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Date::Calc(3)	      User Contributed Perl Documentation	 Date::Calc(3)

NAME
       Date::Calc - Gregorian calendar date calculations

MOTTO
       Keep it small, fast and simple

PREFACE
       This package consists of a C library and a Perl module (which uses the
       C library, internally) for all kinds of date calculations based on the
       Gregorian calendar (the one used in all western countries today),
       thereby complying with all relevant norms and standards:
       ISO/R 2015-1971, DIN 1355 and, to some extent, ISO 8601 (where
       applicable).

       (See also http://www.engelschall.com/u/sb/download/Date-Calc/DIN1355/
       for a scan of part of the "DIN 1355" document (in German)).

       The module of course handles year numbers of 2000 and above correctly
       ("Year 2000" or "Y2K" compliance) -- actually all year numbers from 1
       to the largest positive integer representable on your system (which is
       at least 32767) can be dealt with.

       This is not true, however, for the import/export functions in this
       package which are an interface to the internal POSIX date and time
       functions of your system, which can only cover dates in the following
       ranges:

	01-Jan-1970 00:00:00 GMT .. 19-Jan-2038 03:14:07 GMT [Unix etc.]
	01-Jan-1904 00:00:00 LT	 .. 06-Feb-2040 06:28:15 LT  [MacOS Classic]
	(LT = local time)

       Note that this package projects the Gregorian calendar back until the
       year 1 A.D. -- even though the Gregorian calendar was only adopted in
       1582, mostly by the Catholic European countries, in obedience to the
       corresponding decree of Pope Gregory XIII in that year.

       Some (mainly protestant) countries continued to use the Julian calendar
       (used until then) until as late as the beginning of the 20th century.

       Finally, note that this package is not intended to do everything you
       could ever imagine automagically for you; it is rather intended to
       serve as a toolbox (in the best of UNIX spirit and traditions) which
       should, however, always get you where you want to go.

       See the section "RECIPES" at the bottom of this document for solutions
       to common problems!

       If nevertheless you can't figure out how to solve a particular problem,
       please let me know! (See e-mail address at the end of this document.)

SYNOPSIS
	 use Date::Calc qw(
	     Days_in_Year
	     Days_in_Month
	     Weeks_in_Year
	     leap_year
	     check_date
	     check_time
	     check_business_date
	     Day_of_Year
	     Date_to_Days
	     Day_of_Week
	     Week_Number
	     Week_of_Year
	     Monday_of_Week
	     Nth_Weekday_of_Month_Year
	     Standard_to_Business
	     Business_to_Standard
	     Delta_Days
	     Delta_DHMS
	     Delta_YMD
	     Delta_YMDHMS
	     N_Delta_YMD
	     N_Delta_YMDHMS
	     Normalize_DHMS
	     Add_Delta_Days
	     Add_Delta_DHMS
	     Add_Delta_YM
	     Add_Delta_YMD
	     Add_Delta_YMDHMS
	     Add_N_Delta_YMD
	     Add_N_Delta_YMDHMS
	     System_Clock
	     Today
	     Now
	     Today_and_Now
	     This_Year
	     Gmtime
	     Localtime
	     Mktime
	     Timezone
	     Date_to_Time
	     Time_to_Date
	     Easter_Sunday
	     Decode_Month
	     Decode_Day_of_Week
	     Decode_Language
	     Decode_Date_EU
	     Decode_Date_US
	     Fixed_Window
	     Moving_Window
	     Compress
	     Uncompress
	     check_compressed
	     Compressed_to_Text
	     Date_to_Text
	     Date_to_Text_Long
	     English_Ordinal
	     Calendar
	     Month_to_Text
	     Day_of_Week_to_Text
	     Day_of_Week_Abbreviation
	     Language_to_Text
	     Language
	     Languages
	     Decode_Date_EU2
	     Decode_Date_US2
	     Parse_Date
	     ISO_LC
	     ISO_UC
	 );

	 use Date::Calc qw(:all);

	 Days_in_Year
	     $days = Days_in_Year($year,$month);

	 Days_in_Month
	     $days = Days_in_Month($year,$month);

	 Weeks_in_Year
	     $weeks = Weeks_in_Year($year);

	 leap_year
	     if (leap_year($year))

	 check_date
	     if (check_date($year,$month,$day))

	 check_time
	     if (check_time($hour,$min,$sec))

	 check_business_date
	     if (check_business_date($year,$week,$dow))

	 Day_of_Year
	     $doy = Day_of_Year($year,$month,$day);

	 Date_to_Days
	     $days = Date_to_Days($year,$month,$day);

	 Day_of_Week
	     $dow = Day_of_Week($year,$month,$day);

	 Week_Number
	     $week = Week_Number($year,$month,$day);	      # DEPRECATED

	 Week_of_Year
	     ($week,$year) = Week_of_Year($year,$month,$day); # RECOMMENDED
	     $week = Week_of_Year($year,$month,$day);	      # DANGEROUS

	 Monday_of_Week
	     ($year,$month,$day) = Monday_of_Week($week,$year);

	 Nth_Weekday_of_Month_Year
	     if (($year,$month,$day) =
	     Nth_Weekday_of_Month_Year($year,$month,$dow,$n))

	 Standard_to_Business
	     ($year,$week,$dow) =
	     Standard_to_Business($year,$month,$day);

	 Business_to_Standard
	     ($year,$month,$day) =
	     Business_to_Standard($year,$week,$dow);

	 Delta_Days
	     $Dd = Delta_Days($year1,$month1,$day1,
			      $year2,$month2,$day2);

	 Delta_DHMS
	     ($Dd,$Dh,$Dm,$Ds) =
	     Delta_DHMS($year1,$month1,$day1, $hour1,$min1,$sec1,
			$year2,$month2,$day2, $hour2,$min2,$sec2);

	 Delta_YMD
	     ($Dy,$Dm,$Dd) =
	     Delta_YMD($year1,$month1,$day1,
		       $year2,$month2,$day2);

	 Delta_YMDHMS
	     ($D_y,$D_m,$D_d, $Dh,$Dm,$Ds) =
	     Delta_YMDHMS($year1,$month1,$day1, $hour1,$min1,$sec1,
			  $year2,$month2,$day2, $hour2,$min2,$sec2);

	 N_Delta_YMD
	     ($Dy,$Dm,$Dd) =
	     N_Delta_YMD($year1,$month1,$day1,
			 $year2,$month2,$day2);

	 N_Delta_YMDHMS
	     ($D_y,$D_m,$D_d, $Dhh,$Dmm,$Dss) =
	     N_Delta_YMDHMS($year1,$month1,$day1, $hour1,$min1,$sec1,
			    $year2,$month2,$day2, $hour2,$min2,$sec2);

	 Normalize_DHMS
	     ($Dd,$Dh,$Dm,$Ds) =
	     Normalize_DHMS($Dd,$Dh,$Dm,$Ds);

	 Add_Delta_Days
	     ($year,$month,$day) =
	     Add_Delta_Days($year,$month,$day,
			    $Dd);

	 Add_Delta_DHMS
	     ($year,$month,$day, $hour,$min,$sec) =
	     Add_Delta_DHMS($year,$month,$day, $hour,$min,$sec,
			    $Dd,$Dh,$Dm,$Ds);

	 Add_Delta_YM
	     ($year,$month,$day) =
	     Add_Delta_YM($year,$month,$day,
			  $Dy,$Dm);

	 Add_Delta_YMD
	     ($year,$month,$day) =
	     Add_Delta_YMD($year,$month,$day,
			   $Dy,$Dm,$Dd);

	 Add_Delta_YMDHMS
	     ($year,$month,$day, $hour,$min,$sec) =
	     Add_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec,
			      $D_y,$D_m,$D_d, $Dh,$Dm,$Ds);

	 Add_N_Delta_YMD
	     ($year,$month,$day) =
	     Add_N_Delta_YMD($year,$month,$day,
			     $Dy,$Dm,$Dd);

	 Add_N_Delta_YMDHMS
	     ($year,$month,$day, $hour,$min,$sec) =
	     Add_N_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec,
				$D_y,$D_m,$D_d, $Dhh,$Dmm,$Dss);

	 System_Clock
	     ($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	     System_Clock([$gmt]);

	 Today
	     ($year,$month,$day) = Today([$gmt]);

	 Now
	     ($hour,$min,$sec) = Now([$gmt]);

	 Today_and_Now
	     ($year,$month,$day, $hour,$min,$sec) = Today_and_Now([$gmt]);

	 This_Year
	     $year = This_Year([$gmt]);

	 Gmtime
	     ($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	     Gmtime([time]);

	 Localtime
	     ($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	     Localtime([time]);

	 Mktime
	     $time = Mktime($year,$month,$day, $hour,$min,$sec);

	 Timezone
	     ($D_y,$D_m,$D_d, $Dh,$Dm,$Ds, $dst) = Timezone([time]);

	 Date_to_Time
	     $time = Date_to_Time($year,$month,$day, $hour,$min,$sec);

	 Time_to_Date
	     ($year,$month,$day, $hour,$min,$sec) = Time_to_Date([time]);

	 Easter_Sunday
	     ($year,$month,$day) = Easter_Sunday($year);

	 Decode_Month
	     if ($month = Decode_Month($string[,$lang]))

	 Decode_Day_of_Week
	     if ($dow = Decode_Day_of_Week($string[,$lang]))

	 Decode_Language
	     if ($lang = Decode_Language($string))

	 Decode_Date_EU
	     if (($year,$month,$day) = Decode_Date_EU($string[,$lang]))

	 Decode_Date_US
	     if (($year,$month,$day) = Decode_Date_US($string[,$lang]))

	 Fixed_Window
	     $year = Fixed_Window($yy);

	 Moving_Window
	     $year = Moving_Window($yy);

	 Compress
	     $date = Compress($year,$month,$day);

	 Uncompress
	     if (($century,$year,$month,$day) = Uncompress($date))

	 check_compressed
	     if (check_compressed($date))

	 Compressed_to_Text
	     $string = Compressed_to_Text($date[,$lang]);

	 Date_to_Text
	     $string = Date_to_Text($year,$month,$day[,$lang]);

	 Date_to_Text_Long
	     $string = Date_to_Text_Long($year,$month,$day[,$lang]);

	 English_Ordinal
	     $string = English_Ordinal($number);

	 Calendar
	     $string = Calendar($year,$month[,$orthodox[,$lang]]);

	 Month_to_Text
	     $string = Month_to_Text($month[,$lang]);

	 Day_of_Week_to_Text
	     $string = Day_of_Week_to_Text($dow[,$lang]);

	 Day_of_Week_Abbreviation
	     $string = Day_of_Week_Abbreviation($dow[,$lang]);

	 Language_to_Text
	     $string = Language_to_Text($lang);

	 Language
	     $lang = Language();
	     Language($lang);		    # DEPRECATED
	     $oldlang = Language($newlang); # DEPRECATED

	 Languages
	     $max_lang = Languages();

	 Decode_Date_EU2
	     if (($year,$month,$day) = Decode_Date_EU2($string[,$lang]))

	 Decode_Date_US2
	     if (($year,$month,$day) = Decode_Date_US2($string[,$lang]))

	 Parse_Date
	     if (($year,$month,$day) = Parse_Date($string[,$lang]))

	 ISO_LC
	     $lower = ISO_LC($string);

	 ISO_UC
	     $upper = ISO_UC($string);

	 Version
	     $string = Date::Calc::Version();

IMPORTANT NOTES
       (See the section "RECIPES" at the bottom of this document for solutions
       to common problems!)

       · "Year 2000" ("Y2K") compliance

	 The upper limit for any year number in this module is only given by
	 the size of the largest positive integer that can be represented in a
	 variable of the C type "int" on your system, which is at least 32767,
	 according to the ANSI C standard (exceptions see below).

	 In order to simplify calculations, this module projects the gregorian
	 calendar back until the year 1 A.D. -- i.e., back BEYOND the year
	 1582 when this calendar was first decreed by the Catholic Pope
	 Gregory XIII!

	 Therefore, BE SURE TO ALWAYS SPECIFY "1998" WHEN YOU MEAN "1998", for
	 instance, and DO NOT WRITE "98" INSTEAD, because this will in fact
	 perform a calculation based on the year "98" A.D. and NOT "1998"!

	 An exception from this rule are the functions which contain the word
	 "compress" in their names (which can only handle years between 1970
	 and 2069 and also accept the abbreviations "00" to "99"), and the
	 functions whose names begin with "Decode_Date_" (which translate year
	 numbers below 100 using a technique known as "moving window").

	 If you want to convert a two-digit year number into a full-fledged,
	 four-digit (at least for some years to come ";-)") year number, use
	 the two functions "Fixed_Window()" and "Moving_Window()" (see their
	 description further below).

	 Note also that the following import/export functions (which are
	 interfaces to the POSIX functions "time()", "gmtime()", "localtime()"
	 and "mktime()" or (the last two) substitutes for the BSD function
	 "timegm()" and the POSIX function "gmtime()") have a very limited
	 range of representable dates (in contrast to all other functions in
	 this package, which cover virtually any date including and after
	 January 1st 1 A.D.):

		       System_Clock()
		       Today()
		       Now()
		       Today_and_Now()
		       This_Year()
		       Gmtime()
		       Localtime()
		       Mktime()
		       Timezone()
		       Date_to_Time()
		       Time_to_Date()

	 These functions can only deal with dates in the range from
	 01-Jan-1970 00:00:00 GMT to 19-Jan-2038 03:14:07 GMT (the latter
	 limit is only authoritative on 32 bit systems, however, and can (in
	 principle, through a few code changes) be extended somewhat ":-)" on
	 64 bit systems).

	 On MacOS Classic, the valid range of dates is between (both included)
	 01-Jan-1904 00:00:00 (local time) to 06-Feb-2040 06:28:15 (local
	 time).

	 Note further that the function "Easter_Sunday()" can only be used for
	 years in the range 1583 to 2299.

       · POSIX functions

	 Note that the following functions

		       Gmtime()
		       Localtime()
		       Mktime()
		       Timezone()

	 are actually wrappers around or based upon the corresponding POSIX
	 functions "time()", "gmtime()", "localtime()" and "mktime()".

