Re: Perl arrays and hashes
- From: "Octavian Rasnita" <orasnita@xxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Tue, 14 Oct 2008 08:34:51 +0300
Hi,
You need to write
@{$macs{$key}}
and not
@macs{$key}
because %macs is a hash and not an array to be noted with @ at the beginning.
The %macs hash has a key named $key which happends to have an array as a value.
So you first need to specify that you want to address the key $key of this
hash, using
$macs{$key}
and derefference it to get its value... the array, using @{$macs{$key}}
It is just like when you use
my $hash_key = $macs{$key};
my @array = @$macs_key;
Of course, you need to add more braces like when you use
my @array = @{$hash_key};
because $macs{$key} already contains braces and you need to specify that the
entire $macs{$key} is an array reference, not only $hash.
Octavian
----- Original Message -----
From: "Sina Bahram" <sbahram@xxxxxxxxx>
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Monday, October 13, 2008 11:38 PM
Subject: RE: Perl arrays and hashes
> I'm off to try this out, but can you please explain why that is?
>
> I do understand why you're doing what you're doing, but I'm unclear as to
> why perl isn't doing this automatically?
>
> Take care,
> Sina
>
>
> -----Original Message-----
> From: programmingblind-bounce@xxxxxxxxxxxxx
> [mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Octavian Rasnita
> Sent: Monday, October 13, 2008 4:24 PM
> To: programmingblind@xxxxxxxxxxxxx
> Subject: Re: Perl arrays and hashes
>
> Hi,
>
> You need to use:
>
> for my $key (sort(keys(%macs)))
> {
> print "$key\n";
> for my $val (@{$macs{$key}})
> {
> print "$val\n";
> }
> print "\n";
> }
>
> Octavian
>
> ----- Original Message -----
> From: "Sina Bahram" <sbahram@xxxxxxxxx>
> To: <programmingblind@xxxxxxxxxxxxx>
> Sent: Monday, October 13, 2008 10:50 PM
> Subject: Perl arrays and hashes
>
>
>> Hi all,
>>
>> I have a very simple program that loops through a file, whose structure is
>> like this.
>>
>> Key name:
>> Value1
>> Value2
>> Value3
>> ...
>>
>> Key name:
>> Value1
>> Value2
>> .....
>>
>> Key name:
>> Value1
>> Value2
>> Value3
>> Value4
>> ...
>>
>> And so on
>>
>> Not hard, right?
>>
>> I use the following snippet of code to parse that file.
>>
>> ***
>>
>> open(MACS, "macs.txt");
>>
>> my @macsFromFile = <MACS>;
>> chomp @macsFromFile;
>>
>> my %macs;
>> my $i = 0;
>> for my $mac (@macsFromFile)
>> {
>> if($mac =~ /10.110.0.*/)
>> {
>> $key = $mac;
>> $i = 0;
>> @macs{$key} = ();
>> }
>>
>> $macs{$key}[$i++] = $mac if($mac =~ /05:.*/);
>> }
>>
>> ***
>>
>> Anyways, as far as I can tell, that works fine. When I print out the keys
>> of
>> that hash, I get all the ip addresses I was looking for, but heaven forbid
>
>> I
>> try to get the values. That's an insane nightmare.
>>
>> How can I loop through that hash, with each key, looping through each of
>> the
>> arrays stored at each key's index. After all, each key is an IP address,
>> and
>> each IP address has a series of mac addresses associated with it in this
>> file, in the form of them being in an array assigned to that key in the
>> hash.
>>
>> So I wanted to make sure I parsed the file write. Thus, why not just print
>> it out again and compare against the original. I tried the following.
>>
>> ***
>>
>> for my $key (sort(keys(%macs)))
>> {
>> print "$key\n";
>> for my $val (@macs{$key})
>> {
>> print "$val\n";
>> }
>> print "\n";
>> }
>>
>> ***
>>
>> It prints out a single memory address rather than the list of the contents
>> of that array.
>>
>> Why does it do this?
>>
>> I am using a for each construct to itterate through an array, and I use
>> the
>> @ to indicate that I want array context to be used when I parse
>> @macs{$key}
>> ... What the heck else should I do to make perl understand I want to loop
>> through the array stored at @macs{$key}?
>>
>> Maybe I'm not doing this right up top? That's what I think the problem is.
>> Somehow I've given my hash a reference to an array, rather than the array
>> itself.
>>
>> Help!
>>
>> Take care,
>> Sina
>>
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>
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