Error "Can't use an undefined value as a HASH reference" while working with generated objects

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

Hi,

I'm currently working on a project involving a Perl module which allows me to retreive data from a SAP system.

To do so, I give the Perl module some informations like the connexion parameters to the SAP system and the name of the SAP function-module I want to use (and his parameters as well).

The result is coming back as an Perl object, in which a structure (table of one row) is an hash table structured like key=field name and value = value, and a table an array of hash tables.

My problem is that sometimes, there are no data in the SAP system(not a bug, simply no data for the time period I'm specifying), but when it arrives in the Perl script, I'm suddently having the error Can't use an undefined value as a HASH reference at ./script.pl line 222..

What I'm looking for is a tip on how I could find out right after I retrieved my object that some of his arrays/hashes are empty... I tried to get "blanks" in the array before it was treated, but the array is erased totaly before beeing rewritten... I also tried to use the defined Perl function, but unsuccessfully (altrough I might have used it wrong...)

Here is the code I'm using to unpack my array :

@values = $rc->{parameters}->{$key}->{value};
my %valeur = %{$values[0][0]};

my @fields = keys(%valeur);
my $nb_fields = scalar(@fields);

for my $i (0 .. $nb_fields-1) {
    ${$struc_ref}[$i] = $fields[$i];
}

#recuperation of the number of rows retrieved by the function-module
my $nb_lignes = scalar(@{$values[0]});
#recuperation of the number of rows already in the table
my $nb_lignes_base = scalar(@{$table_ref});

#display of data (for control)
for my $i (0 .. $nb_lignes-1){      #number of rows retrieved by th F-
+M
    for my $j (0 .. $nb_fields-1){      #number of fields in the table
        #storing data in a table
        ${$table_ref}[$nb_lignes_base+$i][$j] = $values[0][$i]{$fields
+[$j]};
    }
}
[download]

The variables named $..._ref are referencies to two tables, struc stand for structure(a particular one row table), the variable $rc contains the massiv object that I get from my Perl module, (the 222 line is the one with "my %valeur = %{$values[0][0]};") and I appologize for other variables names, I'm french so I named them in an intuitive way for me, I tried to translate comments thought

I hope I gave you enough data to help me, if not please tell me and I will provide so... for any trouble with my variable names, I can also explain them ^^"

Regards

Comment on Error "Can't use an undefined value as a HASH reference" while working with generated objects Select or Download Code

Replies are listed 'Best First'.
Re: Error "Can't use an undefined value as a HASH reference" while working with generated objects by McA (Priest) on Oct 11, 2012 at 09:29 UTC
`my %valeur = defined($values[0][0]) && ref($values[0][0]) eq 'HASH' ? +%{$values[0][0]} : ();` [download] Probably somthing like this? Best regards McA	[reply] [d/l]
Re^2: Error "Can't use an undefined value as a HASH reference" while working with generated objects by HJO (Acolyte) on Oct 11, 2012 at 09:41 UTC
Hi McA, Waow, thanks it worked perfectly, but could you just please explain it to me ^^" I'm unused to your use of : `? %{$values[0][0]} : ();`	[reply] [d/l]
Re^3: Error "Can't use an undefined value as a HASH reference" while working with generated objects by Anonymous Monk on Oct 11, 2012 at 10:04 UTC
`my %valeur; if( @values and defined $values[0] and 'ARRAY' eq ref $values[0] and defined $values[0][0] and 'HASH' eq ref $values[0][0] ) { %valeur = %{ $values[0][0] }; }` [download] `my %valeur; if ( my $want = Dive( \@values, qw/ 0 0 / ){ %valeur = %$want; }` [download]	[reply] [d/l] [select]
Re^4: Error "Can't use an undefined value as a HASH reference" while working with generated objects by tobyink (Canon) on Oct 11, 2012 at 14:03 UTC
Re^4: Error "Can't use an undefined value as a HASH reference" while working with generated objects by HJO (Acolyte) on Oct 11, 2012 at 10:28 UTC
Re^5: Error "Can't use an undefined value as a HASH reference" while working with generated objects by Anonymous Monk on Oct 11, 2012 at 10:46 UTC
Some notes below your chosen depth have not been shown here
Re^3: Error "Can't use an undefined value as a HASH reference" while working with generated objects by McA (Priest) on Oct 12, 2012 at 09:07 UTC
Hi! Sorry for the late reply: Please have a look at http://perldoc.perl.org/perlop.html#Conditional-Operator . This operator is also known as triadic operator. It's a kind of if-then-else-operator. Hope it helps Best regards McA	[reply]
Re^4: Error "Can't use an undefined value as a HASH reference" while working with generated objects by HJO (Acolyte) on Oct 12, 2012 at 10:12 UTC
Re: Error "Can't use an undefined value as a HASH reference" while working with generated objects by Anonymous Monk on Oct 11, 2012 at 09:26 UTC
What I'm looking for is a tip on how I could find out right after I retrieved my object that some of his arrays/hashes are empty.. use defined, and exists, or use Data::Diver 'Dive'; `if( my $want = Dive( $foo, qw/ bar anything you want / ) ){ ... }` [download]	[reply] [d/l]
Re^2: Error "Can't use an undefined value as a HASH reference" while working with generated objects by HJO (Acolyte) on Oct 11, 2012 at 09:47 UTC
Well thank you Anonymous Monk, I tried to use http://perldoc.perl.org/functions/defined.html, but I didn't manage to get what I wanted, srely because I don't know very well how to use it... I applied the answer that McA gave me and it worked just fine, so thanks for the answer, I'll look for this Dive function...	[reply]