strftime - format date and time
size_t strftime(char *s, size_t max, const char *format, const struct tm
The strftime() function formats the broken-down time tm
according to the format specification format and places the result in the
character array s of size max.
Ordinary characters placed in the format
string are copied to s without conversion. Conversion specifiers are introduced
by a `%' character, and are replaced in s as follows:
- The abbreviated
weekday name according to the current locale.
- The full weekday name according
to the current locale.
- The abbreviated month name according to the current
- The full month name according to the current locale.
- The preferred
date and time representation for the current locale.
- The century number
(year/100) as a 2-digit integer. (SU)
- The day of the month as a decimal
number (range 01 to 31).
- Equivalent to %m/%d/%y. (Yecch - for Americans
only. Americans should note that in other countries %d/%m/%y is rather common.
This means that in international context this format is ambiguous and should
not be used.) (SU)
- Like %d, the day of the month as a decimal number,
but a leading zero is replaced by a space. (SU)
- Modifier: use alternative
format, see below. (SU)
- Equivalent to %Y-%m-%d (the ISO 8601 date format).
- 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 the ISO week number belongs to the previous
or next year, that year is used instead. (TZ)
- Like %G, but without century,
i.e., with a 2-digit year (00-99). (TZ)
- Equivalent to %b. (SU)
- The hour
as a decimal number using a 24-hour clock (range 00 to 23).
- The hour as
a decimal number using a 12-hour clock (range 01 to 12).
- The day of the
year as a decimal number (range 001 to 366).
- The hour (24-hour clock)
as a decimal number (range 0 to 23); single digits are preceded by a blank.
(See also %H.) (TZ)
- The hour (12-hour clock) as a decimal number (range
1 to 12); single digits are preceded by a blank. (See also %I.) (TZ)
month as a decimal number (range 01 to 12).
- The minute as a decimal number
(range 00 to 59).
- A newline character. (SU)
- Modifier: use alternative
format, see below. (SU)
- Either `AM' or `PM' according to the given time value,
or the corresponding strings for the current locale. Noon is treated as
`pm' and midnight as `am'.
- Like %p but in lowercase: `am' or `pm' or a corresponding
string for the current locale. (GNU)
- The time in a.m. or p.m. notation. In
the POSIX locale this is equivalent to `%I:%M:%S %p'. (SU)
- The time in
24-hour notation (%H:%M). (SU) For a version including the seconds, see %T
- The number of seconds since the Epoch, i.e., since 1970-01-01 00:00:00
- The second as a decimal number (range 00 to 61).
- A tab character.
- The time in 24-hour notation (%H:%M:%S). (SU)
- The day of the week
as a decimal, range 1 to 7, Monday being 1. See also %w. (SU)
- 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.
- 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 the current year, and with Monday as the first day of the week. See also
%U and %W. (SU)
- The day of the week as a decimal, range 0 to 6, Sunday
being 0. See also %u.
- 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.
- The preferred date representation for the current locale
without the time.
- The preferred time representation for the current locale
without the date.
- The year as a decimal number without a century (range
00 to 99).
- The year as a decimal number including the century.
time-zone as hour offset from GMT. Required to emit RFC822-conformant dates
(using "%a, %d %b %Y %H:%M:%S %z"). (GNU)
- The time zone or name or abbreviation.
- The date and time in date(1)
- A literal `%' character.
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 current locale, the behaviour
will be as if 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 structure tm is defined in <time.h>. See also ctime(3)
The strftime() function returns the number of characters placed
in the array s, not including the terminating NUL character, provided the
string, 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 the array was
Note that the return value 0 does not necessarily indicate an
error; for example, in many locales %p yields an empty string.
environment variables TZ and LC_TIME are used.
ANSI C, SVID
3, ISO 9899. There are strict inclusions between the set of conversions
given in ANSI C (unmarked), those given in the Single Unix Specification
(marked SU), those given in Olson's timezone package (marked TZ), and those
given in glibc (marked GNU), except that %+ is not supported in 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 C99 and POSIX 1003.1-2001.