Tribblix: manual page: strftime.3c

STRFTIME(3C) Standard C Library Functions STRFTIME(3C)

NAME

strftime, strftime_l, cftime, ascftime - convert date and time to
string

SYNOPSIS

#include <time.h>

size_t strftime(char *restrict s, size_t maxsize,
const char *restrict format,
const struct tm *restrict timeptr);

size_t strftime_l(char *restrict s, size_t maxsize,
const char *restrict format,
const struct tm *restrict timeptr, locale_t loc);

int cftime(char *s, char *format, const time_t *clock);

int ascftime(char *s, const char *format,
const struct tm *timeptr);

DESCRIPTION

The strftime(), strftime_l(), ascftime(), and cftime() functions
place bytes into the array pointed to by s as controlled by the
string pointed to by format. The format string consists of zero or
more conversion specifications and ordinary characters. A conversion
specification consists of a '%' (percent) character and one or two
terminating conversion characters that determine the conversion
specification's behavior. All ordinary characters (including the
terminating null byte) are copied unchanged into the array pointed to
by s. If copying takes place between objects that overlap, the
behavior is undefined. For strftime(), no more than maxsize bytes are
placed into the array. The strftime_l() function behaves identically
to strftime() function, but instead of operating in the current
locale, it operates in the locale specified by loc.

If format is NULL, then the locale's default format is used. For
strftime() the default format is the same as %c; for cftime() and
ascftime() the default format is the same as %+. cftime() and
ascftime() first try to use the value of the environment variable
CFTIME, and if that is undefined or empty, the default format is
used.

Each conversion specification is replaced by appropriate characters
as described in the following list. The appropriate characters are
determined by the LC_TIME category of the program's locale and by the
values contained in the structure pointed to by timeptr for
strftime() and ascftime(), and by the time represented by clock for
cftime().

%%
Same as %.

%a
Locale's abbreviated weekday name.

%A
Locale's full weekday name.

%b
Locale's abbreviated month name.

%B
Locale's full month name.

%c
Locale's appropriate date and time representation. In the C
locale, this format is:

%a %b %e %H:%M:%S %Y

Other locales may have different locale-specific formats.

%C
Century number (the year divided by 100 and truncated to an
integer as a decimal number [01,99]).

%d
Day of month [01,31].

%D
Date as %m/%d/%y.

%e
Day of month [1,31]; single digits are preceded by a space.

%F
Equivalent to %Y-%m-%d (the ISO 8601:2000 standard date
format).

%g
Week-based year within century [00,99].

%G
Week-based year, including the century [0000,9999].

%h
Locale's abbreviated month name.

%H
Hour (24-hour clock) [00,23].

%I
Hour (12-hour clock) [01,12].

%j
Day number of year [001,366].

%k
Hour (24-hour clock) [0,23]; single digits are preceded by a
space.

%l
Hour (12-hour clock) [1,12]; single digits are preceded by a
space.

%m
Month number [01,12].

%M
Minute [00,59].

%n
Insert a NEWLINE.

%p
Locale's equivalent of either a.m. or p.m.

%r
Appropriate time representation in 12-hour clock format with
%p.

%R
Time as %H:%M.

%s
Seconds since 00:00:00 UTC, January 1, 1970.

%S
Seconds [00,60]; the range of values is [00,60] rather than
[00,59] to allow for the occasional leap second.

%t
Insert a TAB.

%T
Time as %H:%M:%S.

%u
Weekday as a decimal number [1,7], with 1 representing Monday.
See NOTES below.

%U
Week number of year as a decimal number [00,53], with Sunday as
the first day of week 1.

%v
Date as %e-%b-%Y.

%V
The ISO 8601 week number as a decimal number [01,53]. In the
ISO 8601 week-based system, weeks begin on a Monday and week 1
of the year is the week that includes both January 4th and the
first Thursday of the year. If the first Monday of January is
the 2nd, 3rd, or 4th, the preceding days are part of the last
week of the preceding year. See NOTES below.

%w
Weekday as a decimal number [0,6], with 0 representing Sunday.

%W
Week number of year as a decimal number [00,53], with Monday as
the first day of week 1.

%x
Locale's appropriate date representation.

%X
Locale's appropriate time representation.

%y
Year within century [00,99].

%Y
Year, including the century (for example 1993).

