STRFTIME (3)
format date and time
SYNOPSIS
#include <time.h>
size_t strftime(char * s , size_t max , const char * format ,
const struct tm * 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
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)
%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
%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 including 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
%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)
%%
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 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).
RETURN VALUE
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.
CONFORMING TO
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.
SEE ALSO
date(1) - time (2) -
- ctime (3) -
- setlocale (3) -
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