25 Localization library [localization]

25.4 Standard locale categories [locale.categories]

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.244
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.245
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 should 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 mod246 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()247, except that the sequence of characters produced for those specifiers that are described as depending on the C locale are instead implementation-defined.248
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 should 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();
    };
}