using wistringstream = basic_istringstream<wchar_t>;

  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
    class basic_ostringstream;
  using ostringstream  = basic_ostringstream<char>;
  using wostringstream = basic_ostringstream<wchar_t>;

  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
    class basic_stringstream;
  using stringstream  = basic_stringstream<char>;
  using wstringstream = basic_stringstream<wchar_t>;
}

The header <sstream> defines four class templates and eight types that associate stream buffers with objects of class basic_­string, as described in [string.classes].

namespace std {
  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
  class basic_stringbuf : public basic_streambuf<charT, traits> {
  public:
    using char_type      = charT;
    using int_type       = typename traits::int_type;
    using pos_type       = typename traits::pos_type;
    using off_type       = typename traits::off_type;
    using traits_type    = traits;
    using allocator_type = Allocator;

        explicit basic_stringbuf(
      ios_base::openmode which = ios_base::in | ios_base::out);
    explicit basic_stringbuf(
      const basic_string<charT, traits, Allocator>& str,
      ios_base::openmode which = ios_base::in | ios_base::out);
    basic_stringbuf(const basic_stringbuf& rhs) = delete;
    basic_stringbuf(basic_stringbuf&& rhs);

        basic_stringbuf& operator=(const basic_stringbuf& rhs) = delete;
    basic_stringbuf& operator=(basic_stringbuf&& rhs);
    void swap(basic_stringbuf& rhs);

        basic_string<charT, traits, Allocator> str() const;
    void str(const basic_string<charT, traits, Allocator>& s);

  protected:
        int_type underflow() override;
    int_type pbackfail(int_type c = traits::eof()) override;
    int_type overflow (int_type c = traits::eof()) override;
    basic_streambuf<charT, traits>* setbuf(charT*, streamsize) override;

    pos_type seekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;
    pos_type seekpos(pos_type sp,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;

  private:
    ios_base::openmode mode;    };

  template <class charT, class traits, class Allocator>
    void swap(basic_stringbuf<charT, traits, Allocator>& x,
              basic_stringbuf<charT, traits, Allocator>& y);
}

The class basic_­stringbuf is derived from basic_­streambuf to associate possibly the input sequence and possibly the output sequence with a sequence of arbitrary characters. The sequence can be initialized from, or made available as, an object of class basic_­string.

For the sake of exposition, the maintained data is presented here as:

• ios_­base​::​openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written.

explicit basic_stringbuf( ios_base::openmode which = ios_base::in | ios_base::out);

Effects: Constructs an object of class basic_­stringbuf, initializing the base class with basic_­streambuf() ([streambuf.cons]), and initializing mode with which.

Postconditions: str() == "".

explicit basic_stringbuf( const basic_string<charT, traits, Allocator>& s, ios_base::openmode which = ios_base::in | ios_base::out);

Effects: Constructs an object of class basic_­stringbuf, initializing the base class with basic_­streambuf() ([streambuf.cons]), and initializing mode with which. Then calls str(s).

basic_stringbuf(basic_stringbuf&& rhs);

Effects: Move constructs from the rvalue rhs. It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had. Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction. The openmode, locale and any other state of rhs is also copied.

Postconditions: Let rhs_­p refer to the state of rhs just prior to this construction and let rhs_­a refer to the state of rhs just after this construction.

• str() == rhs_­p.str()

• gptr() - eback() == rhs_­p.gptr() - rhs_­p.eback()

• egptr() - eback() == rhs_­p.egptr() - rhs_­p.eback()

• pptr() - pbase() == rhs_­p.pptr() - rhs_­p.pbase()

• epptr() - pbase() == rhs_­p.epptr() - rhs_­p.pbase()

• if (eback()) eback() != rhs_­a.eback()

• if (gptr()) gptr() != rhs_­a.gptr()

• if (egptr()) egptr() != rhs_­a.egptr()

• if (pbase()) pbase() != rhs_­a.pbase()

• if (pptr()) pptr() != rhs_­a.pptr()

• if (epptr()) epptr() != rhs_­a.epptr()

basic_stringbuf& operator=(basic_stringbuf&& rhs);

Effects: After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [stringbuf.cons]).

void swap(basic_stringbuf& rhs);

Effects: Exchanges the state of *this and rhs.

template <class charT, class traits, class Allocator> void swap(basic_stringbuf<charT, traits, Allocator>& x, basic_stringbuf<charT, traits, Allocator>& y);

Effects: As if by x.swap(y).

basic_string<charT, traits, Allocator> str() const;

Returns: A basic_­string object whose content is equal to the basic_­stringbuf underlying character sequence. If the basic_­stringbuf was created only in input mode, the resultant basic_­string contains the character sequence in the range [eback(), egptr()). If the basic_­stringbuf was created with which & ios_­base​::​out being nonzero then the resultant basic_­string contains the character sequence in the range [pbase(), high_­mark), where high_­mark represents the position one past the highest initialized character in the buffer. Characters can be initialized by writing to the stream, by constructing the basic_­stringbuf with a basic_­string, or by calling the str(basic_­string) member function. In the case of calling the str(basic_­string) member function, all characters initialized prior to the call are now considered uninitialized (except for those characters re-initialized by the new basic_­string). Otherwise the basic_­stringbuf has been created in neither input nor output mode and a zero length basic_­string is returned.

void str(const basic_string<charT, traits, Allocator>& s);

Effects: Copies the content of s into the basic_­stringbuf underlying character sequence and initializes the input and output sequences according to mode.

Postconditions: If mode & ios_­base​::​out is nonzero, pbase() points to the first underlying character and epptr() >= pbase() + s.size() holds; in addition, if mode & ios_­base​::​ate is nonzero, pptr() == pbase() + s.size() holds, otherwise pptr() == pbase() is true. If mode & ios_­base​::​in is nonzero, eback() points to the first underlying character, and both gptr() == eback() and egptr() == eback() + s.size() hold.

int_type underflow() override;

Returns: If the input sequence has a read position available, returns traits​::​to_­int_­type(*gptr()). Otherwise, returns traits​::​eof(). Any character in the underlying buffer which has been initialized is considered to be part of the input sequence.

int_type pbackfail(int_type c = traits::eof()) override;

Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if the input sequence has a putback position available, and if traits​::​eq(to_­char_­type(c), gptr()[-1]) returns true, assigns gptr() - 1 to gptr().

  Returns: c.

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if the input sequence has a putback position available, and if mode & ios_­base​::​out is nonzero, assigns c to *--gptr().

  Returns: c.

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns true and if the input sequence has a putback position available, assigns gptr() - 1 to gptr().

  Returns: traits​::​not_­eof(c).

Returns: traits​::​eof() to indicate failure.

Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.

int_type overflow(int_type c = traits::eof()) override;

Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if either the output sequence has a write position available or the function makes a write position available (as described below), the function calls sputc(c).

  Signals success by returning c.

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns true, there is no character to append.

  Signals success by returning a value other than traits​::​eof().

Remarks: The function can alter the number of write positions available as a result of any call.

Returns: traits​::​eof() to indicate failure.

The function can make a write position available only if (mode & ios_­base​::​out) != 0. To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus at least one additional write position. If (mode & ios_­base​::​in) != 0, the function alters the read end pointer egptr() to point just past the new write position.

pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;

Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 115.

Table

—

positioning

For a sequence to be positioned, if its next pointer (either gptr() or pptr()) is a null pointer and the new offset newoff is nonzero, the positioning operation fails. Otherwise, the function determines newoff as indicated in Table 116.

Table

—

values

If (newoff + off) < 0, or if newoff + off refers to an uninitialized character ([stringbuf.members]), the positioning operation fails. Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.

Returns: pos_­type(newoff), constructed from the resultant offset newoff (of type off_­type), that stores the resultant stream position, if possible. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_­type(off_­type(-1)).

pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;

Effects: Equivalent to seekoff(off_­type(sp), ios_­base​::​beg, which).

Returns: sp to indicate success, or pos_­type(off_­type(-1)) to indicate failure.

basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n);

Effects: implementation-defined, except that setbuf(0, 0) has no effect.

namespace std {
  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
  class basic_istringstream : public basic_istream<charT, traits> {
  public:
    using char_type      = charT;
    using int_type       = typename traits::int_type;
    using pos_type       = typename traits::pos_type;
    using off_type       = typename traits::off_type;
    using traits_type    = traits;
    using allocator_type = Allocator;

        explicit basic_istringstream(
      ios_base::openmode which = ios_base::in);
    explicit basic_istringstream(
      const basic_string<charT, traits, Allocator>& str,
      ios_base::openmode which = ios_base::in);
    basic_istringstream(const basic_istringstream& rhs) = delete;
    basic_istringstream(basic_istringstream&& rhs);

        basic_istringstream& operator=(const basic_istringstream& rhs) = delete;
    basic_istringstream& operator=(basic_istringstream&& rhs);
    void swap(basic_istringstream& rhs);

        basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

    basic_string<charT, traits, Allocator> str() const;
    void str(const basic_string<charT, traits, Allocator>& s);
  private:
    basic_stringbuf<charT, traits, Allocator> sb;   };

  template <class charT, class traits, class Allocator>
    void swap(basic_istringstream<charT, traits, Allocator>& x,
              basic_istringstream<charT, traits, Allocator>& y);
}

The class basic_­istringstream<charT, traits, Allocator> supports reading objects of class basic_­string<​charT, traits, Allocator>. It uses a basic_­stringbuf<charT, traits, Allocator> object to control the associated storage. For the sake of exposition, the maintained data is presented here as:

• sb, the stringbuf object.

explicit basic_istringstream(ios_base::openmode which = ios_base::in);

Effects: Constructs an object of class basic_­istringstream<charT, traits>, initializing the base class with basic_­istream(&sb) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(which | ios_­base​::​in)) ([stringbuf.cons]).

explicit basic_istringstream( const basic_string<charT, traits, Allocator>& str, ios_base::openmode which = ios_base::in);

Effects: Constructs an object of class basic_­istringstream<charT, traits>, initializing the base class with basic_­istream(&sb) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(str, which | ios_­base​::​in)) ([stringbuf.cons]).

basic_istringstream(basic_istringstream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_­stringbuf. Next basic_­istream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­stringbuf.

basic_istringstream& operator=(basic_istringstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

void swap(basic_istringstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_­istream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).

template <class charT, class traits, class Allocator> void swap(basic_istringstream<charT, traits, Allocator>& x, basic_istringstream<charT, traits, Allocator>& y);

Effects: As if by x.swap(y).

basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

Returns: const_­cast<basic_­stringbuf<charT, traits, Allocator>*>(&sb).

basic_string<charT, traits, Allocator> str() const;

void str(const basic_string<charT, traits, Allocator>& s);

Effects: Calls rdbuf()->str(s).

namespace std {
  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
  class basic_ostringstream : public basic_ostream<charT, traits> {
  public:
    using char_type      = charT;
    using int_type       = typename traits::int_type;
    using pos_type       = typename traits::pos_type;
    using off_type       = typename traits::off_type;
    using traits_type    = traits;
    using allocator_type = Allocator;

        explicit basic_ostringstream(
      ios_base::openmode which = ios_base::out);
    explicit basic_ostringstream(
      const basic_string<charT, traits, Allocator>& str,
      ios_base::openmode which = ios_base::out);
    basic_ostringstream(const basic_ostringstream& rhs) = delete;
    basic_ostringstream(basic_ostringstream&& rhs);

        basic_ostringstream& operator=(const basic_ostringstream& rhs) = delete;
    basic_ostringstream& operator=(basic_ostringstream&& rhs);
    void swap(basic_ostringstream& rhs);

        basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

    basic_string<charT, traits, Allocator> str() const;
    void str(const basic_string<charT, traits, Allocator>& s);
   private:
    basic_stringbuf<charT, traits, Allocator> sb;   };

  template <class charT, class traits, class Allocator>
    void swap(basic_ostringstream<charT, traits, Allocator>& x,
              basic_ostringstream<charT, traits, Allocator>& y);
}

The class basic_­ostringstream<charT, traits, Allocator> supports writing objects of class basic_­string<​charT, traits, Allocator>. It uses a basic_­stringbuf object to control the associated storage. For the sake of exposition, the maintained data is presented here as:

