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

On the 11th our I look to the great monks for a stay of execution

I have one class: 

package Node
use strict;
 my ($id, $u, $p, $log, @mess);
 sub New {
    my $class =shift;
    my $this  ={};
    @mess =();
    $log  =0;
    bless ($this, $class);
    return ($this);
 }

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and another class: 
package System;
use strict;
 my (@nodes, $n1, $server, @messages);

...

 sub ANodeLogin{
    my $self =shift;

    use Node;
    my $node=Node->New;
    push (@nodes, \$node);

...

 sub ANodeLogout{
    my $self =shift;
    my $node;

    print "What node would you like to log out of\n";
    foreach $node (@nodes){
       print "--->$node->{u}<---\n";#this is line 62
    }
 }

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Which produces this: Not a HASH reference at System.pm line 62, <STDIN> line 6. Please help me see why I cannot defrefrence this object in the array of objects called @nodes. Sincerely, Lost

Replies are listed 'Best First'.
Re: derefrencing an object
by Thelonius (Priest) on May 03, 2004 at 17:01 UTC
    It looks like this line:
      push (@nodes, \$node);

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    is pushing a reference to a scalar. This scalar happens to be a reference to a hash. So you don't have a reference to a hash in line 62, you have a reference to a reference to a hash. Probably what you want to do is:
      push (@nodes, $node);

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      I made the change and I still get the same error. Could it be b/c I use my $node in ANodeLogin and once I leave that methode $node evaporates? thanks for your help!
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        Could it be b/c I use my $node in ANodeLogin and once I leave that methode $node evaporates?

        That shouldn't be a problem. The object should still exist as long as there's a reference to it. It's hard to say what's wrong looking at just these few lines. What I would probably try next is to add:

        use Data::Dumper;
print Dumper($node);

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        right before line 62.

        Update: Given what sgifford says below, I would suspect either (1) you have another code path which adds to @nodes, or (2) you didn't change the code you were running. In fact, one reason I suggested adding the print Dumper statement was to make sure that you were changing (and saving) the right code. Don't feel too bad if this happens to you. I have to be on the guard against this all the time; it has happened to me too many times over the years. Given how Perl can search many places for a module, that I have two different versions of Perl on my PC, that I often edit on a different system from the one I run on, that there are development, test, and production environments, etc., etc. you have to keep on your toes. Eternal vigilance!

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        This fix works for me. I'm running this program:
        Read more... (953 Bytes)
        and it outputs: 
        What node would you like to log out of
--->0<---
--->1<---
--->2<---
--->3<---
        Without the fix from Thelonius, I get the error you were seeing.

        Maybe the problem is being introduced elsewhere in your program.

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