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           #include <time.h>
           size_t strftime(char *s, size_t max, const char *format,
                           const struct tm *tm);


           The  strftime()  function  formats the broken-down time tm according to
           the format specification format and places the result in the  character
           array s of size max.
           The  format  specification  is a null-terminated string and may contain
           special character sequences called conversion specifications,  each  of
           which  is  introduced  by  a '%' character and terminated by some other
           character known as a conversion specifier character.  All other charac-
           ter sequences are ordinary character sequences.
           The  characters  of  ordinary  character  sequences (including the null
           byte) are copied verbatim from format to s.  However, the characters of
           conversion specifications are replaced as follows:
           %a     The  abbreviated  name  of  the day of the week according to the
                  current locale.
           %A     The full name of the day of the week according  to  the  current
           %b     The abbreviated month name according to the current locale.
           %B     The full month name according to the current locale.
           %c     The  preferred  date  and  time  representation  for the current
           %C     The century number (year/100) as a 2-digit integer. (SU)
           %d     The day of the month as a decimal number (range 01 to 31).
           %D     Equivalent to %m/%d/%y.  (Yecch--for Americans  only.   Americans
                  should  note  that in other countries %d/%m/%y is rather common.
                  This means that in international context this format is  ambigu-
                  ous and should not be used.) (SU)
           %e     Like %d, the day of the month as a decimal number, but a leading
                  zero is replaced by a space. (SU)
           %E     Modifier: use alternative format, see below. (SU)
           %F     Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)
           %G     The ISO 8601 week-based year (see NOTES) with century as a deci-
                  mal number.  The 4-digit year corresponding to the ISO week num-
           %j     The day of the year as a decimal number (range 001 to 366).
           %k     The  hour  (24-hour  clock) as a decimal number (range 0 to 23);
                  single digits are preceded by a blank.  (See also %H.)  (TZ)
           %l     The hour (12-hour clock) as a decimal number (range  1  to  12);
                  single digits are preceded by a blank.  (See also %I.)  (TZ)
           %m     The month as a decimal number (range 01 to 12).
           %M     The minute as a decimal number (range 00 to 59).
           %n     A newline character. (SU)
           %O     Modifier: use alternative format, see below. (SU)
           %p     Either  "AM"  or  "PM" according to the given time value, or the
                  corresponding strings for the current locale.  Noon  is  treated
                  as "PM" and midnight as "AM".
           %P     Like %p but in lowercase: "am" or "pm" or a corresponding string
                  for the current locale. (GNU)
           %r     The time in a.m. or p.m. notation.  In the POSIX locale this  is
                  equivalent to %I:%M:%S %p.  (SU)
           %R     The  time  in  24-hour  notation  (%H:%M).   (SU)  For a version
                  including the seconds, see %T below.
           %s     The number of seconds since the Epoch, 1970-01-01 00:00:00 +0000
                  (UTC). (TZ)
           %S     The  second as a decimal number (range 00 to 60).  (The range is
                  up to 60 to allow for occasional leap seconds.)
           %t     A tab character. (SU)
           %T     The time in 24-hour notation (%H:%M:%S).  (SU)
           %u     The day of the week as a decimal, range 1 to 7, Monday being  1.
                  See also %w.  (SU)
           %U     The  week  number of the current year as a decimal number, range
                  00 to 53, starting with the first Sunday as  the  first  day  of
                  week 01.  See also %V and %W.
           %V     The  ISO 8601  week  number (see NOTES) of the current year as a
                  decimal number, range 01 to 53, where week 1 is the  first  week
                  that  has  at least 4 days in the new year.  See also %U and %W.
           %Y     The year as a decimal number including the century.
           %z     The +hhmm or -hhmm numeric  timezone  (that  is,  the  hour  and
                  minute offset from UTC). (SU)
           %Z     The timezone name or abbreviation.
           %+     The  date  and  time  in  date(1) format. (TZ) (Not supported in
           %%     A literal '%' character.
           Some conversion specifications can be modified by preceding the conver-
           sion  specifier  character  by  the E or O modifier to indicate that an
           alternative format should be used.  If the alternative format or speci-
           fication does not exist for the current locale, the behavior will be as
           if the unmodified conversion specification were used. (SU)  The  Single
           UNIX  Specification  mentions  %Ec,  %EC, %Ex, %EX, %Ey, %EY, %Od, %Oe,
           %OH, %OI, %Om, %OM, %OS, %Ou, %OU, %OV, %Ow, %OW, %Oy, where the effect
           of  the  O  modifier  is to use alternative numeric symbols (say, roman
           numerals), and that of the E modifier  is  to  use  a  locale-dependent
           alternative representation.
           The  broken-down  time  structure  tm is defined in <time.h>.  See also


