STRFTIME(3) Linux Programmer's Manual STRFTIME(3)
strftime - format date and time
size_t strftime(char *s, size_t max, const char *format,
const struct tm *tm);
The strftime() function formats the broken-down time tm according to the format specifica-
tion 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. Con-
version specifiers are introduced by a `%' character, and are replaced in s as follows:
%a The abbreviated weekday name according to the current locale.
%A The full weekday name according to the current locale.
%b The abbreviated month name according to the current locale.
%B The full month name according to the current locale.
%c The preferred date and time representation for the current locale.
%C The century number (year/100) as a 2-digit integer. (SU)
%d The day of the month as a decimal number (range 01 to 31).
%D 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)
%e Like %d, the day of the month as a decimal number, but a leading zero is replaced
by a space. (SU)
%E Modifier: use alternative format, see below. (SU)
%F Equivalent to %Y-%m-%d (the ISO 8601 date format). (C99)
%G 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
%g Like %G, but without century, i.e., with a 2-digit year (00-99). (TZ)
%h Equivalent to %b. (SU)
%H The hour as a decimal number using a 24-hour clock (range 00 to 23).
%I The hour as a decimal number using a 12-hour clock (range 01 to 12).
%j The day of the year as a decimal number (range 001 to 366).
%k The hour (24-hour clock) as a decimal number (range 0 to 23); single digits are
preceded by a blank. (See also %H.) (TZ)
%l The hour (12-hour clock) as a decimal number (range 1 to 12); single digits are
preceded by a blank. (See also %I.) (TZ)
%m The month as a decimal number (range 01 to 12).
%M The minute as a decimal number (range 00 to 59).
%n A newline character. (SU)
%O Modifier: use alternative format, see below. (SU)
%p 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'.
%P Like %p but in lowercase: `am' or `pm' or a corresponding string for the current
%r The time in a.m. or p.m. notation. In the POSIX locale this is equivalent to
`%I:%M:%S %p'. (SU)
%R The time in 24-hour notation (%H:%M). (SU) For a version including the seconds, see
%s The number of seconds since the Epoch, i.e., since 1970-01-01 00:00:00 UTC. (TZ)
%S The second as a decimal number (range 00 to 61).
%t A tab character. (SU)
%T The time in 24-hour notation (%H:%M:%S). (SU)
%u The day of the week as a decimal, range 1 to 7, Monday being 1. See also %w. (SU)
%U 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.
%V 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)
%w The day of the week as a decimal, range 0 to 6, Sunday being 0. See also %u.
%W 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.
%x The preferred date representation for the current locale without the time.
%X The preferred time representation for the current locale without the date.
%y The year as a decimal number without a century (range 00 to 99).
%Y The year as a decimal number including the century.
%z The time-zone as hour offset from GMT. Required to emit RFC822-conformant dates
(using "%a, %d %b %Y %H:%M:%S %z"). (GNU)
%Z The time zone or name or abbreviation.
%+ The date and time in date(1) format. (TZ)
%% A literal `%' character.
Some 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 specifi-
cation 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 too small.)
Note that the return value 0 does not necessarily indicate an error; for example, in many
locales %p yields an empty string.
The 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 exten-
sions that could apply to strftime as well. The %F conversion is in C99 and POSIX
date(1), time(2), ctime(3), setlocale(3), sprintf(3)
GNU 1999-03-29 STRFTIME(3)