Perl References

xav0989 · Feb 28, 2010

I started a small project in perl recently, a survey generator. Basically is loads the survey from a XML file and generates the interface from the XML. However, I am having problems with the hashrefs. I would greatly appreciate if someone could help me out on this.

Code:

#!/usr/bin/perl -w
use HTML::Template;
use CGI;
use CGI::Carp qw(warningsToBrowser fatalsToBrowser);
use XML::Simple;
use Data::Dumper;

########################
#  MUST EDIT FOLOWING  #
########################
# path to the data directory
my $dataDir = "PATH/TO/WHERE/THE/SURVEYS/ARE/";

########################
#      DO NOT EDIT     #
########################

my $query  = new CGI;
my $template = HTML::Template->new(filename => 'survey.tmpl', path => $dataDir);
my $XML = new XML::Simple;

my $survey = $query->param('survey');
my $list = $XML->XMLin($dataDir . "surveys/list.xml", KeyAttr => "id");

if (exists $list->{survey}->{$survey}) {
    my $surveyMetaData = $list->{survey}->{$survey};
} else {
    $template->param(TITLE => 'ERROR', CONTENT => 'ERROR (0x0): Undefined survey ID.');
    print "Content-Type: text/html\n\n", $template->output;
    exit;
}

my $surveyData = $XML->XMLin($dataDir . "surveys/" . $surveyMetaData->{file} . ".xml", KeyAttr => "id");

print "Content-Type: text/html\n\n", $template->output;

basically, the $surveyMetaData is being set to an empty hash, when I want it to reference (or hold) the value of $list->{survey}->{$survey}.

misson · Feb 28, 2010

There's more going on than what's in the code. An inconsequential alteration (removing the HTML templates, so I can be lazy and not install HTML::Template) works.

Code:

#!/usr/bin/perl -w
#use HTML::Template;
use CGI;
use CGI::Carp qw(warningsToBrowser fatalsToBrowser);
use XML::Simple;
use Data::Dumper;

########################
#  MUST EDIT FOLOWING  #
########################
# path to the data directory
my $dataDir = $ENV{'DOCUMENT_ROOT'} . "/survey/";

########################
#      DO NOT EDIT     #
########################

my $query  = new CGI;
#my $template = HTML::Template->new(filename => 'survey.tmpl', path => $dataDir);
my $XML = new XML::Simple;

my $survey = $query->param('survey') || 'foo';
my $list = $XML->XMLin($dataDir . "/list.xml", KeyAttr => "id");

print <<EOS ;
Content-Type: text/html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
  <head>
    <title></title>
    <style type="text/css">
    pre {
      padding: 0.5em;
      border: 1px solid black;
    }
    </style>
  </head>

  <body>
EOS

if (exists $list->{survey}->{$survey}) {
    my $surveyMetaData = $list->{survey}->{$survey};

    my $surveyData = $XML->XMLin($dataDir . "/" . $surveyMetaData->{file} . ".xml", KeyAttr => "id");

    print 'survey.xml:<pre>', Dumper($list), '</pre>';

    print 'survey meta data:<pre>', Dumper($surveyMetaData), '</pre>';

    print "survey data (from <a href='/survey/$surveyMetaData->{file}.xml'>$surveyMetaData->{file}.xml</a>):<pre>", Dumper($surveyData), '</pre>';
} else {
    #$template->param(TITLE => 'ERROR', CONTENT => 'ERROR (0x0): Undefined survey ID.');
    #print "Content-Type: text/html\n\n", $template->output;
    print "<p>Error: undefined survey '$survey'.</p>";
}

print <<EOS ;
  </body>
</html>
EOS

Check that the elusive <survey> element in list.xml isn't missing any child elements or attributes.

xav0989 · Mar 1, 2010

Thanks, misson. I will test that out as well.
Here is the code of my list.xml file:

Code:

<?xml version="1.0" encoding="UTF-8"?>
<surveys>
	<survey id="1" name="Testing" file="survey_1" results="survey_1" />
	<survey id="2" name="Second Testing" file="survey_1" results="survey_1" />
</surveys>

EDIT. I think I figured it out. It was because I initialized the $surveyMetaData inside the if block. The reference was only available inside the if block. If I initialize it outside the if block but set is inside, it works. Thanks misson, you opened my eyes

(damn, I can't give you credits nor reputation...

)

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