RE: Perl arrays and hashes
- From: "Sina Bahram" <sbahram@xxxxxxxxx>
- To: <programmingblind@xxxxxxxxxxxxx>
- Date: Tue, 14 Oct 2008 08:50:58 -0400
This is starting to get at what I was trying to say. If I set it equal to
[], then I won't need to do the @{$macs{$key}} but rather could do
@macs{$key}?
Take care,
Sina
-----Original Message-----
From: programmingblind-bounce@xxxxxxxxxxxxx
[mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Jim Dunleavy
Sent: Tuesday, October 14, 2008 4:43 AM
To: programmingblind@xxxxxxxxxxxxx
Subject: Re: Perl arrays and hashes
Hi Sina,
@macs{$key} = ();
has the effect of assigning undefined to that key position.
It's the same as writing:
$macs{$key} = ();
If you have "use strict" perl will warn you of that usage.
When you write:
$macs{$key}[$i++] = $mac;
Perl replaces the previously assigned undefined scalar value with a newly
created array reference, making the previous assignment redundant.
To create an empty array reference for the mac address use:
$macs{$key} = [];
HTH
--Jim
----- Original Message -----
From: Sina Bahram <sbahram@xxxxxxxxx>
To: <programmingblind@xxxxxxxxxxxxx>
Sent: Tuesday, October 14, 2008 7:00 AM
Subject: RE: Perl arrays and hashes
> I did understand all of that, but I suppose I was asking about why perl
was
> treating it as a reference rather than doing the conversion itself.
> Regardless though, it all works and thanks.
>
> Take care,
> Sina
>
> -----Original Message-----
> From: programmingblind-bounce@xxxxxxxxxxxxx
> [mailto:programmingblind-bounce@xxxxxxxxxxxxx] On Behalf Of Octavian
Rasnita
> Sent: Tuesday, October 14, 2008 1:35 AM
> To: programmingblind@xxxxxxxxxxxxx
> Subject: Re: Perl arrays and hashes
>
> 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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