FAQ
Hello,

I have added some features to Date::Simple and renamed it
JTobey::Date::Simple until I manage to get in touch with the author.
Date::Simple is a small, practical date module whose key to success is
its ignorance of times, time zones, and localization. See below for
full details.

The changes are:

* numbers crunched in C unless you give Makefile.PL 'noxs' option

* removed Y2038 bug, can handle dates up to 9999

* can calculate the day of the week

* some new functions and tests

I would like to get this on CPAN but am waiting to hear back from the
author about the Date::Simple namespace. The code is available at:

http://john-edwin-tobey.org/Refs/JTobey-Date-Simple-2.00_jtobey3.tar.gz

Comments are appreciated, but please CC me. I have been unable to
subscribe to this list and have notified the help address.

Best.
-John


NAME
JTobey::Date::Simple - a simple date object

SYNOPSIS
use JTobey::Date::Simple ();
my $date = JTobey::Date::Simple->new('1972-01-17');
my $year = $date->year;
my $month = $date->month;
my $day = $date->day;

use JTobey::Date::Simple (':all');
my $date2 = ymd($year, $month, $day);
my $date3 = d8('19871218');
my $today = today();
my $tomorrow = $today + 1;
print "Tomorrow's date (in ISO 8601 format) is $tomorrow.\n";
if ($tomorrow->year != $today->year) {
print "Today is New Year's Eve!\n";
}

if ($today > $tomorrow) {
die "warp in space-time continuum";
}

print "Today is ";
print(('Sun','Mon','Tues','Wednes','Thurs','Fri','Satur')
[$today->day_of_week]);
print "day.\n";

# you can also do this:
($date cmp "2001-07-01")
# and this
($date <=> [2001, 7, 1])

DESCRIPTION
Dates are complex enough without times and timezones. This module may be
used to create simple date objects. It handles such things as:

Validation.
Reject 1999-02-29 but accept 2000-02-29.

Interval arithmetic.
How many days were between two given dates? What date comes N days
after today?

Day-of-week calculation.
What day of the week is a given date?

It does not deal with hours, minutes, and seconds, time zones, or
locale-aware formatting.

A date is uniquely identified by year, month, and day integers within
valid ranges. This module will not allow the creation of objects for
invalid dates. Attempting to create an invalid date will return undef.
Month numbering starts at 1 for January, unlike in C and Java. Years are
4-digit.

Gregorian dates up to year 9999 are handled correctly, but we rely on
Perl's builtin `localtime' function when the current date is requested.
On some platforms, `localtime' may be vulnerable to rollovers such as
the Unix `time_t' wraparound of January 2038.

Overloading is used so you can compare or subtract two dates using
standard numeric operators such as `==', and the sum of a date object
and an integer is another date object.

JTobey::Date::Simple objects are immutable. After assigning `$date1' to
`$date2', no change to `$date1' can affect `$date2'. This means, for
example, that there is nothing like a `set_year' operation, and
`$date++' assigns a new object to `$date'.

This module contains various undocumented features and functions. They
may not be available on all platforms and are likely to change or
disappear in future releases.

CONSTRUCTORS
Several functions take a string or numeric representation and return a
corresponding date object. The most general is *new*, whose argument
list may be empty (returning the current date), a string in ISO 8601
format (YYYY-MM-DD), a list or arrayref of year, month, and day number,
or a date object.

JTobey::Date::Simple->new ([ARG, ...])
date ([ARG, ...])
my $date = JTobey::Date::Simple->new('1972-01-17');

The *new* method will return a date object if the values passed in
specify a valid date. If an invalid date is passed, the method
returns undef.

The *date* function provides the same functionality but must be
imported or qualified as `JTobey::Date::Simple::date'. (To import all public
functions, do `use JTobey::Date::Simple (':all');'.)

today()
Returns the current date according to `localtime'.

Caution: To get tomorrow's date (or any fixed offset from today), do
not use `today + 1'. Perl parses this as `today(+1)'. You need to
put empty parentheses after the function: `today() + 1'.

