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Welcome to tzcode 2013e:

  Changes affecting API

    The 'zic' command now outputs a dummy transition when far-future
    data can't be summarized using a TZ string, and uses a 402-year
    window rather than a 400-year window.  For the current data, this
    affects only the Asia/Tehran file.  It does not affect any of the
    time stamps that this file represents, so zdump outputs the same
    information as before.  (Thanks to Andrew Main (Zefram).)

    The 'date' command has a new '-r' option, which lets you specify
    the integer time to display, a la FreeBSD.

    The 'tzselect' command has two new options '-c' and '-n', which lets you
    select a zone based on latitude and longitude.

    The 'zic' command's '-v' option now warns about constructs that
    require the new version-3 binary file format.  (Thanks to Arthur
    David Olson for the suggestion.)

    Support for floating-point time_t has been removed.
    It was always dicey, and POSIX no longer requires it.
    (Thanks to Eric Blake for suggesting to the POSIX committee to
    remove it, and thanks to Alan Barrett, Clive D.W. Feather, Andy
    Heninger, Arthur David Olson, and Alois Treindl, for reporting
    bugs and elucidating some of the corners of the old floating-point
    implementation.)

    The signatures of 'offtime', 'timeoff', and 'gtime' have been
    changed back to the old practice of using 'long' to represent UT
    offsets.  This had been inadvertently and mistakenly changed to
    'int_fast32_t'.  (Thanks to Christos Zoulos.)

    The code avoids undefined behavior on integer overflow in some
    more places, including gmtime, localtime, mktime and zdump.

  Changes affecting the zdump utility

    zdump now outputs "UT" when referring to Universal Time, not "UTC".
    "UTC" does not make sense for time stamps that predate the introduction
    of UTC, whereas "UT", a more-generic term, does.  (Thanks to Steve Allen
    for clarifying UT vs UTC.)

  Data changes affecting behavior of tzselect and similar programs

    Country code BQ is now called the more-common name "Caribbean Netherlands"
    rather than the more-official "Bonaire, St Eustatius & Saba".

    Remove from zone.tab the names America/Montreal, America/Shiprock,
    and Antarctica/South_Pole, as they are equivalent to existing
    same-country-code zones for post-1970 time stamps.  The data for
    these names are unchanged, so the names continue to work as before.

  Changes affecting code internals

    zic -c now runs way faster on 64-bit hosts when given large numbers.

    zic now uses vfprintf to avoid allocating and freeing some memory.

    tzselect now computes the list of continents from the data,
    rather than have it hard-coded.

    Minor changes pacify GCC 4.7.3 and GCC 4.8.1.

  Changes affecting the build procedure

    The 'leapseconds' file is now generated automatically from a
    new file 'leap-seconds.list', which is a copy of
    <ftp://time.nist.gov/pub/leap-seconds.list>.
    A new source file 'leapseconds.awk' implements this.
    The goal is simplification of the future maintenance of 'leapseconds'.

    When building the 'posix' or 'right' subdirectories, if the
    subdirectory would be a copy of the default subdirectory, it is
    now made a symbolic link if that is supported.  This saves about
    2 MB of file system space.

    The links America/Shiprock and Antarctica/South_Pole have been
    moved to the 'backward' file.  This affects only nondefault builds
    that omit 'backward'.

  Changes affecting documentation and commentary

    Changes to the 'tzfile' man page

      It now mentions that the binary file format may be extended in
      future versions by appending data.

      It now refers to the 'zdump' and 'zic' man pages.

    Changes to the 'zic' man page

      It lists conditions that elicit a warning with '-v'.

      It says that the behavior is unspecified when duplicate names
      are given, or if the source of one link is the target of another.

      Its examples are updated to match the latest data.

      The definition of white space has been clarified slightly.
      (Thanks to Michael Deckers.)

    Changes to the 'Theory' file

      There is a new section about the accuracy of the tz database,
      describing the many ways that errors can creep in, and
      explaining why so many of the pre-1970 time stamps are wrong or
      misleading (thanks to Steve Allen, Lester Caine, and Garrett
      Wollman for discussions that contributed to this).

      The 'Theory' file describes LMT better (this follows a
      suggestion by Guy Harris).

      It refers to the 2013 edition of POSIX rather than the 2004 edition.

