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STRFTIME(3)                Linux Programmer's Manual               STRFTIME(3)



NAME
       strftime - format date and time

SYNOPSIS
       #include <time.h>

       size_t strftime(char *s, size_t max, const char *format,
                       const struct tm *tm);

DESCRIPTION
       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.

       Ordinary characters placed in the format string are copied to s without conversion.
       Conversion  specifications  are  introduced by a '%' character, and terminated by a
       conversion specifier character, and are replaced in s as follows:

       %a     The abbreviated weekday name according to the current locale.

       %A     The full weekday name according to the current locale.

       %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 locale.

       %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 ambiguous 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  decimal  number.
              The  4-digit  year  corresponding to the ISO week number (see %V).  This has
              the same format and value as %Y, except that if the ISO week number  belongs
              to the previous or next year, that year is used instead. (TZ)

       %g     Like %G, but without century, that is, with a 2-digit year (00-99). (TZ)

       %h     Equivalent to %b.  (SU)

       %H     The hour as a decimal number using a 24-hour clock (range 00 to 23).

       %I     The hour as a decimal number using a 12-hour clock (range 01 to 12).

       %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 sec-
              onds, see %T below.

       %s     The number of seconds since the Epoch, that is,  since  1970-01-01  00:00:00
              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 num-
              ber, 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.  (SU)

       %w     The  day  of  the week as a decimal, range 0 to 6, Sunday being 0.  See also
              %u.

       %W     The week number of the current year as a decimal number,  range  00  to  53,
              starting with the first Monday as the first day of week 01.

       %x     The preferred date representation for the current locale without the time.

       %X     The preferred time representation for the current locale without the date.

       %y     The year as a decimal number without a century (range 00 to 99).

       %Y     The year as a decimal number including the century.

       %z     The  time-zone as hour offset from GMT.  Required to emit RFC 822-conformant
              dates (using "%a, %d %b %Y %H:%M:%S %z"). (GNU)

       %Z     The timezone or name or abbreviation.

       %+     The date and time in date(1) format. (TZ) (Not supported in glibc2.)

       %%     A literal '%' character.

       Some conversion specifications can be modified by preceding the  conversion  speci-
       fier character by the E or O modifier to indicate that an alternative format should
       be used.  If the alternative format or specification 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 ctime(3).

RETURN VALUE
       The strftime() function returns the number of characters placed in the array s, not
       including the terminating null byte, provided the string, including the terminating
       null  byte,  fits.  Otherwise, it returns 0, and the contents of the array is unde-
       fined.  (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.

ENVIRONMENT
       The environment variables TZ and LC_TIME are used.

CONFORMING TO
       SVr4, C89, C99.  There are strict inclusions between the set of  conversions  given
       in  ANSI  C  (unmarked),  those given in the Single Unix Specification (marked SU),
       those given in Olson's timezone package (marked  TZ),  and  those  given  in  glibc
       (marked  GNU), except that %+ is not supported in glibc2.  On the other hand glibc2
       has several more extensions.  POSIX.1 only refers  to  ANSI  C;  POSIX.2  describes
       under  date(1)  several  extensions that could apply to strftime() as well.  The %F
       conversion is in C99 and POSIX.1-2001.

       In SUSv2, the %S specifier allowed a range of 00 to 61, to allow for the  theoreti-
       cal  possibility  of  a  minute that included a double leap second (there never has
       been such a minute).

NOTES
   ISO 8601 Week Dates
       %G, %g, and %V yield values calculated from the  week-based  year  defined  by  the
       ISO 8601  standard.  In this system, weeks start on a Monday, and are numbered from
       01, for the first week, up to 52 or 53, for the last week.  Week  1  is  the  first
       week  where  four  or more days fall within the new year (or, synonymously, week 01
       is: the first week of the year that contains a Thursday; or, the week  that  has  4
       January  in  it).   When  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 Thursday, 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  fea-
       tures.)   Between  the  '%'  character  and  the conversion specifier character, an
       optional flag and field width may be specified.  (These precede the E  or  O  modi-
       fiers, 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 upper case.

       #      Swap the case of the result string.  (This flag only works with certain con-
              version  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.

BUGS
       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 programmers are encouraged
       to use %c, it gives the preferred date and  time  representation.   One  meets  all
       kinds  of  strange  obfuscations  to  circumvent this gcc(1) problem.  A relatively
       clean one is to add an intermediate function

           size_t
           my_strftime(char *s, size_t max, const char *fmt,
                       const struct tm *tm)
           {
               return strftime(s, max, fmt, tm);
           }

       Nowadays, gcc(1) provides the -Wno-format-y2k option to  prevent  the  warning,  so
       that the above workaround is no longer required.

EXAMPLE
       The program below can be used to experiment with strftime().

       Some  examples  of  the result string produced by the glibc implementation of strf-
       time() 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>

       int
       main(int argc, char *argv[])
       {
           char outstr[200];
           time_t t;
           struct tm *tmp;

           t = time(NULL);
           tmp = localtime(&t);
           if (tmp == NULL) {
               perror("localtime");
               exit(EXIT_FAILURE);
           }

           if (strftime(outstr, sizeof(outstr), argv[1], tmp) == 0) {
               fprintf(stderr, "strftime returned 0");
               exit(EXIT_FAILURE);
           }

           printf("Result string is \"%s\"\n", outstr);
           exit(EXIT_SUCCESS);
       } /* main */

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

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the  project, and information about reporting bugs, can be found at http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2009-02-24                       STRFTIME(3)

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