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STRFTIME(3) Library Functions Manual STRFTIME(3)
NAME
strftime - 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_l(char * restrict buf, size_t maxsize,
const char * restrict format, const struct tm * restrict timeptr,
locale_t loc);
size_t
strftime_z(const timezone_t tz, char * restrict buf, size_t maxsize,
const char * restrict format, const struct tm * restrict timeptr);
size_t
strftime_lz(const timezone_t tz, char * restrict buf, size_t maxsize,
const char * restrict format, const struct tm * restrict timeptr,
locale_t loc);
DESCRIPTION
The strftime() function formats the information from timeptr into the
array pointed to by buf according to the string pointed to by format.
The function strftime_l() does the same as strftime() but takes an
explicit locale specified in the locale_t loc argument, rather than using
the current locale.
The function strftime_z() is similar to strftime(), but uses an explicit
timezone specified in the const timezone_t tz argument, instead of using
the default from the environment.
The function strftime_lz() does the same as strftime() but takes both an
explicit timezone and locale arguments.
The format string consists of zero or more conversion specifications and
ordinary characters. All ordinary characters are copied directly into
the array. 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 NUL
character, is not more than maxsize, strftime() returns the number of
characters in the array, not counting the terminating NUL. Otherwise,
zero is returned and the buffer contents are indeterminate.
Each conversion specification is replaced by the characters as follows
which are then copied into the array. The characters depend on the
values of zero or more members of timeptr as specified by brackets in the
description. If a bracketed member name is followed by "+", strftime can
use the named member even though POSIX.1-2024 does not list it; if the
name is followed by "-", strftime ignores the member even though
POSIX.1-2024 lists it which means portable code should set it. For
portability, timeptr should be initialized as if by a successful call to
gmtime(3), localtime(3), mktime(3), timegm(3), or similar functions.
%A is replaced by the locale's full weekday name. [tm_wday]
%a is replaced by the locale's abbreviated weekday name. [tm_wday]
%B is replaced by the locale's full month name. [tm_mon]
%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, with at least two digits by
default.
%c is replaced by the locale's appropriate date and time
representation. [tm_year, tm_yday, tm_mon, tm_mday, tm_wday,
tm_hour, tm_min, tm_sec, tm_gmtoff, tm_zone, tm_isdst -].
%D is replaced by the date in the format "%m/%d/%y". Although used in
the United States for current dates, this format is ambiguous
elsewhere and for dates that might involve other centuries.
[tm_year, tm_mon, tm_mday]
%d is replaced by the day of the month as a decimal number [01,31].
[tm_mday]
%d is replaced by the day of the month as a decimal number (01-31).
%E* %O*
POSIX locale extensions. The sequences %Ec %EC %Ex %EX %Ey %EY %Od
%Oe %OH %OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy are supposed to
provide alternate representations.
Additionally %OB implemented to represent alternative months names
(used standalone, without day mentioned).
%e is replaced by the day of month as a decimal number [1,31]; single
digits are preceded by a blank. [tm_mday]
%F is equivalent to "%Y-%m-%d" (the ISO 8601 date format). [tm_year,
tm_mon, tm_mday]
%G is replaced by the ISO 8601 year with century as a decimal number.
See also the %V conversion specification [tm_year, tm_yday,
tm_wday]
%g is replaced by the ISO 8601 year without century as a decimal
number. 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. [tm_year, tm_yday, tm_wday]
%H is replaced by the hour (24-hour clock) as a decimal number
[00,23]. [tm_hour]
%I is replaced by the hour (12-hour clock) as a decimal number
[01,12]. [tm_hour]
%j is replaced by the day of the year as a decimal number [001,366].
[tm_yday]
%k is replaced by the hour (24-hour clock) as a decimal number [0,23];
single digits are preceded by a blank. [tm_hour]
%l is replaced by the hour (12-hour clock) as a decimal number [1,12];
single digits are preceded by a blank. [tm_hour]
%M is replaced by the minute as a decimal number [00,59]. [tm_min]
%m is replaced by the month as a decimal number [01,12]. [tm_mon]
%n is replaced by a newline.
%p is replaced by the locale's equivalent of either "AM" or "PM".
