I am not expert but I do know the fallowing.
Purl is like driving a car with automatic gear shift. Where other languages
like C are like driving a car with a stick shift.
It is not necessary to use a My Local or Var statement to define a variable,
you can make them on the fly with out them. But it is advisable to pre define
them up front to avoid any surprises like running out of memory. It is
considered good practice to use the stick and warnings at the start of your
code like this:
#!/usr/bin/perl --
use strict;
use warnings;
Witch will stop running you code when you get to the print "non-existent value:
$aList[0][0]\n"; in your code. and thus make you set everything up front of
your program and your sub routines. Personally I hate developing with strict
on, it can be frustrating. But I have discovered that if I do the development
with strick off, then switch it back on just as I'm finishing up and run the
program (and watch is crash), I can use the error log to tell all the variable
I need to be define. Most programs will probably consider this not a
professional way to go about it. But it's my sneaky trick to get the computer
to do some of the work for me.
An arrow with 2 indexes like your $aList[0][[0] in most other languages is
considered a multi dimensional arrow having a sort of X,Y axis. Grate when
doing graphics but I don't think that was what you wanted. To access different
steps in your arrow, you just increment the index such as $aList[0], $aList[1],
$aList[2]. ect but think you probably already know this.
The Push command is usually used like this:
Push (@aList, "First") (with the parenthesis arround everything that the
command is going to be dealing with) to add just one to the array.. You can
push all of anther array to your array with Push (@aList, @blist). So I am
shore there is a way to push mufti values to an array with push, if I could
only remember the details on it.
One command you might find really useful in you research is the exists command
if (exists $aList[0][0]) {print "Yes I do exist so
aList[0][0]=".$aList[0][0]."\n"};
The exists command let you check that something is there with out creating it.
Because if you try to print it like you did in your second example. Purl will
make it just so you can see that it's empty, I know that don't seem to make
much sense. But the exists command will leave your arrays and hashes alone and
just give you a true or false if there exist or not. Also may I point out that
I usually can't got arrows and defiantly not hashes to print out inside of
quotes so if you just brake out of them for a moment, hence my example above
"=".$aList[0][0]."\n". where I brake out of the text with a quote, glued it
with a period and add the variable that I want to print out and then glued it
again with anther period just before going back in with a quote to continue
printing the text and cartridge return.
And that I hope will give you some more tools for your creation. or should I
say your Frankenstein monster. so have a Happy Halloween.
Stefan
----- Original Message -----
From: John DePasquale
To: activeperl@listserv.ActiveState.com
Sent: Wednesday, October 28, 2015 10:13 AM
Subject: it's probably just me
Hi perl mavens,
I'm sure I just don't understand something here, but this one makes zero
sense to me:
The following snippet prints a 1
local @aList;
push @aList, ['first','second','third'];
my $nCount = @aList;
print "count: $nCount";
BUT, if I add one seemingly irrelevant line ( the second one below ),
something crazy happens:
local @aList;
print "non-existent value: $aList[0][0]\n";
push @aList, ['first','second','third'];
my $nCount = @aList;
print "count: $nCount";
instead of printing a 1, the last line prints a 2
So the reference in the first print statement to $aList[0][0] appears to have
the affect of creating a row in the array.
Is this supposed to work this way? Why would such a reference to a
non-existent array row result in the creation of an array row?
Thank you.
- john
John DePasquale
Chief Executive Officer
Paradigm Consulting
"Proudly presenting the Vinopedia System"
www.vinopedia.us
49 Dalby Street
Newton, MA 02458
Mobile: 617-610-2424
Fax: 617-600-7326
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