	 As such, they depend on local settings of the underlying machine such
	 as e.g. the system clock, the time zone and the locale.

	 Their results can therefore sometimes be unexpected or counter-
	 intuitive.

	 Therefore, no support can be provided for these functions.

	 They are supplied "as is", purely for the sake of interoperability.

	 Use at your own risk. (You have been warned!)

       · First index

	 ALL ranges in this module start with "1", NOT "0"!

	 I.e., the day of month, day of week, day of year, month of year, week
	 of year, first valid year number and language ALL start counting at
	 one, NOT zero!

	 The only exception is the function ""Week_Number()"", which may in
	 fact return "0" when the given date actually lies in the last week of
	 the PREVIOUS year, and of course the numbers for hours (0..23),
	 minutes (0..59) and seconds (0..59).

       · Function naming conventions

	 Function names completely in lower case indicate a boolean return
	 value.

       · Boolean values

	 Boolean values returned from functions in this module are always a
	 numeric zero ("0") for "false" and a numeric one ("1") for "true".

       · Exception handling

	 The functions in this module will usually die with a corresponding
	 error message if their input parameters, intermediate results or
	 output values are out of range.

	 The following functions handle errors differently:

	   -  check_date()
	   -  check_time()
	   -  check_business_date()
	   -  check_compressed()

	 (which return a "false" return value when the given input does not
	 represent a valid date or time),

	   -  Nth_Weekday_of_Month_Year()

	 (which returns an empty list if the requested 5th day of week does
	 not exist),

	   -  Decode_Month()
	   -  Decode_Day_of_Week()
	   -  Decode_Language()
	   -  Fixed_Window()
	   -  Moving_Window()
	   -  Compress()

	 (which return "0" upon failure or invalid input), and

	   -  Decode_Date_EU()
	   -  Decode_Date_US()
	   -  Decode_Date_EU2()
	   -  Decode_Date_US2()
	   -  Parse_Date()
	   -  Uncompress()

	 (which return an empty list upon failure or invalid input).

	 Note that you can always catch an exception thrown by any of the
	 functions in this module and handle it yourself by enclosing the
	 function call in an ""eval"" with curly brackets and checking the
	 special variable "$@" (see "eval" in perlfunc(1) for details).

DESCRIPTION
       · "use Date::Calc qw( Days_in_Year Days_in_Month ... );"

       · "use Date::Calc qw(:all);"

	 You can either specify the functions you want to import explicitly by
	 enumerating them between the parentheses of the ""qw()"" operator, or
	 you can use the "":all"" tag instead to import ALL available
	 functions.

       · "$days = Days_in_Year($year,$month);"

	 This function returns the sum of the number of days in the months
	 starting with January up to and including "$month" in the given year
	 "$year".

	 I.e., ""Days_in_Year(1998,1)"" returns "31", ""Days_in_Year(1998,2)""
	 returns "59", ""Days_in_Year(1998,3)"" returns "90", and so on.

	 Note that ""Days_in_Year($year,12)"" returns the number of days in
	 the given year "$year", i.e., either "365" or "366".

       · "$days = Days_in_Month($year,$month);"

	 This function returns the number of days in the given month "$month"
	 of the given year "$year".

	 The year must always be supplied, even though it is only needed when
	 the month is February, in order to determine whether it is a leap
	 year or not.

	 I.e., ""Days_in_Month(1998,1)"" returns "31",
	 ""Days_in_Month(1998,2)"" returns "28", ""Days_in_Month(2000,2)""
	 returns "29", ""Days_in_Month(1998,3)"" returns "31", and so on.

       · "$weeks = Weeks_in_Year($year);"

	 This function returns the number of weeks in the given year "$year",
	 i.e., either "52" or "53".

       · "if (leap_year($year))"

	 This function returns "true" ("1") if the given year "$year" is a
	 leap year and "false" ("0") otherwise.

       · "if (check_date($year,$month,$day))"

	 This function returns "true" ("1") if the given three numerical
	 values "$year", "$month" and "$day" constitute a valid date, and
	 "false" ("0") otherwise.

       · "if (check_time($hour,$min,$sec))"

	 This function returns "true" ("1") if the given three numerical
	 values "$hour", "$min" and "$sec" constitute a valid time ("0 <=
	 $hour < 24", "0 <= $min < 60" and "0 <= $sec < 60"), and "false"
	 ("0") otherwise.

       · "if (check_business_date($year,$week,$dow))"

	 This function returns "true" ("1") if the given three numerical
	 values "$year", "$week" and "$dow" constitute a valid date in
	 business format, and "false" ("0") otherwise.

	 Beware that this function does NOT compute whether a given date is a
	 business day (i.e., Monday to Friday)!

	 To do so, use ""(Day_of_Week($year,$month,$day) < 6)"" instead.

       · "$doy = Day_of_Year($year,$month,$day);"

	 This function returns the (relative) number of the day of the given
	 date in the given year.

	 E.g., ""Day_of_Year($year,1,1)"" returns "1",
	 ""Day_of_Year($year,2,1)"" returns "32", and
	 ""Day_of_Year($year,12,31)"" returns either "365" or "366".

	 The day of year is sometimes also referred to as the Julian day (or
	 date), although it has nothing to do with the Julian calendar, the
	 calendar which was used before the Gregorian calendar.

	 In order to convert the number returned by this function back into a
	 date, use the function ""Add_Delta_Days()"" (described further
	 below), as follows:

	   $doy = Day_of_Year($year,$month,$day);
	   ($year,$month,$day) = Add_Delta_Days($year,1,1, $doy - 1);

       · "$days = Date_to_Days($year,$month,$day);"

	 This function returns the (absolute) number of the day of the given
	 date, where counting starts at the 1st of January of the year 1 A.D.

	 I.e., ""Date_to_Days(1,1,1)"" returns "1", ""Date_to_Days(1,12,31)""
	 returns "365", ""Date_to_Days(2,1,1)"" returns "366",
	 ""Date_to_Days(1998,5,1)"" returns "729510", and so on.

	 This is sometimes also referred to (not quite correctly) as the
	 Julian date (or day). This may cause confusion, because also the
	 number of the day in a year (from 1 to 365 or 366) is frequently
	 called the "Julian day".

	 More confusing still, this has nothing to do with the Julian
	 calendar, which was used BEFORE the Gregorian calendar.

	 The Julian calendar was named after famous Julius Caesar, who had
	 instituted it in Roman times. The Julian calendar is less precise
	 than the Gregorian calendar because it has too many leap years
	 compared to the true mean length of a year (but the Gregorian
	 calendar also still has one day too much every 5000 years). Anyway,
	 the Julian calendar was better than what existed before, because
	 rulers had often changed the calendar used until then in arbitrary
	 ways, in order to lengthen their own reign, for instance.

	 In order to convert the number returned by this function back into a
	 date, use the function ""Add_Delta_Days()"" (described further
	 below), as follows:

	   $days = Date_to_Days($year,$month,$day);
	   ($year,$month,$day) = Add_Delta_Days(1,1,1, $days - 1);

       · "$dow = Day_of_Week($year,$month,$day);"

	 This function returns the number of the day of week of the given
	 date.

	 The function returns "1" for Monday, "2" for Tuesday and so on until
	 "7" for Sunday.

	 Note that in the Hebrew calendar (on which the Christian calendar is
	 based), the week starts with Sunday and ends with the Sabbath or
	 Saturday (where according to the Genesis (as described in the Bible)
	 the Lord rested from creating the world).

	 In medieval times, Catholic Popes have decreed the Sunday to be the
	 official day of rest, in order to dissociate the Christian from the
	 Hebrew belief.

	 It appears that this actually happened with the Emperor Constantin,
	 who converted to Christianity but still worshipped the Sun god and
	 therefore moved the Christian sabbath to the day of the Sun.

	 Nowadays, the Sunday AND the Saturday are commonly considered (and
	 used as) days of rest, usually referred to as the "week-end".

	 Consistent with this practice, current norms and standards (such as
	 ISO/R 2015-1971, DIN 1355 and ISO 8601) define the Monday as the
	 first day of the week.

       · "$week = Week_Number($year,$month,$day);"

	 This function returns the number of the week the given date lies in.

	 If the given date lies in the LAST week of the PREVIOUS year, "0" is
	 returned.

	 If the given date lies in the FIRST week of the NEXT year,
	 ""Weeks_in_Year($year) + 1"" is returned.

       · "($week,$year) = Week_of_Year($year,$month,$day);"

	 This function returns the number of the week the given date lies in,
	 as well as the year that week belongs to.

	 I.e., if the given date lies in the LAST week of the PREVIOUS year,
	 ""(Weeks_in_Year($year-1), $year-1)"" is returned.

	 If the given date lies in the FIRST week of the NEXT year, ""(1,
	 $year+1)"" is returned.

	 Otherwise, ""(Week_Number($year,$month,$day), $year)"" is returned.

       · "$week = Week_of_Year($year,$month,$day);"

	 In scalar context, this function returns just the week number. This
	 allows you to write ""$week = Week_of_Year($year,$month,$day);""
	 instead of ""($week) = Week_of_Year($year,$month,$day);"" (note the
	 parentheses around "$week").

	 If the given date lies in the LAST week of the PREVIOUS year,
	 ""Weeks_in_Year($year-1)"" is returned.

	 If the given date lies in the FIRST week of the NEXT year, "1" is
	 returned.

	 Otherwise the return value is identical with that of
	 ""Week_Number($year,$month,$day)"".

	 BEWARE that using this function in scalar context is a DANGEROUS
	 feature, because without knowing which year the week belongs to, you
	 might inadvertently assume the wrong one!

	 If for instance you are iterating through an interval of dates, you
	 might assume that the week always belongs to the same year as the
	 given date, which unfortunately is WRONG in some cases!

	 In many years, the 31st of December for instance belongs to week
	 number one of the FOLLOWING year. Assuming that the year is the same
	 as your date (31st of December, in this example), sends you back to
	 the first week of the CURRENT year - the Monday of which, by the way,
	 in case of bad luck, might actually lie in the year BEFORE the
	 current year!

	 This actually happens in 2002, for example.

	 So you always need to provide the correct corresponding year number
	 by other means, keeping track of it yourself.

	 In case you do not understand this, never mind, but then simply DO
	 NOT USE this function in scalar context!

       · "($year,$month,$day) = Monday_of_Week($week,$year);"

	 This function returns the date of the first day of the given week,
	 i.e., the Monday.

	 "$year" must be greater than or equal to "1", and "$week" must lie in
	 the range "1" to ""Weeks_in_Year($year)"".

	 Note that you can write ""($year,$month,$day) =
	 Monday_of_Week(Week_of_Year($year,$month,$day));"" in order to
	 calculate the date of the Monday of the same week as the given date.

	 If you want to calculate any other day of week in the same week as a
	 given date, use

	   @date = Add_Delta_Days(Monday_of_Week(Week_of_Year(@date)),$offset);

	 where "$offset = 1" for Tuesday, 2 for Wednesday etc.

       · "if (($year,$month,$day) =
	 Nth_Weekday_of_Month_Year($year,$month,$dow,$n))"

	 This function calculates the date of the "$n"th day of week "$dow" in
	 the given month "$month" and year "$year"; such as, for example, the
	 3rd Thursday of a given month and year.

	 This can be used to send a notification mail to the members of a
	 group which meets regularly on every 3rd Thursday of a month, for
	 instance.

	 (See the section "RECIPES" near the end of this document for a code
	 snippet to actually do so.)

	 "$year" must be greater than or equal to "1", "$month" must lie in
	 the range "1" to "12", "$dow" must lie in the range "1" to "7" and
	 "$n" must lie in the range "1" to "5", or a fatal error (with
	 appropriate error message) occurs.

	 The function returns an empty list when the 5th of a given day of
	 week does not exist in the given month and year.

       · "($year,$week,$dow) = Standard_to_Business($year,$month,$day);"

	 This function converts a given date from standard notation (year,
	 month, day (of month)) to business notation (year, week, day of
	 week).

       · "($year,$month,$day) = Business_to_Standard($year,$week,$dow);"

	 This function converts a given date from business notation (year,
	 week, day of week) to standard notation (year, month, day (of
	 month)).

       · "$Dd = Delta_Days($year1,$month1,$day1, $year2,$month2,$day2);"

	 This function returns the difference in days between the two given
	 dates.

	 The result is positive if the two dates are in chronological order,
	 i.e., if date #1 comes chronologically BEFORE date #2, and negative
	 if the order of the two dates is reversed.

	 The result is zero if the two dates are identical.

       · "($Dd,$Dh,$Dm,$Ds) = Delta_DHMS($year1,$month1,$day1,
	 $hour1,$min1,$sec1, $year2,$month2,$day2, $hour2,$min2,$sec2);"

	 This function returns the difference in days, hours, minutes and
	 seconds between the two given dates with times.

	 All four return values will be positive if the two dates are in
	 chronological order, i.e., if date #1 comes chronologically BEFORE
	 date #2, and negative (in all four return values!) if the order of
	 the two dates is reversed.

	 This is so that the two functions ""Delta_DHMS()"" and
	 ""Add_Delta_DHMS()"" (description see further below) are
	 complementary, i.e., mutually inverse:

	   Add_Delta_DHMS(@date1,@time1, Delta_DHMS(@date1,@time1, @date2,@time2))

	 yields ""(@date2,@time2)"" again, whereas

	   Add_Delta_DHMS(@date2,@time2,
	       map(-$_, Delta_DHMS(@date1,@time1, @date2,@time2)))

	 yields ""(@date1,@time1)"", and

	   Delta_DHMS(@date1,@time1, Add_Delta_DHMS(@date1,@time1, @delta))

	 yields "@delta" again.

	 The result is zero (in all four return values) if the two dates and
	 times are identical.

       · "($Dy,$Dm,$Dd) = Delta_YMD($year1,$month1,$day1,
	 $year2,$month2,$day2);"

	 This function returns the vector

	     ( $year2 - $year1, $month2 - $month1, $day2 - $day1 )

	 This is called the "one-by-one" semantics.