           Provided that the result string, including the terminating  null  byte,
           does  not  exceed  max  bytes,  strftime()  returns the number of bytes
           (excluding the terminating null byte) placed in the array  s.   If  the
           length of the result string (including the terminating null byte) would
           exceed max bytes, then strftime() returns 0, and the  contents  of  the
           array are undefined.  (This behavior applies since at least libc 4.4.4;
           very old versions of libc, such as libc 4.4.1, would return max if  the
           array was too small.)
           Note  that  the  return value 0 does not necessarily indicate an error.
           For example, in many locales %p yields an empty string.  An empty  for-
           mat string will likewise yield an empty string.


           The environment variables TZ and LC_TIME are used.


           SVr4, C89, C99.  There are strict inclusions between the set of conver-
           sions given in ANSI C (unmarked), those given in the Single UNIX Speci-
           fication  (marked  SU), those given in Olson's timezone package (marked
           TZ), and those given in glibc (marked GNU), except that %+ is not  sup-
           ported  in  glibc2.   On  the other hand glibc2 has several more exten-
           sions.  POSIX.1 only refers to ANSI C; POSIX.2 describes under  date(1)
           several extensions that could apply to strftime() as well.  The %F con-
           three of fewer days of the first calendar week of  the  new  year  fall
           within that year, then the ISO 8601 week-based system counts those days
           as part of week 53 of the preceding year.  For example, 1 January  2010
           is a Friday, meaning that just three days of that calendar week fall in
           2010.  Thus, the ISO 8601 week-based system considers these days to  be
           part  of  week  53 (%V) of the year 2009 (%G); week 01 of ISO 8601 year
           2010 starts on Monday, 4 January 2010.
       Glibc notes
           Glibc provides some extensions for conversion  specifications.   (These
           extensions  are  not specified in POSIX.1-2001, but a few other systems
           provide similar features.)  Between the '%' character and  the  conver-
           sion specifier character, an optional flag and field width may be spec-
           ified.  (These precede the E or O modifiers, if present.)
           The following flag characters are permitted:
           _      (underscore) Pad a numeric result string with spaces.
           -      (dash) Do not pad a numeric result string.
           0      Pad a numeric result string with zeros even  if  the  conversion
                  specifier character uses space-padding by default.
           ^      Convert alphabetic characters in result string to uppercase.
           #      Swap  the case of the result string.  (This flag works only with
                  certain conversion specifier characters, and  of  these,  it  is
                  only really useful with %Z.)
           An  optional  decimal  width specifier may follow the (possibly absent)
           flag.  If the natural size of the field is  smaller  than  this  width,
           then  the result string is padded (on the left) to the specified width.


           If the output string would exceed max bytes, errno is  not  set.   This
           makes it impossible to distinguish this error case from cases where the
           format  string  legitimately  produces  a  zero-length  output  string.
           POSIX.1-2001 does not specify any errno settings for strftime().
           Some  buggy  versions  of gcc(1) complain about the use of %c: warning:
           '%c' yields only last 2 digits of year in some locales.  Of course pro-
           grammers are encouraged to use %c, it gives the preferred date and time
           representation.  One meets all kinds of strange obfuscations to circum-
           vent this gcc(1) problem.  A relatively clean one is to add an interme-
           diate function
               my_strftime(char *s, size_t max, const char *fmt,
                           const struct tm *tm)
                   return strftime(s, max, fmt, tm);
       Example program
           The program below can be used to experiment with strftime().
           Some examples of the result string produced by the glibc implementation
           of strftime() are as follows:
               $ ./a.out '%m'
               Result string is "11"
               $ ./a.out '%5m'
               Result string is "00011"
               $ ./a.out '%_5m'
               Result string is "   11"
       Program source
           #include <time.h>
           #include <stdio.h>
           #include <stdlib.h>
           main(int argc, char *argv[])
               char outstr[200];
               time_t t;
               struct tm *tmp;
               t = time(NULL);
               tmp = localtime(&t);
               if (tmp == NULL) {
               if (strftime(outstr, sizeof(outstr), argv[1], tmp) == 0) {
                   fprintf(stderr, "strftime returned 0");
               printf("Result string is \"%s\"\n", outstr);


           date(1), time(2), ctime(3), setlocale(3), sprintf(3), strptime(3)

    GNU 2014-03-18 STRFTIME(3)


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