Looping through nested repeated elements using XML::Simple

[ranjan_jajodia]

Hi,
I am trying to loop through nested repeated elements in my config file but I am unable to find the number of nested elements:
Sample XML File:

<opt>
  <person firstname="Joe" lastname="Smith">
     <email>[e-mail]</email>
     <email>[e-mail]</email>
  </person>
  <person firstname="Bob" lastname="Smith">
     <email>[e-mail]</email>
  </person>
</opt>

Perl Code:

use XML::Simple;
use strict;
use Data::Dumper;
my $config = XMLin("testFile.xml",forcearray => ['person','email']);
my @persons = $config->{person};
print "Size:".@persons;

On running I always get the size as 1. I think the way I am trying to get the size is wrong because in order to get the person blocks I need to do $config->{person}->[0] etc. instead of $config->{person}[0]. I admit I have not used hashes earlier but I did try keys function on $config->{person} which gives "Type of arg 1 to keys must be hash (not hash element)" error. Could anyone please tell me the right way to loop through the elements?
Regards,
Ranjan

[ikegami]

$config->{person} returns a reference to an array, not an array.

my $persons = $config->{person};
print "Size:".@$persons;

Hashes values can't be arrays, only scalars. References are scalars, so references to arrays are valid hash values.

[ranjan_jajodia]

Thanks ikegami for the explanation. I am off to exploring more on the same.
Regards,
Ranjan

[pemungkah]

Well, let's do what we should do when we have a data structure we don't understand: look at it in the debugger.

$ perl -d xml_sample.pl

Loading DB routines from perl5db.pl version 1.28
Editor support available.

Enter h or `h h' for help, or `man perldebug' for more help.

main::(xml_sample.pl:5):        my $config = XMLin("testFile.xml",forc
+earray => ['person','email']);
                                                                      
+            DB<1> l 
5==>    my $config = XMLin("testFile.xml",forcearray => ['person','ema
+il']);
6:      my @persons = $config->{person};
7:      print "Size:".@persons;
   DB<1> c 6  # run continuously to line 6

main::(xml_sample.pl:6):        my @persons = $config->{person};

    DB<2> x $config
0  HASH(0x1988e88)
   'person' => ARRAY(0x19acb00)
      0  HASH(0x1988f30)
         'email' => ARRAY(0x19acba8)
            0  '[e-mail]'
            1  '[e-mail]'
         'firstname' => 'Joe'
         'lastname' => 'Smith'
      1  HASH(0x198a0cc)
         'email' => ARRAY(0x19acab8)
            0  '[e-mail]'
         'firstname' => 'Bob'
         'lastname' => 'Smith'
  DB<3> q
$

So we can see that the value of $config->{person} is actually a reference to an array, not an array itself. You'll have to dereference it to get an actual array. Try @{ $config->{person} }. The elements in the array created by this expression will be the two references to the hashes containing references to arrays containing the email values.

[ranjan_jajodia]

Thanks pemungkah for the explaining the way to solve this kind of problem. I was using DataDumper to see the contents but this way I can do more things while debugging.
Regards,
Ranjan

[pemungkah]

You're very welcome. One other thing: you can play around with expressions in the debugger as well. For instance, if you wanted to see what @{ $config->{person} } would give you, you could just enter x @{ $config->{person} } at the debugger prompt, and the debugger would happily dump it out for you.