      It's mentioned that excluding 'backward' should not affect the
      other data, and it suggests at least one zone.tab name per
      inhabited country (thanks to Stephen Colebourne).

      Some longstanding restrictions on names are documented, e.g.,
      'America/New_York' precludes 'America/New_York/Bronx'.

      It gives more reasons for the 1970 cutoff.

      It now mentions which time_t variants are supported, such as
      signed integer time_t.  (Thanks to Paul Goyette for reporting
      typos in an experimental version of this change.)

      (Thanks to Philip Newton for correcting typos in these changes.)

    Documentation and commentary is more careful to distinguish UT in
    general from UTC in particular.  (Thanks to Steve Allen.)

    Add a better source for the Zurich 1894 transition.
    (Thanks to Pierre-Yves Berger.)

    Update shapefile citations in tz-link.htm.  (Thanks to Guy Harris.)

.\" Copyright (c) 1989, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the American National Standards Committee X3, on Information
.\" Processing Systems.
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.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.\"     from: @(#)strftime.3	5.12 (Berkeley) 6/29/91
.\"	$NetBSD: strftime.3,v 1.30 2013/09/20 19:06:54 christos Exp $
.\"
.Dd April 14, 2011
.Dt STRFTIME 3
.Os
.Sh NAME
.Nm strftime ,
.Nm strftime_z
.Nd format date and time
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In time.h
.Ft size_t
.Fn strftime "char * restrict buf" "size_t maxsize" "const char * restrict format" "const struct tm * restrict timeptr"
.Ft size_t
.Fn strftime_z "const timezone_t tz" "char * restrict buf" "size_t maxsize" "const char * restrict format" "const struct tm * restrict timeptr"
.Sh DESCRIPTION
The
.Fn strftime
function formats the information from
.Fa timeptr
into the buffer
.Fa buf
according to the string pointed to by
.Fa format .
.Pp
The
.Fa format
string consists of zero or more conversion specifications and
ordinary characters.
All ordinary characters are copied directly into the buffer.
A conversion specification consists of a percent sign
.Ql %
and one other character.
.Pp
No more than
.Fa maxsize
characters will be placed into the array.
If the total number of resulting characters, including the terminating
null character, is not more than
.Fa maxsize ,
.Fn strftime
returns the number of characters in the array, not counting the
terminating null.
Otherwise, zero is returned and the contents of the array are undefined.
.Pp
Each conversion specification is replaced by the characters as
follows which are then copied into the buffer.
.Bl -tag -width "xxxx"
.It Cm \&%A
is replaced by the locale's full weekday name.
.It Cm %a
is replaced by the locale's abbreviated weekday name.
.It Cm \&%B
is replaced by the locale's full month name.
.It Cm \&%b No or Cm \&%h
is replaced by the locale's abbreviated month name.
.It Cm \&%C
is replaced by the century (a year divided by 100 and truncated to an integer)
as a decimal number [00,99].
.It Cm \&%c
is replaced by the locale's appropriate date and time representation.
.It Cm \&%D
is replaced by the date in the format
.Dq Li %m/%d/%y .
.It Cm \&%d
is replaced by the day of the month as a decimal number [01,31].
.It Cm \&%e
is replaced by the day of month as a decimal number [1,31];
single digits are preceded by a blank.
.It Cm \&%F
is replaced by the date in the format
.Dq Li %Y-%m-%d
(the ISO 8601 date format).
.It Cm \&%G
is replaced by the ISO 8601 year with century as a decimal number.
.It Cm \&%g
is replaced by the ISO 8601 year without century as a decimal number (00-99).
This is the year that includes the greater part of the week.
(Monday as the first day of a week).
See also the
.Ql \&%V
conversion specification.
.It Cm \&%H
is replaced by the hour (24-hour clock) as a decimal number [00,23].
.It Cm \&%I
is replaced by the hour (12-hour clock) as a decimal number [01,12].
.It Cm \&%j
is replaced by the day of the year as a decimal number [001,366].
.It Cm \&%k
is replaced by the hour (24-hour clock) as a decimal number [0,23];
