Returning Hashes

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I am currently working on a perl module Im returning a hash %dbReturn to the caller. This is the final snippet of the code for the return

        my $row_hash;
        $x=0;
        while($row_hash = $st->fetchrow_hashref) {
                if($wildCard==1) {
                        foreach(@tables) {
                                my $col;
                                foreach $col(@$_) {
                                        $dbReturn{$x}{$col} = $row_has
+h->{$col};
                                        $x++;
                                }
                        }
                }
                else {
                        foreach(@fieldNames) {
                                $dbReturn{$x}{$_} = $row_hash->{$_};
                                #print "$dbReturn{$x}{$_}\n";
                        }
                }
        }

        return $dbReturn;
[download]

The caller is doing

 my $dbData = $dbFunctions->query($queryString)
 my $something = $dbData->{}{};
[download]

I have tried putting known data into the {}{} and it does not work. I know the data in $dbReturn is present because if I call it from the module itself everything works fine. Everything is using strict and warnings. If I try to return the data as

 return %dbReturn;
[download]

I get the following error apon execution Can't use string ("1/8") as a HASH ref while "strict refs" in use at test.cgi line 14. Here is a data demo datatable for $dbReturn

$dbReturn{0}
$dbReturn{0}{'ID'}	$dbReturn{0}{'Firstname'}	$dbReturn{0}{'Lastname'}
0	John	Doe
$dbReturn{1}
$dbReturn{1}{'ID'}	$dbReturn{1}{'Firstname'}	$dbReturn{1}{'Lastname'}
1	Jane	Doe

So My Question is, Im probably returning the hash wrong. How should I be returning it? Thanks in advance

Comment on Returning Hashes Select or Download Code

Replies are listed 'Best First'.
Re: Returning Hashes by cmeyer (Pilgrim) on Jun 03, 2005 at 23:05 UTC
You are storing stuff in the hash `%dbReturn`, but returning the scalar `$dbReturn`. Perhaps you want `return \%dbReturn`? -Colin. Whitepages.com, Inc.	[reply] [d/l] [select]
Re: Returning Hashes by duff (Parson) on Jun 03, 2005 at 23:10 UTC
It looks like you really want to return a reference to a hash rather than the hash itself, so a `return \%dbReturn;` at the end of your subroutine should do it. Also keep in mind that `$dbReturn` bears no relation to `%dbReturn`. You seem to be conflating the two. duff	[reply] [d/l] [select]
Re: Returning Hashes by monarch (Priest) on Jun 04, 2005 at 00:36 UTC
Even the most experienced programmer can make this mistake.. on more occasions than I'd care to admit I've accidently specified a `$` instead of a `\%` etc. For this reason there are two tools available to help protect ourselves.. because odds are you'll do this again (through no intention on your part). They are: - never, ever give both a scalar and a hash the same name! It's possible and valid to do this but fraught with danger..! - try using the following bit of code whenever you're not seeing what you expect (I do this all the time): `{ use Data::Dumper; print( Dumper( $dbReturn ) . "\n"; }` [download] The second tip is what I'll recommend the most, along with pulling out the debugger. I asked my first manager in a software engineering role what his best tip for coding was - and he said "learn to use the debugger". Now that I'm a bit older I know what he meant! Anyway, enough rambling.. PS I think your question was laid out very nicely.. thanks for going to the effort to present a well structured question.	[reply] [d/l] [select]
Re: Returning Hashes by Anonymous Monk on Jun 03, 2005 at 23:15 UTC
Both of you were right I forgot my \ before the %dbReturn at the end of the routine. Everything works as it should now. Have yourselves a great weekend!	[reply]