25 Localization library [localization]

25.4 Standard locale categories [locale.categories]

Each of the standard categories includes a family of facets. Some of these implement formatting or parsing of a datum, for use by standard or users' iostream operators << and >>, as members put() and get(), respectively. Each such member function takes an ios_­base& argument whose members flags(), precision(), and width(), specify the format of the corresponding datum ([ios.base]). Those functions which need to use other facets call its member getloc() to retrieve the locale imbued there. Formatting facets use the character argument fill to fill out the specified width where necessary.

The put() members make no provision for error reporting. (Any failures of the OutputIterator argument must be extracted from the returned iterator.) The get() members take an ios_­base​::​iostate& argument whose value they ignore, but set to ios_­base​::​failbit in case of a parse error.

Within this clause it is unspecified whether one virtual function calls another virtual function.

25.4.1 The ctype category [category.ctype]

namespace std {
  class ctype_base {
  public:
    using mask = see below;

    // numeric values are for exposition only.
    static const mask space  = 1 << 0;
    static const mask print  = 1 << 1;
    static const mask cntrl  = 1 << 2;
    static const mask upper  = 1 << 3;
    static const mask lower  = 1 << 4;
    static const mask alpha  = 1 << 5;
    static const mask digit  = 1 << 6;
    static const mask punct  = 1 << 7;
    static const mask xdigit = 1 << 8;
    static const mask blank  = 1 << 9;
    static const mask alnum  = alpha | digit;
    static const mask graph  = alnum | punct;
  };
}

The type mask is a bitmask type.

25.4.1.1 Class template ctype [locale.ctype]

namespace std {
  template <class charT>
    class ctype : public locale::facet, public ctype_base {
    public:
      using char_type = charT;

      explicit ctype(size_t refs = 0);

      bool         is(mask m, charT c) const;
      const charT* is(const charT* low, const charT* high, mask* vec) const;
      const charT* scan_is(mask m, const charT* low, const charT* high) const;
      const charT* scan_not(mask m, const charT* low, const charT* high) const;
      charT        toupper(charT c) const;
      const charT* toupper(charT* low, const charT* high) const;
      charT        tolower(charT c) const;
      const charT* tolower(charT* low, const charT* high) const;

      charT        widen(char c) const;
      const char*  widen(const char* low, const char* high, charT* to) const;
      char         narrow(charT c, char dfault) const;
      const charT* narrow(const charT* low, const charT* high, char dfault, char* to) const;

      static locale::id id;

    protected:
      ~ctype();
      virtual bool         do_is(mask m, charT c) const;
      virtual const charT* do_is(const charT* low, const charT* high, mask* vec) const;
      virtual const charT* do_scan_is(mask m, const charT* low, const charT* high) const;
      virtual const charT* do_scan_not(mask m, const charT* low, const charT* high) const;
      virtual charT        do_toupper(charT) const;
      virtual const charT* do_toupper(charT* low, const charT* high) const;
      virtual charT        do_tolower(charT) const;
      virtual const charT* do_tolower(charT* low, const charT* high) const;
      virtual charT        do_widen(char) const;
      virtual const char*  do_widen(const char* low, const char* high, charT* dest) const;
      virtual char         do_narrow(charT, char dfault) const;
      virtual const charT* do_narrow(const charT* low, const charT* high,
                                     char dfault, char* dest) const;
    };
}

Class ctype encapsulates the C library <cctype> features. istream members are required to use ctype<> for character classing during input parsing.

The specializations required in Table 69 ([locale.category]), namely ctype<char> and ctype<wchar_­t>, implement character classing appropriate to the implementation's native character set.

25.4.1.1.1 ctype members [locale.ctype.members]

bool is(mask m, charT c) const; const charT* is(const charT* low, const charT* high, mask* vec) const;

Returns: do_­is(m, c) or do_­is(low, high, vec).

const charT* scan_is(mask m, const charT* low, const charT* high) const;

Returns: do_­scan_­is(m, low, high).

const charT* scan_not(mask m, const charT* low, const charT* high) const;

Returns: do_­scan_­not(m, low, high).

charT toupper(charT) const; const charT* toupper(charT* low, const charT* high) const;

Returns: do_­toupper(c) or do_­toupper(low, high).

charT tolower(charT c) const; const charT* tolower(charT* low, const charT* high) const;

Returns: do_­tolower(c) or do_­tolower(low, high).

charT widen(char c) const; const char* widen(const char* low, const char* high, charT* to) const;

Returns: do_­widen(c) or do_­widen(low, high, to).

char narrow(charT c, char dfault) const; const charT* narrow(const charT* low, const charT* high, char dfault, char* to) const;

Returns: do_­narrow(c, dfault) or do_­narrow(low, high, dfault, to).

25.4.1.1.2 ctype virtual functions [locale.ctype.virtuals]

bool do_is(mask m, charT c) const; const charT* do_is(const charT* low, const charT* high, mask* vec) const;

Effects: Classifies a character or sequence of characters. For each argument character, identifies a value M of type ctype_­base​::​mask. The second form identifies a value M of type ctype_­base​::​mask for each *p where (low <= p && p < high), and places it into vec[p - low].

Returns: The first form returns the result of the expression (M & m) != 0; i.e., true if the character has the characteristics specified. The second form returns high.

const charT* do_scan_is(mask m, const charT* low, const charT* high) const;

Effects: Locates a character in a buffer that conforms to a classification m.

Returns: The smallest pointer p in the range [low, high) such that is(m, *p) would return true; otherwise, returns high.

const charT* do_scan_not(mask m, const charT* low, const charT* high) const;

Effects: Locates a character in a buffer that fails to conform to a classification m.

Returns: The smallest pointer p, if any, in the range [low, high) such that is(m, *p) would return false; otherwise, returns high.

charT do_toupper(charT c) const; const charT* do_toupper(charT* low, const charT* high) const;

Effects: Converts a character or characters to upper case. The second form replaces each character *p in the range [low, high) for which a corresponding upper-case character exists, with that character.

Returns: The first form returns the corresponding upper-case character if it is known to exist, or its argument if not. The second form returns high.

charT do_tolower(charT c) const; const charT* do_tolower(charT* low, const charT* high) const;

Effects: Converts a character or characters to lower case. The second form replaces each character *p in the range [low, high) and for which a corresponding lower-case character exists, with that character.

Returns: The first form returns the corresponding lower-case character if it is known to exist, or its argument if not. The second form returns high.

charT do_widen(char c) const; const char* do_widen(const char* low, const char* high, charT* dest) const;

Effects: Applies the simplest reasonable transformation from a char value or sequence of char values to the corresponding charT value or values.233 The only characters for which unique transformations are required are those in the basic source character set.

For any named ctype category with a ctype <charT> facet ctc and valid ctype_­base​::​mask value M, (ctc.​is(M, c) || !is(M, do_­widen(c)) ) is true.234

The second form transforms each character *p in the range [low, high), placing the result in dest[p - low].

Returns: The first form returns the transformed value. The second form returns high.

char do_narrow(charT c, char dfault) const; const charT* do_narrow(const charT* low, const charT* high, char dfault, char* dest) const;

Effects: Applies the simplest reasonable transformation from a charT value or sequence of charT values to the corresponding char value or values.

For any character c in the basic source character set the transformation is such that

do_widen(do_narrow(c, 0)) == c

For any named ctype category with a ctype<char> facet ctc however, and ctype_­base​::​mask value M,

(is(M, c) || !ctc.is(M, do_narrow(c, dfault)) )

is true (unless do_­narrow returns dfault). In addition, for any digit character c, the expression (do_­narrow(c, dfault) - '0') evaluates to the digit value of the character. The second form transforms each character *p in the range [low, high), placing the result (or dfault if no simple transformation is readily available) in dest[p - low].

Returns: The first form returns the transformed value; or dfault if no mapping is readily available. The second form returns high.

The char argument of do_­widen is intended to accept values derived from character literals for conversion to the locale's encoding.

In other words, the transformed character is not a member of any character classification that c is not also a member of.

25.4.1.2 Class template ctype_­byname [locale.ctype.byname]

namespace std {
  template <class charT>
    class ctype_byname : public ctype<charT> {
    public:
      using mask = typename ctype<charT>::mask;
      explicit ctype_byname(const char*, size_t refs = 0);
      explicit ctype_byname(const string&, size_t refs = 0);

    protected:
      ~ctype_byname();
    };
}

25.4.1.3 ctype specializations [facet.ctype.special]

namespace std {
  template <>
    class ctype<char> : public locale::facet, public ctype_base {
    public:
      using char_type = char;

      explicit ctype(const mask* tab = nullptr, bool del = false, size_t refs = 0);

      bool is(mask m, char c) const;
      const char* is(const char* low, const char* high, mask* vec) const;
      const char* scan_is (mask m, const char* low, const char* high) const;
      const char* scan_not(mask m, const char* low, const char* high) const;

      char        toupper(char c) const;
      const char* toupper(char* low, const char* high) const;
      char        tolower(char c) const;
      const char* tolower(char* low, const char* high) const;

      char  widen(char c) const;
      const char* widen(const char* low, const char* high, char* to) const;
      char  narrow(char c, char dfault) const;
      const char* narrow(const char* low, const char* high, char dfault, char* to) const;

      static locale::id id;
      static const size_t table_size = implementation-defined;

      const mask* table() const noexcept;
      static const mask* classic_table() noexcept;

    protected:
      ~ctype();
      virtual char        do_toupper(char c) const;
      virtual const char* do_toupper(char* low, const char* high) const;
      virtual char        do_tolower(char c) const;
      virtual const char* do_tolower(char* low, const char* high) const;

      virtual char        do_widen(char c) const;
      virtual const char* do_widen(const char* low, const char* high, char* to) const;
      virtual char        do_narrow(char c, char dfault) const;
      virtual const char* do_narrow(const char* low, const char* high,
                                    char dfault, char* to) const;
    };
}

A specialization ctype<char> is provided so that the member functions on type char can be implemented inline.235 The implementation-defined value of member table_­size is at least 256.

