| Allegro CL version 8.2 Minimal update since 8.2 release. 8.1 version |
Arguments: date-time &key defaults
This function returns multiple value specifying the extended universal
time associated with the argument date-time
object (modified, as
described below, by defaults). This function is
the inverse of ut-to-date-time. An 'extended
universal time' is one that has values for years prior to 1900 (see
below for mroe information).
The return values are listed below. The second through seventh are
valid argument to encode-universal-time in any Common Lisp because
the year is modified by some multiple of 400 in order that it be
greater than 1899. The eighth return value (the time zone) is a valid
argument to encode-universal-time if it is a number, but not
if it is the symbol :time-zone-not-specified
. The
final return value is the number of multiples of 400 needed to add to
the date-time year needed to bring the year past 1899.
In detail, the nine return values are:
:time-zone-not-specified
.
The universal-time is actually an extension of the Common Lisp universal-time since ISO 8601 allows for dates/times to be specified outside the range of those representable by universal-time (i.e., dates before 1900, or times containing fractional seconds). This extended universal-time allows for negative values to represent dates before 1900. In addition, extended universal-times can be non-integer rationals representing times with fractional seconds.
There are three special date-time designators:
:now
, :today
, and
:zero
. :now
means current time,
:today
means the start (00:00:00) of the current
day, and :zero
means the start of Jan 1, 0000.
(require :datetime) (use-package :util.date-time) ;; You will see different values for :now and :today (date-time :now) => #<date-time "2006-07-11T22:28:08" @ #x7185242a> (date-time :today) => #<date-time "2006-07-11T00:00:00" @ #x7185ec6a> (date-time :zero) => #<date-time "0000-01-01T00:00:00" @ #x717dcad2>
These special date-time instances can be used as
defaults. The default
defaults is :zero
. Thus, the
default behavior is to merge the argument date-time with
(date-time :zero)
to get a complete date-time
instance that can be converted to universal-time. You can override
the default by specifying :today, :now, or any other date-time
instance. You can also specify nil
as the
defaults, in which case no merging occurs.
(require :datetime) (use-package :util.date-time) ;; Here are two examples showing all the return values (date-time-to-ut "1865-11-06") Returns values: -1077724800 0 0 0 6 11 2265 :time-zone-not-specified 400 (date-time-to-ut "1960-04-14T11:20:00+0700") Returns values: 1902370800 0 20 11 14 4 1960 -7 0 ;; In the remaining examples, we show only the first return value ;; of DATE-TIME-TO-UT: (setq d (date-time "1985-04-12T23:20:50+02:00")) => #<date-time "1985-04-12T23:20:50+02:00" @ ...> (setq ut (date-time-to-ut d)) => 2691192050 (setq d (date-time "1885-04-12T23:20:50+02:00")) => #<date-time "1885-04-12T23:20:50+02:00" @ ...> ;; The following returns a negative number since the date is before 1900. ;; (setq ut (date-time-to-ut d)) => -464481550 (ut-to-date-time (date-time-to-ut "1985-04-12")) => #<date-time "1985-04-12T00:00:00+08:00" @ #x718bad0a> (ut-to-date-time (date-time-to-ut "1985-04")) => #<date-time "1985-04-01T00:00:00+08:00" @ #x718c108a> (ut-to-date-time (date-time-to-ut "1985")) => #<date-time "1985-01-01T00:00:00+08:00" @ #x718c7092> ;; Note that the default may not be desirable in the following case: ;; (ut-to-date-time (date-time-to-ut "85-04-12")) => #<date-time "0085-04-12T00:00:00+08:00" @ #x718ebcba> ;; The following are ways to specify different defaults: (ut-to-date-time (date-time-to-ut "85-04-12" :defaults (merge-date-times "1900" :zero))) => #<date-time "1985-04-12T00:00:00+08:00" @ #x7191cc8a> (ut-to-date-time (date-time-to-ut "85-04-12" :defaults :today)) => #<date-time "2085-04-12T00:00:00+08:00" @ #x71924f5a> (ut-to-date-time (date-time-to-ut "85-04-12" :defaults :now)) => #<date-time "2085-04-12T22:36:32+08:00" @ #x7192cce2>
See also string-to-universal-time, which converts a string specifying a date and time (in a variety of formats including ISO 8601) to a universal time. See date-time.htm for information on support in Allegro CL for parsing and generating time expressions using the ISO 8601 standard.
Copyright (c) 1998-2016, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.1 page.
Created 2010.1.21.
| Allegro CL version 8.2 Minimal update since 8.2 release. 8.1 version |