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

by HJO (Acolyte)
on Oct 11, 2012 at 09:19 UTC ( #998396=perlquestion: print w/ replies, xml ) Need Help??
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]}; } }

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

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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 / ) ){ ... }

      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...

Re: Error "Can't use an undefined value as a HASH reference" while working with generated objects
by McA (Curate) on Oct 11, 2012 at 09:29 UTC
    my %valeur = defined($values[0][0]) && ref($values[0][0]) eq 'HASH' ? +%{$values[0][0]} : ();

    Probably somthing like this?

    Best regards
    McA

      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]} : ();

        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] }; }

        my %valeur; if ( my $want = Dive( \@values, qw/ 0 0 / ){ %valeur = %$want; }

        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

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