• sb, the stringbuf object.

explicit basic_ostringstream( ios_base::openmode which = ios_base::out);

Effects: Constructs an object of class basic_­ostringstream, initializing the base class with basic_­ostream(​&sb) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(which | ​ios_­base​::​out)) ([stringbuf.cons]).

explicit basic_ostringstream( const basic_string<charT, traits, Allocator>& str, ios_base::openmode which = ios_base::out);

Effects: Constructs an object of class basic_­ostringstream<charT, traits>, initializing the base class with basic_­ostream(&sb) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(str, which | ios_­base​::​out)) ([stringbuf.cons]).

basic_ostringstream(basic_ostringstream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_­stringbuf. Next basic_­ostream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­stringbuf.

basic_ostringstream& operator=(basic_ostringstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

void swap(basic_ostringstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_­ostream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).

template <class charT, class traits, class Allocator> void swap(basic_ostringstream<charT, traits, Allocator>& x, basic_ostringstream<charT, traits, Allocator>& y);

Effects: As if by x.swap(y).

basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

Returns: const_­cast<basic_­stringbuf<charT, traits, Allocator>*>(&sb).

basic_string<charT, traits, Allocator> str() const;

void str(const basic_string<charT, traits, Allocator>& s);

Effects: Calls rdbuf()->str(s).

namespace std {
  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
  class basic_stringstream : public basic_iostream<charT, traits> {
  public:
    using char_type      = charT;
    using int_type       = typename traits::int_type;
    using pos_type       = typename traits::pos_type;
    using off_type       = typename traits::off_type;
    using traits_type    = traits;
    using allocator_type = Allocator;

        explicit basic_stringstream(
      ios_base::openmode which = ios_base::out | ios_base::in);
    explicit basic_stringstream(
      const basic_string<charT, traits, Allocator>& str,
      ios_base::openmode which = ios_base::out | ios_base::in);
    basic_stringstream(const basic_stringstream& rhs) = delete;
    basic_stringstream(basic_stringstream&& rhs);

        basic_stringstream& operator=(const basic_stringstream& rhs) = delete;
    basic_stringstream& operator=(basic_stringstream&& rhs);
    void swap(basic_stringstream& rhs);

        basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
    basic_string<charT, traits, Allocator> str() const;
    void str(const basic_string<charT, traits, Allocator>& str);

  private:
    basic_stringbuf<charT, traits> sb;    };

  template <class charT, class traits, class Allocator>
    void swap(basic_stringstream<charT, traits, Allocator>& x,
              basic_stringstream<charT, traits, Allocator>& y);
}

The class template basic_­stringstream<charT, traits> supports reading and writing from objects of class basic_­string<charT, traits, Allocator>. It uses a basic_­stringbuf<charT, traits, Allocator> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as

• sb, the stringbuf object.

explicit basic_stringstream( ios_base::openmode which = ios_base::out | ios_base::in);

Effects: Constructs an object of class basic_­stringstream<charT, traits>, initializing the base class with basic_­iostream(&sb) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(which).

explicit basic_stringstream( const basic_string<charT, traits, Allocator>& str, ios_base::openmode which = ios_base::out | ios_base::in);

Effects: Constructs an object of class basic_­stringstream<charT, traits>, initializing the base class with basic_­iostream(&sb) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(str, which).

basic_stringstream(basic_stringstream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_­stringbuf. Next basic_­istream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­stringbuf.

basic_stringstream& operator=(basic_stringstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

void swap(basic_stringstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_­iostream<charT,traits>​::​swap(rhs) and sb.swap(rhs.sb).

template <class charT, class traits, class Allocator> void swap(basic_stringstream<charT, traits, Allocator>& x, basic_stringstream<charT, traits, Allocator>& y);

Effects: As if by x.swap(y).

basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

Returns: const_­cast<basic_­stringbuf<charT, traits, Allocator>*>(&sb)

basic_string<charT, traits, Allocator> str() const;

void str(const basic_string<charT, traits, Allocator>& str);

Effects: Calls rdbuf()->str(str).

namespace std {
  template <class charT, class traits = char_traits<charT>>
    class basic_filebuf;
  using filebuf  = basic_filebuf<char>;
  using wfilebuf = basic_filebuf<wchar_t>;

  template <class charT, class traits = char_traits<charT>>
    class basic_ifstream;
  using ifstream  = basic_ifstream<char>;
  using wifstream = basic_ifstream<wchar_t>;

  template <class charT, class traits = char_traits<charT>>
    class basic_ofstream;
  using ofstream  = basic_ofstream<char>;
  using wofstream = basic_ofstream<wchar_t>;

  template <class charT, class traits = char_traits<charT>>
    class basic_fstream;
  using fstream  = basic_fstream<char>;
  using wfstream = basic_fstream<wchar_t>;
}

The header <fstream> defines four class templates and eight types that associate stream buffers with files and assist reading and writing files.

[ Note: The class template basic_­filebuf treats a file as a source or sink of bytes. In an environment that uses a large character set, the file typically holds multibyte character sequences and the basic_­filebuf object converts those multibyte sequences into wide character sequences.  — end note ]

In this subclause, member functions taking arguments of const filesystem​::​path​::​value_­type* are only be provided on systems where filesystem​::​path​::​value_­type ([fs.class.path]) is not char. [ Note: These functions enable class path support for systems with a wide native path character type, such as wchar_­t.  — end note ]

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_filebuf : public basic_streambuf<charT, traits> {
  public:
    using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        basic_filebuf();
    basic_filebuf(const basic_filebuf& rhs) = delete;
    basic_filebuf(basic_filebuf&& rhs);
    virtual ~basic_filebuf();

        basic_filebuf& operator=(const basic_filebuf& rhs) = delete;
    basic_filebuf& operator=(basic_filebuf&& rhs);
    void swap(basic_filebuf& rhs);

        bool is_open() const;
    basic_filebuf* open(const char* s, ios_base::openmode mode);
    basic_filebuf* open(const filesystem::path::value_type* s,
                        ios_base::openmode mode);      basic_filebuf* open(const string& s,
                        ios_base::openmode mode);
    basic_filebuf* open(const filesystem::path& s,
                        ios_base::openmode mode);
    basic_filebuf* close();

  protected:
        streamsize showmanyc() override;
    int_type underflow() override;
    int_type uflow() override;
    int_type pbackfail(int_type c = traits::eof()) override;
    int_type overflow (int_type c = traits::eof()) override;

    basic_streambuf<charT, traits>* setbuf(char_type* s,
                                           streamsize n) override;
    pos_type seekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;
    pos_type seekpos(pos_type sp,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;
    int      sync() override;
    void     imbue(const locale& loc) override;
  };

  template <class charT, class traits>
    void swap(basic_filebuf<charT, traits>& x,
              basic_filebuf<charT, traits>& y);
}

The class basic_­filebuf<charT, traits> associates both the input sequence and the output sequence with a file.

The restrictions on reading and writing a sequence controlled by an object of class basic_­filebuf<charT, traits> are the same as for reading and writing with the C standard library FILEs.

In particular:

• If the file is not open for reading the input sequence cannot be read.

• If the file is not open for writing the output sequence cannot be written.

• A joint file position is maintained for both the input sequence and the output sequence.

An instance of basic_­filebuf behaves as described in [filebuf] provided traits​::​pos_­type is fpos<traits​::​​state_­type>. Otherwise the behavior is undefined.

In order to support file I/O and multibyte/wide character conversion, conversions are performed using members of a facet, referred to as a_­codecvt in following sections, obtained as if by

const codecvt<charT, char, typename traits::state_type>& a_codecvt =
  use_facet<codecvt<charT, char, typename traits::state_type>>(getloc());

basic_filebuf();

Effects: Constructs an object of class basic_­filebuf<charT, traits>, initializing the base class with basic_­streambuf<charT, traits>() ([streambuf.cons]).

Postconditions: is_­open() == false.

basic_filebuf(basic_filebuf&& rhs);

Effects: Move constructs from the rvalue rhs. It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had. Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction. Additionally *this references the file which rhs did before the construction, and rhs references no file after the construction. The openmode, locale and any other state of rhs is also copied.

Postconditions: Let rhs_­p refer to the state of rhs just prior to this construction and let rhs_­a refer to the state of rhs just after this construction.

• is_­open() == rhs_­p.is_­open()

• rhs_­a.is_­open() == false

• gptr() - eback() == rhs_­p.gptr() - rhs_­p.eback()

• egptr() - eback() == rhs_­p.egptr() - rhs_­p.eback()

• pptr() - pbase() == rhs_­p.pptr() - rhs_­p.pbase()

• epptr() - pbase() == rhs_­p.epptr() - rhs_­p.pbase()

• if (eback()) eback() != rhs_­a.eback()

• if (gptr()) gptr() != rhs_­a.gptr()

• if (egptr()) egptr() != rhs_­a.egptr()

• if (pbase()) pbase() != rhs_­a.pbase()

• if (pptr()) pptr() != rhs_­a.pptr()

• if (epptr()) epptr() != rhs_­a.epptr()

virtual ~basic_filebuf();

Effects: Destroys an object of class basic_­filebuf<charT, traits>. Calls close(). If an exception occurs during the destruction of the object, including the call to close(), the exception is caught but not rethrown (see [res.on.exception.handling]).

basic_filebuf& operator=(basic_filebuf&& rhs);

Effects: Calls close() then move assigns from rhs. After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [filebuf.cons]).

void swap(basic_filebuf& rhs);

Effects: Exchanges the state of *this and rhs.

template <class charT, class traits> void swap(basic_filebuf<charT, traits>& x, basic_filebuf<charT, traits>& y);

Effects: As if by x.swap(y).

bool is_open() const;

Returns: true if a previous call to open succeeded (returned a non-null value) and there has been no intervening call to close.

basic_filebuf* open(const char* s, ios_base::openmode mode); basic_filebuf* open(const filesystem::path::value_type* s, ios_base::openmode mode);

Effects: If is_­open() != false, returns a null pointer. Otherwise, initializes the filebuf as required. It then opens a file, if possible, whose name is the ntbs s (as if by calling fopen(s, modstr)). The ntbs modstr is determined from mode & ~ios_­base​::​ate as indicated in Table 117. If mode is not some combination of flags shown in the table then the open fails.

Table

— File open modes

If the open operation succeeds and (mode & ios_­base​::​ate) != 0, positions the file to the end (as if by calling fseek(file, 0, SEEK_­END)).327

If the repositioning operation fails, calls close() and returns a null pointer to indicate failure.

Returns: this if successful, a null pointer otherwise.

basic_filebuf* open(const string& s, ios_base::openmode mode); basic_filebuf* open(const filesystem::path& s, ios_base::openmode mode);

Returns: open(s.c_­str(), mode);

basic_filebuf* close();

Effects: If is_­open() == false, returns a null pointer. If a put area exists, calls overflow(traits​::​​eof()) to flush characters. If the last virtual member function called on *this (between underflow, overflow, seekoff, and seekpos) was overflow then calls a_­codecvt.unshift (possibly several times) to determine a termination sequence, inserts those characters and calls overflow(traits​::​​eof()) again. Finally, regardless of whether any of the preceding calls fails or throws an exception, the function closes the file (as if by calling fclose(file)). If any of the calls made by the function, including fclose, fails, close fails by returning a null pointer. If one of these calls throws an exception, the exception is caught and rethrown after closing the file.

Returns: this on success, a null pointer otherwise.