Only the char (not unsigned char and signed char) form is provided. The specialization is specified in the standard, and not left as an implementation detail, because it affects the derivation interface for ctype<char>.

25.4.1.3.1 ctype<char> destructor [facet.ctype.char.dtor]

~ctype();

Effects: If the constructor's first argument was nonzero, and its second argument was true, does delete [] table().

25.4.1.3.2 ctype<char> members [facet.ctype.char.members]

In the following member descriptions, for unsigned char values v where v >= table_­size, table()[v] is assumed to have an implementation-specific value (possibly different for each such value v) without performing the array lookup.

explicit ctype(const mask* tbl = nullptr, bool del = false, size_t refs = 0);

Requires: tbl either 0 or an array of at least table_­size elements.

Effects: Passes its refs argument to its base class constructor.

bool is(mask m, char c) const; const char* is(const char* low, const char* high, mask* vec) const;

Effects: The second form, for all *p in the range [low, high), assigns into vec[p - low] the value table()[(unsigned char)*p].

Returns: The first form returns table()[(unsigned char)c] & m; the second form returns high.

const char* scan_is(mask m, const char* low, const char* high) const;

Returns: The smallest p in the range [low, high) such that

table()[(unsigned char) *p] & m

is true.

const char* scan_not(mask m, const char* low, const char* high) const;

Returns: The smallest p in the range [low, high) such that

table()[(unsigned char) *p] & m

is false.

char toupper(char c) const; const char* toupper(char* low, const char* high) const;

Returns: do_­toupper(c) or do_­toupper(low, high), respectively.

char tolower(char c) const; const char* tolower(char* low, const char* high) const;

Returns: do_­tolower(c) or do_­tolower(low, high), respectively.

char widen(char c) const; const char* widen(const char* low, const char* high, char* to) const;

Returns: do_­widen(c) or do_­widen(low, high, to), respectively.

char narrow(char c, char dfault) const; const char* narrow(const char* low, const char* high, char dfault, char* to) const;

Returns: do_­narrow(c, dfault) or do_­narrow(low, high, dfault, to), respectively.

const mask* table() const noexcept;

Returns: The first constructor argument, if it was nonzero, otherwise classic_­table().

25.4.1.3.3 ctype<char> static members [facet.ctype.char.statics]

static const mask* classic_table() noexcept;

Returns: A pointer to the initial element of an array of size table_­size which represents the classifications of characters in the "C" locale.

25.4.1.3.4 ctype<char> virtual functions [facet.ctype.char.virtuals]

char        do_toupper(char) const;
const char* do_toupper(char* low, const char* high) const;
char        do_tolower(char) const;
const char* do_tolower(char* low, const char* high) const;

virtual char        do_widen(char c) const;
virtual const char* do_widen(const char* low, const char* high, char* to) const;
virtual char        do_narrow(char c, char dfault) const;
virtual const char* do_narrow(const char* low, const char* high,
                              char dfault, char* to) const;

These functions are described identically as those members of the same name in the ctype class template.

25.4.1.4 Class template codecvt [locale.codecvt]

namespace std {
  class codecvt_base {
  public:
    enum result { ok, partial, error, noconv };
  };

  template <class internT, class externT, class stateT>
    class codecvt : public locale::facet, public codecvt_base {
    public:
      using intern_type = internT;
      using extern_type = externT;
      using state_type  = stateT;

      explicit codecvt(size_t refs = 0);

      result out(
          stateT& state,
          const internT* from, const internT* from_end, const internT*& from_next,
                externT*   to,       externT*   to_end,       externT*&   to_next) const;

      result unshift(
          stateT& state,
                externT*    to,      externT*   to_end,       externT*&   to_next) const;

      result in(
          stateT& state,
          const externT* from, const externT* from_end, const externT*& from_next,
                internT*   to,       internT*   to_end,       internT*&   to_next) const;

      int encoding() const noexcept;
      bool always_noconv() const noexcept;
      int length(stateT&, const externT* from, const externT* end, size_t max) const;
      int max_length() const noexcept;

      static locale::id id;

    protected:
      ~codecvt();
      virtual result do_out(
          stateT& state,
          const internT* from, const internT* from_end, const internT*& from_next,
                externT* to,         externT*   to_end,       externT*&   to_next) const;
      virtual result do_in(
          stateT& state,
          const externT* from, const externT* from_end, const externT*& from_next,
                internT* to,         internT*   to_end,       internT*&   to_next) const;
      virtual result do_unshift(
          stateT& state,
                externT* to,         externT*   to_end,       externT*&   to_next) const;

      virtual int do_encoding() const noexcept;
      virtual bool do_always_noconv() const noexcept;
      virtual int do_length(stateT&, const externT* from, const externT* end, size_t max) const;
      virtual int do_max_length() const noexcept;
    };
}

The class codecvt<internT, externT, stateT> is for use when converting from one character encoding to another, such as from wide characters to multibyte characters or between wide character encodings such as Unicode and EUC.

The stateT argument selects the pair of character encodings being mapped between.

The specializations required in Table 69 ([locale.category]) convert the implementation-defined native character set. codecvt<char, char, mbstate_­t> implements a degenerate conversion; it does not convert at all. The specialization codecvt<char16_­t, char, mbstate_­t> converts between the UTF-16 and UTF-8 encoding forms, and the specialization codecvt <char32_­t, char, mbstate_­t> converts between the UTF-32 and UTF-8 encoding forms. codecvt<wchar_­t, char, mbstate_­t> converts between the native character sets for narrow and wide characters. Specializations on mbstate_­t perform conversion between encodings known to the library implementer. Other encodings can be converted by specializing on a user-defined stateT type. Objects of type stateT can contain any state that is useful to communicate to or from the specialized do_­in or do_­out members.

25.4.1.4.1 codecvt members [locale.codecvt.members]

result out( stateT& state, const internT* from, const internT* from_end, const internT*& from_next, externT* to, externT* to_end, externT*& to_next) const;

Returns: do_­out(state, from, from_­end, from_­next, to, to_­end, to_­next).

result unshift(stateT& state, externT* to, externT* to_end, externT*& to_next) const;

Returns: do_­unshift(state, to, to_­end, to_­next).

result in( stateT& state, const externT* from, const externT* from_end, const externT*& from_next, internT* to, internT* to_end, internT*& to_next) const;

Returns: do_­in(state, from, from_­end, from_­next, to, to_­end, to_­next).

int encoding() const noexcept;

Returns: do_­encoding().

bool always_noconv() const noexcept;

Returns: do_­always_­noconv().

int length(stateT& state, const externT* from, const externT* from_end, size_t max) const;

Returns: do_­length(state, from, from_­end, max).

int max_length() const noexcept;

Returns: do_­max_­length().

25.4.1.4.2 codecvt virtual functions [locale.codecvt.virtuals]

result do_out( stateT& state, const internT* from, const internT* from_end, const internT*& from_next, externT* to, externT* to_end, externT*& to_next) const; result do_in( stateT& state, const externT* from, const externT* from_end, const externT*& from_next, internT* to, internT* to_end, internT*& to_next) const;

Requires: (from <= from_­end && to <= to_­end) well-defined and true; state initialized, if at the beginning of a sequence, or else equal to the result of converting the preceding characters in the sequence.

Effects: Translates characters in the source range [from, from_­end), placing the results in sequential positions starting at destination to. Converts no more than (from_­end - from) source elements, and stores no more than (to_­end - to) destination elements.

Stops if it encounters a character it cannot convert. It always leaves the from_­next and to_­next pointers pointing one beyond the last element successfully converted. If returns noconv, internT and externT are the same type and the converted sequence is identical to the input sequence [from, from_next). to_­next is set equal to to, the value of state is unchanged, and there are no changes to the values in [to, to_­end).

A codecvt facet that is used by basic_­filebuf ([file.streams]) shall have the property that if

do_out(state, from, from_end, from_next, to, to_end, to_next)

would return ok, where from != from_­end, then

do_out(state, from, from + 1, from_next, to, to_end, to_next)

shall also return ok, and that if

do_in(state, from, from_end, from_next, to, to_end, to_next)

would return ok, where to != to_­end, then

do_in(state, from, from_end, from_next, to, to + 1, to_next)

shall also return ok.236 [Note: As a result of operations on state, it can return ok or partial and set from_­next == from and to_­next != to. end note]

Remarks: Its operations on state are unspecified. [Note: This argument can be used, for example, to maintain shift state, to specify conversion options (such as count only), or to identify a cache of seek offsets. end note]

Returns: An enumeration value, as summarized in Table 71.

Table 71do_­in/do_­out result values
ValueMeaning
ok completed the conversion
partial not all source characters converted
error encountered a character in [from, from_­end) that it could not convert
noconv internT and externT are the same type, and input sequence is identical to converted sequence

A return value of partial, if (from_­next == from_­end), indicates that either the destination sequence has not absorbed all the available destination elements, or that additional source elements are needed before another destination element can be produced.

result do_unshift(stateT& state, externT* to, externT* to_end, externT*& to_next) const;

Requires: (to <= to_­end) well defined and true; state initialized, if at the beginning of a sequence, or else equal to the result of converting the preceding characters in the sequence.

