How do I add entries to a hash array in a different scope?

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

I have a hash array that I want to use to hold useful information for debugging purposes for a large Perl program.

The problem is that while I can add an entry to a hash in a subroutine, when the program flow returns to main(), the entry in the hash is no longer there, due to problems with the scope.

The code is as this:

our %debug = ();
$debug{'level'} = 1;
$debug{'stack'}[0] = "main()";

$rv = MyModule::testStack(\%debug);

my @t = $debug{'stack'};
my $CountMain = scalar (@t);
print "$CountMain \n";  # This prints 1

#Now there is another subroutine defined in another module:

sub testStack {
  my $ptr = $_[0];
  my %h = %$ptr;
  my @a = $h{'stack'};
  push (@a, "testStack()");

  my $count = scalar (@a);
  print "$count \n";  # This prints 2

  return 1;
}
[download]

I am passing the hash array "debug" to testStack() by reference. Yet, when I want to add an element to the array debug{'stack'} in testStack(), it is not added to the debug of main()'s scope.

How do I get around this problem? I would like to refer to $debug{'stack'} as an array so I can use push/pop functions.

Comment on How do I add entries to a hash array in a different scope? Download Code

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Re: How do I add entries to a hash array in a different scope? by jettero (Monsignor) on Oct 10, 2009 at 11:41 UTC
This isn't really a scope question. The problem is: you can't store an array in a hash. You can store an arrayref though. `use strict; # important use warnings; # important my %debug; # you rarely want our (or local) test_push(\%debug); print "hey, it works: $_\n" for @{ $debug{stack} # this probably contains our arrayref \|\| [] # but if it doesn't, don't error out please }; sub test_push { # avoid camel case (imo) my ($debug) = @_; push @{ $debug->{stack} }, "lol"; # avoid unnecessary derefs # or my $ar = $debug->{stack}; push @$ar, "lol2"; return; }` [download] Check out docs like perlreftut, perldata, perllol for further information. -Paul	[reply] [d/l]
Re: How do I add entries to a hash array in a different scope? by zwon (Abbot) on Oct 10, 2009 at 11:43 UTC
You didn't show how are you adding element into `$debug{stack}` in testStack, but if `$ptr` contains reference to `%debug`, you can do it as follows: `push @{$ptr->{stack}}, $new_elem; $ptr->{stack}[7] = $new_value;` [download] Also see References quick reference.	[reply] [d/l] [select]
Re: How do I add entries to a hash array in a different scope? by NetWallah (Canon) on Oct 10, 2009 at 15:36 UTC
Your statement `my %h = %$ptr;` [download] makes a (shallow) COPY of the hash, via the hash-ref. Then `my @a = $h{'stack'};` [download] make a COPY of the array-ref into the zero'th element of @a (probably not what you intended). zwon(++)'s solution works directly off the references to the original objects. If you want to use the syntax you are attempting, you need to make symbolic references, instead of copies: `local h=$ptr; # %h now is synonymous with %debug local a=\$h{stack}; # @a is another name for the anon array @{ $h{ +stack} } # Now, a 'push' into @a will change %debug` [download] (Untested). See 'Typeglobs and Filehandles' in 'Perldata'. You will need to tweak 'use strict', to enable typeglobs. Potentia vobiscum ! (Si hoc legere scis nimium eruditionis habes)	[reply] [d/l] [select]