Date: Sun, 9 Sep 2001 01:05:23 +0200
From: peter pilsl <pilsl_@goldfisch.at>
Subject: Re: sudhir: array references.
Message-Id: <3b9aa444$1@e-post.inode.at>

Sudhir Krishnan wrote:

> Thanks for the response!
> I've tried both setting and retrieving the values in the array as:
> 
> a[i][j][k]=value;
> and it seems to work.
> is this implicitly  the same as a->[i]->[i][k]; ?
>

no. 
$a[i][j][k] will work when @a is defined as array containing anonymous 
arrays. When $a is defined as anonymous array itself, you must use the 
'->' operator. 

@a=([1,2],[3,4]);
$a[1][1]=4;  #  OK !!
$a->[1][1]=4; # ERROR, cause $a is not defined yet, only @a

$b=[[1,2],[3,4]];
$b->[1][1]=4; # OK !!
$b[1][1]=4;  # ERROR, cause @b ist not defined, only $b

but the following is also possible:
$a[1]->[1]=4;
$b->[1]->[1]=4;

You can use or ommit the '->' in the latter indeces as you like, but usage 
before the first index is strictly required _XOR_ strictly forbidden, 
depending how you defined your structure.

When using $a[i][j][k] then perl will implecitely build a structure similar 
to my first example.

> $#{$a}       #DOES NOT WORK (I usually get -1)
> 
> Would u happen to know why the 3rd case does not work?
> 

Cause you use a structure like I used in my first example.
cause $a is not a reference but @a is an array.
You might try $#a instead and it will work.

I recommend not let perl build your structures implecitely, but preset your 
structures (and preallocate if using large matricces) to make yourself 
clear about the structure.
As I said in my last posting, I personally prefer the structure in the 
second example much more than the other, cause using references as 
parameters in functions is much easier than using arrays.

best,
peter



-- 
peter pilsl
pilsl_@goldfisch.at
http://www.goldfisch.at