	 Adding the result of this function to the first date always yields
	 the second date again, and adding the negative result (where the
	 signs of all elements of the result vector have been flipped) to the
	 second date gives the first date. See also the description of the
	 function "Add_Delta_YMD()" further below.

	 Example:

	   (6,2,-30) == Delta_YMD(1996,1,31, 2002,3,1]);

	   [1996,1,31] + ( 6, 2,-30) = [2002,3, 1]
	   [2002,3, 1] + (-6,-2, 30) = [1996,1,31]

	 An error occurs if any of the two given dates is invalid.

       · "($D_y,$D_m,$D_d, $Dh,$Dm,$Ds) = Delta_YMDHMS($year1,$month1,$day1,
	 $hour1,$min1,$sec1, $year2,$month2,$day2, $hour2,$min2,$sec2);"

	 This function is based on the function "Delta_YMD()" above but
	 additionally calculates the time difference. When a carry over from
	 the time difference occurs, the value of "$D_d" is adjusted
	 accordingly, thus giving the correct total date/time difference.

	 Arguments are expected to be in chronological order to yield a
	 (usually) positive result.

	 In any case, adding the result of this function to the first
	 date/time value ("$year1,$month1,$day1," "$hour1,$min1,$sec1") always
	 gives the second date/time value ("$year2,$month2,$day2,"
	 "$hour2,$min2,$sec2") again, and adding the negative result (with the
	 signs of all elements of the result vector flipped) to the second
	 date/time value gives the first date/time value.

	 See the function "Add_Delta_YMDHMS()" further below for adding a
	 date/time value and a date/time difference.

	 An error occurs if any of the given two date/time values is invalid.

       · "($Dy,$Dm,$Dd) = N_Delta_YMD($year1,$month1,$day1,
	 $year2,$month2,$day2);"

	 This function returns the difference between the two given dates in a
	 more intuitive way (as far as possible - more on that see a bit
	 further below) than the function "Delta_YMD()" described above.

	 The "N" which precedes its name is meant to signify "new" or
	 "normalized".

	 This function is loosely based on recipe #17 b) (see the section
	 "RECIPES" below near the end of this document).

	 However, the code of recipe #17 b) actually does not treat positive
	 and negative values symmetrically and consistently.

	 This new routine does.

	 The return values of this function are guaranteed to all have the
	 same sign (or to be zero). This is why this function is called
	 "normalized".

	 Moreover, the results are guaranteed to be "minimal", in the sense
	 that "|$Dm| < 12" and "|$Dd| < 31" (which is equivalent to $Dm lying
	 in the range "[-11..+11]" and $Dd lying in the range "[-30..+30]").

	 When the results are applied (i.e., added) to the first given date in
	 a left-to-right order, the second given date is guaranteed to be
	 obtained, provided that intermediary results are truncated, as done
	 by the function "Add_Delta_YM()" (see further below), i.e., that
	 invalid intermediate dates such as e.g. [2009,2,31] will
	 automatically be transformed into [2009,2,28] (and not "wrapped" into
	 the next month, e.g. to [2009,3,3]).

	 This is called the "left-to-right with truncation" semantics.

	 Note that reversing the order of the given dates and reversing the
	 sign of each of the result values will not always add up.

	 Consider the dates [2008,2,29] and [2009,2,1]: their difference is
	 (0,11,3) ([2008,2,29] plus 11 months is [2009,1,29], which plus 3
	 days is [2009,2,1]), but the difference between [2009,2,1] and
	 [2008,2,29] is (0,-11,-1), and not (0,-11,-3) ([2009,2,1] minus 11
	 months is [2008,3,1], which minus one day is [2008,2,29]).

	 Another example: The difference between [1996,2,29] and [1997,2,28]
	 is (1,0,0) (observe the truncation of the invalid date [1997,2,29] to
	 [1997,2,28] here!), whereas the difference between [1997,2,28] and
	 [1996,2,29] is (0,-11,-28) ([1997,2,28] minus 11 months is
	 [1996,3,28], which minus 28 days is not [1996,3,0] but of course
	 [1996,2,29]).

	 "Benign" examples such as for instance the difference between
	 [1964,1,3] and [2009,9,10] are completely symmetrical: The difference
	 in this example is (45,8,7), whereas the difference between
	 [2009,9,10] and [1964,1,3] is (-45,-8,-7), as would normally be
	 expected. In this example, the result is also the same as the one
	 returned by "Delta_YMD()".

	 All these counter-intuitive effects are due to the fact that months
	 (and due to leap years, also years) do not correspond to a fixed
	 number of days, so the semantics of "plus one month" or "plus one
	 year" are in fact undefined.

	 The present function is an attempt to provide a definition which is
	 intuitive most of the time, and at least consistent the rest of the
	 time.

	 Other definitions are of course possible, but most often lead to
	 contradictions (e.g., the results and the given first date do not add
	 up to the second given date).

	 See the file "datecalc.pl" in the "examples" subdirectory of this
	 distribution for a way to play around with this function, or go to
	 http://www.engelschall.com/u/sb/datecalc/ for the online version.

	 An error occurs if any of the two given dates is invalid, or if any
	 intermediate result leads to an invalid date (this does not apply to
	 truncation, however, as explained above).

       · "($D_y,$D_m,$D_d, $Dhh,$Dmm,$Dss) =
	 N_Delta_YMDHMS($year1,$month1,$day1, $hour1,$min1,$sec1,
	 $year2,$month2,$day2, $hour2,$min2,$sec2);"

	 This function essentially does the same as the function
	 "N_Delta_YMD()" described immediately above, except that also the
	 difference in hours, minutes and seconds is taken into account.

	 This function is loosely based on recipe #17 a) (see the section
	 "RECIPES" below near the end of this document).

	 However, the code of recipe #17 a) actually does not treat positive
	 and negative values symmetrically and consistently.

	 This new routine does.

	 The return values of this function (including the time differences)
	 are guaranteed to all have the same sign (or to be zero). This is the
	 reason for the "N" that precedes the name of this function, which is
	 intended to mean "normalized" (or "new").

	 Moreover, the results are guaranteed to be "minimal", in the sense
	 that "|$D_m| < 12", "|$D_d| < 31", "|$Dhh| < 24", "|$Dmm| < 60" and
	 "|$Dss| < 60" (which is equivalent to $D_m lying in the range
	 "[-11..+11]", $D_d lying in the range "[-30..+30]", $Dhh lying in the
	 range "[-23..+23]", and $Dmm and $Dss both lying in the range
	 "[-59..+59]").

       · "($Dd,$Dh,$Dm,$Ds) = Normalize_DHMS($Dd,$Dh,$Dm,$Ds);"

	 This function takes four arbitrary values for days, hours, minutes
	 and seconds (which may have different signs) and renormalizes them so
	 that the values for hours, minutes and seconds will lie in the ranges
	 "[-23..23]", "[-59..59]" and "[-59..59]", respectively, and so that
	 all four values have the same sign (or are zero).

	 The given values are left untouched, i.e., unchanged.

       · "($year,$month,$day) = Add_Delta_Days($year,$month,$day, $Dd);"

	 This function has two principal uses:

	 First, it can be used to calculate a new date, given an initial date
	 and an offset (which may be positive or negative) in days, in order
	 to answer questions like "today plus 90 days -- which date gives
	 that?".

	 (In order to add a weeks offset, simply multiply the weeks offset
	 with "7" and use that as your days offset.)

	 Second, it can be used to convert the canonical representation of a
	 date, i.e., the number of that day (where counting starts at the 1st
	 of January in 1 A.D.), back into a date given as year, month and day.

	 Because counting starts at "1", you will actually have to subtract
	 "1" from the canonical date in order to get back the original date:

	   $canonical = Date_to_Days($year,$month,$day);

	   ($year,$month,$day) = Add_Delta_Days(1,1,1, $canonical - 1);

	 Moreover, this function is the inverse of the function
	 ""Delta_Days()"":

	   Add_Delta_Days(@date1, Delta_Days(@date1, @date2))

	 yields "@date2" again, whereas

	   Add_Delta_Days(@date2, -Delta_Days(@date1, @date2))

	 yields "@date1", and

	   Delta_Days(@date1, Add_Delta_Days(@date1, $delta))

	 yields "$delta" again.

       · "($year,$month,$day, $hour,$min,$sec) =
	 Add_Delta_DHMS($year,$month,$day, $hour,$min,$sec, $Dd,$Dh,$Dm,$Ds);"

	 This function serves to add a days, hours, minutes and seconds offset
	 to a given date and time, in order to answer questions like "today
	 and now plus 7 days but minus 5 hours and then plus 30 minutes, what
	 date and time gives that?":

	   ($y,$m,$d,$H,$M,$S) = Add_Delta_DHMS(Today_and_Now(), +7,-5,+30,0);

       · "($year,$month,$day) = Add_Delta_YM($year,$month,$day, $Dy,$Dm);"

	 This function can be used to add a year and/or month offset to a
	 given date.

	 In contrast to the function described immediately below
	 (""Add_Delta_YMD()""), this function does no "wrapping" into the next
	 month if the day happens to lie outside the valid range for the
	 resulting year and month (after adding the year and month offsets).
	 Instead, it simply truncates the day to the last possible day of the
	 resulting month.

	 Examples:

	 Adding an offset of 0 years, 1 month to the date [1999,1,31] would
	 result in the (invalid) date [1999,2,31]. The function replaces this
	 result by the (valid) date [1999,2,28].

	 Adding an offset of 1 year, 1 month to the same date [1999,1,31] as
	 above would result in the (still invalid) date [2000,2,31]. The
	 function replaces this result by the valid date [2000,2,29] (because
	 2000 is a leap year).

	 Note that the year and month offsets can be negative, and that they
	 can have different signs.

	 If you want to additionally add a days offset, use the function
	 ""Add_Delta_Days()"" before or after calling ""Add_Delta_YM()"":

	   @date2 = Add_Delta_Days( Add_Delta_YM(@date1, $Dy,$Dm), $Dd );
	   @date2 = Add_Delta_YM( Add_Delta_Days(@date1, $Dd), $Dy,$Dm );

	 Note that your result may depend on the order in which you call these
	 two functions!

	 Consider the date [1999,2,28] and the offsets 0 years, 1 month and 1
	 day:

	 [1999,2,28] plus one month is [1999,3,28], plus one day is
	 [1999,3,29]. [1999,2,28] plus one day is [1999,3,1], plus one month
	 is [1999,4,1].

	 (Which is also the reason why the ""Add_Delta_YM()"" function does
	 not allow to add a days offset, because this would actually require
	 TWO functions: One for adding the days offset BEFORE and one for
	 adding it AFTER applying the year/month offsets.)

	 An error occurs if the initial date is not valid.

	 Note that ""Add_Delta_YM( Add_Delta_YM(@date, $Dy,$Dm), -$Dy,-$Dm
	 );"" will not, in general, return the original date "@date" (consider
	 the examples given above!).

       · "($year,$month,$day) = Add_Delta_YMD($year,$month,$day,
	 $Dy,$Dm,$Dd);"

	 This function serves to add a years, months and days offset to a
	 given date.

	 (In order to add a weeks offset, simply multiply the weeks offset
	 with "7" and add this number to your days offset.)

	 Note that the three offsets for years, months and days are applied
	 independently from each other. This also allows them to have
	 different signs.

	 The years and months offsets are applied first, and the days offset
	 is applied last.

	 If the resulting date happens to fall on a day after the end of the
	 resulting month, like the 32nd of April or the 30th of February, then
	 the date is simply counted forward into the next month (possibly also
	 into the next year) by the number of excessive days (e.g., the 32nd
	 of April will become the 2nd of May).

	 BEWARE that this behaviour differs from that of previous versions of
	 this module! In previous versions, the day was simply truncated to
	 the maximum number of days in the resulting month.

	 If you want the previous behaviour, use the new function
	 ""Add_Delta_YM()"" (described immediately above) plus the function
	 ""Add_Delta_Days()"" instead.

	 BEWARE also that because a year and a month offset is not equivalent
	 to a fixed number of days, the transformation performed by this
	 function is NOT ALWAYS REVERSIBLE!

	 This is in contrast to the functions ""Add_Delta_Days()"" and
	 ""Add_Delta_DHMS()"", which are fully and truly reversible (with the
	 help of the functions ""Delta_Days()"" and ""Delta_DHMS()"", for
	 instance).

	 Note that for this same reason,

	   @date = Add_Delta_YMD(
		   Add_Delta_YMD(@date, $Dy,$Dm,$Dd), -$Dy,-$Dm,-$Dd);

	 will in general NOT return the initial date "@date", even though

	   @date2 = Add_Delta_YMD( @date1, Delta_YMD(@date1, @date2) );

	 will always return the second date "@date2", and

	   @date1 = Add_Delta_YMD( @date2, map(-$_, Delta_YMD(@date1, @date2)) );

	 which is the same as

	   @date1 = Add_Delta_YMD( @date2, Delta_YMD(@date2, @date1) );

	 will always return the first date "@date1".

	 Examples:

	   [1996,1,31] + ( 6, 1,-2) = [2002,3,1]
	   [2002,3, 1] + (-6,-1, 2) = [1996,2,3] # EXPECTED: [1996,1,31]

	   (6,2,-30) == Delta_YMD(1996,1,31, 2002,3,1);

	   [1996,1,31] + ( 6, 2,-30) = [2002,3, 1]
	   [2002,3, 1] + (-6,-2, 30) = [1996,1,31] # OK

	   (6,1,-2) == Delta_YMD(1996,2,3, 2002,3,1);

	   [1996,2,3] + ( 6, 1,-2) = [2002,3,1]
	   [2002,3,1] + (-6,-1, 2) = [1996,2,3] # OK

	 Note that this is NOT a program bug but NECESSARILY so, because of
	 the variable lengths of years and months, and hence because of the
	 ambiguity of the difference between two dates in terms of years,
	 months and days, i.e., the fact that the difference between two dates
	 can be expressed in more than one way:

	   [1996,1,31] + (6,1, -2) = [2002,3,1]
	   [1996,1,31] + (6,2,-30) = [2002,3,1]

       · "($year,$month,$day, $hour,$min,$sec) =
	 Add_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec, $D_y,$D_m,$D_d,
	 $Dh,$Dm,$Ds);"

	 Same as the function above, except that a time offset may be given in
	 addition to the year, month and day offset.

