STRFTIME(3) BSD Library Functions Manual STRFTIME(3)NAME
strftime, strftime_z — format date and time
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <time.h>
size_t
strftime(char * restrict buf, size_t maxsize,
const char * restrict format, const struct tm * restrict timeptr);
size_t
strftime_z(const timezone_t tz, char * restrict buf, size_t maxsize,
const char * restrict format, const struct tm * restrict timeptr);
DESCRIPTION
The strftime() function formats the information from timeptr into the
buffer buf according to the string pointed to by format.
The format string consists of zero or more conversion specifications and
ordinary characters. All ordinary characters are copied directly into
the buffer. A conversion specification consists of a percent sign ‘%’
and one other character.
No more than maxsize characters will be placed into the array. If the
total number of resulting characters, including the terminating null
character, is not more than maxsize, strftime() returns the number of
characters in the array, not counting the terminating null. Otherwise,
zero is returned and the contents of the array are undefined.
Each conversion specification is replaced by the characters as follows
which are then copied into the buffer.
%A is replaced by the locale's full weekday name.
%a is replaced by the locale's abbreviated weekday name.
%B is replaced by the locale's full month name.
%b or %h
is replaced by the locale's abbreviated month name.
%C is replaced by the century (a year divided by 100 and truncated to
an integer) as a decimal number [00,99].
%c is replaced by the locale's appropriate date and time representa‐
tion.
%D is replaced by the date in the format “%m/%d/%y”.
%d is replaced by the day of the month as a decimal number [01,31].
%e is replaced by the day of month as a decimal number [1,31]; single
digits are preceded by a blank.
%F is replaced by the date in the format “%Y-%m-%d” (the ISO 8601 date
format).
%G is replaced by the ISO 8601 year with century as a decimal number.
%g is replaced by the ISO 8601 year without century as a decimal num‐
ber (00-99). This is the year that includes the greater part of
the week. (Monday as the first day of a week). See also the ‘%V’
conversion specification.
%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].
%k is replaced by the hour (24-hour clock) as a decimal number [0,23];
single digits are preceded by a blank.
%l is replaced by the hour (12-hour clock) as a decimal number [1,12];
single digits are preceded by a blank.
%M is replaced by the minute as a decimal number [00,59].
%m is replaced by the month as a decimal number [01,12].
%n is replaced by a newline.
%p is replaced by the locale's equivalent of either “AM” or “PM”.
%R is replaced by the time in the format “%H:%M”.
%r is replaced by the locale's representation of 12-hour clock time
using AM/PM notation.
%S is replaced by the second as a decimal number [00,61]. The range
of seconds is (00-61) instead of (00-59) to allow for the periodic
occurrence of leap seconds and double leap seconds.
%s is replaced by the number of seconds since the Epoch, UTC (see
mktime(3)).
%T is replaced by the time in the format “%H:%M:%S”.
%t is replaced by a tab.
%U is replaced by the week number of the year (Sunday as the first day
of the week) as a decimal number [00,53].
%u is replaced by the weekday (Monday as the first day of the week) as
a decimal number [1,7].
%V is replaced by the week number of the year (Monday as the first day
of the week) as a decimal number [01,53]. According to ISO 8601 the
week containing January 1 is week 1 if it has four or more days in
the new year, otherwise it is week 53 of the previous year, and the
next week is week 1. The year is given by the ‘%G’ conversion
specification.
%v is replaced by the date in the format “%e-%b-%Y”.
%W is replaced by the week number of the year (Monday as the first day
of the week) as a decimal number [00,53].
%w is replaced by the weekday (Sunday as the first day of the week) as
a decimal number [0,6].
%X is replaced by the locale's appropriate time representation.
%x is replaced by the locale's appropriate date representation.
%Y is replaced by the year with century as a decimal number.
%y is replaced by the year without century as a decimal number
[00,99].
%Z is replaced by the time zone name.
%z is replaced by the offset from UTC in the ISO 8601 format
“[-]hhmm”.
%% is replaced by ‘%’.
The strftime_z() function is similar to strftime(), but it also takes a
const timezone_t tz argument.
SEE ALSOdate(1), printf(1), ctime(3), printf(3), strptime(3), tm(3)STANDARDS
The strftime() function conforms to ISO/IEC 9899:1999 (“ISO C99”). The
‘%C’, ‘%D’, ‘%e’, ‘%g’, ‘%G’, ‘%h’, ‘%k’, ‘%l’, ‘%n’, ‘%r’, ‘%R’, ‘%s’,
‘%t’, ‘%T’, ‘%u’, ‘%V’, and ‘%v’ conversion specifications are exten‐
sions.
Use of the ISO 8601 conversions may produce non-intuitive results. Week
01 of a year is per definition the first week which has the Thursday in
this year, which is equivalent to the week which contains the fourth day
of January. In other words, the first week of a new year is the week
which has the majority of its days in the new year. Week 01 might also
contain days from the previous year and the week before week 01 of a year
is the last week (52 or 53) of the previous year even if it contains days
from the new year. A week starts with Monday (day 1) and ends with Sun‐
day (day 7). For example, the first week of the year 1997 lasts from
1996-12-30 to 1997-01-05.
BUGS
There is no conversion specification for the phase of the moon.
A return value of zero does not necessarily indicate an error. If the
resulting string is an empty string, the result value is zero and it is
not possible to distinguish between success and error. For example, in
many locales %p yields an empty string. This problem can be avoided by
inserting an extra space at the beginning of the format string and then
skipping over it or removing it from the result.
BSD April 14, 2011 BSD
