Referenced array dropped in size to one element - arrays

Question

Dear fellow perl programmers,
I wanted to access to this array
my #vsrvAttribs = qw(
Code
Description
vsrv_id
vsrv_name
vsrv_vcpu_no
vsrv_vmem_size
vsrv_vdspace_alloc
vsrv_mgmt_ip
vsrv_os
vsrv_virt_platf
vsrv_owner
vsrv_contact
vsrv_state
);
through a variable composed of a variable and a string suffix, which of course led to the error message like this
Can't use string ("#vsrvAttribs") as an ARRAY ref while "strict refs" in use at cmdbuild.pl line 262.`
Therefore I decided to get the reference to the array through a hash
my %attribs = ( vsrv => #vsrvAttribs );
And this is the code where I need to get the content of aforementioned array
foreach my $classTypeKey (keys %classTypes) {
my #attribs = $attribs{$classTypeKey};
print Dumper(\#attribs);
}
It seems I can get the reference to the array #vsrvAttribs, but when I checked the content of the array with Dumper , the array have got only one element
$VAR1 = [
'Code'
];
Do you have any idea where could be the problem?

Answer 1

How do you store the array in a hash and access it later?
You need to store your array by reference like this:
my %attribs = ( vsrv => \#vsrvAttribs );
Note the backslash before the # sigil. This tells perl that you want a reference to the array.
Then when access the array stored in $attribs{vsrv} you need to treat it as a reference instead of as an array. You'll do something like this:
foreach my $classTypeKey (keys %classTypes) {
# make a copy of the array by dereferencing
my #attribs = #{ $attribs{$classTypeKey} };
# OR just use the array reference if profiling shows performance issues:
my $attribs = $attribs{$classTypeKey}
# these will show the same thing if you haven't done anything to #attribs
# in the interim
print Dumper(\#attribs);
print Dumper($attribs);
}
Why did you only get one value and where did the rest of the array go?
Your missing values from #vsrvAttribs weren't lost they were assigned as keys and values to %attribs itself. Try adding the following just after you made your assignment and you'll see it for yourself:
my %attribs = ( vsrv => #vsrvAttribs );
print Dumper(\%attribs);
You'll see output like this:
$VAR1 = {
'vsrv_contact' => 'vsrv_state',
'vsrv_virt_platf' => 'vsrv_owner',
'vsrv' => 'Code',
'vsrv_name' => 'vsrv_vcpu_no',
'vsrv_mgmt_ip' => 'vsrv_os',
'Description' => 'vsrv_id',
'vsrv_vmem_size' => 'vsrv_vdspace_alloc'
};
This is because perl interpreted your assignment by expanding the contents #vsrvAttribs as multiple arguments to the list literal ():
my %attribs = (
# your key => first value from array
vsrv => 'Code',
# subsequent values of the array
Description => 'vsrv_id',
vsrv_name => 'vsrv_vcpu_no',
vsrv_vmem_size => 'vsrv_vdspace_alloc',
vsrv_mgmt_ip => 'vsrv_os',
vsrv_virt_platf => 'vsrv_owner',
vsrv_contact => 'vsrv_state',
);
This is legal in perl and there are reasons where you might want to do this but in your case it wasn't what you wanted.
Incidentally, you would have been warned that perl was doing something that you might not want if you had an even number of elements in your array. Your 13 elements plush the hash key "vsrv" makes 14 which is even. Perl will take any list with an even number of elements and happily make it into a hash. If your array had another element for 15 elements total with the hash key you would get a warning: Odd number of elements in hash assignment at foo.pl line 28.
See "Making References" and "Using References" in perldoc perlreftut for more information.

Answer 2

If you use a bare array in a hash definition like
my %attribs = ( vsrv => #vsrv_attribs )
the array is expanded and used as key/value pairs, so you will get
my %attribs = (
vsrv => 'Code',
Description => 'vsrv_id',
vsrv_name => 'vsrv_vcpu_no',
vsrv_vmem_size => 'vsrv_vdspace_alloc',
...
)
The value of a Perl hash element can only be a scalar value, so if you want an array of values there you have to take a reference, as shown below
It is also a bad idea to use capitals in Perl identifiers for anything except globals, such as package names. Local names are conventional lower-case alphanumeric plus underscore, so $class_type_key instead of $classTypeKey
use strict;
use warnings;
use Data::Dumper;
my #vsrv_attribs = qw(
Code
Description
vsrv_id
vsrv_name
vsrv_vcpu_no
vsrv_vmem_size
vsrv_vdspace_alloc
vsrv_mgmt_ip
vsrv_os
vsrv_virt_platf
vsrv_owner
vsrv_contact
vsrv_state
);
my %attribs = (
vsrc => \#vsrv_attribs,
);
for my $class_type_key (keys %attribs) {
my $attribs = $attribs{$class_type_key};
print Dumper $attribs;
}
output
$VAR1 = [
'Code',
'Description',
'vsrv_id',
'vsrv_name',
'vsrv_vcpu_no',
'vsrv_vmem_size',
'vsrv_vdspace_alloc',
'vsrv_mgmt_ip',
'vsrv_os',
'vsrv_virt_platf',
'vsrv_owner',
'vsrv_contact',
'vsrv_state'
];