Add Data to Hash Reference

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

I have this code which is not working.

#!/usr/bin/perl

use strict;
use Data::Dumper;

my $test = { record => '' };

$test->{record}->{'a'} = 11;
$test->{record}->{'b'} = 22;
print Dumper \$test;
[download]

I am hoping to get this output.


$VAR1 = \{
            'record' => {
                                  'a' => 11,
                                  'b' => 22
                        }
          };
[download]

I am getting this error:
Can't use string ("") as a HASH ref while "strict refs" in use at 103.pl line 8.

What seem to be wrong with my code?
Thanks.

Comment on Add Data to Hash Reference Select or Download Code

Replies are listed 'Best First'.
Re: Add Data to Hash Reference by moritz (Cardinal) on Dec 07, 2010 at 20:11 UTC
`$test->{record}` is a string - you make it one, explicitly. Which is why you can't use it as a hash ref. Perl 6 - second systems done right	[reply] [d/l]
Re^2: Add Data to Hash Reference by Anonymous Monk on Dec 07, 2010 at 20:25 UTC
So, if I want to construct the data structure in my example, how should I write it?	[reply]
Re^3: Add Data to Hash Reference by moritz (Cardinal) on Dec 07, 2010 at 20:35 UTC
How about `my $test = { 'record' => { 'a' => 11, 'b' => 22 } };` [download] Or just: `my $test; $test->{record}->{'a'} = 11; $test->{record}->{'b'} = 22;` [download] If you want to initialize `$test->{record}` with something (and don't rely on autovivification), initialize it with `{}`. Perl 6 - second systems done right	[reply] [d/l] [select]
Re: Add Data to Hash Reference by roboticus (Chancellor) on Dec 07, 2010 at 20:28 UTC
As moritz said, you told it to create a string, not a hash. You can explicitly tell your code to create an empty hash like this: `my $test = { record => {} };` [download] or you could use `undef`, leaving the slot empty for perl to put in a hash reference when you execute line 8. ...roboticus When your only tool is a hammer, all problems look like your thumb.	[reply] [d/l] [select]
Re: Add Data to Hash Reference by shail (Initiate) on Dec 07, 2010 at 20:36 UTC
You need to specifically create hash reference. Here is better code that prints your new hash. Note: Now dumpvar puts out data but also print another hash with undef value. I believe that is due to auto-vivification but I could be wrong. `#!/usr/bin/perl use strict; use warnings; use Data::Dumper; my %test = { record => ' ' }; my $test = \%test; $test->{record}->{'a'} = 11; $test->{record}->{'b'} = 22; print Dumper \%test;` [download]	[reply] [d/l]
Re^2: Add Data to Hash Reference by Anonymous Monk on Dec 07, 2010 at 21:10 UTC
This produces: `Reference found where even-sized list expected at ./875882.pl line 7. $VAR1 = { 'record' => { 'a' => 11, 'b' => 22 }, 'HASH(0x604290)' => undef };` [download] If you had read the warning, you'd have realized that there's something wrong with the line `my %test = { record => ' ' };` [download]	[reply] [d/l] [select]