Postconditions: is_­open() == false.

streamsize showmanyc() override;

Remarks: An implementation might well provide an overriding definition for this function signature if it can determine that more characters can be read from the input sequence.

int_type underflow() override;

Effects: Behaves according to the description of basic_­streambuf<charT, traits>​::​underflow(), with the specialization that a sequence of characters is read from the input sequence as if by reading from the associated file into an internal buffer (extern_­buf) and then as if by doing:

char   extern_buf[XSIZE];
char*  extern_end;
charT  intern_buf[ISIZE];
charT* intern_end;
codecvt_base::result r =
  a_codecvt.in(state, extern_buf, extern_buf+XSIZE, extern_end,
               intern_buf, intern_buf+ISIZE, intern_end);

This shall be done in such a way that the class can recover the position (fpos_­t) corresponding to each character between intern_­buf and intern_­end. If the value of r indicates that a_­codecvt.in() ran out of space in intern_­buf, retry with a larger intern_­buf.

int_type uflow() override;

Effects: Behaves according to the description of basic_­streambuf<charT, traits>​::​uflow(), with the specialization that a sequence of characters is read from the input with the same method as used by underflow.

int_type pbackfail(int_type c = traits::eof()) override;

Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if the function makes a putback position available and if traits​::​eq(to_­char_­type(c), gptr()[-1]) returns true, decrements the next pointer for the input sequence, gptr().

  Returns: c.

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns false and if the function makes a putback position available and if the function is permitted to assign to the putback position, decrements the next pointer for the input sequence, and stores c there.

  Returns: c.

• If traits​::​eq_­int_­type(c, traits​::​eof()) returns true, and if either the input sequence has a putback position available or the function makes a putback position available, decrements the next pointer for the input sequence, gptr().

  Returns: traits​::​not_­eof(c).

Returns: traits​::​eof() to indicate failure.

Remarks: If is_­open() == false, the function always fails.

The function does not put back a character directly to the input sequence.

If the function can succeed in more than one of these ways, it is unspecified which way is chosen. The function can alter the number of putback positions available as a result of any call.

int_type overflow(int_type c = traits::eof()) override;

Effects: Behaves according to the description of basic_­streambuf<charT, traits>​::​overflow(c), except that the behavior of “consuming characters” is performed by first converting as if by:

charT* b = pbase();
charT* p = pptr();
charT* end;
char   xbuf[XSIZE];
char*  xbuf_end;
codecvt_base::result r =
  a_codecvt.out(state, b, p, end, xbuf, xbuf+XSIZE, xbuf_end);

and then

• If r == codecvt_­base​::​error then fail.

• If r == codecvt_­base​::​noconv then output characters from b up to (and not including) p.

• If r == codecvt_­base​::​partial then output to the file characters from xbuf up to xbuf_­end, and repeat using characters from end to p. If output fails, fail (without repeating).

• Otherwise output from xbuf to xbuf_­end, and fail if output fails. At this point if b != p and b == end (xbuf isn't large enough) then increase XSIZE and repeat from the beginning.

Returns: traits​::​not_­eof(c) to indicate success, and traits​::​eof() to indicate failure. If is_­open() == false, the function always fails.

basic_streambuf* setbuf(char_type* s, streamsize n) override;

Effects: If setbuf(0, 0) is called on a stream before any I/O has occurred on that stream, the stream becomes unbuffered. Otherwise the results are implementation-defined. “Unbuffered” means that pbase() and pptr() always return null and output to the file should appear as soon as possible.

pos_type seekoff(off_type off, ios_base::seekdir way, ios_base::openmode which = ios_base::in | ios_base::out) override;

Effects: Let width denote a_­codecvt.encoding(). If is_­open() == false, or off != 0 && width <= 0, then the positioning operation fails. Otherwise, if way != basic_­ios​::​cur or off != 0, and if the last operation was output, then update the output sequence and write any unshift sequence. Next, seek to the new position: if width > 0, call fseek(file, width * off, whence), otherwise call fseek(file, 0, whence).

Remarks: “The last operation was output” means either the last virtual operation was overflow or the put buffer is non-empty. “Write any unshift sequence” means, if width if less than zero then call a_­codecvt.unshift(state, xbuf, xbuf+XSIZE, xbuf_­end) and output the resulting unshift sequence. The function determines one of three values for the argument whence, of type int, as indicated in Table 118.

Table

—

effects

Returns: A newly constructed pos_­type object that stores the resultant stream position, if possible. If the positioning operation fails, or if the object cannot represent the resultant stream position, returns pos_­type(off_­type(-1)).

pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;

Alters the file position, if possible, to correspond to the position stored in sp (as described below). Altering the file position performs as follows:

1. 1.if (om & ios_­base​::​out) != 0, then update the output sequence and write any unshift sequence;

2. 2.set the file position to sp as if by a call to fsetpos;

3. 3.if (om & ios_­base​::​in) != 0, then update the input sequence;

where om is the open mode passed to the last call to open(). The operation fails if is_­open() returns false.

If sp is an invalid stream position, or if the function positions neither sequence, the positioning operation fails. If sp has not been obtained by a previous successful call to one of the positioning functions (seekoff or seekpos) on the same file the effects are undefined.

Returns: sp on success. Otherwise returns pos_­type(off_­type(-1)).

int sync() override;

Effects: If a put area exists, calls filebuf​::​overflow to write the characters to the file, then flushes the file as if by calling fflush(file). If a get area exists, the effect is implementation-defined.

void imbue(const locale& loc) override;

Requires: If the file is not positioned at its beginning and the encoding of the current locale as determined by a_­codecvt.encoding() is state-dependent ([locale.codecvt.virtuals]) then that facet is the same as the corresponding facet of loc.

Effects: Causes characters inserted or extracted after this call to be converted according to loc until another call of imbue.

Remarks: This may require reconversion of previously converted characters. This in turn may require the implementation to be able to reconstruct the original contents of the file.

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_ifstream : public basic_istream<charT, traits> {
  public:
    using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        basic_ifstream();
    explicit basic_ifstream(const char* s,
                            ios_base::openmode mode = ios_base::in);
    explicit basic_ifstream(const filesystem::path::value_type* s,
                            ios_base::openmode mode = ios_base::in);      explicit basic_ifstream(const string& s,
                            ios_base::openmode mode = ios_base::in);
    explicit basic_ifstream(const filesystem::path& s,
                            ios_base::openmode mode = ios_base::in);
    basic_ifstream(const basic_ifstream& rhs) = delete;
    basic_ifstream(basic_ifstream&& rhs);

        basic_ifstream& operator=(const basic_ifstream& rhs) = delete;
    basic_ifstream& operator=(basic_ifstream&& rhs);
    void swap(basic_ifstream& rhs);

        basic_filebuf<charT, traits>* rdbuf() const;

    bool is_open() const;
    void open(const char* s, ios_base::openmode mode = ios_base::in);
    void open(const filesystem::path::value_type* s,
              ios_base::openmode mode = ios_base::in);      void open(const string& s, ios_base::openmode mode = ios_base::in);
    void open(const filesystem::path& s, ios_base::openmode mode = ios_base::in);
    void close();
  private:
    basic_filebuf<charT, traits> sb;   };

  template <class charT, class traits>
    void swap(basic_ifstream<charT, traits>& x,
              basic_ifstream<charT, traits>& y);
}

The class basic_­ifstream<charT, traits> supports reading from named files. It uses a basic_­filebuf<​charT, traits> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as:

• sb, the filebuf object.

basic_ifstream();

Effects: Constructs an object of class basic_­ifstream<charT, traits>, initializing the base class with basic_­istream(&sb) and initializing sb with basic_­filebuf<charT, traits>()) ([istream.cons], [filebuf.cons]).

explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in); explicit basic_ifstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in);

Effects: Constructs an object of class basic_­ifstream, initializing the base class with basic_­istream(&sb) and initializing sb with basic_­filebuf<charT, traits>()) ([istream.cons], [filebuf.cons]), then calls rdbuf()->open(s, mode | ios_­base​::​in). If that function returns a null pointer, calls setstate(failbit).

explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in); explicit basic_ifstream(const filesystem::path& s, ios_base::openmode mode = ios_base::in);

Effects: The same as basic_­ifstream(s.c_­str(), mode).

basic_ifstream(basic_ifstream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_­filebuf. Next basic_­istream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­filebuf.

basic_ifstream& operator=(basic_ifstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

void swap(basic_ifstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_­istream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).

template <class charT, class traits> void swap(basic_ifstream<charT, traits>& x, basic_ifstream<charT, traits>& y);

Effects: As if by x.swap(y).

basic_filebuf<charT, traits>* rdbuf() const;

Returns: const_­cast<basic_­filebuf<charT, traits>*>(&sb).

bool is_open() const;

Returns: rdbuf()->is_­open().

void open(const char* s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in);

Effects: Calls rdbuf()->open(s, mode | ios_­base​::​in). If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).

void open(const string& s, ios_base::openmode mode = ios_base::in); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::in);

Effects: Calls open(s.c_­str(), mode).

void close();

Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_ofstream : public basic_ostream<charT, traits> {
  public:
    using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        basic_ofstream();
    explicit basic_ofstream(const char* s,
                            ios_base::openmode mode = ios_base::out);
    explicit basic_ofstream(const filesystem::path::value_type* s,
                            ios_base::openmode mode = ios_base::out);      explicit basic_ofstream(const string& s,
                            ios_base::openmode mode = ios_base::out);
    explicit basic_ofstream(const filesystem::path& s,
                            ios_base::openmode mode = ios_base::out);
    basic_ofstream(const basic_ofstream& rhs) = delete;
    basic_ofstream(basic_ofstream&& rhs);

        basic_ofstream& operator=(const basic_ofstream& rhs) = delete;
    basic_ofstream& operator=(basic_ofstream&& rhs);
    void swap(basic_ofstream& rhs);

        basic_filebuf<charT, traits>* rdbuf() const;

    bool is_open() const;
    void open(const char* s, ios_base::openmode mode = ios_base::out);
    void open(const filesystem::path::value_type* s,
              ios_base::openmode mode = ios_base::out);      void open(const string& s, ios_base::openmode mode = ios_base::out);
    void open(const filesystem::path& s, ios_base::openmode mode = ios_base::out);
    void close();
  private:
    basic_filebuf<charT, traits> sb;   };

  template <class charT, class traits>
    void swap(basic_ofstream<charT, traits>& x,
              basic_ofstream<charT, traits>& y);
}

The class basic_­ofstream<charT, traits> supports writing to named files. It uses a basic_­filebuf<​charT, traits> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as:

• sb, the filebuf object.

basic_ofstream();

Effects: Constructs an object of class basic_­ofstream<charT, traits>, initializing the base class with basic_­ostream(&sb) and initializing sb with basic_­filebuf<charT, traits>()) ([ostream.cons], [filebuf.cons]).

explicit basic_ofstream(const char* s, ios_base::openmode mode = ios_base::out); explicit basic_ofstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::out);

Effects: Constructs an object of class basic_­ofstream<charT, traits>, initializing the base class with basic_­ostream(&sb) and initializing sb with basic_­filebuf<charT, traits>()) ([ostream.cons], [filebuf.cons]), then calls rdbuf()->open(s, mode | ios_­base​::​out). If that function returns a null pointer, calls setstate(​failbit).

explicit basic_ofstream(const string& s, ios_base::openmode mode = ios_base::out); explicit basic_ofstream(const filesystem::path& s, ios_base::openmode mode = ios_base::out);

Effects: The same as basic_­ofstream(s.c_­str(), mode).

basic_ofstream(basic_ofstream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_­filebuf. Next basic_­ostream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­filebuf.

basic_ofstream& operator=(basic_ofstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

void swap(basic_ofstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_­ostream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).

template <class charT, class traits> void swap(basic_ofstream<charT, traits>& x, basic_ofstream<charT, traits>& y);

Effects: As if by x.swap(y).

basic_filebuf<charT, traits>* rdbuf() const;

Returns: const_­cast<basic_­filebuf<charT, traits>*>(&sb).

bool is_open() const;

Returns: rdbuf()->is_­open().

void open(const char* s, ios_base::openmode mode = ios_base::out); void open(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::out);

Effects: Calls rdbuf()->open(s, mode | ios_­base​::​out). If that function does not return a null pointer calls clear(), otherwise calls setstate(​failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).

void close();

Effects: Calls rdbuf()->close() and, if that function fails (returns a null pointer), calls setstate(​failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).

void open(const string& s, ios_base::openmode mode = ios_base::out); void open(const filesystem::path& s, ios_base::openmode mode = ios_base::out);

Effects: Calls open(s.c_­str(), mode).

