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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.

       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
       character 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 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 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.
              (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 +hhmm or -hhmm numeric timezone (that is, the hour and
              minute offset from UTC). (SU)

       %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 specifier 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 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.

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 theoretical 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 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
       conversion specifier character, an optional flag and field width may be
       specified.  (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 upper case.

       #      Swap the case of the result string.  (This flag only works 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.

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.

EXAMPLES
       RFC 2822-compliant date format (with an English locale for %a and %b)

         "%a, %d %b %Y %T %z"

       RFC 822-compliant date format (with an English locale for %a and %b)

         "%a, %d %b %y %T %z"

   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"

       Here's the 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);
       }

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

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU                               2010-01-17                       STRFTIME(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ENVIRONMENT | CONFORMING TO | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON

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