[tm_hour]
%R is replaced by the time in the format "%H:%M". [tm_hour, tm_min]
%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 [00,60]. The range
of seconds is [00-60] instead of [00-59] to allow for the periodic
occurrence of leap seconds. [tm_sec]
%s is replaced by the number of seconds since the Epoch (see
ctime(3)). Although %s is reliable in this implementation, it can
have glitches on other platforms (notably obsolescent platforms
lacking tm_gmtoff or where is no wider than int), and POSIX allows
strftime to set errno to EINVAL or EOVERFLOW and return 0 if the
number of seconds would be negative or out of range for Portable
code should therefore format a value directly via something like
snprintf(3) instead of via localtime(3) followed by strftime with
"%s". [tm_year, tm_mon, tm_mday, tm_hour, tm_min, tm_sec,
tm_gmtoff +, tm_isdst -].
%T is replaced by the time in the format "%H:%M:%S". [tm_hour,
tm_min, tm_sec]
%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]. [tm_wday, tm_yday,
tm_year -]
%u is replaced by the weekday (Monday as the first day of the week) as
a decimal number [1,7]. [tm_wday]
%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. [tm_year, tm_yday, tm_wday]
%v is replaced by the date in the format "%e-%b-%Y". [tm_year,
tm_yday, tm_wday]
%W is replaced by the week number of the year (Monday as the first day
of the week) as a decimal number [00,53]. [tm_yday, tm_wday]
%w is replaced by the weekday (Sunday as the first day of the week) as
a decimal number [0,6]. [tm_year, tm_yday, tm_wday]
%X is replaced by the locale's appropriate time representation.
[tm_year -, tm_yday -, tm_mon -, tm_mday -, tm_wday -, tm_hour,
tm_min, tm_sec, tm_gmtoff, tm_zone, tm_isdst -].
%x is replaced by the locale's appropriate date representation.
[tm_year, tm_yday, tm_mon, tm_mday, tm_wday, tm_hour -, tm_min -,
tm_sec -, tm_gmtoff -, tm_zone -, tm_isdst -].
%Y is replaced by the year with century as a decimal number.
[tm_year]
%y is replaced by the year without century as a decimal number
[00,99]. [tm_year]
%Z is replaced by the time zone abbreviation, or the empty string if
this is not determinable. [tm_zone, tm_isdst -]
%z is replaced by the offset from the Prime Meridian in the format
+HHMM or -HHMM (ISO 8601) as appropriate, with positive values
representing locations east of Greenwich, or by the empty string if
this is not determinable. The numeric time zone abbreviation -0000
is used when the time is Universal Time but local time is
indeterminate; by convention this is used for locations while
uninhabited, and corresponds to a zero offset when the time zone
abbreviation begins with "[-]".
%+ is replaced by locale's date and time in date(1) format. On NetBSD
currently this only works for the C locale. [tm_year, tm_yday,
tm_mon, tm_mday, tm_wday, tm_hour, tm_min, tm_sec, tm_gmtoff,
tm_zone]
%-* GNU libc extension. Do not do any padding when performing
numerical outputs.
%_* GNU libc extension. Explicitly specify space for padding.
%0* GNU libc extension. Explicitly specify zero for padding.
%% is replaced by as single `%'.
As a side effect, strftime also behaves as if tzset(3) were called. This
is for compatibility with older platforms, as required by POSIX; it is
not needed for strftime own use.
RETURN VALUES
If the conversion is successful, strftime returns the number of bytes
placed into the array, not counting the terminating NUL; errno is
unchanged if the returned value is zero. Otherwise, errno is set to
indicate the error, zero is returned, and the array contents are
unspecified.
ERRORS
This function fails if:
[ERANGE] The specified file offset is invalid. The total
number of resulting bytes, including the terminating
NUL character, is more than maxsize.
[EOVERFLOW] The format includes an %s conversion and the number of
seconds since the Epoch cannot be represented in a
time_t.
SEE ALSO
date(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
extensions.
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
Sunday (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.
The strftime() function does not correctly handle multibyte characters in
the format argument.
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.
NetBSD 11.99 April 6, 2025 NetBSD 11.99