refs and hashes

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

Hi, I wrote the following piece of code :

open(VHD,"$vhd_file") || die "Can't open $vhd_file $!\n";
while(<VHD>){

  # find all the entities in the current file
  if (/entity\s+(\w+)\s+is/i) {
    $1{'name'} = $1;
    $1{'fname'} = $vhd_file;
    push @entities, \%1;
  }
 if (/architecture (\w+) of (\w+) is/i ... /end $1\;/i) {
    # we are in the architecture of the entity.
    my $arch_entity = $2;
    # match  instance_name : entity
    if (/^\s*(\w+)\s*:\s*(\w+)$/) {
      print STDOUT "$1\t$2\t$arch_entity\n";
      # find the entity and add the deps to it
      foreach my $ent (@entities) {
        if ($$ent{'name'} eq $arch_entity) {
          $$ent{'deps'}{$2}++;
        }
      }
    }
  }
}
close VHD;
}
foreach my $ent (@entities) {
  print "$$ent{'fname'}\t$$ent{'name'}\n";
  foreach my $dep (keys %{ $$ent{'deps'} } ) { 
    print "DEP: $dep $$ent{'deps'}{$dep} ";
    print "\n";
  }
}
[download]

However when I run the script only the last entity is printed from the last foreach loop. The problem seems to be that the %1 hash is overwritten by each successive match or something like that. I'm not sure. I thought what I did was ok output :

/proj/dice/external/adelante/24July2002/PowerBteFPGA/PBTE_FPGA/ref/coo
+lrisc/status_816.vhd      status_816
DEP: latchs_reg 34 
DEP: pc_stack_816 11 
DEP: latchr 367 
DEP: latchr_reg 426 
DEP: cr816lu 10 
/proj/dice/external/adelante/24July2002/PowerBteFPGA/PBTE_FPGA/ref/coo
+lrisc/status_816.vhd      status_816
DEP: latchs_reg 34 
DEP: pc_stack_816 11 
DEP: latchr 367 
DEP: latchr_reg 426 
DEP: cr816lu 10 
etc....
[download]

Comment on refs and hashes Select or Download Code

Replies are listed 'Best First'.
Re: refs and hashes by Abigail-II (Bishop) on Jul 29, 2002 at 13:54 UTC
All you push on `@entities` is a reference to the hash %1. Repeatedly. References to the same hash over and over again. And you are overwriting the values of said hash. It would work if, instead of using `%1`, you'd use a lexical hash, but it should be declared inside the same block you are pushing onto `@entities`. Abigail	[reply] [d/l] [select]
Re: refs and hashes by stajich (Chaplain) on Jul 29, 2002 at 13:58 UTC
You could do the following in your first conditional `if (/entity\s+(\w+)\s+is/i) { push @entities, {'name' => $1, 'fname' => $vhd_file}; }` [download] I don't think you really want to do `%1` setting.	[reply] [d/l] [select]
Re: Re: refs and hashes by diarmuid (Beadle) on Jul 29, 2002 at 14:07 UTC
yea . I kinda knew that when I wrote it . doh ! Sorted it now anyway with a hohoh `if (/entity\s+(\w+)\s+is/i) { $entities{$1}{'name'} = $1; $entities{$1}{'fname'} = $vhd_file; }` [download] ta	[reply] [d/l]
Re: refs and hashes by Ay_Bee (Monk) on Jul 29, 2002 at 14:10 UTC
This piece of code seems suspect to me `# find all the entities in the current file if (/entity\s+(\w+)\s+is/i) { $1{'name'} = $1; $1{'fname'} = $vhd_file; push @entities, \%1; }` [download] I think it should be something like `push @entities, \%{$1};` [download] perhaps using the Data::Dumper module would help to debug it, also I would use a hash of hashes rather than a separate hash for each entity. `use Data::Dumper; .... # find all the entities in the current file if (/entity\s+(\w+)\s+is/i) { $hash{$1}{'name'} = $1; $hash{$1}{'fname'} = $vhd_file; push @entities, $1; } .... close VHD; } print Dumper(%hash);` [download] Hope this is of some use Ay_Bee `-_-_-_-_-_-_-_-_-_-_-_- My memory concerns me - but I forget why !!!` [download]	[reply] [d/l] [select]
Re: Re: refs and hashes by dragonchild (Archbishop) on Jul 29, 2002 at 14:32 UTC
`push @entities, \%{$1};` This is not desirable, because this uses a soft reference, which is a (generally) "Bad Thing"(tm), for a host of reasons. Best is to use a lexically-scoped hash or a HoHoH's (like the poster has ended up doing). ------ We are the carpenters and bricklayers of the Information Age. Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.	[reply] [d/l]