Effects: Places characters starting at to that should be appended to terminate a sequence when the current stateT is given by state.237 Stores no more than (to_­end - to) destination elements, and leaves the to_­next pointer pointing one beyond the last element successfully stored.

Returns: An enumeration value, as summarized in Table 72.

Table 72do_­unshift result values
ValueMeaning
ok completed the sequence
partial space for more than to_­end - to destination elements was needed to terminate a sequence given the value of state
error an unspecified error has occurred
noconv no termination is needed for this state_­type

int do_encoding() const noexcept;

Returns: -1 if the encoding of the externT sequence is state-dependent; else the constant number of externT characters needed to produce an internal character; or 0 if this number is not a constant.238

bool do_always_noconv() const noexcept;

Returns: true if do_­in() and do_­out() return noconv for all valid argument values. codecvt<char, char, mbstate_­t> returns true.

int do_length(stateT& state, const externT* from, const externT* from_end, size_t max) const;

Requires: (from <= from_­end) well-defined and true; state initialized, if at the beginning of a sequence, or else equal to the result of converting the preceding characters in the sequence.

Effects: The effect on the state argument is “as if” it called do_­in(state, from, from_­end, from, to, to+max, to) for to pointing to a buffer of at least max elements.

Returns: (from_­next-from) where from_­next is the largest value in the range [from, from_­end] such that the sequence of values in the range [from, from_­next) represents max or fewer valid complete characters of type internT. The specialization codecvt<char, char, mbstate_­t>, returns the lesser of max and (from_­end-from).

int do_max_length() const noexcept;

Returns: The maximum value that do_­length(state, from, from_­end, 1) can return for any valid range [from, from_­end) and stateT value state. The specialization codecvt<char, char, mbstate_­t>​::​do_­max_­length() returns 1.

Informally, this means that basic_­filebuf assumes that the mappings from internal to external characters is 1 to N: a codecvt facet that is used by basic_­filebuf must be able to translate characters one internal character at a time.

Typically these will be characters to return the state to stateT().

If encoding() yields -1, then more than max_­length() externT elements may be consumed when producing a single internT character, and additional externT elements may appear at the end of a sequence after those that yield the final internT character.

25.4.1.5 Class template codecvt_­byname [locale.codecvt.byname]

namespace std {
  template <class internT, class externT, class stateT>
    class codecvt_byname : public codecvt<internT, externT, stateT> {
    public:
      explicit codecvt_byname(const char*, size_t refs = 0);
      explicit codecvt_byname(const string&, size_t refs = 0);

    protected:
      ~codecvt_byname();
    };
}

25.4.2 The numeric category [category.numeric]

The classes num_­get<> and num_­put<> handle numeric formatting and parsing. Virtual functions are provided for several numeric types. Implementations may (but are not required to) delegate extraction of smaller types to extractors for larger types.239

All specifications of member functions for num_­put and num_­get in the subclauses of [category.numeric] only apply to the specializations required in Tables 69 and 70 ([locale.category]), namely num_­get<char>, num_­get<wchar_­t>, num_­get<C, InputIterator>, num_­put<char>, num_­put<wchar_­t>, and num_­put<C, OutputIterator>. These specializations refer to the ios_­base& argument for formatting specifications ([locale.categories]), and to its imbued locale for the numpunct<> facet to identify all numeric punctuation preferences, and also for the ctype<> facet to perform character classification.

Extractor and inserter members of the standard iostreams use num_­get<> and num_­put<> member functions for formatting and parsing numeric values ([istream.formatted.reqmts], [ostream.formatted.reqmts]).

Parsing "-1" correctly into, e.g., an unsigned short requires that the corresponding member get() at least extract the sign before delegating.

25.4.2.1 Class template num_­get [locale.num.get]

namespace std {
  template <class charT, class InputIterator = istreambuf_iterator<charT>>
    class num_get : public locale::facet {
    public:
      using char_type = charT;
      using iter_type = InputIterator;

      explicit num_get(size_t refs = 0);

      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, bool& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned short& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned int& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, unsigned long long& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, float& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, double& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, long double& v) const;
      iter_type get(iter_type in, iter_type end, ios_base&,
                    ios_base::iostate& err, void*& v) const;

      static locale::id id;

    protected:
      ~num_get();
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, bool& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned short& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned int& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, unsigned long long& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, float& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, long double& v) const;
      virtual iter_type do_get(iter_type, iter_type, ios_base&,
                               ios_base::iostate& err, void*& v) const;
    };
}

The facet num_­get is used to parse numeric values from an input sequence such as an istream.

25.4.2.1.1 num_­get members [facet.num.get.members]

iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, bool& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned short& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned int& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long long& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, float& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, double& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long double& val) const; iter_type get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, void*& val) const;

Returns: do_­get(in, end, str, err, val).

25.4.2.1.2 num_­get virtual functions [facet.num.get.virtuals]

iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned short& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned int& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, unsigned long long& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, float& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, double& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, long double& val) const; iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, void*& val) const;

Effects: Reads characters from in, interpreting them according to str.flags(), use_­facet<ctype<​charT>>(loc), and use_­facet<numpunct<charT>>(loc), where loc is str.getloc().

The details of this operation occur in three stages

  • Stage 1: Determine a conversion specifier

  • Stage 2: Extract characters from in and determine a corresponding char value for the format expected by the conversion specification determined in stage 1.

  • Stage 3: Store results

The details of the stages are presented below.

  • Stage 1: The function initializes local variables via

    fmtflags flags = str.flags();
    fmtflags basefield = (flags & ios_base::basefield);
    fmtflags uppercase = (flags & ios_base::uppercase);
    fmtflags boolalpha = (flags & ios_base::boolalpha);

    For conversion to an integral type, the function determines the integral conversion specifier as indicated in Table 73. The table is ordered. That is, the first line whose condition is true applies.

    Table 73 — Integer conversions
    State stdio equivalent
    basefield == oct %o
    basefield == hex %X
    basefield == 0 %i
    signed integral type %d
    unsigned integral type %u

    For conversions to a floating type the specifier is %g.

    For conversions to void* the specifier is %p.

    A length modifier is added to the conversion specification, if needed, as indicated in Table 74.

    Table 74 — Length modifier
    Type Length modifier
    short h
    unsigned short h
    long l
    unsigned long l
    long long ll
    unsigned long long ll
    double l
    long double L
  • Stage 2: If in == end then stage 2 terminates. Otherwise a charT is taken from in and local variables are initialized as if by

    char_type ct = *in;
    char c = src[find(atoms, atoms + sizeof(src) - 1, ct) - atoms];
    if (ct == use_facet<numpunct<charT>>(loc).decimal_point())
    c = '.';
    bool discard =
      ct == use_facet<numpunct<charT>>(loc).thousands_sep()
      && use_facet<numpunct<charT>>(loc).grouping().length() != 0;

    where the values src and atoms are defined as if by:

    static const char src[] = "0123456789abcdefxABCDEFX+-";
    char_type atoms[sizeof(src)];
    use_facet<ctype<charT>>(loc).widen(src, src + sizeof(src), atoms);

    for this value of loc.

    If discard is true, then if '.' has not yet been accumulated, then the position of the character is remembered, but the character is otherwise ignored. Otherwise, if '.' has already been accumulated, the character is discarded and Stage 2 terminates. If it is not discarded, then a check is made to determine if c is allowed as the next character of an input field of the conversion specifier returned by Stage 1. If so, it is accumulated.

    If the character is either discarded or accumulated then in is advanced by ++in and processing returns to the beginning of stage 2.

  • Stage 3: The sequence of chars accumulated in stage 2 (the field) is converted to a numeric value by the rules of one of the functions declared in the header <cstdlib>:

    • For a signed integer value, the function strtoll.

    • For an unsigned integer value, the function strtoull.

    • For a float value, the function strtof.

    • For a double value, the function strtod.

    • For a long double value, the function strtold.

    The numeric value to be stored can be one of:

    • zero, if the conversion function does not convert the entire field.

    • the most positive (or negative) representable value, if the field to be converted to a signed integer type represents a value too large positive (or negative) to be represented in val.

    • the most positive representable value, if the field to be converted to an unsigned integer type represents a value that cannot be represented in val.

    • the converted value, otherwise.

    The resultant numeric value is stored in val. If the conversion function does not convert the entire field, or if the field represents a value outside the range of representable values, ios_­base​::​failbit is assigned to err.

Digit grouping is checked. That is, the positions of discarded separators is examined for consistency with use_­facet<numpunct<charT>>(loc).grouping(). If they are not consistent then ios_­base​::​failbit is assigned to err.

In any case, if stage 2 processing was terminated by the test for in == end then err |= ios_­base​::​eofbit is performed.

iter_type do_get(iter_type in, iter_type end, ios_base& str, ios_base::iostate& err, bool& val) const;

Effects: If (str.flags()&ios_­base​::​boolalpha) == 0 then input proceeds as it would for a long except that if a value is being stored into val, the value is determined according to the following: If the value to be stored is 0 then false is stored. If the value is 1 then true is stored. Otherwise true is stored and ios_­base​::​failbit is assigned to err.

