subr01 has asked for the wisdom of the Perl Monks concerning the following question:

How to pass a filename or a filehandle, two arrays to a function? I have done this:

open INPUT,"$old";
my (@arrayold,@arraynew);
myfunc(*INPUT,\@arrayold,\@arraynew)


sub myfunc {
my ($file,@array1,@array2) = @_ ;
my $j = 0;
my $k = 0;
while (my $line = <$file)
{ my($word1,$word2) = split(",",$line);
  $array[$j++] = $word1;
  $array[$k++] = $word2;
}
}

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As you can guess, my function reads a file which has info like:

1,//http:abcd
2,//http:avcd

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into two arrays one containing the number and the other containing the address. I am only getting blank arrays. Am I passing it wrong? Kindly help.

Replies are listed 'Best First'.
Re: Passing a file handle and two arrays to a function by reference.
by toolic (Bishop) on May 26, 2015 at 13:34 UTC
    You pass scalars to your sub. Use scalars in your sub: 
    sub myfunc {
    my ($file, $aref1, $aref2) = @_;
    my @array1 = @{ $aref1 };

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    Pass by Reference
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Re: Passing a file handle and two arrays to a function by reference.
by Athanasius (Archbishop) on May 26, 2015 at 13:46 UTC

    Hello subr01,

    I am only getting blank arrays.

    Just a note to add to the answers already given: when assigning to an array, it slurps up all the elements remaining on the right-hand side of the assignment. So after:

    myfunc(*INPUT, \@arrayold, \@arraynew)

...

sub myfunc
{
    my ($file, @array1, @array2) = @_;

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    $file contains the fileglob *INPUT, @array1 contains two elements (both references), \@arrayold and \@arraynew, and @array2 is indeed empty.

    Which is why, when assigning a list of elements to a list of variables, the only place it makes sense to include an array variable on the left-hand side is at the end.

    Hope that helps,

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re: Passing a file handle and two arrays to a function by reference.
by neilwatson (Priest) on May 26, 2015 at 13:32 UTC
    You are passing references to your arrays, thus your sub should be using $array1 and $array2.

    Neil Watson
    watson-wilson.ca

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      ... and you will have to dereference the arrays to store stuff in them:

      $array1->[$j++] = ...

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Re: Passing a file handle and two arrays to a function by reference.
by neilwatson (Priest) on May 26, 2015 at 13:58 UTC

    I like named params when a sub takes multiple args. 

    mysub(
   FH => *INPUT,
   arr1 => \@arr1,
   arr2 => \@arr2
   );

sub mysub
{
   my %args = @_;

   my $first = $args{arr1}->[0];

}

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    As a bonus you can also have default values 

    sub named_params_with_defaults
   {
      my %args = (
         one => 'default value',
         two => 'default value',
         @_, # Will override the above values.
      );
   }

   named_params_with_defaults(
      one => "override arg 'one'"
   );

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    Neil Watson
    watson-wilson.ca

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Re: Passing a file handle and two arrays to a function by reference.
by BillKSmith (Monsignor) on May 26, 2015 at 17:43 UTC
    I recommend that you also use lexical scalars as filehandles (Refer: open). One of their biggest advantages is that they can be passed as simply as any other scalar.
    Bill
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