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

I build a hash and then, I create an array of this hash and want to modify the value of one key of the hash. Although I assign the array to the built hash, it just gets the first key and value:

perl test.pl curr CD 0 AB 1 currhash CD 0 AB 0

and if I pass the reference of the hash, the hash gets modified which is not desired perl test.pl curr AB 1 currhash CD 0 AB 0

What's wrong? see the attached program Thanks carol 

#!/usr/bin/perl

sub parseFiles{
   @currArr=();

    push @currArr,'+1';
    push @currArr,'u';
    push @currArr,%currHash; # push @currArr,%currHash; in the first c
+ase

    $curr{"my"}=[@currArr];

    $curr{"my"}->[2]{"AB"}++;

    #print scalar(keys %{$curr{"my"}->[2]}), "\n";

    #print  $curr{"my"}->[0], " ", $curr{"my"}->[1], "\n";

print "curr\n";

    foreach (keys %{$curr{"my"}->[2]}){
            print  $_, " ", $curr{"my"}->[2]{$_}, " ";
    }
    print "\n";

print "currhash\n";

    foreach (keys %currHash){
            print $_, " ", $currHash{$_}, " ";
    }
    print "\n";
}
 
sub storeHash{
        $currHash{"AB"}=$currHash{"CD"}= 0;
}

sub main{
    storeHash();
    parseFiles();
}

main();

[download]

Replies are listed 'Best First'.
Re: array of hash
by choroba (Cardinal) on May 27, 2014 at 09:35 UTC
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      perhaps I didn't fully understand your comment but i changed my program based on use strict. I still have problem

      If I don't use the hash ref, I get this error Can't use string ("CD") as a HASH ref while "strict refs" in use at ./test.pl line 15.

      and if i use hash ref, I don't get any value for the key CD Don't know why?! curr CD AB 1 currhash CD AB 1

      The desired output is curr CD 0 AB 1 currhash CD 0 AB 0 

      #!/usr/bin/perl
 use strict;

sub parseFiles{
   my @currArr=();
my %curr;
my %tmp = $_[0];

    push @currArr,'+1';
    push @currArr,'u';
    push @currArr,%tmp; # push @currArr,%currHash; in the first case

    $curr{"my"}=[@currArr];

    $curr{"my"}->[2]{"AB"}++;

    #print scalar(keys %{$curr{"my"}->[2]}), "\n";

    #print  $curr{"my"}->[0], " ", $curr{"my"}->[1], "\n";

print "curr\n";

    foreach (keys %{$curr{"my"}->[2]}){
            print  $_, " ", $curr{"my"}->[2]{$_}, " ";
    }
    print "\n";

print "currhash\n";

    foreach (keys %tmp){
            print $_, " ", $tmp{$_}, " ";
    }
    print "\n";
}
 
sub storeHash{
my %currHash;

        $currHash{"AB"}=$currHash{"CD"}= 0;
    return %currHash;
}

sub main{
my %currHash;
    %currHash=storeHash();
    parseFiles(%currHash);
}

main();

      [download]
[reply]
[d/l]
        Can't use string ("CD") as a HASH ref while "strict refs" in use

        [download]

        Yes, that's the point you perhaps didn't fully understand. $cur{my}[2] is "CD", you can't dereference it as a hash under strict. Without strict, it's understood as symbol reference and the hash %CD is used, as I demonstrated in my original reply.

        لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
[reply]
[d/l]
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      Cont.

      by the way, despite use strict, the value of %currHash is modified. So the problem is still there.

[reply]
Re: array of hash
by Lotus1 (Vicar) on May 27, 2014 at 14:59 UTC
    I build a hash and then, I create an array of this hash...
    push @currArr,%currHash;

    As choroba pointed out you are not building an array of hashes here. An array of hashes is actually an array of hash references. The Perl Data Structures Cookbook shows a few different ways to create arrays of hashes. However, from your example code it isn't obvious that an array of hashes is what you need.

    $curr{"my"}->[2]{"AB"}++;

    This looks like you're trying to use a hash of arrays of hashes. Can you describe the data structure you need or the problem you are trying to solve? Maybe check out some tutorials for perl data structures.

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      Choroba's solution, push @currArr,{%currHash}; works like a charm.

      Many thanks

[reply]

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