Passing a file handle and two arrays to a function by reference.

[subr01]

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;
}
}

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

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

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.

[toolic]

You pass scalars to your sub. Use scalars in your sub:

sub myfunc {
    my ($file, $aref1, $aref2) = @_;
    my @array1 = @{ $aref1 };

Pass by Reference

[Athanasius]

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) = @_;

$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,

[neilwatson]

You are passing references to your arrays, thus your sub should be using $array1 and $array2.

[Anonymous Monk]

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

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

[neilwatson]

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];

}

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'"
   );

[BillKSmith]

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.