       · "($year,$month,$day) = Add_N_Delta_YMD($year,$month,$day,
	 $Dy,$Dm,$Dd);"

	 This function is actually a shortcut for applying the function
	 "Add_Delta_YM()" first, followed by the function "Add_Delta_Days()",
	 i.e., this function does exactly the same as

	  ($year,$month,$day) = Add_Delta_Days( Add_Delta_YM($year,$month,$day,$Dy,$Dm), $Dd );

	 Beware that, if necessary, the function "Add_Delta_YM()" truncates
	 the resulting day of the month to the largest allowable value for
	 that month, i.e., the (invalid) result [2009,2,31] is automatically
	 transformed into [2009,2,28].

	 For more details on this truncation, see the description of the
	 function "Add_Delta_YM()" further above.

	 This function is meant to be complementary with the function
	 "N_Delta_YMD()" described further above.

	 This means that it is guaranteed that the result returned by

	   Add_N_Delta_YMD( @date1, N_Delta_YMD(@date1, @date2) );

	 is always identical with the given date "@date2".

	 Note however that unlike with function "Add_Delta_YMD()", the reverse
	 is not true here, i.e.,

	   ($Dy,$Dm,$Dd) = N_Delta_YMD(@date1,@date2);
	   @date = Add_N_Delta_YMD(@date2, -$Dy,-$Dm,-$Dd);

	 will NOT always return the initial date "@date1".

	 Example:

	   (0,11,3) == N_Delta_YMD(2008,2,29, 2009,2,1);

	   [2008,2,29] + (0, 11, 3) = [2009,2, 1]
	   [2009,2, 1] + (0,-11,-3) = [2008,2,27] # EXPECTED: [2008,2,29]

       · "($year,$month,$day, $hour,$min,$sec) =
	 Add_N_Delta_YMDHMS($year,$month,$day, $hour,$min,$sec,
	 $D_y,$D_m,$D_d, $Dhh,$Dmm,$Dss);"

	 This function essentially does the same as the function
	 "Add_N_Delta_YMD()" described immediately above, except that also the
	 difference in hours, minutes and seconds is taken into account.

       · "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	 System_Clock([$gmt]);"

	 If your operating system supports the corresponding system calls
	 (""time()"" and ""localtime()"" or ""gmtime()""), this function will
	 return the information provided by your system clock, i.e., the
	 current date and time, the number of the day of year, the number of
	 the day of week and a flag signaling whether daylight savings time is
	 currently in effect or not.

	 The ranges of values returned (and their meanings) are as follows:

		 $year	 :   1970..2038 (or more)  [Unix etc.]
		 $year	 :   1904..2040		   [MacOS Classic]

		 $month	 :   1..12
		 $day	 :   1..31
		 $hour	 :   0..23
		 $min	 :   0..59
		 $sec	 :   0..59    (0..61 on some systems)
		 $doy	 :   1..366
		 $dow	 :   1..7
		 $dst	 :  -1..1

	 "$doy" is the day of year, sometimes also referred to as the "julian
	 date", which starts at "1" and goes up to the number of days in that
	 year.

	 The day of week ("$dow") will be "1" for Monday, "2" for Tuesday and
	 so on until "7" for Sunday.

	 The daylight savings time flag ("$dst") will be ""-1"" if this
	 information is not available on your system, "0" for no daylight
	 savings time (i.e., winter time) and "1" when daylight savings time
	 is in effect.

	 If your operating system does not provide the necessary system calls,
	 calling this function will result in a fatal "not available on this
	 system" error message.

	 If you want to handle this exception yourself, use ""eval"" as
	 follows:

	   eval { ($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	     System_Clock(); };

	   if ($@)
	   {
	       # Handle missing system clock
	       # (For instance, ask user to enter this information manually)
	   }

	 Note that curlies ("{" and "}") are used here to delimit the
	 statement to be "eval"ed (which is the way to catch exceptions in
	 Perl), and not quotes (which is a way to evaluate Perl expressions at
	 runtime).

	 If the optional (boolean) input parameter "$gmt" is given, a "true"
	 value ("1") will cause ""gmtime()"" to be used instead of
	 ""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
	 or UTC) instead of local time.

       · "($year,$month,$day) = Today([$gmt]);"

	 This function returns a subset of the values returned by the function
	 ""System_Clock()"" (see above for details), namely the current year,
	 month and day.

	 A fatal "not available on this system" error message will appear if
	 the corresponding system calls are not supported by your current
	 operating system.

	 If the optional (boolean) input parameter "$gmt" is given, a "true"
	 value ("1") will cause ""gmtime()"" to be used instead of
	 ""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
	 or UTC) instead of local time.

       · "($hour,$min,$sec) = Now([$gmt]);"

	 This function returns a subset of the values returned by the function
	 ""System_Clock()"" (see above for details), namely the current time
	 (hours, minutes and full seconds).

	 A fatal "not available on this system" error message will appear if
	 the corresponding system calls are not supported by your current
	 operating system.

	 If the optional (boolean) input parameter "$gmt" is given, a "true"
	 value ("1") will cause ""gmtime()"" to be used instead of
	 ""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
	 or UTC) instead of local time.

       · "($year,$month,$day, $hour,$min,$sec) = Today_and_Now([$gmt]);"

	 This function returns a subset of the values returned by the function
	 ""System_Clock()"" (see above for details), namely the current date
	 (year, month, day) and time (hours, minutes and full seconds).

	 A fatal "not available on this system" error message will appear if
	 the corresponding system calls are not supported by your current
	 operating system.

	 If the optional (boolean) input parameter "$gmt" is given, a "true"
	 value ("1") will cause ""gmtime()"" to be used instead of
	 ""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
	 or UTC) instead of local time.

       · "$year = This_Year([$gmt]);"

	 This function returns the current year, according to local time.

	 A fatal "not available on this system" error message will appear if
	 the corresponding system calls are not supported by your current
	 operating system.

	 If the optional (boolean) input parameter "$gmt" is given, a "true"
	 value ("1") will cause ""gmtime()"" to be used instead of
	 ""localtime()"", internally, thus returning Greenwich Mean Time (GMT,
	 or UTC) instead of local time. However, this will only make a
	 difference within a few hours around New Year (unless you are on a
	 Pacific island, where this can be almost 24 hours).

       · "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	 Gmtime([time]);"

	 This is Date::Calc's equivalent of Perl's built-in "gmtime()"
	 function.  See also "gmtime" in perlfunc(1).

	 With the optional argument "time" (i.e., seconds since the epoch),
	 this function will return the corresponding values for that
	 particular time (instead of the current time when this parameter is
	 omitted).

	 The ranges of values returned (and their meanings) are as follows:

		 $year	 :   1970..2038 (or more)  [Unix etc.]
		 $year	 :   1904..2040		   [MacOS Classic]

		 $month	 :   1..12
		 $day	 :   1..31
		 $hour	 :   0..23
		 $min	 :   0..59
		 $sec	 :   0..59
		 $doy	 :   1..366
		 $dow	 :   1..7
		 $dst	 :  -1..1

	 "$doy" is the day of year, sometimes also referred to as the "julian
	 date", which starts at "1" and goes up to the number of days in that
	 year.

	 The day of week ("$dow") will be "1" for Monday, "2" for Tuesday and
	 so on until "7" for Sunday.

	 The daylight savings time flag ("$dst") will be ""-1"" if this
	 information is not available on your system, "0" for no daylight
	 savings time (i.e., winter time) and "1" when daylight savings time
	 is in effect.

	 A fatal "time out of range" error will occur if the given time value
	 is out of range "[0..(~0>>1)]".

	 If the time value is omitted, the "time()" function is called
	 instead, internally.

       · "($year,$month,$day, $hour,$min,$sec, $doy,$dow,$dst) =
	 Localtime([time]);"

	 This is Date::Calc's equivalent of Perl's built-in "localtime()"
	 function.  See also "localtime" in perlfunc(1).

	 The ranges of values returned (and their meanings) are as follows:

		 $year	 :   1970..2038 (or more)  [Unix etc.]
		 $year	 :   1904..2040		   [MacOS Classic]

		 $month	 :   1..12
		 $day	 :   1..31
		 $hour	 :   0..23
		 $min	 :   0..59
		 $sec	 :   0..59
		 $doy	 :   1..366
		 $dow	 :   1..7
		 $dst	 :  -1..1

	 "$doy" is the day of year, sometimes also referred to as the "julian
	 date", which starts at "1" and goes up to the number of days in that
	 year.

	 The day of week ("$dow") will be "1" for Monday, "2" for Tuesday and
	 so on until "7" for Sunday.

	 The daylight savings time flag ("$dst") will be ""-1"" if this
	 information is not available on your system, "0" for no daylight
	 savings time (i.e., winter time) and "1" when daylight savings time
	 is in effect.

	 A fatal "time out of range" error will occur if the given time value
	 is out of range "[0..(~0>>1)]".

	 If the time value is omitted, the "time()" function is called
	 instead, internally.

       · "$time = Mktime($year,$month,$day, $hour,$min,$sec);"

	 This function converts a date into a time value, i.e., into the
	 number of seconds since whatever moment in time your system considers
	 to be the "epoch". On Unix and most other systems this is the number
	 of seconds since January 1st 1970 at midnight (GMT). On MacOS Classic
	 this is the number of seconds since January 1st 1904 at midnight
	 (local time).

	 The function is similar to the "POSIX::mktime()" function (see
	 "mktime" in POSIX(1) for more details), but in contrast to the
	 latter, it expects dates in the usual ranges used throughout this
	 module: The year 2001 stays year 2001, and months are numbered from 1
	 to 12.

	 A fatal "date out of range" error will occur if the given date cannot
	 be expressed in terms of seconds since the epoch (this happens for
	 instance when the date lies before the epoch, or if it is later than
	 19-Jan-2038 03:14:07 GMT on 32 bit Unix systems, or later than
	 06-Feb-2040 06:28:15 (local time) on a Macintosh with MacOS Classic).

	 Just like the "POSIX::mktime()" function, this function uses the
	 "mktime()" system call, internally.

	 This means that the given date and time is considered to be in local
	 time, and that the value returned by this function will depend on
	 your machine's local settings such as the time zone, whether daylight
	 savings time is (or was, at the time) in effect, and the system clock
	 itself.

	 BEWARE that "mktime()" does not always return the same time value as
	 fed into "localtime()", when you feed the output of "localtime()"
	 back into "mktime()", on some systems!

	 I.e., ""Mktime((Localtime($time))[0..5])"" will not always return the
	 same value as given in "$time"!

       · "($D_y,$D_m,$D_d, $Dh,$Dm,$Ds, $dst) = Timezone([time]);"

	 This function returns the difference between ""localtime(time)"" and
	 ""gmtime(time)"", which is the timezone offset in effect for the
	 current location and the given ""time"".

	 This offset is positive if you are located to the east of Greenwich,
	 and is usually negative (except during daylight savings time, in some
	 locations) if you are located to the west of Greenwich.

	 Note that this offset is influenced by all of the relevant system
	 settings and parameters on your machine; such as locales, environment
	 variables (e.g. ""TZ"") and the system clock itself. See the relevant
	 documentation on your system for more details.

	 If the ""time"" is omitted, the ""time()"" function will be called
	 automatically, internally (similar to the built-in functions
	 ""localtime()"" and ""gmtime()"" in Perl).

	 A fatal "time out of range" error will occur if the given time value
	 is out of range "[0..(~0>>1)]".

	 The last item of the returned list is a flag which indicates whether
	 daylight savings time is currently in effect. This flag is negative
	 (-1) if this information is not available on your system. It is zero
	 (0) when daylight savings time is off, and positive (+1) when
	 daylight savings time is on.

	 Thus you can check very quickly whether daylight savings time is
	 currently in effect by evaluating this function in scalar context (in
	 scalar context, Perl returns the last item of a list):

	   if (scalar Timezone > 0) { # yes, daylight savings time

	 However, a slightly more efficient way would be this:

	   if (scalar System_Clock > 0) { # yes, daylight savings time

       · "$time = Date_to_Time($year,$month,$day, $hour,$min,$sec);"

	 This function is a replacement for the BSD function "timegm()" (which
	 is not available on all Unix systems), which converts a given date
	 and time into a time value, i.e., into the number of seconds since
	 whatever moment in time your system considers to be the "epoch". On
	 Unix and most other systems this is the number of seconds since
	 January 1st 1970 at midnight (GMT). On MacOS Classic this is the
	 number of seconds since January 1st 1904 at midnight (local time).

	 Under Unix, the date and time are considered to be in UTC ("Universal
	 Time Coordinated", and so is the resulting time value.

	 UTC is almost the same as GMT (or "Greenwich Mean Time"), except that
	 UTC has leap seconds (in order to account for small variations in the
	 rotation of the earth, for instance), whereas GMT does not.

	 Under MacOS Classic, however, both input and output are considered to
	 be in local time.

	 The ranges of year and month follow the same rules as throughout the
	 rest of this module (and not the contorted rules of its Unix
	 equivalent), i.e., the year "2001" stays "2001" and the month ranges
	 from 1 to 12.

	 A fatal "date out of range" error will occur if the given date cannot
	 be expressed in terms of seconds since the epoch (this happens for
	 instance when the date lies before the epoch, or if it is later than
	 19-Jan-2038 03:14:07 GMT on 32 bit Unix systems, or later than
	 06-Feb-2040 06:28:15 (local time) on a Macintosh with MacOS Classic).

	 This function should be very fast, because it is implemented in a
	 very straightforward manner and doesn't use any internal system
	 calls.

	 Moreover, the functions "Date_to_Time()" and "Time_to_Date()" are
	 guaranteed to be complementary, i.e., that
	 ""Date_to_Time(Time_to_Date($time))"" and
	 ""Time_to_Date(Date_to_Time($year,$month,$day, $hour,$min,$sec))""
	 will always return the initial values.