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_fstream : public basic_iostream<charT, traits> {
  public:
    using char_type   = charT;
    using int_type    = typename traits::int_type;
    using pos_type    = typename traits::pos_type;
    using off_type    = typename traits::off_type;
    using traits_type = traits;

        basic_fstream();
    explicit basic_fstream(
      const char* s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    explicit basic_fstream(
      const std::filesystem::path::value_type* s,
      ios_base::openmode mode = ios_base::in|ios_base::out);      explicit basic_fstream(
      const string& s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    explicit basic_fstream(
      const filesystem::path& s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    basic_fstream(const basic_fstream& rhs) = delete;
    basic_fstream(basic_fstream&& rhs);

        basic_fstream& operator=(const basic_fstream& rhs) = delete;
    basic_fstream& operator=(basic_fstream&& rhs);
    void swap(basic_fstream& rhs);

        basic_filebuf<charT, traits>* rdbuf() const;
    bool is_open() const;
    void open(
      const char* s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    void open(
      const std::filesystem::path::value_type* s,
      ios_base::openmode mode = ios_base::in|ios_base::out);      void open(
      const string& s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    void open(
      const filesystem::path& s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    void close();

  private:
    basic_filebuf<charT, traits> sb;   };

  template <class charT, class traits>
    void swap(basic_fstream<charT, traits>& x,
              basic_fstream<charT, traits>& y);
}

The class template basic_­fstream<charT, traits> supports reading and writing from named files. It uses a basic_­filebuf<charT, traits> object to control the associated sequences. For the sake of exposition, the maintained data is presented here as:

• sb, the basic_­filebuf object.

basic_fstream();

Effects: Constructs an object of class basic_­fstream<charT, traits>, initializing the base class with basic_­iostream(&sb) and initializing sb with basic_­filebuf<charT, traits>().

explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: Constructs an object of class basic_­fstream<charT, traits>, initializing the base class with basic_­iostream(&sb) and initializing sb with basic_­filebuf<charT, traits>(). Then calls rdbuf()->open(s, mode). If that function returns a null pointer, calls setstate(failbit).

explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: The same as basic_­fstream(s.c_­str(), mode).

basic_fstream(basic_fstream&& rhs);

Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_­filebuf. Next basic_­istream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­filebuf.

basic_fstream& operator=(basic_fstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

void swap(basic_fstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_­iostream<charT,traits>​::​swap(rhs) and sb.swap(rhs.sb).

template <class charT, class traits> void swap(basic_fstream<charT, traits>& x, basic_fstream<charT, traits>& y);

Effects: As if by x.swap(y).

basic_filebuf<charT, traits>* rdbuf() const;

Returns: const_­cast<basic_­filebuf<charT, traits>*>(&sb).

bool is_open() const;

Returns: rdbuf()->is_­open().

void open( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: Calls rdbuf()->open(s, mode). If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).

void open( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: Calls open(s.c_­str(), mode).

void close();

Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).

This subclause describes operations on file systems and their components, such as paths, regular files, and directories.

Conformance is specified in terms of behavior. Ideal behavior is not always implementable, so the conformance subclauses take that into account.

Some behavior is specified by reference to POSIX ([fs.norm.ref]). How such behavior is actually implemented is unspecified. [ Note: This constitutes an “as if” rule allowing implementations to call native operating system or other APIs.  — end note ]

Implementations are encouraged to provide such behavior as it is defined by POSIX. Implementations shall document any behavior that differs from the behavior defined by POSIX. Implementations that do not support exact POSIX behavior are encouraged to provide behavior as close to POSIX 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 as specified in [fs.err.report]. [ Note: This allows users to rely on an exception being thrown or an error code being set when an implementation cannot provide any reasonable behavior. — 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 disks does not support hard links, symlinks, and many other features of more capable file systems, so implementations are not required to support those features on the FAT file system but instead are required to report an error as described above.  — end example ]

Some behavior is specified as being operating system dependent. The operating 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 underlying operating system.

Behavior is undefined if calls to functions provided by this subclause introduce a file system race.

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 herein, Requires: is not specified for the function. [ 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 ]

This subclause mentions commercially available operating systems for purposes of exposition.328

A path that unambiguously identifies the location of a file without reference to an additional starting location. The elements of a path that determine if it is absolute are operating system dependent.

A file within a file system that acts as a container of directory entries that contain information about other files, possibly including other directory files.

An object within a file system that holds user or system data. Files 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.

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

The name of a file. Filenames dot and dot-dot, consisting solely of one and two period characters respectively, have special meaning. The following characteristics of filenames are operating system dependent:

• The permitted characters. [ Example: Some operating systems prohibit the ASCII control characters (0x00 – 0x1F) in filenames.  — end example ]

• The maximum permitted length.

• Filenames that are not permitted.

• Filenames that have special meaning.

• Case awareness and sensitivity during path resolution.

• Special rules that may apply to file types other than regular files, such as directories.

A 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 ]

An object that associates a filename with a file. Several links can associate names with the same file.

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

⟨of a directory⟩ the directory that both contains a directory entry for the given directory and is represented by the filename dot-dot in the given directory.

⟨of other types of files⟩ a directory containing a directory entry for the file under discussion.

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. The maximum number of elements in the sequence is operating system dependent.

Pathname resolution is the operating system dependent mechanism for resolving a pathname to a particular file in a file hierarchy. There may be multiple pathnames that resolve to the same file. [ Example: POSIX specifies the mechanism in section 4.11, Pathname resolution.  — end example ]

A path that is not absolute, and as such, only unambiguously identifies the location of a file when resolved ([fs.def.pathres]) relative to an implied starting location. The elements of a path that determine if it is relative are operating system dependent. [ Note: Pathnames “.” and “..” are relative paths.  — end note ]

A type of file with the property that when the file is encountered during pathname resolution, a string stored by the file is used to modify the pathname resolution. [ Note: Symbolic links are often called symlinks. 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 ]

Functions with template parameters named EcharT shall not participate in overload resolution unless EcharT is one of the encoded character types.

Template parameters named InputIterator shall meet the input iterator requirements and shall have a value type that is one of the encoded character types.

[ Note: Use of an encoded character type implies an associated character set and encoding. Since signed char and unsigned char have no implied character set and encoding, they are not included as permitted types.  — end note ]

Unless otherwise specified, references to entities described in this subclause are assumed to be qualified with ​::​std​::​filesystem​::​.

namespace std::filesystem {
    class path;

    void swap(path& lhs, path& rhs) noexcept;
  size_t hash_value(const path& p) 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;
  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;

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

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

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

    class filesystem_error;

    class directory_entry;

    class directory_iterator;

    directory_iterator begin(directory_iterator iter) noexcept;
  directory_iterator end(const directory_iterator&) noexcept;

    class recursive_directory_iterator;

    recursive_directory_iterator begin(recursive_directory_iterator iter) noexcept;
  recursive_directory_iterator end(const recursive_directory_iterator&) noexcept;

    class file_status;

  struct space_info {
    uintmax_t capacity;
    uintmax_t free;
    uintmax_t available;
  };

    enum class file_type;
  enum class perms;
  enum class perm_options;
  enum class copy_options;
  enum class directory_options;

  using file_time_type = chrono::time_point<trivial-clock>;

    path absolute(const path& p, const path& base = current_path());

  path canonical(const path& p, const path& base = current_path());
  path canonical(const path& p, error_code& ec);
  path canonical(const path& p, const path& base, error_code& ec);

  void copy(const path& from, const path& to);
  void copy(const path& from, const path& to, error_code& ec) noexcept;
  void copy(const path& from, const path& to, copy_options options);
  void copy(const path& from, const path& to, copy_options options,
            error_code& ec) noexcept;

  bool copy_file(const path& from, const path& to);
  bool copy_file(const path& from, const path& to, error_code& ec) noexcept;
  bool copy_file(const path& from, const path& to, copy_options option);
  bool copy_file(const path& from, const path& to, copy_options option,
                 error_code& ec) noexcept;

  void copy_symlink(const path& existing_symlink, const path& new_symlink);
  void copy_symlink(const path& existing_symlink, const path& new_symlink,
                    error_code& ec) noexcept;

  bool create_directories(const path& p);
  bool create_directories(const path& p, error_code& ec) noexcept;

  bool create_directory(const path& p);
  bool create_directory(const path& p, error_code& ec) noexcept;

  bool create_directory(const path& p, const path& attributes);
  bool create_directory(const path& p, const path& attributes,
                        error_code& ec) noexcept;

  void create_directory_symlink(const path& to, const path& new_symlink);
  void create_directory_symlink(const path& to, const path& new_symlink,
                                error_code& ec) noexcept;

  void create_hard_link(const path& to, const path& new_hard_link);
  void create_hard_link(const path& to, const path& new_hard_link,
                        error_code& ec) noexcept;

  void create_symlink(const path& to, const path& new_symlink);
  void create_symlink(const path& to, const path& new_symlink,
                      error_code& ec) noexcept;

  path current_path();
  path current_path(error_code& ec);
  void current_path(const path& p);
  void current_path(const path& p, error_code& ec) noexcept;

  bool exists(file_status s) noexcept;
  bool exists(const path& p);
  bool exists(const path& p, error_code& ec) noexcept;

  bool equivalent(const path& p1, const path& p2);
  bool equivalent(const path& p1, const path& p2, error_code& ec) noexcept;

  uintmax_t file_size(const path& p);
  uintmax_t file_size(const path& p, error_code& ec) noexcept;

  uintmax_t hard_link_count(const path& p);
  uintmax_t hard_link_count(const path& p, error_code& ec) noexcept;

  bool is_block_file(file_status s) noexcept;
  bool is_block_file(const path& p);
  bool is_block_file(const path& p, error_code& ec) noexcept;

  bool is_character_file(file_status s) noexcept;
  bool is_character_file(const path& p);
  bool is_character_file(const path& p, error_code& ec) noexcept;

  bool is_directory(file_status s) noexcept;
  bool is_directory(const path& p);
  bool is_directory(const path& p, error_code& ec) noexcept;

  bool is_empty(const path& p);
  bool is_empty(const path& p, error_code& ec) noexcept;

  bool is_fifo(file_status s) noexcept;
  bool is_fifo(const path& p);
  bool is_fifo(const path& p, error_code& ec) noexcept;

  bool is_other(file_status s) noexcept;
  bool is_other(const path& p);
  bool is_other(const path& p, error_code& ec) noexcept;

  bool is_regular_file(file_status s) noexcept;
  bool is_regular_file(const path& p);
  bool is_regular_file(const path& p, error_code& ec) noexcept;

  bool is_socket(file_status s) noexcept;
  bool is_socket(const path& p);
  bool is_socket(const path& p, error_code& ec) noexcept;

  bool is_symlink(file_status s) noexcept;
  bool is_symlink(const path& p);
  bool is_symlink(const path& p, error_code& ec) noexcept;

  file_time_type last_write_time(const path& p);
  file_time_type last_write_time(const path& p, error_code& ec) noexcept;
  void last_write_time(const path& p, file_time_type new_time);
  void last_write_time(const path& p, file_time_type new_time,
                       error_code& ec) noexcept;

  void permissions(const path& p, perms prms, perm_options opts=perm_options::replace);
  void permissions(const path& p, perms prms, error_code& ec) noexcept;
  void permissions(const path& p, perms prms, perm_options opts, error_code& ec);

  path proximate(const path& p, error_code& ec);
  path proximate(const path& p, const path& base = current_path());
  path proximate(const path& p, const path& base, error_code& ec);

  path read_symlink(const path& p);
  path read_symlink(const path& p, error_code& ec);

  path relative(const path& p, error_code& ec);
  path relative(const path& p, const path& base = current_path());
  path relative(const path& p, const path& base, error_code& ec);

  bool remove(const path& p);
  bool remove(const path& p, error_code& ec) noexcept;

  uintmax_t remove_all(const path& p);
  uintmax_t remove_all(const path& p, error_code& ec) noexcept;

  void rename(const path& from, const path& to);
  void rename(const path& from, const path& to, error_code& ec) noexcept;

  void resize_file(const path& p, uintmax_t size);
  void resize_file(const path& p, uintmax_t size, error_code& ec) noexcept;

  space_info space(const path& p);
  space_info space(const path& p, error_code& ec) noexcept;

  file_status status(const path& p);
  file_status status(const path& p, error_code& ec) noexcept;

  bool status_known(file_status s) noexcept;

  file_status symlink_status(const path& p);
  file_status symlink_status(const path& p, error_code& ec) noexcept;

  path temp_directory_path();
  path temp_directory_path(error_code& ec);

  path weakly_canonical(const path& p);
  path weakly_canonical(const path& p, error_code& ec);
}

trivial-clock is an implementation-defined type that satisfies the TrivialClock requirements and that is capable of representing and measuring file time values. Implementations should ensure that the resolution and range of file_­time_­type reflect the operating system dependent resolution and range of file time values.

