Perl subroutine array and scalar variable parameters

Question

How exactly can I pass both scalar variables and array variables to a subroutine in Perl?

 my $currVal = 1;
 my $currValTwo = 1;
 my @currArray = ('one','two','three');
 my @currArrayTwo =('one','two','three');

 &mysub($currVal, $currValTwo,\@currArray, \@currArrayTwo);

 sub mysub() {

     # That doesn't work for the array as I only get the first element of the array
     my($inVal, $inValTwo, @inArray, @inArrayTwo) = @_;
 }

I have been looking for this question all day. Thank you for asking this!!! — Rob L
– Rob L, Commented Mar 25, 2014 at 0:19

Blagovest Buyukliev · Accepted Answer · 2011-06-09 14:32:43Z

15

You need to fetch them as references because you've already passed them as references (by using the \ operator):

my($inVal, $inValTwo, $inArray, $inArrayTwo) = @_;

and then use the references as arrays:

@{$inArray}

edited Jun 9, 2011 at 14:32

answered Jun 9, 2011 at 14:23

Blagovest Buyukliev

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TLP · Accepted Answer · 2011-06-09 14:50:51Z

6

You pass the arguments as references, so you need to dereference them to use the values. Be careful about whether you want to change the original array or not.

sub mysub {
    my($inVal, $inValTwo, $inArray, $inArrayTwo) = @_;
    @{$inArrayTwo} = ('five','six','seven');
}

This will change the original @currArrayTwo, which might not be what you want.

sub mysub {
    my($inVal, $inValTwo, $inArray, $inArrayTwo) = @_;
    my @ATwo = @{$inArrayTwo};
    @ATwo = ('five','six','seven');
}

This will only copy the values and leave the original array intact.

Also, you do not need the ampersand in front of the sub name, from perldoc perlsub:

If a subroutine is called using the & form, the argument list is optional, and if omitted, no @_ array is set up for the subroutine: the @_ array at the time of the call is visible to subroutine instead. This is an efficiency mechanism that new users may wish to avoid.

You do not need empty parens after your sub declaration. Those are used to set up prototypes, which is something you do not need to do, unless you really want to.

answered Jun 9, 2011 at 14:50

TLP

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2 Comments

user391986 Over a year ago

Any idea how I can pass an XML::Writer by reference"? How would I dereference it in the subroutine?

TLP Over a year ago

I am not familiar with that module, but I would say any object gets passed with a scalar value.

Peter Mortensen · Accepted Answer · 2016-04-11 23:41:19Z

0

So, for example: This is a using statement to search something in an array:

use List::Util qw(first);

This is the sub declaration:

sub GetIndex($$$);

This is the call to the sub (last parameter is: Default index value to give back if not found)

$searchedIndex = GetIndex(\@theArr, "valuesearched", 1);

This is the routine:

sub GetIndex($$$)
{
    my $inArray=shift;
    my @theArray= @{$inArray};
    my $searchedTag= shift;
    my $defaultVal= shift;

    my $retVal = first { $theArray[$_] eq $searchedTag} 0 .. $#theArray;
    if ((! defined $retVal)|| ($retVal<0)||($retVal>@theArray))
    {
        $retVal = $defaultVal;
    }
    return $retVal;
}

edited Apr 11, 2016 at 23:41

Peter Mortensen

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answered Mar 12, 2013 at 16:09

Cesare Imperiali

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