illumos: 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)