pointers in perl

djgerbavore · 04-10-2005, 12:59 AM

hello,

i'm trying to reference an array in perl. I read alot of information on the internet about this, but i'm still having a problem for so reason,

he is my code:

Code:

#! /usr/bin/perl

$array[0] = 1;
$array[1] = 2;
$array[2] = 3;
print "array $array[0] \n";
@ref_array = \@array;
print "Dereference: $$ref_array[0]\n";

the output i get is

Code:

array 1
Dereference:

and nothing shows up for the reference (pointer) array, however, when i take out one of hte $ on the

Code:

 print "Dereference: $$ref_array[0]\n";

it prints out hte memory location, how can i dereference this array correctly?

thanks,

djgerbavor3

djgerbavore · 04-10-2005, 01:17 AM

nevermind, 2 minutes after i posted this, i saw what i was doing wrong:

when referencing arrays you need to do this:

Code:

$ref_array = \@array

INSTEAD OF

Code:

@ref_array = \@array

Sorry for the double post,

basically a good way to think about pointers or reference in perl is to think that pointers are a special kind of scalar.
So when initalizing a pointer you need create a "special scalar". However pointers can be of two things in perl. One is a regular reference like in C. and another kind of reference is an anonymous copy. An Anonymous is hte same as a regular reference but instead of indirectly referencing the value it makes a copies of value.
For example:
A reference declaration:

Code:

$ref_array = \@array or $ref_var = \$i;

anonymous copy is alittle different

Code:

$ref_array = [@array] ; like so wiht a scalar

and to deference your pointer you can do:

Code:

print "Deference $$ref_array[$i] \n";

this works both for reference and anonymous copies also.

hope this helps!!! this is a good way to create mult-dimenisonal arrays.. for more information about pointers and reference you can go here
http://linux.skavt.net/teach_perl_in_21days/ch18.htm

thanks,

djgerbavor3

johnMG · 04-10-2005, 09:49 AM

Thanks for the pointers djgerbavore!