%z
Replaced by offset from UTC in ISO 8601:2000 standard format
(+hhmm or -hhmm), or by no characters if no time zone is
determinable. For example, "-0430" means 4 hours 30 minutes
behind UTC (west of Greenwich). If tm_isdst is zero, the
standard time offset is used. If tm_isdst is greater than
zero, the daylight savings time offset if used. If tm_isdst is
negative, no characters are returned.

%Z
Time zone name or abbreviation, or no bytes if no time zone
information exists.

%+
Locale's date and time representation as produced by date(1).

If a conversion specification does not correspond to any of the above
or to any of the modified conversion specifications listed below, the
behavior is undefined and 0 is returned.

The difference between %U and %W (and also between modified
conversion specifications %OU and %OW) lies in which day is counted
as the first of the week. Week number 1 is the first week in January
starting with a Sunday for %U or a Monday for %W. Week number 0
contains those days before the first Sunday or Monday in January for
%U and %W, respectively.

Modified Conversion Specifications

Some conversion specifications can be modified by the E and O
modifiers to indicate that an alternate format or specification
should be used rather than the one normally used by the unmodified
conversion specification. If the alternate format or specification
does not exist in the current locale, the behavior will be as if the
unmodified specification were used.

%Ec
Locale's alternate appropriate date and time representation.

%EC
Name of the base year (period) in the locale's alternate
representation.

%Eg
Offset from %EC of the week-based year in the locale's
alternative representation.

%EG
Full alternative representation of the week-based year.

%Ex
Locale's alternate date representation.

%EX
Locale's alternate time representation.

%Ey
Offset from %EC (year only) in the locale's alternate
representation.

%EY
Full alternate year representation.

%Od
Day of the month using the locale's alternate numeric symbols.

%Oe
Same as %Od.

%Og
Week-based year (offset from %C) in the locale's alternate
representation and using the locale's alternate numeric
symbols.

%OH
Hour (24-hour clock) using the locale's alternate numeric
symbols.

%OI
Hour (12-hour clock) using the locale's alternate numeric
symbols.

%Om
Month using the locale's alternate numeric symbols.

%OM
Minutes using the locale's alternate numeric symbols.

%OS
Seconds using the locale's alternate numeric symbols.

%Ou
Weekday as a number in the locale's alternate numeric symbols.

%OU
Week number of the year (Sunday as the first day of the week)
using the locale's alternate numeric symbols.

%Ow
Number of the weekday (Sunday=0) using the locale's alternate
numeric symbols.

%OW
Week number of the year (Monday as the first day of the week)
using the locale's alternate numeric symbols.

%Oy
Year (offset from %C) in the locale's alternate representation
and using the locale's alternate numeric symbols.

Selecting the Output Language

These routines produce output that is formatted according to the
LC_TIME locale category. They use either the current locale, or in
the case of strftime_l(), the locale supplied by loc.

Time Zone

Local time zone information is used as though tzset(3C) were called.

RETURN VALUES

These functions return the number of characters placed into the array
pointed to by s, not including the terminating null character. If the
total number of resulting characters including the terminating null
character is more than maxsize, strftime() returns 0 and the contents
of the array are indeterminate.

EXAMPLES

Example 1: An example of the strftime() function.

The following example illustrates the use of strftime() for the POSIX
locale. It shows what the string in str would look like if the
structure pointed to by tmptr contains the values corresponding to
Thursday, August 28, 1986 at 12:44:36.

strftime(str, strsize, "%A %b %d %j", tmptr);

This results in str containing "Thursday Aug 28 240".

ATTRIBUTES

NOTES

The conversion specification for %V was changed in the Solaris 7
release. This change was based on the public review draft of the ISO
C9x standard at that time. Previously, the specification stated that
if the week containing 1 January had fewer than four days in the new
year, it became week 53 of the previous year. The ISO C9x standard
committee subsequently recognized that that specification had been
incorrect.

The conversion specifications for %g, %G, %Eg, %EG, and %Og were
added in the Solaris 7 release. This change was based on the public
review draft of the ISO C9x standard at that time. The %g and %G
specifications were adopted in the formal standard. The other two
were not, and should not be used in portable applications.

The conversion specification for %u was changed in the Solaris 8
release. This change was based on the XPG4 specification.

If using the %Z specifier and zoneinfo timezones and if the input
date is outside the range 20:45:52 UTC, December 13, 1901 to
03:14:07 UTC, January 19, 2038, the timezone name may not be correct.

The conversion specification for %+ was added in illumos. It is not
part of any standard, although it is available on a number of other
platforms. Its use is discouraged for conforming applications.

November 8, 2020 STRFTIME(3C)