in reply to "undef" is not NULL and what to do about it

Good Day Ovid,

You stated:

I'm confused by your example, and the code below shows why I'm confused. In memory the value for 'salary' is undefined, but once it written to disk, whenever it is accessed after the initial 'write', the field is defined. So if this is a quirk of the DB you're using, why expect Perl to fix it? Everyone else seems to understand you're problem, but it seems related to the DB you're using and not to a specific Perl problem.

use strict; use warnings; my %Undef = ( Show => 'okay', Go => 'maybe', ); foreach my $key ( keys %Undef ) { if ( ! defined $Undef{$key} ) { print "1. $key value is undef +ined!\n"; } } $Undef{Salary} = undef; foreach my $key ( keys %Undef ) { if ( ! defined $Undef{$key} ) { print "2. $key value is undef +ined!\n"; } } open ( my $file, ">","./ondisk") || die " ! open |./ondisk| $!\n"; foreach my $key ( keys %Undef ) { print $file "$key\t$Undef{$key}\n"; ## line 20 } close $file; my %Defined; print "\n"; open ( $file, "<","./ondisk") || die " ! open |./ondisk| $!\n"; while ( my $value = <$file> ) { chomp $value; my ( $newkey, $newvalue ) = split(/\t/,$value); $Defined{$newkey} = $newvalue; } close $file; foreach my $key ( keys %Defined ) { if ( defined $Defined{$key} ) { print "$key\t|$Defined{$key}| +\n"; } } 1;
> perl unknown.plx 2. Salary value is undefined! Use of uninitialized value $Undef{"Salary"} in concatenation (.) or st +ring at unknown.plx line 20. Go |maybe| Salary || Show |okay|

Now if this is to solve a DB related flaw, then I see your point. But I don't understand how 'unknown' is better then 'undef/defined' in Perl scripts. YMMV!

Maybe the title should have SQL in front of "NULL" to clarify the intent of the 'unknown'.


"Well done is better than well said." - Benjamin Franklin