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

I have a large hash from which I want to pass a portion of it to a subroutine. My problem is, how do I dereference it within the subroutine? 
report_block(\$report_data{$domain}{$provider});


sub report_block
{
  my ($rpt_ref) = shift;

  print Dumper($rpt_ref);
  #access elements here!
}

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That dump yields: 
$VAR1 = \{
            'error' => 0,
            'total' => 7,
            'soft_error' => 0,
            'hard_error' => 0,
            'ok' => 7
          };

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But I can't seem to figure out how to access the individual elements. After searching around I've tried the following, but neither of them are what I need. 
print $rpt_ref{total};
#Global symbol "%rpt_ref" requires explicit package name...

print $rpt_ref->{total};
#Not a HASH reference at...

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Obviously something escapes me here. ;)


-THRAK
www.polarlava.com

Replies are listed 'Best First'.
Re: Dereferencing a portion of a hash
by tall_man (Parson) on Feb 18, 2005 at 16:08 UTC
    What you have passed is a reference to a reference. If you do this instead: 
    report_block($report_data{$domain}{$provider});

sub report_block
{
  my ($rpt_ref) = shift;

  print Dumper($rpt_ref);
  #access elements here!
  print $rpt_ref->{total};
}

    [download]
    Then you will have a simple hash reference and the arrow notation will work.
[reply]
[d/l]
      Maybe this is a stupid question, but how is that passing a reference as a reference? Isn't what you've done (which does work) pass a copy of that portion of the hash? Or is it such that when you pass a portion of a hash it automagically passes it as a reference?


      -THRAK
      www.polarlava.com
[reply]
        $report_data{$domain}{$provider} is a hash reference already. This is shown by your data dumper (which shows that it contains hash key/values).

        You are then taking the reference to that hash reference by passing it as \$report_data{$domain}{$provider} which makes it a reference to a reference.

        Hence, you need to either not pass it that way or dereference it twice.

        $,=" : ";$\="\n"; print $_, $$rpt_ref->{$_} for keys %{$$rpt_ref};

        [download]
        --------------
        It's sad that a family can be torn apart by such a such a simple thing as a pack of wild dogs
[reply]
[d/l]
Re: Dereferencing a portion of a hash
by Anonymous Monk on Feb 18, 2005 at 16:27 UTC 
        print $$rpt_ref->{total};
    print $$$rpt_ref{total};

    [download]
[reply]
[d/l]

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