Re: array references

[Ed Summers]

Hi Eric:

On Mon, Nov 01, 2004 at 10:40:36PM -0500, Eric Lease Morgan wrote:
 In a package I'm writing I initialize an array reference (I think) 
 through DBI like this:
 
   $self-{author_ids} = $dbh-selectall_arrayref($query);
 
 First of all, what sort of foreach loop can I write to iterate through 
 the contents of $self-{author_ids}?

De-reference the array reference, here's one example:

foreach my $id ( @{ $self-{author_ids} } ) {
...
}

 Second, how do I undefine the value of $self-{author_ids}?

$self-{author_ids} = undef;

But if I were you I'd have your constructor initialize the slots that can
contain array references to an empty array reference:

sub new {
my $class = shift;
my $self = bless {}, $class;
$self-{author_ids} = [];
}

The advantage here is that you won't attempt to use undef as an array 
reference somewhere in your code. This is a runtime error in Perl, so 
it can result in an unpredictable program if the code isn't exercised
all the time.

 Third, if I have a list of integers, how to I assign the items in this 
 list to $self-{author_ids}?

$self-{author_ids} = [ @list_of_integers ];

or if you don't mind the list being referenced from two locations:

$self-{author_ids} = [EMAIL PROTECTED];

Hope this helps!
//Ed

-- 
Ed Summers
aim: inkdroid
web: http://www.inkdroid.org

The deeper I go the darker it gets. [Peter Gabriel]

Re: array references

[Michael McDonnell]

Eric Lease Morgan wrote:
How do I manipulate array references?
In a package I'm writing I initialize an array reference (I think) 
through DBI like this:

  $self-{author_ids} = $dbh-selectall_arrayref($query);

This gets tricky because selectall_arrayref returns an reference to an 
array.  Each value of that array is a reference to an array as well.

$self-{author_ids} is a reference to an array whose elements are in 
fact references to arrays (that contains scalars thank goodness).

@{$self-{author_ids}} is the array.
$#{$self-{author_ids}} is the number of elements in the array.
@{$self-{authors_ids}-[0]} is the first row of data (an array).
$#{$self-{authors_ids}-[0]} is the number of columsn in the first row 
of data.

$self-{author_ids}-[0] is a reference to an array representing one row 
of data.
$self-{author_ids}-[0]-[0] would be the first field of the first row 
of data.

First of all, what sort of foreach loop can I write to iterate through 
the contents of $self-{author_ids}?
foreach $i (0..$#{$self-{authors_ids}}) {
   foreach $j (0..$#{$self-{authors_ids}-[$i]}) {
 print $self-{authors_ids}-[$i]-[$j];
   }
   print \n;
}
Second, how do I undefine the value of $self-{author_ids}?

$self-{author_ids} = undef;
Third, if I have a list of integers, how to I assign the items in this 
list to $self-{author_ids}?

$self-{author_ids}-[0] = 1;
$self-{author_ids}-[1] = 2;
$self-{author_ids}-[2] = 3;
or
$self-{author_ids} = [1, 2, 3];
Or if you want something similar to what selectall_arrayref() is producing:
$self-{author_ids} = [ [1,2,3], [3,7,9], [2,8,4]];
Which could be printed like so:
foreach $i (0..$#{$self-{authors_ids}}) {
   foreach $j (0..$#{$self-{authors_ids}-[$i]}) {
   print $self-{authors_ids}-[$i]-[$j];
   }
   print \n;
}
I would strongly recommend adding quotation marks to {authors_ids} so 
that it is {'authors_ids'} or defining it as a constant.  The only 
reason why {authors_ids} is equivalent to {'authors_ids'} is because 
PERL is converting it to a constant on the fly for you.  If you 
accidentally picked a name that was already a constant in your namespace 
you might end up with results that are hard to debug (imagine if a 
module put a constant in your name space that you didn't know about).

--
Michael McDonnell, GCIA
Winterstorm Solutions, Inc.
[EMAIL PROTECTED]