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 an appropriate response.

• 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 error_­code& handle 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 shall be thrown. For functions with a single path argument, that argument shall be passed to the filesystem_­error constructor with a single path argument. For functions with two path arguments, the first of these arguments shall be passed to the filesystem_­error constructor as the path1 argument, and the second shall be passed as the path2 argument. The filesystem_­error constructor's error_­code argument is set as appropriate for the specific operating system dependent error.

• Failure to allocate storage is reported by throwing an exception as described in [res.on.exception.handling].

• Destructors throw nothing.

Functions having an argument of type error_­code& handle 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 error_­code& argument is set as appropriate for the specific operating system dependent error. Otherwise, clear() is called on the error_­code& argument.

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 ]

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

• The generic format is acceptable as a native path.

• There is no need to distinguish between native format and generic format in function arguments.

• Paths for regular files and paths for directories share the same syntax.

 — 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 ]

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:

• char: The encoding is the native narrow encoding ([fs.def.native.encode]). The method of conversion, if any, is operating system dependent. [ Note: For POSIX-based operating systems path​::​value_­type is char so no conversion from char value type arguments or to char value type return values is performed. For Windows-based operating systems, the native narrow encoding is determined by calling a Windows API function.  — end note ] [ Note: This results in behavior identical to other C and C++ standard library functions that perform file operations using narrow character strings to identify paths. Changing this behavior would be surprising and error prone.  — end note ]

• wchar_­t: The encoding is the native wide encoding. The method of conversion is unspecified. [ Note: For Windows-based operating systems path​::​value_­type is wchar_­t so no conversion from wchar_­t value type arguments or to wchar_­t value type return values is performed.  — end note ]

• char16_­t: The encoding is UTF-16. The method of conversion is unspecified.

• char32_­t: The encoding is UTF-32. The method of conversion is unspecified.

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.

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

• basic_­string<EcharT, traits, Allocator>. A function argument const Source& source shall have an effective range [source.begin(), source.end()).

• basic_­string_­view<EcharT, traits>. A function argument const Source& source shall have an effective range [source.begin(), source.end()).

• A type meeting the input iterator requirements that iterates over a NTCTS. The value type shall be an encoded character type. A function argument const Source& source shall have an effective range [source, end) where end is the first iterator value with an element value equal to iterator_­traits<Source>​::​value_­type().

• A character array that after array-to-pointer decay results in a pointer to the start of a NTCTS. The value type shall be an encoded character type. A function argument const Source& source shall have an effective range [source, end) where end is the first iterator value with an element value equal to iterator_­traits<decay_­t<Source>>​::​value_­type().

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

• Source is a specialization of basic_­string or basic_­string_­view, or

• the qualified-id iterator_­traits<decay_­t<Source>>​::​value_­type is valid and denotes a possibly const encoded character type ([temp.deduct]).

[ 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.

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:

• If value_­type is wchar_­t, converts to the native wide encoding ([fs.def.native.encode]) using the codecvt<​wchar_­t, char, mbstate_­t> facet of loc.

• Otherwise a conversion is performed using the codecvt<wchar_­t, char, mbstate_­t> facet of loc, and then a second conversion to the current narrow 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.

[ 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 ]

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.

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:

• 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: 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));

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).

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:

• 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.

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.

[ 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.

int compare(const path& p) const noexcept;

Returns:

• A value less than 0, if native() for the elements of *this are lexicographically less than native() for the elements of p; otherwise,

• a value greater than 0, if native() for the elements of *this are lexicographically greater than native() for the elements of p; otherwise,

• 0.

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)).

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

• 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:

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 ]

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;

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,

• 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 minus the number that are dot-dot. If n<0, 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()).

[ 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 ]

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 root-name element, if present.

• The root-directory element, if present. [ Note: The generic format is required to ensure lexicographical comparison works correctly.  — end note ]

• Each successive filename element, if present.

• An empty element, if a trailing non-root directory-separator is present.

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.

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.

• Equality is determined by the path non-member operator==, which considers the two path's lexical representations only. [ Example: path("foo") == "bar" is never true.  — end example ]

• Equivalence is determined by the equivalent() non-member function, which determines if two paths resolve to the same file system entity. [ Example: equivalent("foo", "bar") will be true when both paths resolve to the same file.  — end example ]

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;

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;

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:

• If value_­type is char and the current native narrow encoding is UTF-8, return path(source) or path(first, last); otherwise,

• if value_­type is wchar_­t and the native wide encoding is UTF-16, or if value_­type is char16_­t or char32_­t, convert source or [first, last) to a temporary, tmp, of type string_­type and return path(tmp); otherwise,

• convert source or [first, last) to a temporary, tmp, of type u32string and return path(tmp).

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 ]

namespace std::filesystem {
  class filesystem_error : public system_error {
  public:
    filesystem_error(const string& what_arg, error_code ec);
    filesystem_error(const string& what_arg,
                     const path& p1, error_code ec);
    filesystem_error(const string& what_arg,
                     const path& p1, const path& p2, error_code ec);

    const path& path1() const noexcept;
    const path& path2() const noexcept;
    const char* what() const noexcept override;
  };
}

The class filesystem_­error defines the type of objects thrown as exceptions to report file system errors from functions described in this subclause.

Constructors are provided that store zero, one, or two paths associated with an error.

filesystem_error(const string& what_arg, error_code ec);

Postconditions: The postconditions of this function are indicated in Table 119.

Table

—

effects

filesystem_error(const string& what_arg, const path& p1, error_code ec);

Postconditions: The postconditions of this function are indicated in Table 120.

Table

—

effects

filesystem_error(const string& what_arg, const path& p1, const path& p2, error_code ec);

Postconditions: The postconditions of this function are indicated in Table 121.

Table

—

effects

const path& path1() const noexcept;

Returns: A reference to the copy of p1 stored by the constructor, or, if none, an empty path.

const path& path2() const noexcept;

Returns: A reference to the copy of p2 stored by the constructor, or, if none, an empty path.

const char* what() const noexcept override;

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.

This enum specifies constants used to identify the format of the character sequence, with the meanings listed in Table 122.

Table

— Enum

This enum class specifies constants used to identify file types, with the meanings listed in Table 123.

Table

— Enum class

The enum class type copy_­options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to control the semantics of copy operations. The constants are specified in option groups with the meanings listed in Table 124. Constant none is shown in each option group for purposes of exposition; implementations shall provide only a single definition.

Table

— Enum class

The enum class type perms is a bitmask type that specifies bitmask constants used to identify file permissions, with the meanings listed in Table 125.

Table

— Enum class

The enum class type perm_­options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to control the semantics of permissions operations, with the meanings listed in Table 126. The bitmask constants are bitmask elements. In Table 126 perm denotes a value of type perms passed to permissions.

Table

— Enum class

The enum class type directory_­options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to identify directory traversal options, with the meanings listed in Table 127.

Table

— Enum class

namespace std::filesystem {
  class file_status {
  public:
        file_status() noexcept : file_status(file_type::none) {}
    explicit file_status(file_type ft,
                         perms prms = perms::unknown) noexcept;
    file_status(const file_status&) noexcept = default;
    file_status(file_status&&) noexcept = default;
    ~file_status();

        file_status& operator=(const file_status&) noexcept = default;
    file_status& operator=(file_status&&) noexcept = default;

        void       type(file_type ft) noexcept;
    void       permissions(perms prms) noexcept;

        file_type  type() const noexcept;
    perms      permissions() const noexcept;
  };
}

An object of type file_­status stores information about the type and permissions of a file.

explicit file_status(file_type ft, perms prms = perms::unknown) noexcept;

Postconditions: type() == ft and permissions() == prms.

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 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.

void type(file_type ft) noexcept;

Postconditions: type() == ft.

void permissions(perms prms) noexcept;

Postconditions: permissions() == prms.

namespace std::filesystem {
  class directory_entry {
  public:
        directory_entry() noexcept = default;
    directory_entry(const directory_entry&) = default;
    directory_entry(directory_entry&&) noexcept = default;
    explicit directory_entry(const path& p);
    directory_entry(const path& p, error_code& ec);
    ~directory_entry();

        directory_entry& operator=(const directory_entry&) = default;
    directory_entry& operator=(directory_entry&&) noexcept = default;

        void assign(const path& p);
    void assign(const path& p, error_code& ec);
    void replace_filename(const path& p);
    void replace_filename(const path& p, error_code& ec);
    void refresh();
    void refresh(error_code& ec) noexcept;

        const path& path() const noexcept;
    operator const path&() const noexcept;
    bool exists() const;
    bool exists(error_code& ec) const noexcept;
    bool is_block_file() const;
    bool is_block_file(error_code& ec) const noexcept;
    bool is_character_file() const;
    bool is_character_file(error_code& ec) const noexcept;
    bool is_directory() const;
    bool is_directory(error_code& ec) const noexcept;
    bool is_fifo() const;
    bool is_fifo(error_code& ec) const noexcept;
    bool is_other() const;
    bool is_other(error_code& ec) const noexcept;
    bool is_regular_file() const;
    bool is_regular_file(error_code& ec) const noexcept;
    bool is_socket() const;
    bool is_socket(error_code& ec) const noexcept;
    bool is_symlink() const;
    bool is_symlink(error_code& ec) const noexcept;
    uintmax_t file_size() const;
    uintmax_t file_size(error_code& ec) const noexcept;
    uintmax_t hard_link_count() const;
    uintmax_t hard_link_count(error_code& ec) const noexcept;
    file_time_type last_write_time() const;
    file_time_type last_write_time(error_code& ec) const noexcept;
    file_status status() const;
    file_status status(error_code& ec) const noexcept;
    file_status symlink_status() const;
    file_status symlink_status(error_code& ec) const noexcept;

    bool operator< (const directory_entry& rhs) const noexcept;
    bool operator==(const directory_entry& rhs) const noexcept;
    bool operator!=(const directory_entry& rhs) const noexcept;
    bool operator<=(const directory_entry& rhs) const noexcept;
    bool operator> (const directory_entry& rhs) const noexcept;
    bool operator>=(const directory_entry& rhs) const noexcept;

  private:
    path pathobject;                     friend class directory_iterator;   };
}

A directory_­entry object stores a path object and may store additional objects for file attributes such as hard link count, status, symlink status, file size, and last write time.

Implementations are encouraged to store such additional file attributes during directory iteration if their values are available and storing the values would allow the implementation to eliminate file system accesses by directory_­entry observer functions ([fs.op.funcs]). Such stored file attribute values are said to be cached.

[ Note: For purposes of exposition, class directory_­iterator ([fs.class.directory_iterator]) is shown above as a friend of class directory_­entry. Friendship allows the directory_­iterator implementation to cache already available attribute values directly into a directory_­entry object without the cost of an unneeded call to refresh().  — end note ]

[ Example:

using namespace std::filesystem;

for (auto&& x : directory_iterator("."))
{
  std::cout << x.path() << " " << x.last_write_time() << std::endl;
}

for (auto&& x : directory_iterator("."))
{
  lengthy_function(x.path());    x.refresh();
  std::cout << x.path() << " " << x.last_write_time() << std::endl;
}

On implementations that do not cache the last write time, both loops will result in a potentially expensive call to the std​::​filesystem​::​last_­write_­time function. On implementations that do cache the last write time, the first loop will use the cached value and so will not result in a potentially expensive call to the std​::​filesystem​::​last_­write_­time function. The code is portable to any implementation, regardless of whether or not it employs caching.  — end example ]

explicit directory_entry(const path& p); directory_entry(const path& p, error_code& ec);

Effects: Constructs an object of type directory_­entry, then refresh() or refresh(ec), respectively.