Otherwise target sequences are determined “as if” by calling the members falsename() and truename() of the facet obtained by use_­facet<numpunct<charT>>(str.getloc()). Successive characters in the range [in, end) (see [sequence.reqmts]) are obtained and matched against corresponding positions in the target sequences only as necessary to identify a unique match. The input iterator in is compared to end only when necessary to obtain a character. If a target sequence is uniquely matched, val is set to the corresponding value. Otherwise false is stored and ios_­base​::​failbit is assigned to err.

The in iterator is always left pointing one position beyond the last character successfully matched. If val is set, then err is set to str.goodbit; or to str.eofbit if, when seeking another character to match, it is found that (in == end). If val is not set, then err is set to str.failbit; or to (str.failbit|str.eofbit) if the reason for the failure was that (in == end). [Example: For targets true: "a" and false: "abb", the input sequence "a" yields val == true and err == str.eofbit; the input sequence "abc" yields err = str.failbit, with in ending at the 'c' element. For targets true: "1" and false: "0", the input sequence "1" yields val == true and err == str.goodbit. For empty targets (""), any input sequence yields err == str.failbit. end example]

Returns: in.

25.4.2.2 Class template num_­put [locale.nm.put]

namespace std {
  template <class charT, class OutputIterator = ostreambuf_iterator<charT>>
    class num_put : public locale::facet {
    public:
      using char_type = charT;
      using iter_type = OutputIterator;

      explicit num_put(size_t refs = 0);

      iter_type put(iter_type s, ios_base& f, char_type fill, bool v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, long v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, long long v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, unsigned long v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, unsigned long long v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, double v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, long double v) const;
      iter_type put(iter_type s, ios_base& f, char_type fill, const void* v) const;

      static locale::id id;

    protected:
      ~num_put();
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, bool v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, long v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, long long v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, unsigned long) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, unsigned long long) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, double v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, long double v) const;
      virtual iter_type do_put(iter_type, ios_base&, char_type fill, const void* v) const;
    };
}

The facet num_­put is used to format numeric values to a character sequence such as an ostream.

25.4.2.2.1 num_­put members [facet.num.put.members]

iter_type put(iter_type out, ios_base& str, char_type fill, bool val) const; iter_type put(iter_type out, ios_base& str, char_type fill, long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, long long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, unsigned long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, unsigned long long val) const; iter_type put(iter_type out, ios_base& str, char_type fill, double val) const; iter_type put(iter_type out, ios_base& str, char_type fill, long double val) const; iter_type put(iter_type out, ios_base& str, char_type fill, const void* val) const;

Returns: do_­put(out, str, fill, val).

25.4.2.2.2 num_­put virtual functions [facet.num.put.virtuals]

iter_type do_put(iter_type out, ios_base& str, char_type fill, long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, long long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, unsigned long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, unsigned long long val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, double val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, long double val) const; iter_type do_put(iter_type out, ios_base& str, char_type fill, const void* val) const;

Effects: Writes characters to the sequence out, formatting val as desired. In the following description, a local variable initialized with:

locale loc = str.getloc();

The details of this operation occur in several stages:

  • Stage 1: Determine a printf conversion specifier spec and determine the characters that would be printed by printf ([c.files]) given this conversion specifier for

    printf(spec, val)

    assuming that the current locale is the "C" locale.

  • Stage 2: Adjust the representation by converting each char determined by stage 1 to a charT using a conversion and values returned by members of use_­facet<numpunct<charT>>(str.getloc())

  • Stage 3: Determine where padding is required.

  • Stage 4: Insert the sequence into the out.

Detailed descriptions of each stage follow.

Returns: out.

  • Stage 1: The first action of stage 1 is to determine a conversion specifier. The tables that describe this determination use the following local variables

    fmtflags flags = str.flags();
    fmtflags basefield =  (flags & (ios_base::basefield));
    fmtflags uppercase =  (flags & (ios_base::uppercase));
    fmtflags floatfield = (flags & (ios_base::floatfield));
    fmtflags showpos =    (flags & (ios_base::showpos));
    fmtflags showbase =   (flags & (ios_base::showbase));
    fmtflags showpoint =  (flags & (ios_base::showpoint));

    All tables used in describing stage 1 are ordered. That is, the first line whose condition is true applies. A line without a condition is the default behavior when none of the earlier lines apply.

    For conversion from an integral type other than a character type, the function determines the integral conversion specifier as indicated in Table 75.

    Table 75 — Integer conversions
    State stdio equivalent
    basefield == ios_­base​::​oct %o
    (basefield == ios_­base​::​hex) && !uppercase %x
    (basefield == ios_­base​::​hex) %X
    for a signed integral type %d
    for an unsigned integral type %u

    For conversion from a floating-point type, the function determines the floating-point conversion specifier as indicated in Table 76.

    Table 76 — Floating-point conversions
    State stdio equivalent
    floatfield == ios_­base​::​fixed %f
    floatfield == ios_­base​::​scientific && !uppercase %e
    floatfield == ios_­base​::​scientific %E
    floatfield == (ios_­base​::​fixed | ios_­base​::​scientific) && !uppercase %a
    floatfield == (ios_­base​::​fixed | ios_­base​::​scientific) %A
    !uppercase %g
    otherwise %G

    For conversions from an integral or floating-point type a length modifier is added to the conversion specifier as indicated in Table 77.

    Table 77 — Length modifier
    Type Length modifier
    long l
    long long ll
    unsigned long l
    unsigned long long ll
    long double L
    otherwise none

    The conversion specifier has the following optional additional qualifiers prepended as indicated in Table 78.

    Table 78 — Numeric conversions
    Type(s)State stdio equivalent
    an integral type showpos +
    showbase #
    a floating-point type showpos +
    showpoint #

    For conversion from a floating-point type, if floatfield != (ios_­base​::​fixed | ios_­base​::​​scientific), str.precision() is specified as precision in the conversion specification. Otherwise, no precision is specified.

    For conversion from void* the specifier is %p.

    The representations at the end of stage 1 consists of the char's that would be printed by a call of printf(s, val) where s is the conversion specifier determined above.

  • Stage 2: Any character c other than a decimal point(.) is converted to a charT via use_­facet<ctype<charT>>(loc).widen( c )

    A local variable punct is initialized via

    const numpunct<charT>& punct = use_facet<numpunct<charT>>(str.getloc());

    For arithmetic types, punct.thousands_­sep() characters are inserted into the sequence as determined by the value returned by punct.do_­grouping() using the method described in [facet.numpunct.virtuals]

    Decimal point characters(.) are replaced by punct.decimal_­point()

  • Stage 3: A local variable is initialized as

    fmtflags adjustfield = (flags & (ios_base::adjustfield));

    The location of any padding240 is determined according to Table 79.

    Table 79 — Fill padding
    StateLocation
    adjustfield == ios_­base​::​left pad after
    adjustfield == ios_­base​::​right pad before
    adjustfield == internal and a sign occurs in the representation pad after the sign
    adjustfield == internal and representation after stage 1 began with 0x or 0X pad after x or X
    otherwise pad before

    If str.width() is nonzero and the number of charT's in the sequence after stage 2 is less than str.​width(), then enough fill characters are added to the sequence at the position indicated for padding to bring the length of the sequence to str.width().

    str.width(0) is called.

  • Stage 4: The sequence of charT's at the end of stage 3 are output via

    *out++ = c

iter_type do_put(iter_type out, ios_base& str, char_type fill, bool val) const;

Returns: If (str.flags() & ios_­base​::​boolalpha) == 0 returns do_­put(out, str, fill,
(int)val)
, otherwise obtains a string s as if by

string_type s =
  val ? use_facet<numpunct<charT>>(loc).truename()
      : use_facet<numpunct<charT>>(loc).falsename();

and then inserts each character c of s into out via *out++ = c and returns out.

The conversion specification #o generates a leading 0 which is not a padding character.

25.4.3 The numeric punctuation facet [facet.numpunct]

25.4.3.1 Class template numpunct [locale.numpunct]

namespace std {
  template <class charT>
    class numpunct : public locale::facet {
    public:
      using char_type   = charT;
      using string_type = basic_string<charT>;

      explicit numpunct(size_t refs = 0);

      char_type    decimal_point()   const;
      char_type    thousands_sep()   const;
      string       grouping()        const;
      string_type  truename()        const;
      string_type  falsename()       const;

      static locale::id id;

    protected:
      ~numpunct();                // virtual
      virtual char_type    do_decimal_point() const;
      virtual char_type    do_thousands_sep() const;
      virtual string       do_grouping()      const;
      virtual string_type  do_truename()      const;      // for bool
      virtual string_type  do_falsename()     const;      // for bool
    };
}

numpunct<> specifies numeric punctuation. The specializations required in Table 69 ([locale.category]), namely numpunct<​wchar_­t> and numpunct<char>, provide classic "C" numeric formats, i.e., they contain information equivalent to that contained in the "C" locale or their wide character counterparts as if obtained by a call to widen.

The syntax for number formats is as follows, where digit represents the radix set specified by the fmtflags argument value, and thousands-sep and decimal-point are the results of corresponding numpunct<charT> members. Integer values have the format:

integer   ::= [sign] units
sign      ::= plusminus
plusminus ::= '+' | '-'
units     ::= digits [thousands-sep units]
digits    ::= digit [digits]

and floating-point values have:

floatval ::= [sign] units [decimal-point [digits]] [e [sign] digits] |
             [sign]        decimal-point  digits   [e [sign] digits]
e        ::= 'e' | 'E'

where the number of digits between thousands-seps is as specified by do_­grouping(). For parsing, if the digits portion contains no thousands-separators, no grouping constraint is applied.

