Calculate the day of the week for a give date. 0 is Sunday. Valid from 14 September 1752 onwards.

Algorithm by Tomohiko Sakamoto from the C FAQ, section 20.31.



######################################################################
+#########
#
# day_of_week($year, $month, $day)
#
# Valid from 14 September 1752 onwards. $month and $day are 1 indexed.
#
# Returns: 0 .. 6 where 0 is Sunday.
#
# Algorithm by Tomohiko Sakamoto from the C FAQ, section 20.31.
#
sub day_of_week {

    my ($year, $month, $day) = @_;

    my @offset  = (0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4);
    $year      -= $month < 3;

    return ($year + int($year/4) - int($year/100) + int($year/400)
                  + $offset[$month-1] + $day) % 7;
}

[download]

See also Day of week for an arbitary date using core modules, Date::Calc, Date::Manip, Time::Piece.

Replies are listed 'Best First'.
Re: Day of the week
by RMGir (Prior) on Apr 11, 2003 at 11:50 UTC
    Nice one...

    Here's a test case for you; it lets you crosscheck your sub against localtime for localtime's range. 

    #!/usr/bin/perl -w

use strict;

sub day_of_week {

    my ($year, $month, $day) = @_;

    my @offset  = (0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4);
    $year      -= $month < 3;

    return ($year + int($year/4) - int($year/100) + int($year/400)
                  + $offset[$month-1] + $day) % 7;
}


my $i=0;
for(my $time=1; $time<2**31; $time+=86400) {
    my ($mday,$mon,$year,$wday)=(localtime($time))[3..6];
    $mon++;
    $year+=1900;

    my $day=day_of_week($year,$mon,$mday);

    # progress info...
    print ((scalar localtime($time))," $day, $wday\n") unless ($i++%10
+00);

    if($day != $wday) {
        print "Mismatch between sub ($day) and localtime ($wday) for "
+,
               (scalar localtime($time)),"\n";
    }
}

    [download]
    Obviously needs a bit of work to be recast as a test case, sorry.

    Your routine passes on my system :)
    --
    Mike

[reply]
[d/l]

      Thanks. I did test it myself as well. ;-)

      See below.

      Read more... (989 Bytes)
[reply]
[d/l]

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