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strftime(3) - strftime, strftime - format date and time - man 3 strftime

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



NAME
       strftime - format date and time(1,2,n)

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(1,2,n) tm according to
       the format specification format and places the result in(1,8) the  character
       array s of size max.

       Ordinary characters placed in(1,8) the format string(3,n) are copied to s without
       conversion.  Conversion specifiers are introduced by a  `%'  character,
       and are replaced in(1,8) 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(1,2,n)  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(1,8) other countries %d/%m/%y is rather common.
              This means that in(1,8) 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 year 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(3,n)  the  ISO  week
              number  belongs  to the previous or next year, that year is used
              instead. (TZ)

       %g     Like %G, but without century, i.e., 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(3,n) (range 00 to
              23).

       %I     The hour as a decimal number using a 12-hour clock(3,n) (range 01  to
              12).

       %j     The day of the year as a decimal number (range 001 to 366).

       %k     The  hour  (24-hour  clock(3,n)) 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(3,n)) 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(1,2,n) value, or the
              corresponding strings for the current locale.  Noon  is  treated
              as `pm' and midnight as `am'.

       %P     Like %p but in(1,8) lowercase: `am' or `pm' or a corresponding string(3,n)
              for the current locale. (GNU)

       %r     The time(1,2,n) in(1,8) a.m. or p.m. notation.  In the POSIX locale(3,5,7) this  is
              equivalent to `%I:%M:%S %p'. (SU)

       %R     The time(1,2,n) in(1,8) 24-hour notation (%H:%M). (SU) For a version(1,3,5) includ-
              ing the seconds, see %T below.

       %s     The number of seconds since the Epoch,  i.e.,  since  1970-01-01
              00:00:00 UTC. (TZ)

       %S     The second as a decimal number (range 00 to 61).

       %t     A tab character. (SU)

       %T     The time(1,2,n) in(1,8) 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 8601:1988 week number 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(1,8) the current year,  and  with  Monday  as  the
              first day of the week. 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(3,5,7) without
              the time.

       %X     The preferred time(1,2,n) representation for the current locale(3,5,7) 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
              RFC822-conformant dates (using "%a,  %d  %b  %Y  %H:%M:%S  %z").
              (GNU)

       %Z     The time(1,2,n) zone or name or abbreviation.

       %+     The date and time(1,2,n) in(1,8) date(1) format. (TZ)

       %%     A literal `%' character.

       Some  conversion  specifiers can be modified by preceding them 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 cur-
       rent locale(3,5,7), the behaviour will be  as  if(3,n)  the  unmodified  conversion
       specification  were  used.  (SU) The Single Unix Specification mentions
       %Ec, %EC, %Ex, %EX, %Ry, %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(1,2,n)  structure  tm is defined in(1,8) <time.h>.  See also
       ctime(3).


RETURN VALUE
       The strftime() function returns the number of characters placed in(1,8)  the
       array  s,  not  including  the  terminating NUL character, provided the
       string(3,n), including the terminating NUL, fits.  Otherwise, it returns  0,
       and  the contents of the array is undefined.  (Thus at least since libc
       4.4.4; very old versions of libc, such as libc 4.4.1, would return  max
       if(3,n) the array was too small.)

       Note  that  the  return value 0 does not necessarily indicate an error(8,n);
       for example, in(1,8) many locales %p yields an empty string.

ENVIRONMENT
       The environment variables TZ and LC_TIME are used.

CONFORMING TO
       ANSI C, SVID 3, ISO 9899.  There are strict inclusions between the  set(7,n,1 builtins)
       of  conversions  given  in(1,8) ANSI C (unmarked), those given in(1,8) the Single
       Unix Specification (marked SU), those given in(1,8) Olson's timezone package
       (marked  TZ),  and those given in(1,8) glibc (marked GNU), except that %+ is
       not supported in(1,8) 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(1,8) C99 and POSIX 1003.1-2001.

BUGS
       Some  buggy versions of gcc complain about the use of %c: warning: `%c'
       yields only last 2 digits of year in(1,8) some locales.  Of course  program-
       mers  are  encouraged  to  use %c, it gives the preferred date and time(1,2,n)
       representation. One meets all kinds of strange obfuscations to  circum-
       vent this gcc 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);
              }

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



GNU                               1999-03-29                       STRFTIME(3)

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