       · "($year,$month,$day, $hour,$min,$sec) = Time_to_Date([time]);"

	 This function is an alternative to the POSIX "gmtime()" function (and
	 its built-in Perl equivalent), which converts a given time value into
	 the corresponding date and time. The given time value must be the
	 number of seconds since whatever moment in time your system considers
	 to be the "epoch". On Unix and most other systems this is the number
	 of seconds since January 1st 1970 at midnight (GMT). On MacOS Classic
	 this is the number of seconds since January 1st 1904 at midnight
	 (local time).

	 Under Unix, the given time value is considered to be in UTC
	 ("Universal Time Coordinated", and so is the resulting date and time.

	 UTC is almost the same as GMT (or "Greenwich Mean Time"), except that
	 UTC has leap seconds (in order to account for small variations in the
	 rotation of the earth, for instance), whereas GMT does not.

	 Under MacOS Classic, however, both input and output are considered to
	 be in local time.

	 If the input value ""time"" is omitted, the ""time()"" function will
	 be called automatically, internally (similar to the built-in
	 functions ""localtime()"" and ""gmtime()"" in Perl).

	 A fatal "time out of range" error will occur if the given time value
	 is negative.

	 This function should be very fast, because it is implemented in a
	 very straightforward manner and doesn't use any internal system calls
	 (except for "time()", if the input value is omitted).

	 Moreover, the functions "Date_to_Time()" and "Time_to_Date()" are
	 guaranteed to be complementary, i.e., that
	 ""Date_to_Time(Time_to_Date($time))"" and
	 ""Time_to_Date(Date_to_Time($year,$month,$day, $hour,$min,$sec))""
	 will always return the initial values.

       · "($year,$month,$day) = Easter_Sunday($year);"

	 This function calculates the date of Easter Sunday for all years in
	 the range from 1583 to 2299 (all other year numbers will result in a
	 fatal "year out of range" error message) using the method known as
	 the "Gaussian Rule".

	 Some related christian feast days which depend on the date of Easter
	 Sunday:

	   Carnival Monday / Rosenmontag / Veille du Mardi Gras	  =  -48 days
	   Mardi Gras / Karnevalsdienstag / Mardi Gras		  =  -47 days
	   Ash Wednesday / Aschermittwoch / Mercredi des Cendres  =  -46 days
	   Palm Sunday / Palmsonntag / Dimanche des Rameaux	  =   -7 days
	   Easter Friday / Karfreitag / Vendredi Saint		  =   -2 days
	   Easter Saturday / Ostersamstag / Samedi de Paques	  =   -1 day
	   Easter Monday / Ostermontag / Lundi de Paques	  =   +1 day
	   Ascension of Christ / Christi Himmelfahrt / Ascension  =  +39 days
	   Whitsunday / Pfingstsonntag / Dimanche de Pentecote	  =  +49 days
	   Whitmonday / Pfingstmontag / Lundi de Pentecote	  =  +50 days
	   Feast of Corpus Christi / Fronleichnam / Fete-Dieu	  =  +60 days

	 Use the offsets shown above to calculate the date of the
	 corresponding feast day as follows:

	   ($year,$month,$day) = Add_Delta_Days(Easter_Sunday($year), $offset));

       · "if ($month = Decode_Month($string[,$lang]))"

	 This function takes a string as its argument, which should contain
	 the name of a month in the given or currently selected language (see
	 further below for details about the multi-language support of this
	 package), or any uniquely identifying abbreviation of a month's name
	 (i.e., the first few letters), and returns the corresponding number
	 (1..12) upon a successful match, or "0" otherwise (therefore, the
	 return value can also be used as the conditional expression in an
	 "if" statement).

	 Note that the input string may not contain any other characters which
	 do not pertain to the month's name, especially no leading or trailing
	 whitespace.

	 Note also that matching is performed in a case-insensitive manner
	 (this may depend on the "locale" setting on your current system,
	 though!)

	 With "1" ("English") as the given language, the following examples
	 will all return the value "9":

	   $month = Decode_Month("s",1);
	   $month = Decode_Month("Sep",1);
	   $month = Decode_Month("septemb",1);
	   $month = Decode_Month("September",1);

       · "if ($dow = Decode_Day_of_Week($string[,$lang]))"

	 This function takes a string as its argument, which should contain
	 the name of a day of week in the given or currently selected language
	 (see further below for details about the multi-language support of
	 this package), or any uniquely identifying abbreviation of the name
	 of a day of week (i.e., the first few letters), and returns the
	 corresponding number (1..7) upon a successful match, or "0" otherwise
	 (therefore, the return value can also be used as the conditional
	 expression in an "if" statement).

	 Note that the input string may not contain any other characters which
	 do not pertain to the name of the day of week, especially no leading
	 or trailing whitespace.

	 Note also that matching is performed in a case-insensitive manner
	 (this may depend on the "locale" setting on your current system,
	 though!)

	 With "1" ("English") as the given language, the following examples
	 will all return the value "3":

	   $dow = Decode_Day_of_Week("w",1);
	   $dow = Decode_Day_of_Week("Wed",1);
	   $dow = Decode_Day_of_Week("wednes",1);
	   $dow = Decode_Day_of_Week("Wednesday",1);

       · "if ($lang = Decode_Language($string))"

	 This function takes a string as its argument, which should contain
	 the name of one of the languages supported by this package (IN THIS
	 VERY LANGUAGE ITSELF), or any uniquely identifying abbreviation of
	 the name of a language (i.e., the first few letters), and returns its
	 corresponding internal number (1..14 in the original distribution)
	 upon a successful match, or "0" otherwise (therefore, the return
	 value can also be used as the conditional expression in an "if"
	 statement).

	 Note that the input string may not contain any other characters which
	 do not pertain to the name of a language, especially no leading or
	 trailing whitespace.

	 Note also that matching is performed in a case-insensitive manner
	 (this may depend on the "locale" setting on your current system,
	 though!)

	 The original distribution supports the following fourteen languages:

		     English			==>    1    (default)
		     Francais	 (French)	==>    2
		     Deutsch	 (German)	==>    3
		     Espan~ol	  (Spanish)	 ==>	4
		     Portugues	 (Portuguese)	==>    5
		     Nederlands	 (Dutch)	==>    6
		     Italiano	 (Italian)	==>    7
		     Norsk	 (Norwegian)	==>    8
		     Svenska	 (Swedish)	==>    9
		     Dansk	 (Danish)	==>   10
		     suomi	 (Finnish)	==>   11
		     Magyar	 (Hungarian)	==>   12
		     polski	 (Polish)	==>   13
		     Romaneste	 (Romanian)	==>   14

	 See the section "How to install additional languages" in the file
	 "INSTALL.txt" in this distribution for how to add more languages to
	 this package.

	 In the original distribution (no other languages installed), the
	 following examples will all return the value "3":

	   $lang = Decode_Language("d");
	   $lang = Decode_Language("de");
	   $lang = Decode_Language("Deutsch");

	 Note that you may not be able to enter the special international
	 characters in some of the languages' names over the keyboard directly
	 on some systems.

	 This should never be a problem, though; just enter an abbreviation of
	 the name of the language consisting of the first few letters up to
	 the character before the first special international character.

       · "if (($year,$month,$day) = Decode_Date_EU($string[,$lang]))"

	 This function scans a given string and tries to parse any date which
	 might be embedded in it.

	 The function returns an empty list if it can't successfully extract a
	 valid date from its input string, or else it returns the date found.

	 The function accepts almost any format, as long as the date is given
	 in the european order (hence its name) day-month-year.

	 Thereby, zero or more NON-NUMERIC characters may PRECEDE the day and
	 FOLLOW the year.

	 Moreover, zero or more NON-ALPHANUMERIC characters are permitted
	 BETWEEN these three items (i.e., between day and month and between
	 month and year).

	 The month may be given either numerically (i.e., a number from "1" to
	 "12"), or alphanumerically, i.e., as the name of the month in the
	 given or currently selected language, or any uniquely identifying
	 abbreviation thereof.

	 (See further below for details about the multi-language support of
	 this package!)

	 If the year is given as one or two digits only (i.e., if the year is
	 less than 100), it is mapped to a "window" of +/- 50 years around the
	 current year, as described by the "Moving_Window()" function (see
	 further below).

	 If the day, month and year are all given numerically but WITHOUT any
	 delimiting characters between them, this string of digits will be
	 mapped to the day, month and year as follows:

			 Length:	Mapping:
			   3		  dmy
			   4		  dmyy
			   5		  dmmyy
			   6		  ddmmyy
			   7		  dmmyyyy
			   8		  ddmmyyyy

	 (Where "d" stands for "day", "m" stands for "month" and "y" stands
	 for "year".)

	 All other strings consisting purely of digits (without any
	 intervening delimiters) are rejected, i.e., not recognized.

	 Examples:

	   "3.1.64"
	   "3 1 64"
	   "03.01.64"
	   "03/01/64"
	   "3. Jan 1964"
	   "Birthday: 3. Jan '64 in Backnang/Germany"
	   "03-Jan-64"
	   "3.Jan1964"
	   "3Jan64"
	   "030164"
	   "3ja64"
	   "3164"

	 Experiment! (See the corresponding example applications in the
	 "examples" subdirectory of this distribution in order to do so.)

       · "if (($year,$month,$day) = Decode_Date_US($string[,$lang]))"

	 This function scans a given string and tries to parse any date which
	 might be embedded in it.

	 The function returns an empty list if it can't successfully extract a
	 valid date from its input string, or else it returns the date found.

	 The function accepts almost any format, as long as the date is given
	 in the U.S. american order (hence its name) month-day-year.

	 Thereby, zero or more NON-ALPHANUMERIC characters may PRECEDE and
	 FOLLOW the month (i.e., precede the month and separate it from the
	 day which follows behind).

	 Moreover, zero or more NON-NUMERIC characters are permitted BETWEEN
	 the day and the year, as well as AFTER the year.

	 The month may be given either numerically (i.e., a number from "1" to
	 "12"), or alphanumerically, i.e., as the name of the month in the
	 given or currently selected language, or any uniquely identifying
	 abbreviation thereof.

	 (See further below for details about the multi-language support of
	 this package!)

	 If the year is given as one or two digits only (i.e., if the year is
	 less than 100), it is mapped to a "window" of +/- 50 years around the
	 current year, as described by the "Moving_Window()" function (see
	 further below).

	 If the month, day and year are all given numerically but WITHOUT any
	 delimiting characters between them, this string of digits will be
	 mapped to the month, day and year as follows:

			 Length:	Mapping:
			   3		  mdy
			   4		  mdyy
			   5		  mddyy
			   6		  mmddyy
			   7		  mddyyyy
			   8		  mmddyyyy

	 (Where "m" stands for "month", "d" stands for "day" and "y" stands
	 for "year".)

	 All other strings consisting purely of digits (without any
	 intervening delimiters) are rejected, i.e., not recognized.

	 If only the day and the year form a contiguous string of digits, they
	 will be mapped as follows:

			 Length:	Mapping:
			   2		  dy
			   3		  dyy
			   4		  ddyy
			   5		  dyyyy
			   6		  ddyyyy

	 (Where "d" stands for "day" and "y" stands for "year".)

	 Examples:

	   "1 3 64"
	   "01/03/64"
	   "Jan 3 '64"
	   "Jan 3 1964"
	   "===> January 3rd 1964 (birthday)"
	   "Jan31964"
	   "Jan364"
	   "ja364"
	   "1364"

	 Experiment! (See the corresponding example applications in the
	 "examples" subdirectory of this distribution in order to do so.)

       · "$year = Fixed_Window($yy);"

	 This function applies a "fixed window" strategy to two-digit year
	 numbers in order to convert them into four-digit year numbers.

	 All other year numbers are passed through unchanged, except for
	 negative year numbers, which cause the function to return zero ("0")
	 instead.

	 Two-digit year numbers ""yy"" below 70 are converted to ""20yy"",
	 whereas year numbers equal to or greater than 70 (but less than 100)
	 are converted to ""19yy"".

	 In the original distribution of this package, the base century is set
	 to "1900" and the base year to "70" (which is a standard on UNIX
	 systems), but these constants (also called the "epoch") can actually
	 be chosen at will (in the files "DateCalc.c" and "DateCalc.h") at
	 compile time of this module.

       · "$year = Moving_Window($yy);"

	 This function applies a "moving window" strategy to two-digit year
	 numbers in order to convert them into four-digit year numbers,
	 provided the necessary system calls (system clock) are available.
	 Otherwise the function falls back to the "fixed window" strategy
	 described in the function above.

	 All other year numbers are passed through unchanged, except for
	 negative year numbers, which cause the function to return zero ("0")
	 instead.

	 Two-digit year numbers are mapped according to a "window" of 50 years
	 in both directions (past and future) around the current year.

	 That is, two-digit year numbers are first mapped to the same century
	 as the current year. If the resulting year is smaller than the
	 current year minus 50, then one more century is added to the result.
	 If the resulting year is equal to or greater than the current year
	 plus 50, then a century is subtracted from the result.

       · "$date = Compress($year,$month,$day);"

	 WARNING: This function is legacy code, its use is deprecated!

	 This function encodes a date in 16 bits, which is the value being
	 returned.

	 The encoding scheme is as follows:

		     Bit number:    FEDCBA9 8765 43210
		     Contents:	    yyyyyyy mmmm ddddd

	 (Where the "yyyyyyy" contain the number of the year, "mmmm" the
	 number of the month and "ddddd" the number of the day.)

	 The function returns "0" if the given input values do not represent a
	 valid date. Therefore, the return value of this function can also be
	 used as the conditional expression in an "if" statement, in order to
	 check whether the given input values constitute a valid date).

	 Through this special encoding scheme, it is possible to COMPARE
	 compressed dates for equality and order (less than/greater than)
	 WITHOUT any previous DECODING!

	 Note however that contiguous dates do NOT necessarily have contiguous
	 compressed representations!

	 I.e., incrementing the compressed representation of a date MAY OR MAY
	 NOT yield a valid new date!

	 Note also that this function can only handle dates within one
	 century.

