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STRFTIME(3) Library Functions Manual 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, be-
ginning 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 fol-
lowing 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).
%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 conver-
sions 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.
%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.
POSIX 1003.2 EXTENSIONS
If POSIX2_DATE is defined, then all of the conversions available with SYSV_EXT are avail-
able, 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 week 53 of the previous
year 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
Sunday are considered to be in week 0. (Note: this last statement is quoted verba-
tim from the POSIX standard. It probably means to say ``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 represen-
tations are used.
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)
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.
STRFTIME(3)
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