CODEWITHSUNDEEP
perlhashtable
SemperFly
SemperFly

Reputation: 1583

Perl Hash of Hashes Issue

I've seen similar questions asked on here ad nauseum but none of those could answer my own question specifically.

I am trying to programatically create a hash of hashes. My problem code is as follows:

my %this_hash = ();
if ($user_hash{$uuid})
{
    %this_hash = $user_hash{$uuid};
}

$this_hash{$action} = 1;

$user_hash{$uuid} = %this_hash;
my %test_hash = $user_hash{$uuid};
my $hello_dumper = Dumper \%this_hash;

According to my output, $this_hash is being assigned properly but 

$user_hash{$uuid} = %this_hash

is showing a value of 1/8 in the debugger; not sure what his means. I'm also getting a warning: "odd number of elements in hash assignment..."

Upvotes: 2

Views: 559

Answers (2)

hobbs
hobbs

Reputation: 239861

Any time you write

%anything = $anything

you're doing something wrong. Almost any time you write

$anything = %anything

you're doing something wrong. That includes when $anything is an array or a hash access (i.e. $array[$index] or $hash{$key}). The values stored in arrays and hashes are always scalars, and arrays and hashes themselves aren't scalars. So, when you want to store a hash in a hash, you store a reference to it: $hash{$key} = \%another_hash. And when you want to access a hash that's had a reference to it stored in a hash, you dereference: %another_hash = %{ $hash{$key} } or $hashref = $hash{$key}; $value = $hashref->{ $another_key } or $value = $hash{$key}{$another_key}.

For getting up to speed with references I strongly recommend reading the Perl References Tutorial and the Perl Data Structures Cookbook.

Upvotes: 12

Nemo
Nemo

Reputation: 71525

It's not really a "hash of hashes"; it's a "hash of references to hashes".

Try:

$user_hash{$uuid} = \%this_hash;

Upvotes: 5

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