	 This century can be chosen at will (at compile time of this module)
	 by defining a base century and year (also called the "epoch"). In the
	 original distribution of this package, the base century is set to
	 "1900" and the base year to "70" (which is standard on UNIX systems).

	 This allows this function to handle dates from "1970" up to "2069".

	 If the given year is equal to, say, "95", this package will
	 automatically assume that you really meant "1995" instead. However,
	 if you specify a year number which is SMALLER than 70, like "64", for
	 instance, this package will assume that you really meant "2064".

	 You are not confined to two-digit (abbreviated) year numbers, though.

	 The function also accepts "full-length" year numbers, provided that
	 they lie in the supported range (i.e., from "1970" to "2069", in the
	 original configuration of this package).

	 Note that this function is maintained mainly for backward
	 compatibility, and that its use is not recommended.

       · "if (($century,$year,$month,$day) = Uncompress($date))"

	 WARNING: This function is legacy code, its use is deprecated!

	 This function decodes dates that were encoded previously using the
	 function ""Compress()"".

	 It returns the century, year, month and day of the date encoded in
	 "$date" if "$date" represents a valid date, or an empty list
	 otherwise.

	 The year returned in "$year" is actually a two-digit year number
	 (i.e., the year number taken modulo 100), and only the expression
	 ""$century + $year"" yields the "full-length" year number (for
	 example, "1900 + 95 = 1995").

	 Note that this function is maintained mainly for backward
	 compatibility, and that its use is not recommended.

       · "if (check_compressed($date))"

	 WARNING: This function is legacy code, its use is deprecated!

	 This function returns "true" ("1") if the given input value
	 constitutes a valid compressed date, and "false" ("0") otherwise.

	 Note that this function is maintained mainly for backward
	 compatibility, and that its use is not recommended.

       · "$string = Compressed_to_Text($date[,$lang]);"

	 WARNING: This function is legacy code, its use is deprecated!

	 This function returns a string of fixed length (always 9 characters
	 long) containing a textual representation of the compressed date
	 encoded in "$date".

	 This string has the form "dd-Mmm-yy", where "dd" is the two-digit
	 number of the day, "Mmm" are the first three letters of the name of
	 the month in the given or currently selected language (see further
	 below for details about the multi-language support of this package),
	 and "yy" is the two-digit year number (i.e., the year number taken
	 modulo 100).

	 If "$date" does not represent a valid date, the string "??-???-??" is
	 returned instead.

	 Note that this function is maintained mainly for backward
	 compatibility, and that its use is not recommended.

       · "$string = Date_to_Text($year,$month,$day[,$lang]);"

	 This function returns a string containing a textual representation of
	 the given date of the form "www dd-Mmm-yyyy", where "www" are the
	 first three letters of the name of the day of week in the given or
	 currently selected language, or a special abbreviation, if special
	 abbreviations have been defined for the given or currently selected
	 language (see further below for details about the multi-language
	 support of this package), "dd" is the day (one or two digits), "Mmm"
	 are the first three letters of the name of the month in the given or
	 currently selected language, and "yyyy" is the number of the year in
	 full length.

	 If the given input values do not constitute a valid date, a fatal
	 "not a valid date" error occurs.

	 (See the section "RECIPES" near the end of this document for a code
	 snippet for how to print dates in any format you like.)

       · "$string = Date_to_Text_Long($year,$month,$day[,$lang]);"

	 This function returns a string containing a textual representation of
	 the given date roughly of the form "Wwwwww, dd Mmmmmm yyyy", where
	 "Wwwwww" is the name of the day of week in the given or currently
	 selected language (see further below for details about the multi-
	 language support of this package), "dd" is the day (one or two
	 digits), "Mmmmmm" is the name of the month in the given or currently
	 selected language, and "yyyy" is the number of the year in full
	 length.

	 The exact format of the output string depends on the given or
	 currently selected language. In the original distribution of this
	 package, these formats are defined as follows:

	   1  English	 :  "Wwwwww, Mmmmmm ddth yyyy"
	   2  French	 :  "Wwwwww dd mmmmmm yyyy"
	   3  German	 :  "Wwwwww, den dd. Mmmmmm yyyy"
	   4  Spanish	 :  "Wwwwww, dd de mmmmmm de yyyy"
	   5  Portuguese :  "Wwwwww, dia dd de mmmmmm de yyyy"
	   6  Dutch	 :  "Wwwwww, dd mmmmmm yyyy"
	   7  Italian	 :  "Wwwwww, dd Mmmmmm yyyy"
	   8  Norwegian	 :  "wwwwww, dd. mmmmmm yyyy"
	   9  Swedish	 :  "wwwwww, dd mmmmmm yyyy"
	  10  Danish	 :  "wwwwww, dd. mmmmmm yyyy"
	  11  Finnish	 :  "wwwwww, dd. mmmmmmta yyyy"
	  12  Hungarian	 :  "dd. Mmmmmm yyyy., wwwwww"
	  13  Polish	 :  "Wwwwww, dd Mmmmmm yyyy"
	  14  Romanian	 :  "Wwwwww dd Mmmmmm yyyy"

	 (You can change these formats in the file "DateCalc.c" before
	 building this module in order to suit your personal preferences.)

	 If the given input values do not constitute a valid date, a fatal
	 "not a valid date" error occurs.

	 In order to capitalize the day of week at the beginning of the string
	 in Norwegian, use
	 ""ucfirst(Date_to_Text_Long($year,$month,$day,8));"".

	 (See the section "RECIPES" near the end of this document for an
	 example on how to print dates in any format you like.)

       · "$string = English_Ordinal($number);"

	 This function returns a string containing the (english) abbreviation
	 of the ordinal number for the given (cardinal) number "$number".

	 I.e.,

	     0	=>  '0th'    10	 =>  '10th'    20  =>  '20th'
	     1	=>  '1st'    11	 =>  '11th'    21  =>  '21st'
	     2	=>  '2nd'    12	 =>  '12th'    22  =>  '22nd'
	     3	=>  '3rd'    13	 =>  '13th'    23  =>  '23rd'
	     4	=>  '4th'    14	 =>  '14th'    24  =>  '24th'
	     5	=>  '5th'    15	 =>  '15th'    25  =>  '25th'
	     6	=>  '6th'    16	 =>  '16th'    26  =>  '26th'
	     7	=>  '7th'    17	 =>  '17th'    27  =>  '27th'
	     8	=>  '8th'    18	 =>  '18th'    28  =>  '28th'
	     9	=>  '9th'    19	 =>  '19th'    29  =>  '29th'

	 etc.

       · "$string = Calendar($year,$month[,$orthodox[,$lang]]);"

	 This function returns a calendar of the given month in the given year
	 (somewhat similar to the UNIX ""cal"" command), in the given or
	 currently selected language (see further below for details about the
	 multi-language support of this package).

	 Example:

	   print Calendar(1998,5);

	 This will print:

		    May 1998
	   Mon Tue Wed Thu Fri Sat Sun
			     1	 2   3
	     4	 5   6	 7   8	 9  10
	    11	12  13	14  15	16  17
	    18	19  20	21  22	23  24
	    25	26  27	28  29	30  31

	 If the optional boolean parameter "$orthodox" is given and true, the
	 calendar starts on Sunday instead of Monday.

       · "$string = Month_to_Text($month[,$lang]);"

	 This function returns the name of the given month in the given or
	 currently selected language (see further below for details about the
	 multi-language support of this package).

	 If the given month lies outside of the valid range from "1" to "12",
	 a fatal "month out of range" error will occur.

       · "$string = Day_of_Week_to_Text($dow[,$lang]);"

	 This function returns the name of the given day of week in the given
	 or currently selected language (see further below for details about
	 the multi-language support of this package).

	 If the given day of week lies outside of the valid range from "1" to
	 "7", a fatal "day of week out of range" error will occur.

       · "$string = Day_of_Week_Abbreviation($dow[,$lang]);"

	 This function returns the special abbreviation of the name of the
	 given day of week, IF such special abbreviations have been defined
	 for the given or currently selected language (see further below for
	 details about the multi-language support of this package).

	 (In the original distribution of this package, this was only true for
	 Portuguese. Starting with version 5.1, abbreviations for Polish have
	 also been introduced. Starting with version 5.7, the abbreviations
	 for Portuguese have been disabled. So Polish is currently the only
	 language to define such special abbreviations.)

	 If not, the first three letters of the name of the day of week in the
	 given or currently selected language are returned instead.

	 If the given day of week lies outside of the valid range from "1" to
	 "7", a fatal "day of week out of range" error will occur.

	 Currently, this table of special abbreviations is only used by the
	 functions ""Date_to_Text()"" and ""Calendar()"", internally.

       · "$string = Language_to_Text($lang);"

	 This function returns the name of any language supported by this
	 package when the internal number representing that language is given
	 as input.

	 The original distribution supports the following fourteen languages:

		     1	 ==>   English			   (default)
		     2	 ==>   Francais	   (French)
		     3	 ==>   Deutsch	   (German)
		     4	 ==>   Espan~ol	    (Spanish)
		     5	 ==>   Portugues   (Portuguese)
		     6	 ==>   Nederlands  (Dutch)
		     7	 ==>   Italiano	   (Italian)
		     8	 ==>   Norsk	   (Norwegian)
		     9	 ==>   Svenska	   (Swedish)
		    10	 ==>   Dansk	   (Danish)
		    11	 ==>   suomi	   (Finnish)
		    12	 ==>   Magyar	   (Hungarian)
		    13	 ==>   polski	   (Polish)
		    14	 ==>   Romaneste   (Romanian)

	 See the section "How to install additional languages" in the file
	 "INSTALL.txt" in this distribution for how to add more languages to
	 this package.

	 See the description of the function ""Languages()"" further below to
	 determine how many languages are actually available in a given
	 installation of this package.

       · "$lang = Language();"

       · "Language($lang); # DEPRECATED"

       · "$oldlang = Language($newlang); # DEPRECATED"

	 This function can be used to determine which language is currently
	 selected, and to change the selected language (this latter use is
	 deprecated, because this global setting may cause conflicts between
	 threads or modules running concurrently).

	 Thereby, each language has a unique internal number.

	 The original distribution contains the following fourteen languages:

		     1	 ==>   English			   (default)
		     2	 ==>   Francais	   (French)
		     3	 ==>   Deutsch	   (German)
		     4	 ==>   Espan~ol	    (Spanish)
		     5	 ==>   Portugues   (Portuguese)
		     6	 ==>   Nederlands  (Dutch)
		     7	 ==>   Italiano	   (Italian)
		     8	 ==>   Norsk	   (Norwegian)
		     9	 ==>   Svenska	   (Swedish)
		    10	 ==>   Dansk	   (Danish)
		    11	 ==>   suomi	   (Finnish)
		    12	 ==>   Magyar	   (Hungarian)
		    13	 ==>   polski	   (Polish)
		    14	 ==>   Romaneste   (Romanian)

	 See the section "How to install additional languages" in the file
	 "INSTALL.txt" in this distribution for how to add more languages to
	 this package.

	 See the description of the function ""Languages()"" further below to
	 determine how many languages are actually available in a given
	 installation of this package.

	 BEWARE that in order for your programs to be portable, you should
	 NEVER actually use the internal number of a language in this package
	 EXPLICITLY, because the same number could mean different languages on
	 different systems, depending on what languages have been added to any
	 given installation of this package.

	 Therefore, you should always use a statement such as

	   Language(Decode_Language("Name_of_Language")); # DEPRECATED

	 or

	   DateCalc_Function(@parameters,Decode_Language("Name_of_Language")); # RECOMMENDED

	 to select the desired language, and

	   $language = Language_to_Text(Language());

	 or

	   $old_language = Language_to_Text(Language("Name_of_new_Language")); # DEPRECATED

	 to determine the (previously) selected language.

	 If the so chosen language is not available in the current
	 installation, this will result in an appropriate error message,
	 instead of silently using the wrong (a random) language (which just
	 happens to have the same internal number in the other installation).

	 BEWARE that when using the function ""Language()"", the selected
	 language is a global setting, shared by all threads or modules you
	 might be running concurrently, thus possibly causing conflicts
	 between them.

	 In order to avoid these conflicts, you should NEVER use the function
	 ""Language()"", but should ALWAYS pass a language number (as returned
	 by the function ""Decode_Language()"") to the functions which are
	 language-dependent, which are:

	 "Decode_Month()", "Decode_Day_of_Week()", "Compressed_to_Text()",
	 "Date_to_Text()", "Date_to_Text_Long()", "Calendar()",
	 "Month_to_Text()", "Day_of_Week_to_Text()",
	 "Day_of_Week_Abbreviation()", "Decode_Date_EU()", "Decode_Date_US()",
	 "Decode_Date_EU2()", "Decode_Date_US2()", "Parse_Date()".

	 Note that when you pass an invalid number, such as e.g. zero, or no
	 language parameter at all, these functions will revert to their
	 behaviour in the versions of this module prior to 6.0, which means
	 that the global setting (as set by ""Language()"") becomes active
	 again (only in case of an invalid or missing language parameter!).

	 In the C library "DateCalc.c", where omitting a parameter is not an
	 option, passing a zero for the language is therefore the recommended
	 way to guarantee backward compatibility.

       · "$max_lang = Languages();"

	 This function returns the (maximum) number of languages which are
	 currently available in your installation of this package.

	 (This may vary from installation to installation.)

	 See the section "How to install additional languages" in the file
	 "INSTALL.txt" in this distribution for how to add more languages to
	 this package.

	 In the original distribution of this package there are fourteen
	 built-in languages, therefore the value returned by this function
	 will be "14" if no other languages have been added to your particular
	 installation.

       · "if (($year,$month,$day) = Decode_Date_EU2($string[,$lang))"

	 This function is the Perl equivalent of the function
	 ""Decode_Date_EU()"" (implemented in C), included here merely as an
	 example to demonstrate how easy it is to write your own routine in
	 Perl (using regular expressions) adapted to your own special needs,
	 should the necessity arise, and intended primarily as a basis for
	 your own development.

	 In one particular case this Perl version is actually slightly more
	 permissive than its C equivalent, as far as the class of permitted
	 intervening (i.e., delimiting) characters is concerned.

