在perl中初始化哈希引用

Question

The following Perl code prints Value:0 . Is there a way to fix it other than by adding a dummy key to the hash before hash reference is passed to the subroutine ?

#!/usr/bin/perl 
use warnings;
use strict;

my $Hash;

#$Hash->{Key1} = 1234;

Init($Hash);

printf("Value:%d\n",$Hash->{Key});

sub Init
{
    my ($Hash) = @_;
    $Hash->{Key}=10;
}

Answer 1

Initialize an empty hash reference.

#!/usr/bin/perl 
use warnings;
use strict;

my $Hash = {};

Init($Hash);

printf("Value:%d\n",$Hash->{Key});

sub Init
{
    my ($Hash) = @_;
    $Hash->{Key}=10;
}

Answer 2

I know that an answer has already been accepted, but I figured it was worth explaining why the program acted this way in the first place.

The hash is not created until the second line of the Init function ( $Hash->{Key}=10 ), which automatically creates a hash and stores a reference in the $Hash scalar. This scalar is local to the function, and has nothing to do with the $Hash variable in the body of the script.

This can be changed by modifying the way that the Init function handles its arguments:

sub Init {
    my $Hash = $_[0] = {};
    $Hash->{'Key'} = 10;
}