Hi.

In this situation, you could make the assumption that the times are from some sort of application log. In which case, the main circumstance you might need to handle would be the hour rolling over to 00:00:00.0000 (or greater). This implies, as before, that this is a rolling 24 hour period and the sub can't handle more than one day.

If you state that the first parameter must be the earliest time, the second parameter the latest, you can handle this case quite easily. e.g.

use strict;

use constant BASE => 10000;

print diff("23:59:59.9999", "00:00:00.0000"), "\n";
print diff("00:00:00.0000", "23:59:59.9999"), "\n";

sub diff {
    my ($before, $after) = @_;
    my ($h1, $m1, $s1, $ss1) = ($before =~ m/(\d+):(\d+):(\d+)\.(\d+)/
+);
    my ($h2, $m2, $s2, $ss2) = ($after  =~ m/(\d+):(\d+):(\d+)\.(\d+)/
+);
    my $diff = (($h2-$h1)*3600 + ($m2-$m1)*60 + $s2-$s1)*BASE + $ss2-$
+ss1;

    return ($diff >= 0) ? $diff : $diff + (86400 * BASE);    
}
[download]

For anything more complicated (e.g. handling daylight saving time transitions such as from GMT to BST, or vice versa), I would suggest looking into one of the Date::* or Time::* modules on CPAN.

Updated: My sub didn't handle the case where the start and end times were the same, i.e. it returned 86400*BASE instead of 0. Fixed it with >= rather than >.

Cheers,

-- Dave :-)