25.4.3.1.1 numpunct members [facet.numpunct.members]

char_type decimal_point() const;

Returns: do_­decimal_­point().

char_type thousands_sep() const;

Returns: do_­thousands_­sep().

string grouping() const;

Returns: do_­grouping().

string_type truename() const; string_type falsename() const;

Returns: do_­truename() or do_­falsename(), respectively.

25.4.3.1.2 numpunct virtual functions [facet.numpunct.virtuals]

char_type do_decimal_point() const;

Returns: A character for use as the decimal radix separator. The required specializations return '.' or L'.'.

char_type do_thousands_sep() const;

Returns: A character for use as the digit group separator. The required specializations return ',' or L','.

string do_grouping() const;

Returns: A basic_string<char> vec used as a vector of integer values, in which each element vec[i] represents the number of digits241 in the group at position i, starting with position 0 as the rightmost group. If vec.size() <= i, the number is the same as group (i - 1); if (i < 0 || vec[i] <= 0 || vec[i] == CHAR_­MAX), the size of the digit group is unlimited.

The required specializations return the empty string, indicating no grouping.

string_type do_truename() const; string_type do_falsename() const;

Returns: A string representing the name of the boolean value true or false, respectively.

In the base class implementation these names are "true" and "false", or L"true" and L"false".

Thus, the string "\003" specifies groups of 3 digits each, and "3" probably indicates groups of 51 (!) digits each, because 51 is the ASCII value of "3".

25.4.3.2 Class template numpunct_­byname [locale.numpunct.byname]

namespace std {
  template <class charT>
    class numpunct_byname : public numpunct<charT> {
    // this class is specialized for char and wchar_­t.
    public:
      using char_type   = charT;
      using string_type = basic_string<charT>;

      explicit numpunct_byname(const char*, size_t refs = 0);
      explicit numpunct_byname(const string&, size_t refs = 0);

    protected:
      ~numpunct_byname();
    };
}

25.4.4 The collate category [category.collate]

25.4.4.1 Class template collate [locale.collate]

namespace std {
  template <class charT>
    class collate : public locale::facet {
    public:
      using char_type   = charT;
      using string_type = basic_string<charT>;

      explicit collate(size_t refs = 0);

      int compare(const charT* low1, const charT* high1,
                  const charT* low2, const charT* high2) const;
      string_type transform(const charT* low, const charT* high) const;
      long hash(const charT* low, const charT* high) const;

      static locale::id id;

    protected:
      ~collate();
      virtual int do_compare(const charT* low1, const charT* high1,
                             const charT* low2, const charT* high2) const;
      virtual string_type do_transform(const charT* low, const charT* high) const;
      virtual long do_hash (const charT* low, const charT* high) const;
    };
}

The class collate<charT> provides features for use in the collation (comparison) and hashing of strings. A locale member function template, operator(), uses the collate facet to allow a locale to act directly as the predicate argument for standard algorithms (Clause [algorithms]) and containers operating on strings. The specializations required in Table 69 ([locale.category]), namely collate<char> and collate<wchar_­t>, apply lexicographic ordering.

Each function compares a string of characters *p in the range [low, high).

25.4.4.1.1 collate members [locale.collate.members]

int compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const;

Returns: do_­compare(low1, high1, low2, high2).

string_type transform(const charT* low, const charT* high) const;

Returns: do_­transform(low, high).

long hash(const charT* low, const charT* high) const;

Returns: do_­hash(low, high).

25.4.4.1.2 collate virtual functions [locale.collate.virtuals]

int do_compare(const charT* low1, const charT* high1, const charT* low2, const charT* high2) const;

Returns: 1 if the first string is greater than the second, -1 if less, zero otherwise. The specializations required in Table 69 ([locale.category]), namely collate<char> and collate<wchar_­t>, implement a lexicographical comparison.

string_type do_transform(const charT* low, const charT* high) const;

Returns: A basic_­string<charT> value that, compared lexicographically with the result of calling transform() on another string, yields the same result as calling do_­compare() on the same two strings.242

long do_hash(const charT* low, const charT* high) const;

Returns: An integer value equal to the result of calling hash() on any other string for which do_­compare() returns 0 (equal) when passed the two strings. [Note: The probability that the result equals that for another string which does not compare equal should be very small, approaching (1.0/numeric_­limits<unsigned long>​::​max()). end note]

This function is useful when one string is being compared to many other strings.

25.4.4.2 Class template collate_­byname [locale.collate.byname]

namespace std {
  template <class charT>
    class collate_byname : public collate<charT> {
    public:
      using string_type = basic_string<charT>;

      explicit collate_byname(const char*, size_t refs = 0);
      explicit collate_byname(const string&, size_t refs = 0);

    protected:
      ~collate_byname();
    };
}

25.4.5 The time category [category.time]

Templates time_­get<charT, InputIterator> and time_­put<charT, OutputIterator> provide date and time formatting and parsing. All specifications of member functions for time_­put and time_­get in the subclauses of [category.time] only apply to the specializations required in Tables 69 and 70 ([locale.category]). Their members use their ios_­base&, ios_­base​::​iostate&, and fill arguments as described in [locale.categories], and the ctype<> facet, to determine formatting details.

25.4.5.1 Class template time_­get [locale.time.get]

namespace std {
  class time_base {
  public:
    enum dateorder { no_order, dmy, mdy, ymd, ydm };
  };

  template <class charT, class InputIterator = istreambuf_iterator<charT>>
    class time_get : public locale::facet, public time_base {
    public:
      using char_type = charT;
      using iter_type = InputIterator;

      explicit time_get(size_t refs = 0);

      dateorder date_order()  const { return do_date_order(); }
      iter_type get_time(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t)  const;
      iter_type get_date(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t)  const;
      iter_type get_weekday(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t) const;
      iter_type get_monthname(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t) const;
      iter_type get_year(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t) const;
      iter_type get(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t, char format, char modifier = 0) const;
      iter_type get(iter_type s, iter_type end, ios_base& f,
                         ios_base::iostate& err, tm* t, const char_type* fmt,
                         const char_type* fmtend) const;

      static locale::id id;

    protected:
      ~time_get();
      virtual dateorder do_date_order()  const;
      virtual iter_type do_get_time(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_date(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_weekday(iter_type s, iter_type end, ios_base&,
                                       ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_monthname(iter_type s, iter_type end, ios_base&,
                                         ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get_year(iter_type s, iter_type end, ios_base&,
                                    ios_base::iostate& err, tm* t) const;
      virtual iter_type do_get(iter_type s, iter_type end, ios_base& f,
                               ios_base::iostate& err, tm* t, char format, char modifier) const;
    };
}

time_­get is used to parse a character sequence, extracting components of a time or date into a struct tm object. Each get member parses a format as produced by a corresponding format specifier to time_­put<>​::​put. If the sequence being parsed matches the correct format, the corresponding members of the struct tm argument are set to the values used to produce the sequence; otherwise either an error is reported or unspecified values are assigned.243

If the end iterator is reached during parsing by any of the get() member functions, the member sets ios_­base​::​eofbit in err.

In other words, user confirmation is required for reliable parsing of user-entered dates and times, but machine-generated formats can be parsed reliably. This allows parsers to be aggressive about interpreting user variations on standard formats.

25.4.5.1.1 time_­get members [locale.time.get.members]

dateorder date_order() const;

Returns: do_­date_­order().

iter_type get_time(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Returns: do_­get_­time(s, end, str, err, t).

iter_type get_date(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Returns: do_­get_­date(s, end, str, err, t).

iter_type get_weekday(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const; iter_type get_monthname(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Returns: do_­get_­weekday(s, end, str, err, t) or do_­get_­monthname(s, end, str, err, t).

iter_type get_year(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Returns: do_­get_­year(s, end, str, err, t).

iter_type get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, char format, char modifier = 0) const;

Returns: do_­get(s, end, f, err, t, format, modifier).

iter_type get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, const char_type* fmt, const char_type* fmtend) const;

Requires: [fmt, fmtend) shall be a valid range.

Effects: The function starts by evaluating err = ios_­base​::​goodbit. It then enters a loop, reading zero or more characters from s at each iteration. Unless otherwise specified below, the loop terminates when the first of the following conditions holds:

  • The expression fmt == fmtend evaluates to true.

  • The expression err == ios_­base​::​goodbit evaluates to false.

  • The expression s == end evaluates to true, in which case the function evaluates err = ios_­base​::​eofbit | ios_­base​::​failbit.

  • The next element of fmt is equal to '%', optionally followed by a modifier character, followed by a conversion specifier character, format, together forming a conversion specification valid for the ISO/IEC 9945 function strptime. If the number of elements in the range [fmt, fmtend) is not sufficient to unambiguously determine whether the conversion specification is complete and valid, the function evaluates err = ios_­base​::​failbit. Otherwise, the function evaluates s = do_­get(s, end, f, err, t, format, modifier), where the value of modifier is '\0' when the optional modifier is absent from the conversion specification. If err == ios_­base​::​goodbit holds after the evaluation of the expression, the function increments fmt to point just past the end of the conversion specification and continues looping.

  • The expression isspace(*fmt, f.getloc()) evaluates to true, in which case the function first increments fmt until fmt == fmtend || !isspace(*fmt, f.getloc()) evaluates to true, then advances s until s == end || !isspace(*s, f.getloc()) is true, and finally resumes looping.