JTobey::Date::Simple->from_ymd (YEAR, MONTH, DAY)
ymd (YEAR, MONTH, DAY)
Returns a date object with the given year, month, and day numbers.
If the arguments do not specify a valid date, undef is returned.

Example:

use JTobey::Date::Simple ('ymd');
$pbd = ymd(1987, 12, 18);

JTobey::Date::Simple->from_d8 (STRING)
d8 (STRING)
Parses STRING as "YYYYMMDD" and returns the corresponding date
object, or undef if STRING has the wrong format or specifies an
invalid date.

Example:

use JTobey::Date::Simple ('d8');
$doi = d8('17760704');

Mnemonic: The string matches `/\d{8}/'. Also, "d8" spells "date", if
8 is expanded phonetically.

INSTANCE METHODS
DATE->next
my $tomorrow = $today->next;

Returns an object representing tomorrow.

DATE->prev
my $yesterday = $today->prev;

Returns an object representing yesterday.

DATE->year
my $year = $date->year;

Return the year of DATE as an integer.

DATE->month
my $month = $date->month;

Return the month of DATE as an integer from 1 to 12.

DATE->day
my $day = $date->day;

Return the DATE's day of the month as an integer from 1 to 31.

DATE->day_of_week
Return a number representing DATE's day of the week from 0 to 6,
where 0 means Sunday.

DATE->as_ymd
my ($year, $month, $day) = $date->as_ymd;

Returns a list of three numbers: year, month, and day.

DATE->as_d8
Returns the "d8" representation (see *d8*), like
`$date->format("%Y%m%d")'.

DATE->format (STRING)
DATE->strftime (STRING)
Returns a string representing the date, in the format specified. If
you don't pass a parameter, an ISO 8601 formatted date is returned.

my $change_date = $date->format("%d %b %y");
my $iso_date1 = $date->format("%Y-%m-%d");
my $iso_date2 = $date->format;

The formatting parameter is similar to one you would pass to
strftime(3). This is because we actually do pass it to strftime to
format the date. This may result in differing behavior across
platforms and locales and may not even work everywhere.

OPERATORS
Some operators can be used with JTobey::Date::Simple instances. If one side of
an expression is a date object, and the operator expects two date
objects, the other side is interpreted as `date(ARG)', so an array
reference or ISO 8601 string will work.

DATE + NUMBER
DATE - NUMBER
You can construct a new date offset by a number of days using the
`+' and `-' operators.

DATE1 - DATE2
You can subtract two dates to find the number of days between them.

DATE1 == DATE2
DATE1 < DATE2
DATE1 <=> DATE2
DATE1 cmp DATE2
... You can compare two dates using the arithmetic or string comparison
operators.

DATE += NUMBER
DATE -= NUMBER
You can increment or decrement a date by a number of days using the
+= and -= operators. This actually generates a new date object and
is equivalent to `$date = $date + $number'.

"$date"
You can interpolate a date instance directly into a string, in the
format specified by ISO 8601 (eg: 2000-01-17).

UTILITIES
leap_year (YEAR)
Returns true if YEAR is a leap year.

days_in_month (YEAR, MONTH)
Returns the number of days in MONTH, YEAR.

AUTHOR
Marty Pauley <marty@kasei.com>
John Tobey <jtobey@john-edwin-tobey.org>

COPYRIGHT
Copyright (C) 2001 Kasei
Copyright (C) 2001 John Tobey.

This program is free software; you can redistribute it and/or
modify it under the terms of either:

a) the GNU General Public License;
either version 2 of the License, or (at your option) any later
version. You should have received a copy of the GNU General
Public License along with this program; see the file COPYING.
If not, write to the Free Software Foundation, Inc., 59
Temple Place, Suite 330, Boston, MA 02111-1307 USA

b) the Perl Artistic License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.



--
John Tobey, late nite hacker <jtobey@john-edwin-tobey.org>
``I just dont want to worry about my word processor dropping its core.
It simply isnt my job to whip out GDB and debug my word processor.''
-Emily K. Dresner-Thornber

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