P0w3rK!d has asked for the wisdom of the Perl Monks concerning the following question:

Hello,

I have a piece of code calls a function in a module A. That function calls a function in module B along with using one of the global variables in module B as an argument to that function. 

package Foo::A;

use 5.008;
use strict;
use warnings;

require Exporter;
#use AutoLoader qw(AUTOLOAD);
use Carp;
use Foo::B ':all';

our @ISA = qw(Exporter);

@EXPORT or @EXPORT_OK

our %EXPORT_TAGS = ( 'all' => [ qw(
    aMethod
    ...
) ] );

our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
our @EXPORT = qw();
our $VERSION = '1.00';

...
sub aMethod {

    bMethod("$OURVAR test data");
}
...

1;
__END__

############################################3

package Foo:B;

use 5.008;
use strict;
use warnings;

require Exporter;
#use AutoLoader qw(AUTOLOAD);

our @ISA = qw(Exporter);

our %EXPORT_TAGS = ( 'all' => [ qw(
    bMethod
    $OURVAR
) ] );

our @EXPORT_OK = ( @{ $EXPORT_TAGS{'all'} } );
our @EXPORT = qw();
our $VERSION = '1.00';

# something like this
sub bMethod {
    my $foo = shift;
    print "$foo\n";
}
...

1;
__END__

[download]
The error is as follows:

Use of uninitialized value in concatenation (.) or string at C:/Perl/site/lib/Foo/B.pm line 141.

The error refers to the $OURVAR which is exported by the "B" module along with the bMethod().

Why am I getting this error? How do I fix it?

Thank you :)

-P0w3rK!d

Replies are listed 'Best First'.
Re: Use of uninitialized value in concatenation (.) or string
by japhy (Canon) on May 20, 2003 at 14:28 UTC
    You never defined $OURVAR. Put something in it, or it will remain uninitialized.

    _____________________________________________________
    Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
    s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

[reply]
[d/l]
      Funny. I thought I replied to this. ...

      I put in a request to fix the code example. For some reason, my cut+paste failed when I copied things over in the "real" module. The code you see is just an example of the problem. Nonetheless, I fixed the "real" problem.

      And yes...it is a warning.

      Thanks :)

      -P0w3rK!d

[reply]
Re: Use of uninitialized value in concatenation (.) or string
by KPeter0314 (Deacon) on May 20, 2003 at 14:48 UTC
    Japhy is right, initialization is the key.

    I sheepishly admit I come from the old school where declaring variables is necessary. A sideline from starting as a COBOL, RPG, and Transact programmer. It became a habit and use strict; requires it. See Perldoc strict for more info.

    This will get you there: 

    use vars qw($OURVAR) = ();

    [download]
    Add other variables inside the parens to initialize them too.

    -Kurt

[reply]
[d/l]
      Read the code again. use strict; is everywhere.
      Thanks :)
[reply]
        What is meant is that use strict; requires that variables be initialized.

        To quote from the perldoc:strict where strict vars is implied by not specifying what to be strict about: 

             "strict vars"
           This generates a compile-time error if you access a
           variable that wasn't declared via "our" or "use vars",
           localized via "my()", or wasn't fully qualified.

        [download]
        The use vars qw($OURVAR) = (); pragma actually declares the variable $OURVAR and initializes it to a known null value instead of leaving it uninitialized. Perl cares about the difference.

        -Kurt

[reply]
[d/l]
Re: Use of uninitialized value in concatenation (.) or string
by Joost (Canon) on May 20, 2003 at 14:43 UTC
    Why am I getting this error? How do I fix it?

    • <pedantic>It's not an error, it's a warning</pedantic>
    • use our $OURVAR = "somevalue" in module B
    perldiag or use diagnostics; will probably help you.

    Joost 

    -- 
#!/usr/bin/perl -np
BEGIN{@ARGV=$0}s(^([^=].*)|=)()s;
=Just another perl hacker\

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