single digits are preceded by a blank.
.It Cm \&%l
is replaced by the hour (12-hour clock) as a decimal number [1,12];
single digits are preceded by a blank.
.It Cm \&%M
is replaced by the minute as a decimal number [00,59].
.It Cm %m
is replaced by the month as a decimal number [01,12].
.It Cm %n
is replaced by a newline.
.It Cm %p
is replaced by the locale's equivalent of either
.Dq Tn AM
or
.Dq Tn PM .
.It Cm \&%R
is replaced by the time in the format
.Dq Li %H:%M .
.It Cm \&%r
is replaced by the locale's representation of 12-hour clock time
using AM/PM notation.
.It Cm \&%S
is replaced by the second as a decimal number [00,61].
The range of
seconds is (00-61) instead of (00-59) to allow for the periodic occurrence
of leap seconds and double leap seconds.
.It Cm %s
is replaced by the number of seconds since the Epoch (see
.Xr ctime 3 ) .
.It Cm \&%T
is replaced by the time in the format
.Dq Li %H:%M:%S .
.It Cm \&%t
is replaced by a tab.
.It Cm \&%U
is replaced by the week number of the year (Sunday as the first day of
the week) as a decimal number [00,53].
.It Cm \&%u
is replaced by the weekday (Monday as the first day of the week)
as a decimal number [1,7].
.It Cm \&%V
is replaced by the week number of the year (Monday as the first day of
the week) as a decimal number [01,53]. According to ISO 8601 the week
containing January 1 is week 1 if it has four or more days in the new year,
otherwise it is week 53 of the previous year, and the next week is week 1.
The year is given by the
.Ql \&%G
conversion specification.
.It Cm \&%v
is replaced by the date in the format
.Dq Li %e-%b-%Y .
.It Cm \&%W
is replaced by the week number of the year (Monday as the first day of
the week) as a decimal number [00,53].
.It Cm \&%w
is replaced by the weekday (Sunday as the first day of the week)
as a decimal number [0,6].
.It Cm \&%X
is replaced by the locale's appropriate time representation.
.It Cm \&%x
is replaced by the locale's appropriate date representation.
.It Cm \&%Y
is replaced by the year with century as a decimal number.
.It Cm \&%y
is replaced by the year without century as a decimal number [00,99].
.It Cm \&%Z
is replaced by the time zone name.
.It Cm \&%z
is replaced by the offset from the Prime Meridian in the format
+HHMM or -HHMM (ISO 8601) as appropriate, with positive values representing
locations east of Greenwich, or by the empty string if this is
not determinable.
.Dq Li [-]hhmm .
.It Cm %%
is replaced by
.Ql % .
.El
.Pp
The
.Fn strftime_z
function is similar to
.Fn strftime ,
but it also takes a
.Ft "const timezone_t"
.Fa tz
argument.
.Sh SEE ALSO
.Xr date 1 ,
.Xr printf 1 ,
.Xr ctime 3 ,
.Xr printf 3 ,
.Xr strptime 3 ,
.Xr tm 3
.Sh STANDARDS
The
.Fn strftime
function
conforms to
.St -isoC-99 .
The
.Ql \&%C ,
.Ql \&%D ,
.Ql \&%e ,
.Ql \&%g ,
.Ql \&%G ,
.Ql \&%h ,
.Ql \&%k ,
.Ql \&%l ,
.Ql \&%n ,
.Ql \&%r ,
.Ql \&%R ,
.Ql \&%s ,
.Ql \&%t ,
.Ql \&%T ,
.Ql \&%u ,
.Ql \&%V ,
and
.Ql \&%v
conversion specifications are extensions.
.Pp
Use of the ISO 8601 conversions may produce non-intuitive results.
Week 01 of a year is per definition the first week which has the Thursday
in this year, which is equivalent to the week which contains the fourth
day of January.
In other words, the first week of a new year is the week which has the
majority of its days in the new year.
Week 01 might also contain days from the previous year and the week
before week 01 of a year is the last week (52 or 53) of the previous
year even if it contains days from the new year.
A week starts with Monday (day 1) and ends with Sunday (day 7).
For example, the first week of the year 1997 lasts from
1996-12-30 to 1997-01-05.
.Sh BUGS
There is no conversion specification for the phase of the moon.
.Pp
A return value of zero does not necessarily indicate an error.
If the resulting string is an empty string, the result value is
zero and it is not possible to distinguish between success and error.
For example, in many locales
.Cm \&%p
yields an empty string.
This problem can be avoided by inserting an extra space at the
beginning of the format string and then skipping over it or removing
it from the result.