ptkdb: 'my' variable in sub retains value between calls

leonidlm has asked for the wisdom of the Perl Monks concerning the following question:

Hi all again :)
How much things you can lern by using ptkdb!
I am running a big perl program with this beautiful debugging module and I noticed something I want someone here to clarify for me:
When I declare a sub routine and there I write:

my $a,$b;

while ( somethingHere ) {
$b .= "s";
}
[download]

If I run this subroutine couple of times the $b value is saved from call to call !!!!
How can it be? I am using a "my" declaration, it should be cleared as fast as the subroutine will end!
Someone please help me to understand this perl's behavior.

Comment on ptkdb: 'my' variable in sub retains value between calls Download Code

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Re: ptkdb: 'my' variable in sub retains value between calls by betterworld (Curate) on Aug 10, 2008 at 15:53 UTC
If you want to declare two my-variables, use either of the following: `my ($a, $b); my $a; my $b; my $a, my $b;` [download] By the way, the usage of the variables `$a` and `$b` for something other than sort is generally frowned upon. Probably that's why strict (if you use it) did not complain that the variable `$b` is not declared: Because it's a special variable and it's declared internally.	[reply] [d/l] [select]
Re: ptkdb: 'my' variable in sub retains value between calls by FunkyMonk (Bishop) on Aug 10, 2008 at 16:07 UTC
`my $a,$b;` doesn't declare $b, only $a. Had you included `use strict; use warnings;` [download] at the start of the program (see strict and warnings), perl would have told you "Parentheses missing around "my" list ...". The correct way is `my ($a, $b);`. But, $a and $b aren't good names to use as they are somewhat magical for their use with sort. You should choose more meaningful names. Unless I state otherwise, all my code runs with strict and warnings	[reply] [d/l] [select]
Re^2: ptkdb: 'my' variable in sub retains value between calls by leonidlm (Pilgrim) on Aug 10, 2008 at 16:11 UTC
Thank you all. The variable names are just for an example, of course I used a proper names in my program, it is more than 2000 lines, I don't think I would manage elsewhere.	[reply]
Re^3: ptkdb: 'my' variable in sub retains value between calls by GrandFather (Saint) on Aug 10, 2008 at 22:53 UTC
$foo and $bar are good time honored place holder names for variables and are almost as easy to type as $a and $b. Perl reduces RSI - it saves typing	[reply]
Re^3: ptkdb: 'my' variable in sub retains value between calls by Anonymous Monk on Aug 11, 2008 at 02:16 UTC
If, in addition to using `warnings` with its very helpful message referred to in other replies, you had been using `strict`, Perl would never have let you make the mistake in the first place if you were using names other than `$a` and `$b`!	[reply] [d/l] [select]
Re: ptkdb: 'my' variable in sub retains value between calls by Herkum (Parson) on Aug 10, 2008 at 16:05 UTC
Don't use $b, in fact don't use single letter variable names, EVER!. Besides $a, $b being special Perl variables for use with sorting, it is totally ambiguous. It does not tell you want is supposed to be there and creates maintenance headaches. Be polite and spell out what the variable is supposed to represent and the next time you look at this code, you will be able to quickly identify what it is supposed to do.	[reply]
Re^2: ptkdb: 'my' variable in sub retains value between calls by JavaFan (Canon) on Aug 11, 2008 at 12:12 UTC
Never say "never" (or "ever") in programming. Never using single letter variables would mean you wouldn't use $_. Or for that matter, $i, $j, etc.	[reply]