reference of hash

[steph_bow]

Hello Dear Monks

I am usin a hash reference in my program but I made a mistake. Could you check ? Thanks. I just wrote the parts where the problem lies. I have not written what has been tested.

I have updated the code with bits I found important to write

sub flow_count{
    
    my $HASH_OF_FLOW;
    my $view = $_[0]; # FTFM or CTFM

        ...
        ...
        foreach my $file(@FILES_IN_THE_FOLDER){
           my $key = "$reg;$date";
           # M2 is a number which has been computed
       $HASH_OF_FLOW->{'$key'} = 'M2';
        }

     return $HASH_OF_FLOW; 
}

my $FTFM_HASH_OF_FLOW = flow_count("FTFM");
my $CTFM_HASH_OF_FLOW = flow_count("CTFM");
my @FTFM_KEYS = keys %$FTFM_HASH_OF_FLOW;


foreach my $key(@FTFM_KEYS){
    my $FTFM_CTFM_diff = $FTFM_HASH_OF_FLOW{$key} - $CTFM_HASH_OF_FLOW
+{$key};
    print $OUTFILE "$key;$FTFM_HASH_OF_FLOW{$key};$CTFM_HASH_OF_FLOW{$
+key};$FTFM_CTFM_diff\n";
}

[toolic]

    $HASH_OF_FLOW->{'$key'} = 'M2';

Single quotes prevent variable interpolation of $key. You probably want:

    $HASH_OF_FLOW->{$key} = 'M2';

[radiantmatrix]

I see a couple of problems:

1. Inside flow_count, you say $HASH_OF_FLOW->{'$key'} = 'M2'. By surrounding $key with single quotes, you're getting the string '$key' rather than the value in the variable $key. Drop those quotes.
2. In your foreach loop, you're not dereferencing your hashrefs. For example, where you say $FTFM_HASH_OF_FLOW{$key}, you should be saying $FTFM_HASH_OF_FLOW->{$key}.
3. You're not using strict and warnings -- if you were, you'd have been scolded for #2, above.

As an aside, you may want to read up on How (Not) To Ask A Question; it will advise you on how to get better responses. For example, providing the text of the error you're receiving would have been useful.

You might also want to take a look at Data::Dumper; if you'd used that to inspect the contents of $HASH_OF_FLOW, you'd have very quickly seen problem #1.