Excellent info!
-----Original Message-----
From: david [mailto:[EMAIL PROTECTED]]
Sent: Monday, January 13, 2003 1:59 PM
To: [EMAIL PROTECTED]
Subject: RE: reference problem (i think)
Joe Mecklin wrote:
> Dan,
>
> here is the output with your additions.
>
> BEFORE :: ID - 101
> NM - Arapaho Elementary
> AD - 1300 Cypress Dr.
>
> # this is the call to clear_input in ISD.pm
> $fields = school_id, school_name, school_address
> @field = school_id school_name school_address
> $f = school_id = ..
> $f = school_name = ..
> $f = school_address = ..
>
> AFTER :: ID - 101
> NM - Arapaho Elementary
> AD - 1300 Cypress Dr.
>
> # this is the output to clear_input2 in school_data (all code in
> the same file)
> $fields = school_id, school_name, school_address
> @field = school_id school_name school_address
> $f = school_id = .101.
> $f = school_name = .Arapaho Elementary.
> $f = school_address = .1300 Cypress Dr..
>
> both routines are carbon copies of each other. i used "our" simply to
> see if it might affect how the data got passed to ISD. no effect.
> but while writing this, i changed them back to "my" and the
> clear_input2 call no longer displayed the values. God keep me from
> being bored with simplicity *g*.
>
> also, while the ultimate goal is to null the variables, currently all
> i'm doing is printing out the values of the variables being referred
> to in the arguments being passed to clear_input() and clear_input2(),
> on the premise if i can't read the existing data in those variables, i
> won't be able to write new data to those variables.
i didn't follow the thread closely but what you are missing could be the
name of the package where the variables are declared. without it, Perl
search the variable in the current package (and it's Export list for one)
and if it can't find it, it wouldn't be able to use it. also remember that
once you tag your variables with 'my' ('our' is ok of course), they won't
exist in the symbol table and thus you can't effectively symbolic
de-reference them. to give you an idea, take a look at the following
script:
#!/usr/bin/perl -w
use strict;
package Apple;
sub apple{
#--
#-- without caller(), the following won't
#-- work because Perl doesn't know which symbol
#-- table to search for $j
#--
my $i = caller() . '::' . shift;
no strict 'refs';
print "$$i\n";
#--
#-- change it
#--
$$i = 5678;
}
package main;
#--
#-- if you tag $j with 'my', you are telling
#-- Perl that you don't want $j to be in the symbol
#-- table of main which you can't effectively symbolic
#-- de-reference it in your Apple package
#--
our $j = 1234;
Apple::apple('j');
#--
#-- reflect new value
#--
print "$j\n";
__END__
prints:
1234
5678
i don't know why you want symbolic reference but many people (including me)
will tell you that this's very dangerous and you should avoid that as much
as possible.
david
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