Postconditions: path() == p if no error occurs, otherwise path() == std​::​filesystem​::​path().

void assign(const path& p); void assign(const path& p, error_code& ec);

Effects: Equivalent to pathobject = p, then refresh() or refresh(ec), respectively. If an error occurs, the values of any cached attributes are unspecified.

void replace_filename(const path& p); void replace_filename(const path& p, error_code& ec);

Effects: Equivalent to pathobject.replace_­filename(p), then refresh() or refresh(ec), respectively. If an error occurs, the values of any cached attributes are unspecified.

Throws: As specified in [fs.err.report].

void refresh(); void refresh(error_code& ec) noexcept;

Effects: Stores the current values of any cached attributes of the file p resolves to. If an error occurs, an error is reported ([fs.err.report]) and the values of any cached attributes are unspecified.

[ Note: Implementations of directory_­iterator ([fs.class.directory_iterator]) are prohibited from directly or indirectly calling the refresh function since it must access the external file system, and the objective of caching is to avoid unnecessary file system accesses.  — end note ]

Unqualified function names in the Returns: elements of the directory_­entry observers described below refer to members of the std​::​filesystem namespace.

const path& path() const noexcept; operator const path&() const noexcept;

bool exists() const; bool exists(error_code& ec) const noexcept;

Returns: exists(this->status()) or exists(this->status(), ec), respectively.

bool is_block_file() const; bool is_block_file(error_code& ec) const noexcept;

Returns: is_­block_­file(this->status()) or is_­block_­file(this->status(), ec), respectively.

bool is_character_file() const; bool is_character_file(error_code& ec) const noexcept;

Returns: is_­character_­file(this->status()) or is_­character_­file(this->status(), ec), respectively.

bool is_directory() const; bool is_directory(error_code& ec) const noexcept;

Returns: is_­directory(this->status()) or is_­directory(this->status(), ec), respectively.

bool is_fifo() const; bool is_fifo(error_code& ec) const noexcept;

Returns: is_­fifo(this->status()) or is_­fifo(this->status(), ec), respectively.

bool is_other() const; bool is_other(error_code& ec) const noexcept;

Returns: is_­other(this->status()) or is_­other(this->status(), ec), respectively.

bool is_regular_file() const; bool is_regular_file(error_code& ec) const noexcept;

Returns: is_­regular_­file(this->status()) or is_­regular_­file(this->status(), ec), respectively.

bool is_socket() const; bool is_socket(error_code& ec) const noexcept;

Returns: is_­socket(this->status()) or is_­socket(this->status(), ec), respectively.

bool is_symlink() const; bool is_symlink(error_code& ec) const noexcept;

Returns: is_­symlink(this->symlink_­status()) or is_­symlink(this->symlink_­status(), ec), respectively.

uintmax_t file_size() const; uintmax_t file_size(error_code& ec) const noexcept;

Returns: If cached, the file size attribute value. Otherwise, file_­size(path()) or file_­size(path(), ec), respectively.

uintmax_t hard_link_count() const; uintmax_t hard_link_count(error_code& ec) const noexcept;

Returns: If cached, the hard link count attribute value. Otherwise, hard_­link_­count(path()) or hard_­link_­count(path(), ec), respectively.

file_time_type last_write_time() const; file_time_type last_write_time(error_code& ec) const noexcept;

Returns: If cached, the last write time attribute value. Otherwise, last_­write_­time(path()) or last_­write_­time(path(), ec), respectively.

file_status status() const; file_status status(error_code& ec) const noexcept;

Returns: If cached, the status attribute value. Otherwise, status(path()) or status(path(), ec), respectively.

file_status symlink_status() const; file_status symlink_status(error_code& ec) const noexcept;

Returns: If cached, the symlink status attribute value. Otherwise, symlink_­status(path()) or symlink_­status(path(), ec), respectively.

bool operator==(const directory_entry& rhs) const noexcept;

Returns: pathobject == rhs.pathobject.

bool operator!=(const directory_entry& rhs) const noexcept;

Returns: pathobject != rhs.pathobject.

bool operator< (const directory_entry& rhs) const noexcept;

Returns: pathobject < rhs.pathobject.

bool operator<=(const directory_entry& rhs) const noexcept;

Returns: pathobject <= rhs.pathobject.

bool operator> (const directory_entry& rhs) const noexcept;

Returns: pathobject > rhs.pathobject.

bool operator>=(const directory_entry& rhs) const noexcept;

Returns: pathobject >= rhs.pathobject.

An object of type directory_­iterator provides an iterator for a sequence of directory_­entry elements representing the path and any cached attribute values ([fs.class.directory_entry]) for each file in a directory or in an implementation-defined directory-like file type. [ Note: For iteration into sub-directories, see class recursive_­directory_­iterator ([fs.class.rec.dir.itr]).  — end note ]

namespace std::filesystem {
  class directory_iterator {
  public:
    using iterator_category = input_iterator_tag;
    using value_type        = directory_entry;
    using difference_type   = ptrdiff_t;
    using pointer           = const directory_entry*;
    using reference         = const directory_entry&;

        directory_iterator() noexcept;
    explicit directory_iterator(const path& p);
    directory_iterator(const path& p, directory_options options);
    directory_iterator(const path& p, error_code& ec) noexcept;
    directory_iterator(const path& p, directory_options options,
                       error_code& ec) noexcept;
    directory_iterator(const directory_iterator& rhs);
    directory_iterator(directory_iterator&& rhs) noexcept;
    ~directory_iterator();

    directory_iterator& operator=(const directory_iterator& rhs);
    directory_iterator& operator=(directory_iterator&& rhs) noexcept;

    const directory_entry& operator*() const;
    const directory_entry* operator->() const;
    directory_iterator&    operator++();
    directory_iterator&    increment(error_code& ec) noexcept;

      };
}

If an iterator of type directory_­iterator reports an error or is advanced past the last directory element, that iterator shall become equal to the end iterator value. The directory_­iterator default constructor shall create an iterator equal to the end iterator value, and this shall be the only valid iterator for the end condition.

The end iterator is not dereferenceable.

Two end iterators are always equal. An end iterator shall not be equal to a non-end iterator.

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.

Constructors and non-const directory_­iterator member functions store the values of any cached attributes ([fs.class.directory_entry]) in the directory_­entry element returned by operator*(). directory_­iterator member functions shall not directly or indirectly call any directory_­entry refresh function. [ Note: The exact mechanism for storing cached attribute values is not exposed to users. For exposition, class directory_­iterator is shown in [fs.class.directory_entry] as a friend of class directory_­entry.  — end note ]

[ 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.  — end note ]

[ Note: 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 subsequently incrementing the iterator will ever result in an iterator referencing the removed or added directory entry. See POSIX readdir_­r.  — end note ]

directory_iterator() noexcept;

Effects: Constructs the end iterator.

explicit directory_iterator(const path& p); directory_iterator(const path& p, directory_options options); directory_iterator(const path& p, error_code& ec) noexcept; directory_iterator(const path& p, directory_options options, error_code& ec) noexcept;

Effects: For the directory that p resolves to, constructs an iterator for the first element in a sequence of directory_­entry elements representing the files in the directory, if any; otherwise the end iterator. However, if

(options & directory_options::skip_permission_denied) != directory_options::none

and construction encounters an error indicating that permission to access p is denied, constructs the end iterator and does not report an error.

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

directory_iterator(const directory_iterator& rhs); directory_iterator(directory_iterator&& rhs) noexcept;

Effects: Constructs an object of class directory_­iterator.

Postconditions: *this has the original value of rhs.

directory_iterator& operator=(const directory_iterator& rhs); directory_iterator& operator=(directory_iterator&& rhs) noexcept;

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

Postconditions: *this has the original value of rhs.

directory_iterator& operator++(); directory_iterator& increment(error_code& ec) noexcept;

Effects: As specified for the prefix increment operation of Input iterators.

These functions enable range access for directory_­iterator.

directory_iterator begin(directory_iterator iter) noexcept;

directory_iterator end(const directory_iterator&) noexcept;

Returns: directory_­iterator().

An object of type recursive_­directory_­iterator provides an iterator for a sequence of directory_­entry elements representing the files in a directory or in an implementation-defined directory-like file type, and its sub-directories.

namespace std::filesystem {
  class recursive_directory_iterator {
  public:
    using iterator_category = input_iterator_tag;
    using value_type        = directory_entry;
    using difference_type   = ptrdiff_t;
    using pointer           = const directory_entry*;
    using reference         = const directory_entry&;

        recursive_directory_iterator() noexcept;
    explicit recursive_directory_iterator(const path& p);
    recursive_directory_iterator(const path& p, directory_options options);
    recursive_directory_iterator(const path& p, directory_options options,
                                 error_code& ec) noexcept;
    recursive_directory_iterator(const path& p, error_code& ec) noexcept;
    recursive_directory_iterator(const recursive_directory_iterator& rhs);
    recursive_directory_iterator(recursive_directory_iterator&& rhs) noexcept;
    ~recursive_directory_iterator();

        directory_options  options() const;
    int                depth() const;
    bool               recursion_pending() const;

    const directory_entry& operator*() const;
    const directory_entry* operator->() const;

        recursive_directory_iterator&
      operator=(const recursive_directory_iterator& rhs);
    recursive_directory_iterator&
      operator=(recursive_directory_iterator&& rhs) noexcept;

    recursive_directory_iterator& operator++();
    recursive_directory_iterator& increment(error_code& ec) noexcept;

    void pop();
    void pop(error_code& ec);
    void disable_recursion_pending();

      };
}

Calling options, depth, recursion_­pending, pop or disable_­recursion_­pending on an iterator that is not dereferenceable results in undefined behavior.

The behavior of a recursive_­directory_­iterator is the same as a directory_­iterator unless otherwise specified.

[ Note: If the directory structure being iterated over contains cycles then the end iterator may be unreachable.  — end note ]

recursive_directory_iterator() noexcept;

Effects: Constructs the end iterator.

explicit recursive_directory_iterator(const path& p); recursive_directory_iterator(const path& p, directory_options options); recursive_directory_iterator(const path& p, directory_options options, error_code& ec) noexcept; recursive_directory_iterator(const path& p, error_code& ec) noexcept;

Effects: Constructs a iterator representing the first entry in the directory p resolves to, if any; otherwise, the end iterator. However, if

(options & directory_options::skip_permission_denied) != directory_options::none

and construction encounters an error indicating that permission to access p is denied, constructs the end iterator and does not report an error.

Postconditions: options() == options for the signatures with a directory_­options argument, otherwise options() == directory_­options​::​none.

[ 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 options as directory_­options​::​follow_­directory_­symlink  — end note ]

recursive_directory_iterator(const recursive_directory_iterator& rhs);

Effects: Constructs an object of class recursive_­directory_­iterator.

Postconditions:

• options() == rhs.options()

• depth() == rhs.depth()

• recursion_­pending() == rhs.recursion_­pending()

recursive_directory_iterator(recursive_directory_iterator&& rhs) noexcept;

Effects: Constructs an object of class recursive_­directory_­iterator.

Postconditions: options(), depth(), and recursion_­pending() have the values that rhs.options(), rhs.depth(), and rhs.recursion_­pending(), respectively, had before the function call.

recursive_directory_iterator& operator=(const recursive_directory_iterator& rhs);

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

Postconditions:

• options() == rhs.options()

• depth() == rhs.depth()

• recursion_­pending() == rhs.recursion_­pending()

recursive_directory_iterator& operator=(recursive_directory_iterator&& rhs) noexcept;

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

Postconditions: options(), depth(), and recursion_­pending() have the values that rhs.options(), rhs.depth(), and rhs.recursion_­pending(), respectively, had before the function call.

directory_options options() const;

Returns: The value of the argument passed to the constructor for the options parameter, if present, otherwise directory_­options​::​none.

int depth() const;

Returns: The current depth of the directory tree being traversed. [ Note: The initial directory is depth 0, its immediate subdirectories are depth 1, and so forth.  — end note ]

bool recursion_pending() const;

Returns: true if disable_­recursion_­pending() has not been called subsequent to the prior construction or increment operation, otherwise false.

recursive_directory_iterator& operator++(); recursive_directory_iterator& increment(error_code& ec) noexcept;

Effects: As specified for the prefix increment operation of Input iterators, except that:

• If there are no more entries at the current depth, then if depth() != 0 iteration over the parent directory resumes; otherwise *this = recursive_­directory_­iterator().