  • The next character read from s matches the element pointed to by fmt in a case-insensitive comparison, in which case the function evaluates ++fmt, ++s and continues looping. Otherwise, the function evaluates err = ios_­base​::​failbit.

[Note: The function uses the ctype<charT> facet installed in f's locale to determine valid whitespace characters. It is unspecified by what means the function performs case-insensitive comparison or whether multi-character sequences are considered while doing so. end note]

Returns: s.

25.4.5.1.2 time_­get virtual functions [locale.time.get.virtuals]

dateorder do_date_order() const;

Returns: An enumeration value indicating the preferred order of components for those date formats that are composed of day, month, and year.244 Returns no_­order if the date format specified by 'x' contains other variable components (e.g., Julian day, week number, week day).

iter_type do_get_time(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Effects: Reads characters starting at s until it has extracted those struct tm members, and remaining format characters, used by time_­put<>​::​put to produce the format specified by "%H:%M:%S", or until it encounters an error or end of sequence.

Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid time.

iter_type do_get_date(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Effects: Reads characters starting at s until it has extracted those struct tm members and remaining format characters used by time_­put<>​::​put to produce one of the following formats, or until it encounters an error. The format depends on the value returned by date_­order() as shown in Table 80.

Table 80do_­get_­date effects
date_­order()Format
no_­order "%m%d%y"
dmy "%d%m%y"
mdy "%m%d%y"
ymd "%y%m%d"
ydm "%y%d%m"

An implementation may also accept additional implementation-defined formats.

Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid date.

iter_type do_get_weekday(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const; iter_type do_get_monthname(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Effects: Reads characters starting at s until it has extracted the (perhaps abbreviated) name of a weekday or month. If it finds an abbreviation that is followed by characters that could match a full name, it continues reading until it matches the full name or fails. It sets the appropriate struct tm member accordingly.

Returns: An iterator pointing immediately beyond the last character recognized as part of a valid name.

iter_type do_get_year(iter_type s, iter_type end, ios_base& str, ios_base::iostate& err, tm* t) const;

Effects: Reads characters starting at s until it has extracted an unambiguous year identifier. It is implementation-defined whether two-digit year numbers are accepted, and (if so) what century they are assumed to lie in. Sets the t->tm_­year member accordingly.

Returns: An iterator pointing immediately beyond the last character recognized as part of a valid year identifier.

iter_type do_get(iter_type s, iter_type end, ios_base& f, ios_base::iostate& err, tm* t, char format, char modifier) const;

Requires: t shall point to an object.

Effects: The function starts by evaluating err = ios_­base​::​goodbit. It then reads characters starting at s until it encounters an error, or until it has extracted and assigned those struct tm members, and any remaining format characters, corresponding to a conversion directive appropriate for the ISO/IEC 9945 function strptime, formed by concatenating '%', the modifier character, when non-NUL, and the format character. When the concatenation fails to yield a complete valid directive the function leaves the object pointed to by t unchanged and evaluates err |= ios_­base​::​failbit. When s == end evaluates to true after reading a character the function evaluates err |= ios_­base​::​eofbit.

For complex conversion directives such as %c, %x, or %X, or directives that involve the optional modifiers E or O, when the function is unable to unambiguously determine some or all struct tm members from the input sequence [s, end), it evaluates err |= ios_­base​::​eofbit. In such cases the values of those struct tm members are unspecified and may be outside their valid range.

Remarks: It is unspecified whether multiple calls to do_­get() with the address of the same struct tm object will update the current contents of the object or simply overwrite its members. Portable programs must zero out the object before invoking the function.

Returns: An iterator pointing immediately beyond the last character recognized as possibly part of a valid input sequence for the given format and modifier.

This function is intended as a convenience only, for common formats, and may return no_­order in valid locales.

25.4.5.2 Class template time_­get_­byname [locale.time.get.byname]

namespace std {
  template <class charT, class InputIterator = istreambuf_iterator<charT>>
    class time_get_byname : public time_get<charT, InputIterator> {
    public:
      using dateorder = time_base::dateorder;
      using iter_type = InputIterator;

      explicit time_get_byname(const char*, size_t refs = 0);
      explicit time_get_byname(const string&, size_t refs = 0);

    protected:
      ~time_get_byname();
    };
}

25.4.5.3 Class template time_­put [locale.time.put]

namespace std {
  template <class charT, class OutputIterator = ostreambuf_iterator<charT>>
    class time_put : public locale::facet {
    public:
      using char_type = charT;
      using iter_type = OutputIterator;

      explicit time_put(size_t refs = 0);

      // the following is implemented in terms of other member functions.
      iter_type put(iter_type s, ios_base& f, char_type fill, const tm* tmb,
                    const charT* pattern, const charT* pat_end) const;
      iter_type put(iter_type s, ios_base& f, char_type fill,
                    const tm* tmb, char format, char modifier = 0) const;

      static locale::id id;

    protected:
      ~time_put();
      virtual iter_type do_put(iter_type s, ios_base&, char_type, const tm* t,
                               char format, char modifier) const;
    };
}

25.4.5.3.1 time_­put members [locale.time.put.members]

iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t, const charT* pattern, const charT* pat_end) const; iter_type put(iter_type s, ios_base& str, char_type fill, const tm* t, char format, char modifier = 0) const;

Effects: The first form steps through the sequence from pattern to pat_­end, identifying characters that are part of a format sequence. Each character that is not part of a format sequence is written to s immediately, and each format sequence, as it is identified, results in a call to do_­put; thus, format elements and other characters are interleaved in the output in the order in which they appear in the pattern. Format sequences are identified by converting each character c to a char value as if by ct.narrow(c, 0), where ct is a reference to ctype<charT> obtained from str.getloc(). The first character of each sequence is equal to '%', followed by an optional modifier character mod245 and a format specifier character spec as defined for the function strftime. If no modifier character is present, mod is zero. For each valid format sequence identified, calls do_­put(s, str, fill, t, spec, mod).

The second form calls do_­put(s, str, fill, t, format, modifier).

[Note: The fill argument may be used in the implementation-defined formats or by derivations. A space character is a reasonable default for this argument. end note]

Returns: An iterator pointing immediately after the last character produced.

Although the C programming language defines no modifiers, most vendors do.

25.4.5.3.2 time_­put virtual functions [locale.time.put.virtuals]

iter_type do_put(iter_type s, ios_base&, char_type fill, const tm* t, char format, char modifier) const;

Effects: Formats the contents of the parameter t into characters placed on the output sequence s. Formatting is controlled by the parameters format and modifier, interpreted identically as the format specifiers in the string argument to the standard library function strftime()246, except that the sequence of characters produced for those specifiers that are described as depending on the C locale are instead implementation-defined.247

Returns: An iterator pointing immediately after the last character produced. [Note: The fill argument may be used in the implementation-defined formats or by derivations. A space character is a reasonable default for this argument. end note]

Interpretation of the modifier argument is implementation-defined, but should follow POSIX conventions.

Implementations are encouraged to refer to other standards such as POSIX for these definitions.

25.4.5.4 Class template time_­put_­byname [locale.time.put.byname]

namespace std {
  template <class charT, class OutputIterator = ostreambuf_iterator<charT>>
    class time_put_byname : public time_put<charT, OutputIterator> {
    public:
      using char_type = charT;
      using iter_type = OutputIterator;

      explicit time_put_byname(const char*, size_t refs = 0);
      explicit time_put_byname(const string&, size_t refs = 0);

    protected:
      ~time_put_byname();
    };
}

25.4.6 The monetary category [category.monetary]

These templates handle monetary formats. A template parameter indicates whether local or international monetary formats are to be used.

All specifications of member functions for money_­put and money_­get in the subclauses of [category.monetary] only apply to the specializations required in Tables 69 and 70 ([locale.category]). Their members use their ios_­base&, ios_­base​::​iostate&, and fill arguments as described in [locale.categories], and the moneypunct<> and ctype<> facets, to determine formatting details.

25.4.6.1 Class template money_­get [locale.money.get]

namespace std {
  template <class charT, class InputIterator = istreambuf_iterator<charT>>
    class money_get : public locale::facet {
    public:
      using char_type   = charT;
      using iter_type   = InputIterator;
      using string_type = basic_string<charT>;

      explicit money_get(size_t refs = 0);

      iter_type get(iter_type s, iter_type end, bool intl,
                    ios_base& f, ios_base::iostate& err,
                    long double& units) const;
      iter_type get(iter_type s, iter_type end, bool intl,
                    ios_base& f, ios_base::iostate& err,
                    string_type& digits) const;

      static locale::id id;

    protected:
      ~money_get();
      virtual iter_type do_get(iter_type, iter_type, bool, ios_base&,
                               ios_base::iostate& err, long double& units) const;
      virtual iter_type do_get(iter_type, iter_type, bool, ios_base&,
                               ios_base::iostate& err, string_type& digits) const;
    };
}

25.4.6.1.1 money_­get members [locale.money.get.members]

iter_type get(iter_type s, iter_type end, bool intl, ios_base& f, ios_base::iostate& err, long double& quant) const; iter_type get(iter_type s, iter_type end, bool intl, ios_base& f, ios_base::iostate& err, string_type& quant) const;

Returns: do_­get(s, end, intl, f, err, quant).

