STRFTIME(3) Linux Programmer's Manual STRFTIME(3)
NAME
strftime - format date and time
SYNOPSIS
#include<time.h>
size_tstrftime(char*s,size_t max,constchar*format,
conststructtm*tm);
DESCRIPTION
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:
%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 ambigu-
ous 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
instead. (TZ)
%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 locale. (GNU)
%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 includ-
ing the seconds, see %T below.
%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 specification does not exist for the cur-
rent 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).
RETURNVALUE
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.
ENVIRONMENT
The environment variables TZ and LC_TIME are used.
CONFORMINGTO
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.
BUGS
Some buggy versions of gcc complain about the use of %c: warning: '%c'
yields only last 2 digits of year in some locales. Of course program-
mers are encouraged to use %c, it gives the preferred date and time
representation. One meets all kinds of strange obfuscations to circum-
vent this gcc problem. A relatively clean one is to add an intermediate
function
size_t my_strftime(char *s, size_t max, const char *fmt, const
struct tm *tm) {
return strftime(s, max, fmt, tm);
}
SEEALSO
date(1), time(2), ctime(3), setlocale(3), sprintf(3)
GNU 1999-03-29 STRFTIME(3)
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