STRFTIME(3) STRFTIME(3)
NAME
strftime - generate formatted time information
SYNOPSIS
#include <sys/types.h>
#include <time.h>
size_t strftime(char *s, size_t maxsize, const char *format,
const struct tm *timeptr);
DESCRIPTION
The following description is transcribed verbatim from the December 7,
1988 draft standard for ANSI C. This draft is essentially identical
in technical content to the final version of the standard. The
strftime function places characters into the array pointed to by s as
controlled by the string pointed to by format. The format shall be a
multibyte character sequence, beginning and ending in its initial
shift state. The format string consists of zero or more conversion
specifiers and ordinary multibyte characters. A conversion specifier
consists of a % character followed by a character that determines the
behavior of the conversion specifier. All ordinary multibyte
characters (including the terminating null character) are copied
unchanged into the array. If copying takes place between objects that
overlap the behavior is undefined. No more than maxsize characters
are placed into the array. Each conversion specifier is replaced by
appropriate characters as described in the following list. The
appropriate characters are determined by the LC_TIME category of the
current locale and by the values contained in the structure pointed to
by timeptr.
%a is replaced by the locale's abbreviated weekday name.
%A is replaced by the locale's full weekday name.
%b is replaced by the locale's abbreviated month name.
%B is replaced by the locale's full month name.
%c is replaced by the locale's appropriate date and time
representation.
%d is replaced by the day of the month as a decimal number (01-31).
%H is replaced by the hour (24-hour clock) as a decimal number (00-
23).
%I is replaced by the hour (12-hour clock) as a decimal number (01-
12).
%j is replaced by the day of the year as a decimal number (001-366).
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STRFTIME(3) STRFTIME(3)
%m is replaced by the month as a decimal number (01-12).
%M is replaced by the minute as a decimal number (00-59).
%p is replaced by the locale's equivalent of the AM/PM designations
associated with a 12-hour clock.
%S is replaced by the second as a decimal number (00-61).
%U is replaced by the week number of the year (the first Sunday as
the first day of week 1) as a decimal number (00-53).
%w is replaced by the weekday as a decimal number [0 (Sunday)-6].
%W is replaced by the week number of the year (the first Monday as
the first day of week 1) as a decimal number (00-53).
%x is replaced by the locale's appropriate date representation.
%X is replaced by the locale's appropriate time representation.
%y is replaced by the year without century as a decimal number (00-
99).
%Y is replaced by the year with century as a decimal number.
%Z is replaced by the time zone name or abbreviation, or by no
characters if no time zone is determinable.
%% is replaced by %. If a conversion specifier is not one of the
above, the behavior is undefined.
RETURNS
If the total number of resulting characters including the terminating
null character is not more than maxsize, the strftime function returns
the number of characters placed into the array pointed to by s not
including the terminating null character. Otherwise, zero is returned
and the contents of the array are indeterminate.
NON-ANSI EXTENSIONS
If SYSV_EXT is defined when the routine is compiled, then the
following additional conversions will be available. These are
borrowed from the System V cftime(3) and ascftime(3) routines.
%D is equivalent to specifying %m/%d/%y.
%e is replaced by the day of the month, padded with a blank if it is
only one digit.
%h is equivalent to %b, above.
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STRFTIME(3) STRFTIME(3)
%n is replaced with a newline character (ASCII LF).
%r is equivalent to specifying %I:%M:%S %p.
%R is equivalent to specifying %H:%M.
%T is equivalent to specifying %H:%M:%S.
%t is replaced with a TAB character.
If SUNOS_EXT is defined when the routine is compiled, then the
following additional conversions will be available. These are
borrowed from the SunOS version of strftime.
%k is replaced by the hour (24-hour clock) as a decimal number (0-
23). Single digit numbers are padded with a blank.
%l is replaced by the hour (12-hour clock) as a decimal number (1-
12). Single digit numbers are padded with a blank.
POSIX 1003.2 EXTENSIONS
If POSIX2_DATE is defined, then all of the conversions available with
SYSV_EXT and SUNOS_EXT are available, as well as the following
additional conversions:
%C The century, as a number between 00 and 99.
%u is replaced by the weekday as a decimal number [1 (Monday)-7].
%V is replaced by the week number of the year (the first Monday as
the first day of week 1) as a decimal number (01-53). The method
for determining the week number is as specified by ISO 8601 (to
wit: if the week containing January 1 has four or more days in
the new year, then it is week 1, otherwise it is the highest
numbered week of the previous year (52 or 53) and the next week
is week 1). The text of the POSIX standard for the date utility
describes %U and %W this way:
%U is replaced by the week number of the year (the first Sunday as
the first day of week 1) as a decimal number (00-53). All days
in a new year preceding the first Sunday are considered to be in
week 0.
%W is replaced by the week number of the year (the first Monday as
the first day of week 1) as a decimal number (00-53). All days
in a new year preceding the first Monday are considered to be in
week 0. In addition, the alternate representations %Ec, %EC,
%Ex, %Ey, %EY, %Od, %Oe, %OH, %OI, %Om, %OM, %OS, %Ou, %OU, %OV,
%Ow, %OW, and %Oy are recognized, but their normal
representations are used.
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STRFTIME(3) STRFTIME(3)
VMS EXTENSIONS
If VMS_EXT is defined, then the following additional conversion is
available:
%v The date in VMS format (e.g. 20-JUN-1991).
SEE ALSO
time(2), ctime(3), localtime(3), tzset(3)
BUGS
This version does not handle multibyte characters or pay attention to
the setting of the LC_TIME environment variable. It is not clear what
is ``appropriate'' for the C locale; the values returned are a best
guess on the author's part.
CAVEATS
The pre-processor symbol POSIX_SEMANTICS is automatically defined,
which forces the code to call tzset(3) whenever the TZ environment
variable has changed. If this routine will be used in an application
that will not be changing TZ, then there may be some performance
improvements by not defining POSIX_SEMANTICS.
AUTHOR
Arnold Robbins
INTERNET: arnold@skeeve.atl.ga.us
UUCP: emory!skeeve!arnold
Phone: +1 404 248 9324
ACKNOWLEDGEMENTS
Thanks to Geoff Clare <gwc@root.co.uk> for helping debug earlier
versions of this routine, and for advice about POSIX semantics.
Additional thanks to Arthur David Olsen <ado@elsie.nci.nih.gov> for
some code improvements. Thanks also to Tor Lillqvist <tml@tik.vtt.fi>
for code fixes to the ISO 8601 code.
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