• Otherwise if

  recursion_pending() && is_directory((*this)->status()) &&
  (!is_symlink((*this)->symlink_status()) ||
   (options() & directory_options::follow_directory_symlink) != directory_options::none)

  then either directory (*this)->path() is recursively iterated into or, if

  (options() & directory_options::skip_permission_denied) != directory_options::none

  and an error occurs indicating that permission to access directory (*this)->path() is denied, then directory (*this)->path() is treated as an empty directory and no error is reported.

void pop(); void pop(error_code& ec);

Effects: If depth() == 0, set *this to recursive_­directory_­iterator(). Otherwise, cease iteration of the directory currently being iterated over, and continue iteration over the parent directory.

void disable_recursion_pending();

Postconditions: recursion_­pending() == false.

[ Note: disable_­recursion_­pending() is used to prevent unwanted recursion into a directory.  — end note ]

These functions enable use of recursive_­directory_­iterator with range-based for statements.

recursive_directory_iterator begin(recursive_directory_iterator iter) noexcept;

recursive_directory_iterator end(const recursive_directory_iterator&) noexcept;

Returns: recursive_­directory_­iterator().

Filesystem operation functions query or modify files, including directories, in external storage.

[ 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 operation function, no matter how apparently innocuous, may encounter an error; see [fs.err.report].  — end note ]

path absolute(const path& p); path absolute(const path& p, error_code& ec);

Effects: Composes an absolute path referencing the same file system location as p according to the operating system ([fs.conform.os]).

Returns: The composed path. The signature with argument ec returns path() if an error occurs.

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

[ Note: To resolve symlinks, or perform other sanitization which might require queries to secondary storage, such as hard disks, consider canonical ([fs.op.canonical]).  — end note ]

[ Note: Implementations are strongly encouraged to not query secondary storage, and not consider !exists(p) an error.  — end note ]

[ Example: For POSIX-based operating systems, absolute(p) is simply current_­path()/p. For Windows-based operating systems, absolute might have the same semantics as GetFullPathNameW.  — end example ]

path canonical(const path& p, const path& base = current_path()); path canonical(const path& p, error_code& ec); path canonical(const path& p, const path& base, error_code& ec);

Effects: Converts p, which must exist, to an absolute path that has no symbolic link, dot, or dot-dot elements in its pathname in the generic format.

Returns: A path that refers to the same file system object as absolute(p, base). For the overload without a base argument, base is current_­path(). Signatures with argument ec return path() if an error occurs.

Remarks: !exists(p) is an error.

void copy(const path& from, const path& to);

Effects: Equivalent to copy(from, to, copy_­options​::​none).

void copy(const path& from, const path& to, error_code& ec) noexcept;

Effects: Equivalent to copy(from, to, copy_­options​::​none, ec).

void copy(const path& from, const path& to, copy_options options); void copy(const path& from, const path& to, copy_options options, error_code& ec) noexcept;

Effects: Before the first use of f and t:

• If

  (options & copy_options::create_symlinks) != copy_options::none ||
  (options & copy_options::skip_symlinks) != copy_options::none

  then auto f = symlink_­status(from) and if needed auto t = symlink_­status(to).

• Otherwise, if

  (options & copy_options::copy_symlinks) != copy_options::none

  then auto f = symlink_­status(from) and if needed auto t = status(to).

• Otherwise, auto f = status(from) and if needed auto t = status(to).

Effects are then as follows:

• If f.type() or t.type() is an implementation-defined file type ([fs.enum.file_type]), then the effects are implementation-defined.

• Otherwise, an error is reported as specified in [fs.err.report] 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 an error as specified in [fs.err.report].

• 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 a symbolic link to the source file.

  • Otherwise, if (options & copy_­options​::​create_­hard_­links) != copy_­options​::​none, then create a hard link to the source file.

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

  • Otherwise, copy_­file(from, to, options).

• Otherwise, if

  is_directory(f) &&
  ((options & copy_options::recursive) != copy_options::none ||
   options == copy_options::none)

  then:

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

  • Then, iterate over the files in from, as if by

    for (const directory_entry& x : directory_iterator(from))
      copy(x.path(), to/x.path().filename(), options | copy_options::unspecified)

• Otherwise, for the signature with argument ec, ec.clear().

• Otherwise, no effects.

Remarks: For the signature with argument ec, any library functions called by the implementation shall have an error_­code argument if applicable.

[ Example: Given this directory structure:

/dir1
  file1
  file2
  dir2
    file3

Calling copy("/dir1", "/dir3") would result in:

/dir1
  file1
  file2
  dir2
    file3
/dir3
  file1
  file2

Alternatively, calling copy("/dir1", "/dir3", copy_­options​::​recursive) would result in:

/dir1
  file1
  file2
  dir2
    file3
/dir3
  file1
  file2
  dir2
    file3

 — end example ]

bool copy_file(const path& from, const path& to); bool copy_file(const path& from, const path& to, error_code& ec) noexcept;

Returns: copy_­file(from, to, copy_­options​::​none) or
copy_­file(from, to, copy_­options​::​none, ec), respectively.

bool copy_file(const path& from, const path& to, copy_options options); bool copy_file(const path& from, const path& to, copy_options options, error_code& ec) noexcept;

Effects: As follows:

• Report a file already exists error as specified in [fs.err.report] if:

  • !is_­regular_­file(from), or

  • exists(to) and !is_­regular_­file(to), or

  • exists(to) and equivalent(from, to), or

  • exists(to) and

    (options & (copy_options::skip_existing |
                copy_options::overwrite_existing |
                copy_options::update_existing)) == copy_options::none

• Otherwise, copy the contents and attributes of the file from resolves to, to the file to resolves to, if:

  • !exists(to), or

  • (options & copy_­options​::​overwrite_­existing) != copy_­options​::​none, or

  • (options & copy_­options​::​update_­existing) != copy_­options​::​none and from is more recent than to, determined as if by use of the last_­write_­time function ([fs.op.last_write_time]).

• Otherwise, no effects.

Returns: true if the from file was copied, otherwise false. The signature with argument ec returns false if an error occurs.

Complexity: At most one direct or indirect invocation of status(to).

void copy_symlink(const path& existing_symlink, const path& new_symlink); void copy_symlink(const path& existing_symlink, const path& new_symlink, error_code& ec) noexcept;

Effects: Equivalent to function(read_­symlink(existing_­symlink), new_­symlink) or
function(read_­symlink(existing_­symlink, ec), new_­symlink, ec), respectively, where in each case function is create_­symlink or create_­directory_­symlink as appropriate.

bool create_directories(const path& p); bool create_directories(const path& p, error_code& ec) noexcept;

Effects: Establishes the postcondition by calling create_­directory() for any element of p that does not exist.

Postconditions: is_­directory(p).

Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.

Complexity: O(n) where n is the number of elements of p that do not exist.

bool create_directory(const path& p); bool create_directory(const path& p, error_code& ec) noexcept;

Effects: Establishes the postcondition by attempting to create the directory p resolves to, as if by POSIX mkdir() with a second argument of static_­cast<int>(perms​::​all). Creation failure because p resolves to an existing directory shall not be treated as an error.

Postconditions: is_­directory(p).

Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.

bool create_directory(const path& p, const path& existing_p); bool create_directory(const path& p, const path& existing_p, error_code& ec) noexcept;

Effects: Establishes the postcondition by attempting to create the directory p resolves to, with attributes copied from directory existing_­p. The set of attributes copied is operating system dependent. Creation failure because p resolves to an existing directory shall not be treated as an error. [ Note: For POSIX-based operating systems, the attributes are those copied by native API stat(existing_­p.c_­str(), &attributes_­stat) followed by mkdir(p.c_­str(), attributes_­stat.st_­mode). For Windows-based operating systems, the attributes are those copied by native API CreateDirectoryExW(existing_­p.c_­str(), p.c_­str(), 0).  — end note ]

Postconditions: is_­directory(p).

Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.

void create_directory_symlink(const path& to, const path& new_symlink); void create_directory_symlink(const path& to, const path& new_symlink, error_code& ec) noexcept;

Effects: Establishes the postcondition, as if by POSIX symlink().

Postconditions: new_­symlink resolves to a symbolic link file that contains an unspecified representation of to.

[ Note: Some operating systems 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 (such as the FAT file system) do not support symbolic links regardless of the operating system.  — end note ]

void create_hard_link(const path& to, const path& new_hard_link); void create_hard_link(const path& to, const path& new_hard_link, error_code& ec) noexcept;

Effects: Establishes the postcondition, as if by POSIX link().

Postconditions:

• exists(to) && exists(new_­hard_­link) && equivalent(to, new_­hard_­link)

• The contents of the file or directory to resolves to are unchanged.

[ Note: Some operating systems do not support hard links at all or support them only for regular files. Some file systems (such as the FAT file system) do not support hard links regardless of the operating system. Some file systems limit the number of links per file.  — end note ]

void create_symlink(const path& to, const path& new_symlink); void create_symlink(const path& to, const path& new_symlink, error_code& ec) noexcept;

Effects: Establishes the postcondition, as if by POSIX symlink().

Postconditions: new_­symlink resolves to a symbolic link file that contains an unspecified representation of to.

[ Note: Some operating systems do not support symbolic links at all or support them only for regular files. Some file systems (such as the FAT file system) do not support symbolic links regardless of the operating system.  — end note ]

path current_path(); path current_path(error_code& ec);

Returns: The absolute path of the current working directory, whose pathname in the native format is obtained as if by POSIX getcwd(). The signature with argument ec returns path() if an error occurs.

Remarks: The current working directory is the directory, associated with the process, that is used as the starting location in pathname resolution for relative paths.

[ Note: The current_­path() name was chosen to emphasize that the returned value is a path, not just a single directory name.  — end note ]

[ Note: 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, error_code& ec) noexcept;

Effects: Establishes the postcondition, as if by POSIX chdir().

Postconditions: equivalent(p, current_­path()).

[ Note: The current path for many operating systems is a dangerous global state. It may be changed unexpectedly by a third-party or system library functions, or by another thread.  — end note ]

bool equivalent(const path& p1, const path& p2); bool equivalent(const path& p1, const path& p2, error_code& ec) noexcept;

Let s1 and s2 be file_­statuss, determined as if by status(p1) and status(p2), respectively.

Effects: Determines s1 and s2. If (!exists(s1) && !exists(s2)) || (is_­other(s1) && is_­other(s2)) an error is reported ([fs.err.report]).

Returns: true, if s1 == s2 and p1 and p2 resolve to the same file system entity, else false. The signature with argument ec returns false if an error occurs.

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

bool exists(file_status s) noexcept;

Returns: status_­known(s) && s.type() != file_­type​::​not_­found.

bool exists(const path& p); bool exists(const path& p, error_code& ec) noexcept;

Let s be a file_­status, determined as if by status(p) or status(p, ec), respectively.

Effects: The signature with argument ec calls ec.clear() if status_­known(s).

uintmax_t file_size(const path& p); uintmax_t file_size(const path& p, error_code& ec) noexcept;

Returns:

• If !exists(p) an error is reported ([fs.err.report]).

• Otherwise, if is_­regular_­file(p), the size in bytes of the file p resolves to, determined as if by the value of the POSIX stat structure member st_­size obtained as if by POSIX stat().

• Otherwise, the result is implementation-defined.

