Passing reference to subroutine

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

Hi Monks, I used to pass scalars into subroutine and uses the $#variable to get the length. Now I am passing them as reference as shown below. However, I ca'nt figure out how to get the length. Can anyone advice? Thanks.

my @apple = (1,2,3,4);
my @pear = (5,6,7,8);

&test(\@apple, \@pear);

sub test ()
{
        my ($one, $two) = @_;


foreach ( @{$one} ) {
        print "\n$_";
}
print "\n========================";
foreach ( @{$two} ) {
        print "\n$_";
}



}

print "\nThere are @{$two} items in Two.";

print "\n";
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Re: Passing reference to subroutine by ikegami (Patriarch) on Oct 03, 2008 at 06:29 UTC
For starters, `$#array` doesn't return the length, but the index of the last element (one less than length). Dereferencing Syntax shows how simple it is to convert to using a reference. References Quick Reference goes into more detail. What was `$#array` becomes `$#{ $ref }` which can also be written as `$#$ref` And if you want the size of the array, `@array` (in scalar context) becomes `@{ $ref }` which can also be written as `@$ref`	[reply] [d/l] [select]
Re: Passing reference to subroutine by Narveson (Chaplain) on Oct 03, 2008 at 06:32 UTC
By the time you say `print "\nThere are @{$two} items in Two.";` your `$two` has gone out of scope. Move this print statement inside the sub, and you will get `There are 5 6 7 8 items in Two.` which will lead you to say something like `my $count = scalar @{$two}; print "\nThere are $count items in Two.";` [download]	[reply] [d/l] [select]
Re: Passing reference to subroutine by kubrat (Scribe) on Oct 03, 2008 at 09:02 UTC
Try to make a habit of using strict and warnigs in all of your perl scripts. That would have revealed the out of scope error that Narveson has told you about. `use strict; use warnings;` [download]	[reply] [d/l]
Re: Passing reference to subroutine by aukjan (Friar) on Oct 03, 2008 at 06:33 UTC
Actually $#var gives you the subscript of the last item in the list, the scalar value of @var gives you the number of elements in the list. So if you want the number of elements in a list reference, you can get it by: `my $size = scalar @$var;` [download]	[reply] [d/l]
Re: Passing reference to subroutine by Skeeve (Parson) on Oct 03, 2008 at 06:31 UTC
$# doesn't give you the length but the last index. scalar gives the length. Did you try $#{$variable}? `s$$([},&%#}/&/]+}%&{});#$&&s&&$^X.($'^"%]=\&(\|?{%` `+`.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e	[reply] [d/l] [select]