Proper way to initialize local variables

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

Hello,

I have a question about the following code, which is in a Perl CGI script that runs on web servers:

sub anySub
{
:
local (@recArray) ;
while (defined ($_ = <$fileHandle>))
{
push (@recArray, $_) ;
}
:
}

Is it possible for recArray to start off not empty? If so, what's the best way to make sure recArray starts off empty? How about local (@recArray) = ();?

This is an older script, so maybe using my instead of local would be better also, as in my (@recArray) = ();?

Thank you in advance for your help.

Richard

Comment on Proper way to initialize local variables

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Re: Proper way to initialize local variables by tlm (Prior) on May 11, 2005 at 22:03 UTC
Both `local @recArray;` and `my @recArray;` will give you an empty array to start with, but the latter is considered better because it has lexical scope, while the former has dynamic scope. This means that, for example, in `our @foo = ( 0 ); my @bar = ( 'a' ); { local @foo = ( 1 ); my @bar = ( 'b' ); baz(); print "$foo[ 0 ] $bar[ 0 ]\n"; # may not print "1 b" } sub baz { $foo[ 0 ] = 3; $bar[ 0 ] = 'x'; } __END__ 3 b` [download] ...calling the function `baz()` has the effect of changing the value of `$foo[ 0 ]` inside the block; in contrast, the lexical variable `@bar` remains unaffected by what happens in `baz()`. By the way, the scoping behavior described above is not specific to arrays; it applies equally to hashes, scalars, and typeglobs as well. the lowliest monk	[reply] [d/l]
Re^2: Proper way to initialize local variables by rzward (Monk) on May 11, 2005 at 22:45 UTC
Thank you for your explanation of local vs. my. I actually asked a question about this topic some time ago. Unfortunately, I don't know how to put a link in this discussion to point to it! It sounds like it's impossible for an array declared with local or my to start off not empty even if the array is not explicitly initialized. Thank you again. Richard	[reply]
Re^3: Proper way to initialize local variables by Tanktalus (Canon) on May 11, 2005 at 23:17 UTC
You mean this conversation? "Some time ago", he says. September 2002! As for putting a link - that was one of the first things I figured out how to do here ... even before figuring out how to post a question, or even figuring out how to sign up ;-) Linking the old fashioned way: What shortcuts can I use for linking to other information? Linking the new way: grab Firefox, and then see: Monk Links - Copy Perlmonks-links to the clipboard in on-site-format. Way easier. Well, it is for me. :-)	[reply]
Re: Proper way to initialize local variables by borisz (Canon) on May 11, 2005 at 22:09 UTC
Your array is empty. `local @recarray;` is enough. Maybe your sub is better done this way: `sub any { my @recArray; local $_; ... while ( defined ($_ = <$fh> ) ) { push @recArray, $_; ... } }` [download] but that is just a guess. Boris	[reply] [d/l]
Re: Proper way to initialize local variables by Zaxo (Archbishop) on May 12, 2005 at 21:34 UTC
You can initialize in a declaration by assignment: `my @recArray = <$fileHandle>;` or `local @recArray = <$fileHandle>;` In array context, the diamond operator returns the entire content of the file, from the current position to the end, as a list of lines. You probably want lexical my instead of local here. After Compline, Zaxo	[reply] [d/l] [select]