big bug in Date::Calc?

[luca76]

Hi, I think I've found a bug in Date::Calc with add_delta_days function. I get a week number and a year in my function and I want to calculate the date starting and ending that week. To calculate it, I use supplied Monday_of_week (first day), then I add 6 days to it to get the Sunday. Trying this function with:

  print weeksToDays ( 1, 2013) ; (1st week of 2013)

it returns:

  31/12/2012 to 8/1/2012  (it should be ...to 6/1/2013)

while:

  print weeksToDays ( 2, 2013) ; (2nd week of 2013)

it returns:

  7/1/2013 to 13/1/2013

which is correct.

use Date::Calc qw ( Monday_of_Week Add_Delta_Days );

sub weekToDays {
    $week = shift;
    $year = shift;

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

    ($y, $m, $d) = Add_Delta_Days( Monday_of_Week( $week, $year ), 6);

    return "$day/$month/$year to $d/$m/$y";
}

print "First week of 2013: ".weekToDays ( 1, 2013) ."\n" ;

print "Second week of 2013: ".weekToDays ( 2, 2013) ."\n" ;

Update: Thank you to all. One word: I'm a dumb idiot :D

[choroba]

Use strict and warnings. Do not use global variables.

#!/usr/bin/perl
use warnings;
use strict;

use Date::Calc qw ( Monday_of_Week Add_Delta_Days );

sub weekToDays {
    my $week = shift;
    my $year = shift;

    my ($year2, $month, $day) = Monday_of_Week($week, $year);

    my ($y, $m, $d) = Add_Delta_Days( Monday_of_Week($week, $year), 6)
+; # Not $year2 here!

    return "$day/$month/$year2 to $d/$m/$y";
}
print "First week of 2013: ".weekToDays ( 1, 2013) ."\n" ;
print "Second week of 2013: ".weekToDays ( 2, 2013) ."\n" ;

Output:

First week of 2013: 31/12/2012 to 6/1/2013
Second week of 2013: 7/1/2013 to 13/1/2013

Update: You can even avoid calling the function again when you already know the result:

my ($y, $m, $d) = Add_Delta_Days($year2, $month, $day, 6);

[tangent]

I think the problem is that you are calling Monday_of_Week() twice:

($y, $m, $d) = Add_Delta_Days( Monday_of_Week( $week, $year ), 6);

# Change line above to:

($y, $m, $d) = Add_Delta_Days( $year, $month, $day, 6);

First week of 2013: 31/12/2012 to 6/1/2013
Second week of 2013: 7/1/2013 to 13/1/2013

[ww]

Looks to me like the bug is in your logic. You're working with the LAST day of 2012 (2012 Dec 31, Mon) but expecting that to be treated as the first day of the first week of 2013.

Yes, it's part of a week that's MOSTLY in 2013, but Date::Calc isn't on board for that very human interpretation. Like most programs, it's quite literal minded. Day 1 of 2013 is 2013 Jan 1, Tues, and 2013 Jan 8 is one week later.

[ww]

Whoops! It's another bug (or something):   "dumb idiot" look a lot like TWO (2) words where I come from.   :-)

And please, don't delete text of a question. It leaves the answers without context... which just might be helpful to some future worshipper.

[sundialsvc4]

Please don’t remove the content of a post once you have solved the problem.   Someone else will eventually have the same problem.   We are all “dumb idiots,” merely at differing times.