use strict; #Always
use Dumpvalue;

###just an example of nested data
my @example = (
{'firstname'=>'Justin', 'lastname'=>'Tyme', 'Age'=>'21'},
{'firstname'=>'Ima', 'lastname'=>'Geek','Age'=>'21'}
);

dump_ref(\@example);###you need to pass a reference to your data since
+ the dumpValues method only takes references.

sub dump_ref
{
   my $ref = shift;
   my $dumper = new Dumpvalue;
   $dumper->dumpValues($ref);
}
___OUTPUT___
0  ARRAY(0x80628f0)
   0  HASH(0x804c8d4)
      'Age' => 21
      'firstname' => 'Justin'
      'lastname' => 'Tyme'
   1  HASH(0x80628b4)
      'Age' => 21
      'firstname' => 'Ima'
      'lastname' => 'Geek'
[download]

$example[1]->{firstname};
[download]

my @first_elm_keys = keys %{$example[0]};
[download]

$hash{$key} = [ qw(foo bar baz) ];   # The [ ] make an anonymous array
+ reference

print "@{$hash{$key}}\n";            # output the whole array
print $hash{$key}->[0], "\n";        # output an individual element of
+ an array
[download]

my %packet_fields = (
  $Idents{ Format_7 }    => qw(    ident
           flags
[download]

I'm not entirely clear on what you're hoping for here: $%packet_fields{ $ident} , but you can bet that $% is not going to be a useful combination of sigils. It's probably parsed as a special variable followed by a bareword and panic.

When in doubt, use the general form of dereferencing, which is the sigil you would use if you had an ordinary variable, then a curly-wrapped expression returning a rereference, and then any indexing you would use on an ordinary variable of the referenced type. You can nest these as deeply as you need to.

Check out perldoc perlreftut again.

References are a big spicy meatball! And, of course, there's more than one way to do it.

The following snippet might help:

use strict;

my %packet_fields = (
  'Format_X' => ['ident', 'flags', 'x', 'y', 'mode3'],
  'Format_Y' => ['ident', 'RDP_Ident', 'Radar_Site_Ident', 'site_x']
);

foreach my $format (keys %packet_fields) {
  foreach my $field (@{$packet_fields{$format}}) {    #line 9
    print "$format -> $field\n";
  }
}

foreach my $format (keys %packet_fields) {
  print "$format's 2nd field = ", $packet_fields{$format}->[1], "\n"; 
+#line 15
  print "$format's 3rd field = ", $packet_fields{$format}[2], "\n"; #l
+ine 16
}
[download]

In this sample, %packet_fields is a regular old hash. The keys for this hash are garden-variety scalars. The value associated w/ each key is a reference to an anonymous (unnamed) array. These two anon. arrays are the only references that we have to deal with, and the only things that require any dereferencing syntax.

The @{} in line 9 is using a form of dereferencing notation to give me an array.

There's another form of dereferencing that I can use, too, as seen in lines 15 and 16.

Hi, Thanks for all the replies - most informative!

I've now got working code, something like this:

# Declaration of the data structure
my %packet_fields = (
   $Idents{ Format_7 } => [qw(    ident
                x
                    y
                    flight_level
                chksum
                    )],
   $Idents{ Rotation_Marker } => [qw(    ident
                            site_x
                            site_y
                            chksum
                      )],
);

# This structure listed for completeness of this example!
my %packet_template = (
    $Idents{ Rotation_Marker } => "C3 n n n n n n n n n n n n C3",
    $Idents{ Format_7 }                => "C B16 n2 A4 A8 A2 A A A3 C2
+",
);
# Referencing the data structure
# code here to read $buffer from STDIN
# $ident is extracted from $buffer
    @packet{ @{$packet_fields{ $ident }} } =
        unpack ( $packet_template{ $ident }, $buffer);
[download]

I've got one further question about creating and accessing a hash of hashes.

I'm currently using the following structures:

my %ARP_GLA = (
    x    =>    247866.9,
    y    =>    666999.7,
);

my %ARP_EDI = (
    x    =>    314382.0,
    y    =>    673841.9,
[download]

I'd like to combine these into one data structure which I guess is a hash of hashes.

I believe I know enough to create the hash. This should do the trick:

my %ARP = (
    GLA => {
        x    =>    247866.9,
        y    =>    666999.7
        },
    EDI => {
        x    =>    314382.0,
        y    =>    673841.9
        }
);
[download]

How do I now access the elements in this structure?

Is it something like:

my $edi_arp = $ARP{EDI}->{x};
[download]

Thanks.

R.

--
Robin Bowes | http://robinbowes.com