	 (Can you tell the subtle, almost insignificant difference by looking
	 at the code? Or by experimenting? Hint: Try the string "a3b1c64d"
	 with both functions.)

       · "if (($year,$month,$day) = Decode_Date_US2($string[,$lang))"

	 This function is the Perl equivalent of the function
	 ""Decode_Date_US()"" (implemented in C), included here merely as an
	 example to demonstrate how easy it is to write your own routine in
	 Perl (using regular expressions) adapted to your own special needs,
	 should the necessity arise, and intended primarily as a basis for
	 your own development.

	 In one particular case this Perl version is actually slightly more
	 permissive than its C equivalent.

	 (Hint: This is the same difference as with the ""Decode_Date_EU()""
	 and ""Decode_Date_EU2()"" pair of functions.)

	 In a different case, the C version is a little bit more permissive
	 than its Perl equivalent.

	 (Can you tell the difference by looking at the code? Or by
	 experimenting?	 Hint: Try the string "(1/364)" with both functions.)

       · "if (($year,$month,$day) = Parse_Date($string[,$lang))"

	 This function is useful for parsing dates as returned by the UNIX
	 ""date"" command or as found in the headers of e-mail (in order to
	 determine the date at which some e-mail has been sent or received,
	 for instance).

	 Example #1:

	   ($year,$month,$day) = Parse_Date(`/bin/date`);

	 Example #2:

	   while (<MAIL>)
	   {
	       if (/^From \S/)
	       {
		   ($year,$month,$day) = Parse_Date($_);
		   ...
	       }
	       ...
	   }

	 The function returns an empty list if it can't extract a valid date
	 from the input string.

       · "$lower = ISO_LC($string);"

	 Returns a copy of the given string where all letters of the
	 ISO-Latin-1 character set have been replaced by their lower case
	 equivalents.

	 Similar to Perl's built-in function ""lc()"" (see "lc" in
	 perlfunc(1)) but for the whole ISO-Latin-1 character set, not just
	 plain ASCII.

       · "$upper = ISO_UC($string);"

	 Returns a copy of the given string where all letters of the
	 ISO-Latin-1 character set have been replaced by their upper case
	 equivalents.

	 Similar to Perl's built-in function ""uc()"" (see "uc" in
	 perlfunc(1)) but for the whole ISO-Latin-1 character set, not just
	 plain ASCII.

       · "$string = Date::Calc::Version();"

	 This function returns a string with the (numeric) version number of
	 the C library ("DateCalc.c") at the core of this package (which is
	 also (automatically) the version number of the "Calc.xs" file).

	 Note that under all normal circumstances, this version number should
	 be identical with the one found in the Perl variable
	 "$Date::Calc::VERSION" (the version number of the "Calc.pm" file).

	 Since this function is not exported, you always have to qualify it
	 explicitly, i.e., ""Date::Calc::Version()"".

	 This is to avoid possible name space conflicts with version functions
	 from other modules.

RECIPES
       1)  How do I compare two dates?

	   Solution #1:

	     use Date::Calc qw( Date_to_Days );

	     if (Date_to_Days($year1,$month1,$day1)  <
		 Date_to_Days($year2,$month2,$day2))

	     if (Date_to_Days($year1,$month1,$day1)  <=
		 Date_to_Days($year2,$month2,$day2))

	     if (Date_to_Days($year1,$month1,$day1)  >
		 Date_to_Days($year2,$month2,$day2))

	     if (Date_to_Days($year1,$month1,$day1)  >=
		 Date_to_Days($year2,$month2,$day2))

	     if (Date_to_Days($year1,$month1,$day1)  ==
		 Date_to_Days($year2,$month2,$day2))

	     if (Date_to_Days($year1,$month1,$day1)  !=
		 Date_to_Days($year2,$month2,$day2))

	     $cmp = (Date_to_Days($year1,$month1,$day1)	 <=>
		     Date_to_Days($year2,$month2,$day2));

	   Solution #2:

	     use Date::Calc qw( Delta_Days );

	     if (Delta_Days($year1,$month1,$day1,
			    $year2,$month2,$day2) > 0)

	     if (Delta_Days($year1,$month1,$day1,
			    $year2,$month2,$day2) >= 0)

	     if (Delta_Days($year1,$month1,$day1,
			    $year2,$month2,$day2) < 0)

	     if (Delta_Days($year1,$month1,$day1,
			    $year2,$month2,$day2) <= 0)

	     if (Delta_Days($year1,$month1,$day1,
			    $year2,$month2,$day2) == 0)

	     if (Delta_Days($year1,$month1,$day1,
			    $year2,$month2,$day2) != 0)

       2)  How do I check whether a given date lies within a certain range of
	   dates?

	     use Date::Calc qw( Date_to_Days );

	     $lower = Date_to_Days($year1,$month1,$day1);
	     $upper = Date_to_Days($year2,$month2,$day2);

	     $date = Date_to_Days($year,$month,$day);

	     if (($date >= $lower) && ($date <= $upper))
	     {
		 # ok
	     }
	     else
	     {
		 # not ok
	     }

       3)  How do I compare two dates with times? How do I check whether two
	   dates and times lie more or less than a given time interval apart?

	   Solution #1:

	     use Date::Calc qw( Add_Delta_DHMS Date_to_Days );

	     @date1 = (2002,8,31,23,59,1);
	     @date2 = (2002,9,1,11,30,59); # ==> less than 12 hours

	     #@date1 = (2002,8,31,22,59,1);
	     #@date2 = (2002,9,1,11,30,59); # ==> more than 12 hours

	     # Omit the next line if you just want to compare the two dates
	     # (and change @date3 and @d3 to @date1 and @d1, respectively):

	     @date3 = Add_Delta_DHMS(@date1, 0,12,0,0); # ==> is the difference within 12 hours?

	     @d2 = ( Date_to_Days(@date2[0..2]), ($date2[3]*60+$date2[4])*60+$date2[5] );
	     @d3 = ( Date_to_Days(@date3[0..2]), ($date3[3]*60+$date3[4])*60+$date3[5] );

	     @diff = ( $d2[0]-$d3[0], $d2[1]-$d3[1] );

	     if ($diff[0] > 0 and $diff[1] < 0) { $diff[0]--; $diff[1] += 86400; }
	     if ($diff[0] < 0 and $diff[1] > 0) { $diff[0]++; $diff[1] -= 86400; }

	     if (($diff[0] || $diff[1]) >= 0) { print "More than 12 hours.\n"; }
	     else			      { print "Less than 12 hours.\n"; }

	   Solution #2:

	   This solution is only feasible if your dates are guaranteed to lie
	   within the range given by your system's epoch and overflow date and
	   time!

		Unix:	 1-Jan-1970 00:00:00  to  19-Jan-2038 03:14:07
		MacOS:	 1-Jan-1904 00:00:00  to   6-Feb-2040 06:28:15

	     use Date::Calc qw( Date_to_Time );

	     @date1 = (2002,8,31,23,59,1);
	     @date2 = (2002,9,1,11,30,59); # ==> less than 12 hours

	     #@date1 = (2002,8,31,22,59,1);
	     #@date2 = (2002,9,1,11,30,59); # ==> more than 12 hours

	     $d1 = Date_to_Time(@date1);
	     $d2 = Date_to_Time(@date2);

	     if ($d1 <= $d2) { print "The two dates are in chronological order.\n"; }
	     else	     { print "The two dates are in reversed order.\n"; }

	     if ($d1 + 12*60*60 <= $d2) { print "More than 12 hours.\n"; }
	     else			{ print "Less than 12 hours.\n"; }

       4)  How do I verify whether someone has a certain age?

	     use Date::Calc qw( Decode_Date_EU Today leap_year Delta_Days );

	     $date = <STDIN>; # get birthday

	     ($year1,$month1,$day1) = Decode_Date_EU($date);

	     ($year2,$month2,$day2) = Today();

	     if (($day1 == 29) && ($month1 == 2) && !leap_year($year2))
		 { $day1--; }

	     if ( (($year2 - $year1) >	18) ||
		( (($year2 - $year1) == 18) &&
		(Delta_Days($year2,$month1,$day1, $year2,$month2,$day2) >= 0) ) )
	     {
		 print "Ok - you are over 18.\n";
	     }
	     else
	     {
		 print "Sorry - you aren't 18 yet!\n";
	     }

	     Or, alternatively (substituting the last "if" statement above):

	     if (($year1+18 <=> $year2 || $month1 <=> $month2 || $day1 <=> $day2) <= 0)
		 { print "Ok - you are over 18.\n"; }
	     else
		 { print "Sorry - you aren't 18 yet!\n"; }

       5)  How do I calculate the number of the week of month the current date
	   lies in?

	   For example:

		       April 1998
	       Mon Tue Wed Thu Fri Sat Sun
			 1   2	 3   4	 5  =  week #1
		 6   7	 8   9	10  11	12  =  week #2
		13  14	15  16	17  18	19  =  week #3
		20  21	22  23	24  25	26  =  week #4
		27  28	29  30		    =  week #5

	   Solution:

	     use Date::Calc qw( Today Day_of_Week );

	     ($year,$month,$day) = Today();

	     $week = int(($day + Day_of_Week($year,$month,1) - 2) / 7) + 1;

       6)  How do I calculate whether a given date is the 1st, 2nd, 3rd, 4th
	   or 5th of that day of week in the given month?

	   For example:

		      October 2000
	       Mon Tue Wed Thu Fri Sat Sun
					 1
		 2   3	 4   5	 6   7	 8
		 9  10	11  12	13  14	15
		16  17	18  19	20  21	22
		23  24	25  26	27  28	29
		30  31

	   Is Sunday, the 15th of October 2000, the 1st, 2nd, 3rd, 4th or 5th
	   Sunday of that month?

	   Solution:

	     use Date::Calc qw( Day_of_Week Delta_Days
				Nth_Weekday_of_Month_Year
				Date_to_Text_Long English_Ordinal
				Day_of_Week_to_Text Month_to_Text );

	     ($year,$month,$day) = (2000,10,15);

	     $dow = Day_of_Week($year,$month,$day);

	     $n = int( Delta_Days(
		       Nth_Weekday_of_Month_Year($year,$month,$dow,1),
		       $year,$month,$day)
		       / 7) + 1;

	     printf("%s is the %s %s in %s %d.\n",
		 Date_to_Text_Long($year,$month,$day),
		 English_Ordinal($n),
		 Day_of_Week_to_Text($dow),
		 Month_to_Text($month),
		 $year);

	   This prints:

	     Sunday, October 15th 2000 is the 3rd Sunday in October 2000.

       7)  How do I calculate the date of the Wednesday of the same week as
	   the current date?

	   Solution #1:

	     use Date::Calc qw( Today Day_of_Week Add_Delta_Days );

	     $searching_dow = 3; # 3 = Wednesday

	     @today = Today();

	     $current_dow = Day_of_Week(@today);

	     @date = Add_Delta_Days(@today, $searching_dow - $current_dow);

	   Solution #2:

	     use Date::Calc qw( Today Add_Delta_Days
				Monday_of_Week Week_of_Year );

	     $searching_dow = 3; # 3 = Wednesday

	     @today = Today();

	     @date = Add_Delta_Days( Monday_of_Week( Week_of_Year(@today) ),
				     $searching_dow - 1 );

	   Solution #3:

	     use Date::Calc qw( Standard_to_Business Today
				Business_to_Standard );

	     @business = Standard_to_Business(Today());

	     $business[2] = 3; # 3 = Wednesday

	     @date = Business_to_Standard(@business);

       8)  How can I add a week offset to a business date (including across
	   year boundaries)?

	     use Date::Calc qw( Business_to_Standard Add_Delta_Days
				Standard_to_Business );

	     @temp = Business_to_Standard($year,$week,$dow);

	     @temp = Add_Delta_Days(@temp, $week_offset * 7);

	     ($year,$week,$dow) = Standard_to_Business(@temp);

       9)  How do I calculate the last and the next Saturday for any given
	   date?

	     use Date::Calc qw( Today Day_of_Week Add_Delta_Days
				Day_of_Week_to_Text Date_to_Text );

	     $searching_dow = 6; # 6 = Saturday

	     @today = Today();

	     $current_dow = Day_of_Week(@today);

	     if ($searching_dow == $current_dow)
	     {
		 @prev = Add_Delta_Days(@today,-7);
		 @next = Add_Delta_Days(@today,+7);
	     }
	     else
	     {
		 if ($searching_dow > $current_dow)
		 {
		     @next = Add_Delta_Days(@today,
			       $searching_dow - $current_dow);
		     @prev = Add_Delta_Days(@next,-7);
		 }
		 else
		 {
		     @prev = Add_Delta_Days(@today,
			       $searching_dow - $current_dow);
		     @next = Add_Delta_Days(@prev,+7);
		 }
	     }

	     $dow = Day_of_Week_to_Text($searching_dow);

	     print "Today is:	   ", ' ' x length($dow),
					  Date_to_Text(@today), "\n";
	     print "Last $dow was:     ", Date_to_Text(@prev),	"\n";
	     print "Next $dow will be: ", Date_to_Text(@next),	"\n";

	   This will print something like:

	     Today is:		    Sun 12-Apr-1998
	     Last Saturday was:	    Sat 11-Apr-1998
	     Next Saturday will be: Sat 18-Apr-1998

       10) How can I calculate the last business day (payday!) of a month?

	   Solution #1 (holidays NOT taken into account):

	     use Date::Calc qw( Days_in_Month Day_of_Week Add_Delta_Days );

	     $day = Days_in_Month($year,$month);
	     $dow = Day_of_Week($year,$month,$day);
	     if ($dow > 5)
	     {
		 ($year,$month,$day) =
		     Add_Delta_Days($year,$month,$day, 5-$dow);
	     }

	   Solution #2 (holidays taken into account):

	   This solution expects a multi-dimensional array "@holiday", which
	   contains all holidays, as follows: ""$holiday[$year][$month][$day]
	   = 1;"".

	   (See the description of the function ""Easter_Sunday()"" further
	   above for how to calculate the moving (variable) christian feast
	   days!)