The signature with argument ec returns static_­cast<uintmax_­t>(-1) if an error occurs.

uintmax_t hard_link_count(const path& p); uintmax_t hard_link_count(const path& p, error_code& ec) noexcept;

Returns: The number of hard links for p. The signature with argument ec returns static_­cast<uintmax_­t>(-1) if an error occurs.

bool is_block_file(file_status s) noexcept;

Returns: s.type() == file_­type​::​block.

bool is_block_file(const path& p); bool is_block_file(const path& p, error_code& ec) noexcept;

Returns: is_­block_­file(status(p)) or is_­block_­file(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.

bool is_character_file(file_status s) noexcept;

Returns: s.type() == file_­type​::​character.

bool is_character_file(const path& p); bool is_character_file(const path& p, error_code& ec) noexcept;

Returns: is_­character_­file(status(p)) or is_­character_­file(status(p, ec)), respectively.
The signature with argument ec returns false if an error occurs.

bool is_directory(file_status s) noexcept;

Returns: s.type() == file_­type​::​directory.

bool is_directory(const path& p); bool is_directory(const path& p, error_code& ec) noexcept;

Returns: is_­directory(status(p)) or is_­directory(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.

bool is_empty(const path& p); bool is_empty(const path& p, error_code& ec) noexcept;

Effects:

• Determine file_­status s, as if by status(p) or status(p, ec), respectively.

• For the signature with argument ec, return false if an error occurred.

• Otherwise, if is_­directory(s):

  • Create a variable itr, as if by directory_­iterator itr(p) or directory_­iterator itr(p, ec), respectively.

  • For the signature with argument ec, return false if an error occurred.

  • Otherwise, return itr == directory_­iterator().

• Otherwise:

  • Determine uintmax_­t sz, as if by file_­size(p) or file_­size(p, ec), respectively.

  • For the signature with argument ec, return false if an error occurred.

  • Otherwise, return sz == 0.

bool is_fifo(file_status s) noexcept;

Returns: s.type() == file_­type​::​fifo.

bool is_fifo(const path& p); bool is_fifo(const path& p, error_code& ec) noexcept;

Returns: is_­fifo(status(p)) or is_­fifo(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.

bool is_other(file_status s) noexcept;

Returns: exists(s) && !is_­regular_­file(s) && !is_­directory(s) && !is_­symlink(s).

bool is_other(const path& p); bool is_other(const path& p, error_code& ec) noexcept;

Returns: is_­other(status(p)) or is_­other(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.

bool is_regular_file(file_status s) noexcept;

Returns: s.type() == file_­type​::​regular.

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, error_code& ec) noexcept;

Effects: Sets ec as if by status(p, ec). [ Note: file_­type​::​none, file_­type​::​not_­found and file_­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)). Returns false if an error occurs.

bool is_socket(file_status s) noexcept;

Returns: s.type() == file_­type​::​socket.

bool is_socket(const path& p); bool is_socket(const path& p, error_code& ec) noexcept;

Returns: is_­socket(status(p)) or is_­socket(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.

bool is_symlink(file_status s) noexcept;

Returns: s.type() == file_­type​::​symlink.

bool is_symlink(const path& p); bool is_symlink(const path& p, error_code& ec) noexcept;

Returns: is_­symlink(symlink_­status(p)) or is_­symlink(symlink_­status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.

file_time_type last_write_time(const path& p); file_time_type last_write_time(const path& p, error_code& ec) noexcept;

Returns: The time of last data modification of p, determined as if by the value of the POSIX stat structure member st_­mtime obtained as if by POSIX stat(). The signature with argument ec returns file_­time_­type​::​min() if an error occurs.

void last_write_time(const path& p, file_time_type new_time); void last_write_time(const path& p, file_time_type new_time, error_code& ec) noexcept;

Effects: Sets the time of last data modification of the file resolved to by p to new_­time, as if by POSIX futimens().

[ 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, perm_options opts=perm_options::replace); void permissions(const path& p, perms prms, error_code& ec) noexcept; void permissions(const path& p, perms prms, perm_options opts, error_code& ec);

Requires: Exactly one of the perm_­options constants replace, add, or remove is present in opts.

Remarks: The second signature behaves as if it had an additional parameter perm_­options opts with an argument of perm_­options​::​replace.

Effects: Applies the action specified by opts to the file p resolves to, or to file p itself if p is a symbolic link and perm_­options​::​nofollow is set in opts. The action is applied as if by POSIX fchmodat().

[ Note: Conceptually permissions are viewed as bits, but the actual implementation may use some other mechanism.  — end note ]

path proximate(const path& p, error_code& ec);

Returns: proximate(p, current_­path(), ec).

path proximate(const path& p, const path& base = current_path()); path proximate(const path& p, const path& base, error_code& ec);

Returns: For the first form:

weakly_canonical(p).lexically_proximate(weakly_canonical(base));

For the second form:

weakly_canonical(p, ec).lexically_proximate(weakly_canonical(base, ec));

or path() at the first error occurrence, if any.

path read_symlink(const path& p); path read_symlink(const path& p, error_code& ec);

Returns: If p resolves to a symbolic link, a path object containing the contents of that symbolic link. The signature with argument ec returns path() if an error occurs.

Throws: As specified in [fs.err.report]. [ Note: It is an error if p does not resolve to a symbolic link.  — end note ]

path relative(const path& p, error_code& ec);

Returns: relative(p, current_­path(), ec).

path relative(const path& p, const path& base = current_path()); path relative(const path& p, const path& base, error_code& ec);

Returns: For the first form:

weakly_canonical(p).lexically_relative(weakly_canonical(base));

For the second form:

weakly_canonical(p, ec).lexically_relative(weakly_canonical(base, ec));

or path() at the first error occurrence, if any.

bool remove(const path& p); bool remove(const path& p, error_code& ec) noexcept;

Effects: If exists(symlink_­status(p, ec)), the file p is removed as if by POSIX remove(). [ Note: A symbolic link is itself removed, rather than the file it resolves to.  — end note ]

Postconditions: !exists(symlink_­status(p)).

Returns: false if p did not exist, otherwise true. The signature with argument ec returns false if an error occurs.

uintmax_t remove_all(const path& p); uintmax_t remove_all(const path& p, error_code& ec) noexcept;

Effects: Recursively deletes the contents of p if it exists, then deletes file p itself, as if by POSIX remove(). [ Note: A symbolic link is itself removed, rather than the file it resolves to.  — end note ]

Postconditions: !exists(symlink_­status(p)).

Returns: The number of files removed. The signature with argument ec returns static_­cast< uintmax_­t>(-1) if an error occurs.

void rename(const path& old_p, const path& new_p); void rename(const path& old_p, const path& new_p, error_code& ec) noexcept;

Effects: Renames old_­p to new_­p, as if by POSIX rename().

[ Note:

• If old_­p and new_­p resolve to the same existing file, no action is taken.

• Otherwise, the rename may include the following effects:

  • if new_­p resolves to an existing non-directory file, new_­p is removed; otherwise,

  • if new_­p resolves to an existing directory, new_­p is removed if empty on POSIX compliant operating systems but may be an error on other operating systems.

A symbolic link is itself renamed, rather than the file it resolves to.  — end note ]

void resize_file(const path& p, uintmax_t new_size); void resize_file(const path& p, uintmax_t new_size, error_code& ec) noexcept;

Postconditions: file_­size(p) == new_­size.

Remarks: Achieves its postconditions as if by POSIX truncate().

space_info space(const path& p); space_info space(const path& p, error_code& ec) noexcept;

Returns: An object of type space_­info. The value of the space_­info object is determined as if by using POSIX statvfs to obtain a POSIX 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 static_­cast<uintmax_­t>(-1). For the signature with argument ec, all members are set to static_­cast<uintmax_­t>(-1) if an error occurs.

Remarks: The value of member space_­info​::​available is operating system dependent. [ Note: available may be less than free.  — end note ]

file_status status(const path& p);

Effects: As if:

error_code ec;
file_status result = status(p, ec);
if (result.type() == file_type::none)
  throw filesystem_error(implementation-supplied-message, p, ec);
return result;

Throws: filesystem_­error. [ Note: result values of file_­status(file_­type​::​not_­found) and file_­status(file_­type​::​unknown) are not considered failures and do not cause an exception to be thrown. — end note ]

file_status status(const path& p, error_code& ec) noexcept;

Effects: If possible, determines the attributes of the file p resolves to, as if by using POSIX stat() to obtain a POSIX struct 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(file_­type​::​none).  — end note ]

Let prms denote the result of (m & perms​::​mask), where m is determined as if by converting the st_­mode member of the obtained struct stat to the type perms.

Returns:

• If ec != error_­code():

  • If the specific error indicates that p cannot be resolved because some element of the path does not exist, returns file_­status(file_­type​::​not_­found).

  • Otherwise, if the specific error indicates that p can be resolved but the attributes cannot be determined, returns file_­status(file_­type​::​unknown).

  • Otherwise, returns file_­status(file_­type​::​none).

  [ 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 POSIX S_­ISREG, returns file_­status(file_­type​::​regular, prms). [ Note: file_­type​::​regular implies appropriate <fstream> operations would succeed, assuming no hardware, permission, access, or file system race errors. Lack of file_­type​::​regular does not necessarily imply <fstream> operations would fail on a directory.  — end note ]

  • Otherwise, if the attributes indicate a directory, as if by POSIX S_­ISDIR, returns file_­status(file_­type​::​directory, prms). [ Note: file_­type​::​directory implies that calling directory_­iterator(p) would succeed.  — end note ]

  • Otherwise, if the attributes indicate a block special file, as if by POSIX S_­ISBLK, returns file_­status(file_­type​::​block, prms).

  • Otherwise, if the attributes indicate a character special file, as if by POSIX S_­ISCHR, returns file_­status(file_­type​::​character, prms).

  • Otherwise, if the attributes indicate a fifo or pipe file, as if by POSIX S_­ISFIFO, returns file_­status(file_­type​::​fifo, prms).

  • Otherwise, if the attributes indicate a socket, as if by POSIX S_­ISSOCK, returns file_­status(file_­type​::​socket, prms).

  • Otherwise, if the attributes indicate an implementation-defined file type ([fs.enum.file_type]), returns file_­status(file_­type​::​A, prms), where A is the constant for the implementation-defined file type.

  • Otherwise, returns file_­status(file_­type​::​unknown, prms).

Remarks: If a symbolic link is encountered during pathname resolution, pathname resolution continues using the contents of the symbolic link.

file_status symlink_status(const path& p); file_status symlink_status(const path& p, error_code& ec) noexcept;

Effects: Same as status(), above, except that the attributes of p are determined as if by using POSIX lstat() to obtain a POSIX struct stat.

Let prms denote the result of (m & perms​::​mask), where m is determined as if by converting the st_­mode member of the obtained struct stat to the type perms.

Returns: Same as status(), above, except that if the attributes indicate a symbolic link, as if by POSIX S_­ISLNK, returns file_­status(file_­type​::​symlink, prms). The signature with argument ec returns file_­status(file_­type​::​none) if an error occurs.

Remarks: Pathname resolution terminates if p names a symbolic link.

path temp_directory_path(); path temp_directory_path(error_code& ec);

Returns: An unspecifed directory path suitable for temporary files. An error shall be reported if !exists(p) || !is_­directory(p), where p is the path to be returned. The signature with argument ec returns path() if an error occurs.

[ Example: For POSIX-based operating systems, an implementation might return the path supplied by the first environment variable found in the list TMPDIR, TMP, TEMP, TEMPDIR, or if none of these are found, "/tmp".

For Windows-based operating systems, an implementation might return the path reported by the Windows GetTempPath API function.  — end example ]

path weakly_canonical(const path& p); path weakly_canonical(const path& p, error_code& ec);

Returns: p with symlinks resolved and the result normalized.

Effects: Using status(p) or status(p, ec), respectively, to determine existence, return a path composed by operator/= from the result of calling canonical() without a base argument and with a path argument composed of the leading elements of p that exist, if any, followed by the elements of p that do not exist, if any. For the first form, canonical() is called without an error_­code argument. For the second form, canonical() is called with ec as an error_­code argument, and path() is returned at the first error occurrence, if any.

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

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