cLive ;-) has asked for the wisdom of the Perl Monks concerning the following question:

Once again, more niggle than desperate, but...

Why does CGI.pm not store a null value in param() if one is sent?

eg, 

my $q = new CGI;

my %conf = ... hash defined elsewhere

for ( $q->param() ) {
  $conf{$_} = $q->param($_);
}

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All well and good, but if the field sent contains an empty value, it doesn't appear when looping through param().

So for each conf var that *can* be empty, I'm having to add: 

$conf{'var_name'} = $q->param('var_name');

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explicitly.

Or am I missing some hidden feature of CGI.pm that covers this? It's just getting a little messy and umm i don't like that much...

.02 please :)

cLive ;-)

Replies are listed 'Best First'.
(crazyinsomniac) Re: CGI.pm and blank form fields
by crazyinsomniac (Prior) on Nov 28, 2001 at 12:50 UTC
    hmm, intersting results 
    #!/usr/bin/perl -wT
use strict;
use CGI;
my $q = new CGI;
my %Q = $q->Vars();
if(exists $Q{a})
{
    print "a exists ",
           (defined $Q{a} )?("and it is"):("but it isn't"),
          " defined ($Q{a})\n";
}

use Data::Dumper;
print Dumper \%Q;
__END__
F:\>perl -T f a=b
a exists and it is defined (b)
$VAR1 = {
          'a' => 'b'
        };

F:\>perl -T f a=
a exists and it is defined ()
$VAR1 = {
          'a' => ''
        };

F:\>perl -T f a=
a exists and it is defined ()
$VAR1 = {
          'a' => ''
        };

F:\>perl -T f a
$VAR1 = {
          'keywords' => 'a'
        };

F:\>perl -T f a b c d
$VAR1 = {
          'keywords' => 'a b c d'
        };

F:\>perl -T f a=b;a=c;a=d;
a exists and it is defined (b c d)
$VAR1 = {
          'a' => 'b c d'
        };

F:\>

    [download]

     
    ___crazyinsomniac_______________________________________
    Disclaimer: Don't blame. It came from inside the void
    perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"

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Re: CGI.pm and blank form fields
by tachyon (Chancellor) on Nov 28, 2001 at 16:42 UTC

    There is a $NO_UNDEF_PARAMS var in new versions of CGI.pm (in 2.78, not in 2.74) but the default is 0 so this is not the problem. I presume you understand the difference between exists and defined with respect to hashes. Your results are not repeatable vis: 

    use strict;
use CGI;
use Data::Dumper;
my %fields;

my $q = new CGI ( 'name=&value=&void=' );
print "got param '$_'\n" for $q->param;
$fields{$_} = $q->param($_) for $q->param;
print Dumper($q, \%fields);


__END__
got param 'name'
got param 'value'
got param 'void'
$VAR1 = bless( {
                 'void' => [
                             ''
                           ],
                 '.charset' => 'ISO-8859-1',
                 '.parameters' => [
                                    'name',
                                    'value',
                                    'void'
                                  ],
                 '.fieldnames' => {},
                 'value' => [
                              ''
                            ],
                 'name' => [
                             ''
                           ]
               }, 'CGI' );
$VAR2 = {
          'void' => '',
          'value' => '',
          'name' => ''
        };

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    The .fieldnames should actually contain the fieldnames (this is really a bug) but the ultimate behaviour is not broken. I presume you have an old version of CGI.pm which does not have the .parameters part in the object and works off .fieldnames which was the behaviour pre 2.63? I think. Which version do you have?

    cheers

    tachyon

    s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

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[d/l]
      Version 2.753 - $NO_UNDEF_PARAMS is there.

      So, i'm beginning to think the vars aren't sent in the first place from IE. Hmmm.

      Ah well, don't worry. I really can't be bothered with it right now :-)

      cLive ;-)

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Re: CGI.pm and blank form fields
by tstock (Curate) on Nov 28, 2001 at 12:07 UTC
    Are you sure the browser is sending name= in the query line ? I tried a bit of code and couldn't duplicate your example: 

    use CGI;
my $q= new CGI;

print "content-type: text/plain\n\n";

if ($q->param()) {
  print "got param $_\n" for ($q->param());
}

print "the end\n";

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    This on CGI version '2.56', calling it as http://script?name= did print out "got param name".

    Tiago
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Re: CGI.pm and blank form fields
by rob_au (Abbot) on Nov 28, 2001 at 15:18 UTC
    The following is the code that I use for this task and null fields are certainly incorporated into the hash (as determined by parsing of parameter values by HTML::FormValidator):

    my $cgi = CGI->new;
my %param = map { $_ => $cgi->param($_) } $cgi->param();

    [download]

     

    Ooohhh, Rob no beer function well without!

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