passing (hash)refs through subroutines

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

Dear monks,

In a program I've got two subroutines, one of these initializes a reference to a DB connection, the other wants to use this reference through a parameter hash.

I thought someting like this would work:

 my %parameterhash;
 my $hashref = \%parameterhash;
 a($hashref);
 b($hashref);
sub a{
 my $hash_ref = @_;
 my $dbconnection= makeDBconnection();
 my $handle = \$dbconnection;
 connect($handle);
 $hash_ref->{dbhandle} = $handle;
}

sub b{
 my $hash_ref = @_;
 my $hand = $hash_ref->{dbhandle};
 connect($hand);
}
[download]

The first connect works fine, the second fails with error message:
Use of uninitialized value in connect at line ##

I started playing with (de)referencing but I don't find what's wrong. Any help would be appreciated

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Re: passing (hash)refs through subroutines by wfsp (Abbot) on Nov 03, 2009 at 10:58 UTC
With regards the question in the title, in both subs you need either `my ($hash_ref) = @_;` [download] or `my $hash_ref = shift;` [download] `@_` is an array. Update Just to note your snippet doesn't compile `Not enough arguments for connect at C:\perm\dev\monk.pl line 15, near +"$handle)"` [download] `connect` is a perl function and after changing the name to `my_connect` we then get `Can't use string ("1") as a HASH ref while "strict refs" in use at C:\ +perm\dev\monk.pl line 16.` [download] Line 16 is in `sub a` so for me the first connect doesn't work fine (because I'm using `strict` and `warnings`). What the error is telling you is that `my $hash_ref = @_;` sees the array in scalar context and returns the length of the array i.e. 1. This compiles and runs but obviously I don't know what your `connect()` or `makeDBconnection()` does. `#!/usr/bin/perl use warnings; use strict; my %parameterhash; my $hashref = \%parameterhash; a($hashref); b($hashref); sub a{ my $hash_ref = shift; my $dbconnection= makeDBconnection(); my $handle = \$dbconnection; my_connect($handle); # line 15 $hash_ref->{dbhandle} = $handle; # line 16 } sub b{ my $hash_ref = shift; my $hand = $hash_ref->{dbhandle}; my_connect($hand); } sub my_connect { } sub makeDBconnection{ }` [download]	[reply] [d/l] [select]

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Re: passing (hash)refs through subroutines
by wfsp (Abbot) on Nov 03, 2009 at 10:58 UTC

my ($hash_ref) = @_;
[download]

my $hash_ref = shift;
[download]

@_

Update
Just to note your snippet doesn't compile

Not enough arguments for connect at C:\perm\dev\monk.pl line 15, near 
+"$handle)"
[download]

connect

my_connect

Can't use string ("1") as a HASH ref while "strict refs" in use at C:\
+perm\dev\monk.pl line 16.
[download]

sub a

strict

warnings

my $hash_ref = @_;

This compiles and runs but obviously I don't know what your connect() or makeDBconnection() does.

#!/usr/bin/perl

use warnings;
use strict;

 my %parameterhash;
 my $hashref = \%parameterhash;
 a($hashref);
 b($hashref);

sub a{
 my $hash_ref = shift;
 my $dbconnection= makeDBconnection();
 my $handle = \$dbconnection;
 my_connect($handle);             # line 15
 $hash_ref->{dbhandle} = $handle; # line 16
}

sub b{
 my $hash_ref = shift;
 my $hand = $hash_ref->{dbhandle};
 my_connect($hand);
}

sub my_connect {
}

sub makeDBconnection{
}
[download]

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