	   Days which are not holidays remain undefined or should have a value
	   of zero in this array.

	     use Date::Calc qw( Days_in_Month Add_Delta_Days Day_of_Week );

	     $day = Days_in_Month($year,$month);
	     while (1)
	     {
		 while ($holiday[$year][$month][$day])
		 {
		     ($year,$month,$day) =
			 Add_Delta_Days($year,$month,$day, -1);
		 }
		 $dow = Day_of_Week($year,$month,$day);
		 if ($dow > 5)
		 {
		     ($year,$month,$day) =
			 Add_Delta_Days($year,$month,$day, 5-$dow);
		 }
		 else { last; }
	     }

	   Solution #3 (holidays taken into account, more comfortable, but
	   requires Date::Calendar(3) and Date::Calc::Object(3)):

	     use Date::Calc::Object qw( Today Add_Delta_YM Date_to_Text_Long );
	     use Date::Calendar::Profiles qw($Profiles);
	     use Date::Calendar;

	     $calendar = Date::Calendar->new( $Profiles->{'DE-BW'} );

	     @today = Today();
	     @nextmonth = Add_Delta_YM(@today[0,1],1, 0,1);

	     $workaround = $calendar->add_delta_workdays(@nextmonth,+1);
	     $payday	 = $calendar->add_delta_workdays($workaround,-2);

	     print "Pay day = ", Date_to_Text_Long($payday->date()), "\n";

	   The "workaround" is necessary due to a bug in the method
	   "add_delta_workdays()" when adding a negative number of workdays.

       11) How do I convert a MS Visual Basic "DATETIME" value into its date
	   and time constituents?

	     use Date::Calc qw( Add_Delta_DHMS Date_to_Text );

	     $datetime = "35883.121653";

	     ($Dd,$Dh,$Dm,$Ds) = ($datetime =~ /^(\d+)\.(\d\d)(\d\d)(\d\d)$/);

	     ($year,$month,$day, $hour,$min,$sec) =
		 Add_Delta_DHMS(1900,1,1, 0,0,0, $Dd,$Dh,$Dm,$Ds);

	     printf("The given date is %s %02d:%02d:%02d\n",
		 Date_to_Text($year,$month,$day), $hour, $min, $sec);

	   This prints:

	     The given date is Tue 31-Mar-1998 12:16:53

	   Since I do not have or use Visual Basic, I can't guarantee that the
	   number format assumed here is really the one used by Visual Basic -
	   but you get the general idea. ":-)"

	   Moreover, consider the following:

	   Morten Sickel <Morten.Sickel@nrpa.no> wrote:

	   I discovered a bug in Excel (2000): Excel thinks that 1900 was a
	   leap year. Users should use 31-Dec-1899 as the date to add an Excel
	   date value to in order to get the correct date.

	   I found out on the web that this bug originated in Lotus 123, which
	   made 29-Feb-1900 an "industrial standard". MS chose to keep the bug
	   in order to be compatible with Lotus 123. But they have not
	   mentioned anything about it in the help files.

       12) How can I send a reminder to members of a group on the day before a
	   meeting which occurs every first Friday of a month?

	     use Date::Calc qw( Today Date_to_Days Add_Delta_YMD
				Nth_Weekday_of_Month_Year );

	     ($year,$month,$day) = Today();

	     $tomorrow = Date_to_Days($year,$month,$day) + 1;

	     $dow = 5; # 5 = Friday
	     $n	  = 1; # 1 = First of that day of week

	     $meeting_this_month = Date_to_Days(
		 Nth_Weekday_of_Month_Year($year,$month,$dow,$n) );

	     ($year,$month,$day) = Add_Delta_YMD($year,$month,$day, 0,1,0);

	     $meeting_next_month = Date_to_Days(
		 Nth_Weekday_of_Month_Year($year,$month,$dow,$n) );

	     if (($tomorrow == $meeting_this_month) ||
		 ($tomorrow == $meeting_next_month))
	     {
		 # Send reminder e-mail!
	     }

       13) How can I print a date in a different format than provided by the
	   functions ""Date_to_Text()"", ""Date_to_Text_Long()"" or
	   ""Compressed_to_Text()""?

	     use Date::Calc qw( Today Day_of_Week_to_Text
				Day_of_Week Month_to_Text
				English_Ordinal );

	     ($year,$month,$day) = Today();

	   For example with leading zeros for the day: "Fri 03-Jan-1964"

	     printf("%.3s %02d-%.3s-%d\n",
		 Day_of_Week_to_Text(Day_of_Week($year,$month,$day)),
		 $day,
		 Month_to_Text($month),
		 $year);

	   For example in U.S. american format: "April 12th, 1998"

	     $string = sprintf("%s %s, %d",
			   Month_to_Text($month),
			   English_Ordinal($day),
			   $year);

	   For example in one of the possible formats as specified by
	   ISO 8601:

	     @date = ($year,$month,$day,$hour,$min,$sec);
	     $date = sprintf("%d-%02d-%02d %02d:%02d:%02d", @date);

	   (See also "printf" in perlfunc(1) and/or "sprintf" in perlfunc(1)!)

       14) How can I iterate through a range of dates?

	     use Date::Calc qw( Delta_Days Add_Delta_Days );

	     @start = (1999,5,27);
	     @stop  = (1999,6,1);

	     $j = Delta_Days(@start,@stop);

	     for ( $i = 0; $i <= $j; $i++ )
	     {
		 @date = Add_Delta_Days(@start,$i);
		 printf("%4d/%02d/%02d\n", @date);
	     }

	   Note that the loop can be improved; see also the recipe below.

       15) How can I create a (Perl) list of dates in a certain range?

	     use Date::Calc qw( Delta_Days Add_Delta_Days Date_to_Text );

	     sub date_range
	     {
		 my(@date) = (@_)[0,1,2];
		 my(@list);
		 my($i);

		 $i = Delta_Days(@_);
		 while ($i-- >= 0)
		 {
		     push( @list, [ @date ] );
		     @date = Add_Delta_Days(@date, 1) if ($i >= 0);
		 }
		 return(@list);
	     }

	     @range = &date_range(1999,11,3, 1999,12,24); # in chronological order

	     foreach $date (@range)
	     {
		 print Date_to_Text(@{$date}), "\n";
	     }

	   Note that you probably shouldn't use this one, because it is much
	   more efficient to iterate through all the dates (as shown in the
	   recipe immediately above) than to construct such an array and then
	   to loop through it. Also, it is much more space-efficient not to
	   create this array.

       16) How can I calculate the difference in days between dates, but
	   without counting Saturdays and Sundays?

	     sub Delta_Business_Days
	     {
		 my(@date1) = (@_)[0,1,2];
		 my(@date2) = (@_)[3,4,5];
		 my($minus,$result,$dow1,$dow2,$diff,$temp);

		 $minus	 = 0;
		 $result = Delta_Days(@date1,@date2);
		 if ($result != 0)
		 {
		     if ($result < 0)
		     {
			 $minus = 1;
			 $result = -$result;
			 $dow1 = Day_of_Week(@date2);
			 $dow2 = Day_of_Week(@date1);
		     }
		     else
		     {
			 $dow1 = Day_of_Week(@date1);
			 $dow2 = Day_of_Week(@date2);
		     }
		     $diff = $dow2 - $dow1;
		     $temp = $result;
		     if ($diff != 0)
		     {
			 if ($diff < 0)
			 {
			     $diff += 7;
			 }
			 $temp -= $diff;
			 $dow1 += $diff;
			 if ($dow1 > 6)
			 {
			     $result--;
			     if ($dow1 > 7)
			     {
				 $result--;
			     }
			 }
		     }
		     if ($temp != 0)
		     {
			 $temp /= 7;
			 $result -= ($temp << 1);
		     }
		 }
		 if ($minus) { return -$result; }
		 else	     { return  $result; }
	     }

	   This solution is probably of little practical value, however,
	   because it doesn't take legal holidays into account.

	   See Date::Calendar(3) for how to do that.

       17) How can I "normalize" the output of the "Delta_YMDHMS()" (or
	   "Delta_YMD()") function so that it contains only positive values?

	   I.e., how can I show a difference in date (and time) in a more
	   human-readable form, for example in order to show how much time
	   until (or since) the expiration of something (e.g. an account, a
	   domain, a credit card, etc.) is left (has passed)?

	   Correct solution: Use the functions "N_Delta_YMDHMS()" and
	   "N_Delta_YMD()" instead!

	   The following gives a rudimentary sketch of a (much inferior)
	   solution, which is maintained here only for historical reasons of
	   this module:

	   a) Delta_YMDHMS():

	     #!perl
	     use strict;
	     use Date::Calc qw(Today_and_Now Delta_YMDHMS Add_Delta_YMDHMS Delta_DHMS Date_to_Text);

	     my $today = [Today_and_Now()];
	     my $target = [2005,1,1,0,0,0];

	     my $sign = "until";
	     my $delta = Normalize_Delta_YMDHMS($today,$target);
	     if ($delta->[0] < 0)
	     {
		 $sign = "since";
		 $delta = Normalize_Delta_YMDHMS($target,$today);
	     }
	     printf("Today is %s %02d:%02d:%02d\n", Date_to_Text(@{$today}[0..2]), @{$today}[3..5]);
	     printf
	     (
		 "%d year%s, %d month%s, %d day%s, %d hour%s, %d minute%s, %d second%s %s %s %02d:%02d:%02d\n",
		 $delta->[0], (($delta->[0]==1)?'':'s'),
		 $delta->[1], (($delta->[1]==1)?'':'s'),
		 $delta->[2], (($delta->[2]==1)?'':'s'),
		 $delta->[3], (($delta->[3]==1)?'':'s'),
		 $delta->[4], (($delta->[4]==1)?'':'s'),
		 $delta->[5], (($delta->[5]==1)?'':'s'),
		 $sign,
		 Date_to_Text(@{$target}[0..2]),
		 @{$target}[3..5]
	     );

	     sub Normalize_Delta_YMDHMS
	     {
		 my($date1,$date2) = @_;
		 my(@delta);

		 @delta = Delta_YMDHMS(@$date1,@$date2);
		 while ($delta[1] < 0 or
			$delta[2] < 0 or
			$delta[3] < 0 or
			$delta[4] < 0 or
			$delta[5] < 0)
		 {
		     if ($delta[1] < 0) { $delta[0]--; $delta[1] += 12; }
		     if ($delta[2] < 0)
		     {
			 $delta[1]--;
			 @delta[2..5] = (0,0,0,0);
			 @delta[2..5] = Delta_DHMS(Add_Delta_YMDHMS(@$date1,@delta),@$date2);
		     }
		     if ($delta[3] < 0) { $delta[2]--; $delta[3] += 24; }
		     if ($delta[4] < 0) { $delta[3]--; $delta[4] += 60; }
		     if ($delta[5] < 0) { $delta[4]--; $delta[5] += 60; }
		 }
		 return \@delta;
	     }

	   b) Delta_YMD():

	     #!perl
	     use strict;
	     use Date::Calc qw(Today Delta_YMD Add_Delta_YM Delta_Days Date_to_Text);

	     my($sign,$delta);
	     my $today = [Today()];
	     my $target = [2005,1,1];

	     if (Delta_Days(@$today,@$target) < 0)
	     {
		 $sign = "since";
		 $delta = Normalize_Delta_YMD($target,$today);
	     }
	     else
	     {
		 $sign = "until";
		 $delta = Normalize_Delta_YMD($today,$target);
	     }
	     print "Today is ", Date_to_Text(@$today), "\n";
	     printf
	     (
		 "%d year%s, %d month%s, %d day%s %s %s\n",
		 $delta->[0], (($delta->[0]==1)?'':'s'),
		 $delta->[1], (($delta->[1]==1)?'':'s'),
		 $delta->[2], (($delta->[2]==1)?'':'s'),
		 $sign,
		 Date_to_Text(@$target)
	     );

	     sub Normalize_Delta_YMD
	     {
		 my($date1,$date2) = @_;
		 my(@delta);

		 @delta = Delta_YMD(@$date1,@$date2);
		 while ($delta[1] < 0 or $delta[2] < 0)
		 {
		     if ($delta[1] < 0) { $delta[0]--; $delta[1] += 12; }
		     if ($delta[2] < 0)
		     {
			 $delta[1]--;
			 $delta[2] = Delta_Days(Add_Delta_YM(@$date1,@delta[0,1]),@$date2);
		     }
		 }
		 return \@delta;
	     }

	   Note that for normalizing just a time vector, you can use the
	   built-in function "Normalize_DHMS()". However, this will yield
	   either all positive OR all negative values, NOT all positive values
	   as above.

SEE ALSO
       Date::Calc::Util(3), Date::Calc::Object(3), Date::Calendar(3),
       Date::Calendar::Year(3), Date::Calendar::Profiles(3).

	 "The Calendar FAQ":
	 http://www.tondering.dk/claus/calendar.html
	 by Claus Tondering <claus@tondering.dk>

BEWARE
       When you are using the (deprecated) function "Language()", the language
       setting is stored in a global variable.

       This may cause conflicts between threads or modules running
       concurrently.

       Therefore, in order to avoid such conflicts, NEVER use the function
       "Language()", but ALWAYS pass a language parameter to the functions
       which are language-dependent.

VERSION
       This man page documents "Date::Calc" version 6.3.

AUTHOR
	 Steffen Beyer
	 mailto:STBEY@cpan.org
	 http://www.engelschall.com/u/sb/download/

COPYRIGHT
       Copyright (c) 1995 - 2009 by Steffen Beyer. All rights reserved.

LICENSE
       This package is free software; you can use, modify and redistribute it
       under the same terms as Perl itself, i.e., at your option, under the
       terms either of the "Artistic License" or the "GNU General Public
       License".

       The C library at the core of the module "Date::Calc::XS" can, at your
       discretion, also be used, modified and redistributed under the terms of
       the "GNU Library General Public License".

       Please refer to the files "Artistic.txt", "GNU_GPL.txt" and
       "GNU_LGPL.txt" in the "license" subdirectory of this distribution for
       any details!

DISCLAIMER
       This package 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.

       See the "GNU General Public License" for more details.

perl v5.16.2			  2009-10-30			 Date::Calc(3)
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