How do I pass a local variable to a Perl subroutine and modify it?
use strict;
use warnings;
sub modify_a
{
# ????
}
{
my $a = 5;
modify_a($a);
print "$a\n"; # want this to print 10
}
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2 Answers
sub modify_a {
$_[0] *= 2;
}
The elements of @_ are aliases to the values passed in, so if you modify that directly, you'll change the caller's values. This can be useful sometimes, but is generally discouraged as it is usually a surprise to the caller.
3 Comments
nahano
What if I have a long list of variables that are passed in and I want to refer to them by name?
Tanktalus
@jeffythedragonslayer - check out the Data::Alias module. References are better, though, IMO, because of the surprise factor.
nahano
I was just about to say I figured it out with references, I'll check out Data::Alias too.
A less magical approach is to pass a reference.
use strict;
use warnings;
sub modify_a
{
my ($a_ref) = @_;
$$a_ref = 10;
}
{
my $a = 5;
modify_a(\$a);
print "$a\n";
}
1 Comment
stevieb
You should always discourage people from using
$a or $b as variables, as they are reserved specifically for the sort function.