25.4.6.1.2 money_­get virtual functions [locale.money.get.virtuals]

iter_type do_get(iter_type s, iter_type end, bool intl, ios_base& str, ios_base::iostate& err, long double& units) const; iter_type do_get(iter_type s, iter_type end, bool intl, ios_base& str, ios_base::iostate& err, string_type& digits) const;

Effects: Reads characters from s to parse and construct a monetary value according to the format specified by a moneypunct<charT, Intl> facet reference mp and the character mapping specified by a ctype<charT> facet reference ct obtained from the locale returned by str.getloc(), and str.flags(). If a valid sequence is recognized, does not change err; otherwise, sets err to (err|str.failbit), or (err|str.failbit|str.eofbit) if no more characters are available, and does not change units or digits. Uses the pattern returned by mp.neg_­format() to parse all values. The result is returned as an integral value stored in units or as a sequence of digits possibly preceded by a minus sign (as produced by ct.widen(c) where c is '-' or in the range from '0' through '9', inclusive) stored in digits. [Example: The sequence $1,056.23 in a common United States locale would yield, for units, 105623, or, for digits, "105623". end example] If mp.grouping() indicates that no thousands separators are permitted, any such characters are not read, and parsing is terminated at the point where they first appear. Otherwise, thousands separators are optional; if present, they are checked for correct placement only after all format components have been read.

Where money_­base​::​space or money_­base​::​none appears as the last element in the format pattern, no white space is consumed. Otherwise, where money_­base​::​space appears in any of the initial elements of the format pattern, at least one white space character is required. Where money_­base​::​none appears in any of the initial elements of the format pattern, white space is allowed but not required. If (str.flags() & str.showbase) is false, the currency symbol is optional and is consumed only if other characters are needed to complete the format; otherwise, the currency symbol is required.

If the first character (if any) in the string pos returned by mp.positive_­sign() or the string neg returned by mp.negative_­sign() is recognized in the position indicated by sign in the format pattern, it is consumed and any remaining characters in the string are required after all the other format components. [Example: If showbase is off, then for a neg value of "()" and a currency symbol of "L", in "(100 L)" the "L" is consumed; but if neg is "-", the "L" in "-100 L" is not consumed. end example] If pos or neg is empty, the sign component is optional, and if no sign is detected, the result is given the sign that corresponds to the source of the empty string. Otherwise, the character in the indicated position must match the first character of pos or neg, and the result is given the corresponding sign. If the first character of pos is equal to the first character of neg, or if both strings are empty, the result is given a positive sign.

Digits in the numeric monetary component are extracted and placed in digits, or into a character buffer buf1 for conversion to produce a value for units, in the order in which they appear, preceded by a minus sign if and only if the result is negative. The value units is produced as if by248

for (int i = 0; i < n; ++i)
  buf2[i] = src[find(atoms, atoms+sizeof(src), buf1[i]) - atoms];
buf2[n] = 0;
sscanf(buf2, "%Lf", &units);

where n is the number of characters placed in buf1, buf2 is a character buffer, and the values src and atoms are defined as if by

static const char src[] = "0123456789-";
charT atoms[sizeof(src)];
ct.widen(src, src + sizeof(src) - 1, atoms);

Returns: An iterator pointing immediately beyond the last character recognized as part of a valid monetary quantity.

The semantics here are different from ct.narrow.

25.4.6.2 Class template money_­put [locale.money.put]

namespace std {
  template <class charT, class OutputIterator = ostreambuf_iterator<charT>>
    class money_put : public locale::facet {
    public:
      using char_type   = charT;
      using iter_type   = OutputIterator;
      using string_type = basic_string<charT>;

      explicit money_put(size_t refs = 0);

      iter_type put(iter_type s, bool intl, ios_base& f,
                    char_type fill, long double units) const;
      iter_type put(iter_type s, bool intl, ios_base& f,
                    char_type fill, const string_type& digits) const;

      static locale::id id;

    protected:
      ~money_put();
      virtual iter_type do_put(iter_type, bool, ios_base&, char_type fill,
                               long double units) const;
      virtual iter_type do_put(iter_type, bool, ios_base&, char_type fill,
                               const string_type& digits) const;
    };
}

25.4.6.2.1 money_­put members [locale.money.put.members]

iter_type put(iter_type s, bool intl, ios_base& f, char_type fill, long double quant) const; iter_type put(iter_type s, bool intl, ios_base& f, char_type fill, const string_type& quant) const;

Returns: do_­put(s, intl, f, loc, quant).

25.4.6.2.2 money_­put virtual functions [locale.money.put.virtuals]

iter_type do_put(iter_type s, bool intl, ios_base& str, char_type fill, long double units) const; iter_type do_put(iter_type s, bool intl, ios_base& str, char_type fill, const string_type& digits) const;

Effects: Writes characters to s according to the format specified by a moneypunct<charT, Intl> facet reference mp and the character mapping specified by a ctype<charT> facet reference ct obtained from the locale returned by str.getloc(), and str.flags(). The argument units is transformed into a sequence of wide characters as if by

ct.widen(buf1, buf1 + sprintf(buf1, "%.0Lf", units), buf2)

for character buffers buf1 and buf2. If the first character in digits or buf2 is equal to ct.widen('-'), then the pattern used for formatting is the result of mp.neg_­format(); otherwise the pattern is the result of mp.pos_­format(). Digit characters are written, interspersed with any thousands separators and decimal point specified by the format, in the order they appear (after the optional leading minus sign) in digits or buf2. In digits, only the optional leading minus sign and the immediately subsequent digit characters (as classified according to ct) are used; any trailing characters (including digits appearing after a non-digit character) are ignored. Calls str.width(0).

Remarks: The currency symbol is generated if and only if (str.flags() & str.showbase) is nonzero. If the number of characters generated for the specified format is less than the value returned by str.width() on entry to the function, then copies of fill are inserted as necessary to pad to the specified width. For the value af equal to (str.flags() & str.adjustfield), if (af == str.internal) is true, the fill characters are placed where none or space appears in the formatting pattern; otherwise if (af == str.left) is true, they are placed after the other characters; otherwise, they are placed before the other characters. [Note: It is possible, with some combinations of format patterns and flag values, to produce output that cannot be parsed using num_­get<>​::​get. end note]

Returns: An iterator pointing immediately after the last character produced.

25.4.6.3 Class template moneypunct [locale.moneypunct]

namespace std {
  class money_base {
  public:
    enum part { none, space, symbol, sign, value };
    struct pattern { char field[4]; };
  };

  template <class charT, bool International = false>
    class moneypunct : public locale::facet, public money_base {
    public:
      using char_type   = charT;
      using string_type = basic_string<charT>;

      explicit moneypunct(size_t refs = 0);

      charT        decimal_point() const;
      charT        thousands_sep() const;
      string       grouping()      const;
      string_type  curr_symbol()   const;
      string_type  positive_sign() const;
      string_type  negative_sign() const;
      int          frac_digits()   const;
      pattern      pos_format()    const;
      pattern      neg_format()    const;

      static locale::id id;
      static const bool intl = International;

    protected:
      ~moneypunct();
      virtual charT        do_decimal_point() const;
      virtual charT        do_thousands_sep() const;
      virtual string       do_grouping()      const;
      virtual string_type  do_curr_symbol()   const;
      virtual string_type  do_positive_sign() const;
      virtual string_type  do_negative_sign() const;
      virtual int          do_frac_digits()   const;
      virtual pattern      do_pos_format()    const;
      virtual pattern      do_neg_format()    const;
    };
}

The moneypunct<> facet defines monetary formatting parameters used by money_­get<> and money_­put<>. A monetary format is a sequence of four components, specified by a pattern value p, such that the part value static_­cast<part>(p.field[i]) determines the ith component of the format249 In the field member of a pattern object, each value symbol, sign, value, and either space or none appears exactly once. The value none, if present, is not first; the value space, if present, is neither first nor last.

Where none or space appears, white space is permitted in the format, except where none appears at the end, in which case no white space is permitted. The value space indicates that at least one space is required at that position. Where symbol appears, the sequence of characters returned by curr_­symbol() is permitted, and can be required. Where sign appears, the first (if any) of the sequence of characters returned by positive_­sign() or negative_­sign() (respectively as the monetary value is non-negative or negative) is required. Any remaining characters of the sign sequence are required after all other format components. Where value appears, the absolute numeric monetary value is required.

The format of the numeric monetary value is a decimal number:

value ::= units [ decimal-point [ digits ]] |
  decimal-point digits

if frac_­digits() returns a positive value, or

value ::= units

otherwise. The symbol decimal-point indicates the character returned by decimal_­point(). The other symbols are defined as follows:

units ::= digits [ thousands-sep units ]
digits ::= adigit [ digits ]

In the syntax specification, the symbol adigit is any of the values ct.widen(c) for c in the range '0' through '9', inclusive, and ct is a reference of type const ctype<charT>& obtained as described in the definitions of money_­get<> and money_­put<>. The symbol thousands-sep is the character returned by thousands_­sep(). The space character used is the value ct.widen(' '). White space characters are those characters c for which ci.is(space, c) returns true. The number of digits required after the decimal point (if any) is exactly the value returned by frac_­digits().

The placement of thousands-separator characters (if any) is determined by the value returned by grouping(), defined identically as the member numpunct<>​::​do_­grouping().

An array of char, rather than an array of part, is specified for pattern​::​field purely for efficiency.

25.4.6.3.1 moneypunct members [locale.moneypunct.members]

charT        decimal_point() const;
charT        thousands_sep() const;
string       grouping()      const;
string_type  curr_symbol()   const;
string_type  positive_sign() const;
string_type  negative_sign() const;
int          frac_digits()   const;
pattern      pos_format()    const;
pattern      neg_format()    const;

Each of these functions F returns the result of calling the corresponding virtual member function do_­F().

25.4.6.3.2 moneypunct virtual functions [locale.moneypunct.virtuals]

charT do_decimal_point() const;

Returns: The radix separator to use in case do_­frac_­digits() is greater than zero.250

charT do_thousands_sep() const;

Returns: The digit group separator to use in case do_­grouping() specifies a digit grouping pattern.251

string do_grouping() const;

Returns: A pattern defined identically as, but not necessarily equal to, the result of numpunct<charT>​::​​do_­grouping().252

string_type do_curr_symbol() const;

Returns: A string to use as the currency identifier symbol.253

string_type do_positive_sign() const; string_type do_negative_sign() const;

Returns: do_­positive_­sign() returns the string to use to indicate a positive monetary value;254 do_­negative_­sign() returns the string to use to indicate a negative value.

int do_frac_digits() const;

Returns: The number of digits after the decimal radix separator, if any.255

pattern do_pos_format() const; pattern do_neg_format() const;

Returns: The specializations required in Table 70 ([locale.category]), namely moneypunct<char>, moneypunct<​wchar_­t>, moneypunct<char, true>, and moneypunct<wchar_­t, true>, return an object of type pattern initialized to { symbol, sign, none, value }.256

In common U.S. locales this is '.'.

In common U.S. locales this is ','.

To specify grouping by 3s, the value is "\003" not "3".

For international specializations (second template parameter true) this is typically four characters long, usually three letters and a space.

This is usually the empty string.

In common U.S. locales, this is 2.

Note that the international symbol returned by do_­curr_­sym() usually contains a space, itself; for example, "USD ".

25.4.6.4 Class template moneypunct_­byname [locale.moneypunct.byname]

namespace std {
  template <class charT, bool Intl = false>
  class moneypunct_byname : public moneypunct<charT, Intl> {
    public:
      using pattern     = money_base::pattern;
      using string_type = basic_string<charT>;

      explicit moneypunct_byname(const char*, size_t refs = 0);
      explicit moneypunct_byname(const string&, size_t refs = 0);

    protected:
      ~moneypunct_byname();
    };
}

25.4.7 The message retrieval category [category.messages]

Class messages<charT> implements retrieval of strings from message catalogs.

25.4.7.1 Class template messages [locale.messages]

namespace std {
  class messages_base {
  public:
    using catalog = unspecified signed integer type;
  };

  template <class charT>
    class messages : public locale::facet, public messages_base {
    public:
      using char_type   = charT;
      using string_type = basic_string<charT>;

      explicit messages(size_t refs = 0);

      catalog open(const basic_string<char>& fn, const locale&) const;
      string_type get(catalog c, int set, int msgid,
                       const string_type& dfault) const;
      void close(catalog c) const;

      static locale::id id;

    protected:
      ~messages();
      virtual catalog do_open(const basic_string<char>&, const locale&) const;
      virtual string_type do_get(catalog, int set, int msgid,
                                 const string_type& dfault) const;
      virtual void do_close(catalog) const;
    };
}

Values of type messages_­base​::​catalog usable as arguments to members get and close can be obtained only by calling member open.

25.4.7.1.1 messages members [locale.messages.members]

catalog open(const basic_string<char>& name, const locale& loc) const;

Returns: do_­open(name, loc).

string_type get(catalog cat, int set, int msgid, const string_type& dfault) const;

Returns: do_­get(cat, set, msgid, dfault).

void close(catalog cat) const;

Effects: Calls do_­close(cat).

25.4.7.1.2 messages virtual functions [locale.messages.virtuals]

catalog do_open(const basic_string<char>& name, const locale& loc) const;

Returns: A value that may be passed to get() to retrieve a message from the message catalog identified by the string name according to an implementation-defined mapping. The result can be used until it is passed to close().

Returns a value less than 0 if no such catalog can be opened.

Remarks: The locale argument loc is used for character set code conversion when retrieving messages, if needed.

string_type do_get(catalog cat, int set, int msgid, const string_type& dfault) const;

Requires: cat shall be a catalog obtained from open() and not yet closed.

Returns: A message identified by arguments set, msgid, and dfault, according to an implementation-defined mapping. If no such message can be found, returns dfault.

void do_close(catalog cat) const;

Requires: cat shall be a catalog obtained from open() and not yet closed.

Effects: Releases unspecified resources associated with cat.

Remarks: The limit on such resources, if any, is implementation-defined.

25.4.7.2 Class template messages_­byname [locale.messages.byname]

namespace std {
  template <class charT>
    class messages_byname : public messages<charT> {
    public:
      using catalog     = messages_base::catalog;
      using string_type = basic_string<charT>;

      explicit messages_byname(const char*, size_t refs = 0);
      explicit messages_byname(const string&, size_t refs = 0);

    protected:
      ~messages_byname();
    };
}

25.4.8 Program-defined facets [facets.examples]

A C++ program may define facets to be added to a locale and used identically as the built-in facets. To create a new facet interface, C++ programs simply derive from locale​::​facet a class containing a static member: static locale​::​id id.

[Note: The locale member function templates verify its type and storage class. end note]

[Example: Traditional global localization is still easy:

#include <iostream>
#include <locale>
int main(int argc, char** argv) {
  using namespace std;
  locale::global(locale(""));           // set the global locale
                                        // imbue it on all the std streams
  cin.imbue(locale());
  cout.imbue(locale());
  cerr.imbue(locale());
  wcin.imbue(locale());
  wcout.imbue(locale());
  wcerr.imbue(locale());

  return MyObject(argc, argv).doit();
}

end example]

[Example: Greater flexibility is possible:

#include <iostream>
#include <locale>
int main() {
  using namespace std;
  cin.imbue(locale(""));        // the user's preferred locale
  cout.imbue(locale::classic());
  double f;
  while (cin >> f) cout << f << endl;
  return (cin.fail() != 0);
}

In a European locale, with input 3.456,78, output is 3456.78. end example]

This can be important even for simple programs, which may need to write a data file in a fixed format, regardless of a user's preference.

[Example: Here is an example of the use of locales in a library interface.

// file: Date.h
#include <iosfwd>
#include <string>
#include <locale>

class Date {
public:
  Date(unsigned day, unsigned month, unsigned year);
  std::string asString(const std::locale& = std::locale());
};

std::istream& operator>>(std::istream& s, Date& d);
std::ostream& operator<<(std::ostream& s, Date d);

This example illustrates two architectural uses of class locale.

The first is as a default argument in Date​::​asString(), where the default is the global (presumably user-preferred) locale.

The second is in the operators << and >>, where a locale “hitchhikes” on another object, in this case a stream, to the point where it is needed.

// file: Date.C
#include "Date"                 // includes <ctime>
#include <sstream>
std::string Date::asString(const std::locale& l) {
  using namespace std;
  ostringstream s; s.imbue(l);
  s << *this; return s.str();
}

std::istream& operator>>(std::istream& s, Date& d) {
  using namespace std;
  istream::sentry cerberos(s);
  if (cerberos) {
    ios_base::iostate err = goodbit;
    struct tm t;
    use_facet<time_get<char>>(s.getloc()).get_date(s, 0, s, err, &t);
    if (!err) d = Date(t.tm_day, t.tm_mon + 1, t.tm_year + 1900);
    s.setstate(err);
  }
  return s;
}

end example]

A locale object may be extended with a new facet simply by constructing it with an instance of a class derived from locale​::​facet. The only member a C++ program must define is the static member id, which identifies your class interface as a new facet.

[Example: Classifying Japanese characters:

// file: <jctype>
#include <locale>
namespace My {
  using namespace std;
  class JCtype : public locale::facet {
  public:
    static locale::id id;       // required for use as a new locale facet
    bool is_kanji (wchar_t c) const;
    JCtype() { }
  protected:
    ~JCtype() { }
  };
}

// file: filt.C
#include <iostream>
#include <locale>
#include "jctype"               // above
std::locale::id My::JCtype::id; // the static JCtype member declared above.

int main() {
  using namespace std;
  using wctype = ctype<wchar_t>;
  locale loc(locale(""),        // the user's preferred locale ...
         new My::JCtype);       // and a new feature ...
  wchar_t c = use_facet<wctype>(loc).widen('!');
  if (!use_facet<My::JCtype>(loc).is_kanji(c))
    cout << "no it isn't!" << endl;
}

The new facet is used exactly like the built-in facets. end example]

[Example: Replacing an existing facet is even easier. The code does not define a member id because it is reusing the numpunct<charT> facet interface:

// file: my_­bool.C
#include <iostream>
#include <locale>
#include <string>
namespace My {
  using namespace std;
  using cnumpunct = numpunct_byname<char>;
  class BoolNames : public cnumpunct {
  protected:
    string do_truename()  const { return "Oui Oui!"; }
    string do_falsename() const { return "Mais Non!"; }
    ~BoolNames() { }
  public:
    BoolNames(const char* name) : cnumpunct(name) { }
  };
}

int main(int argc, char** argv) {
  using namespace std;
  // make the user's preferred locale, except for...
  locale loc(locale(""), new My::BoolNames(""));
  cout.imbue(loc);
  cout << boolalpha << "Any arguments today? " << (argc > 1) << endl;
}

end example]