but the referrence still exist

Of course. You never changed $arr_r.

Is it same as "Dangling Pointer" in C???

No. A dangling pointer is a pointer to something that doesn't exist anymore. You didn't even try to get rid of the array — undef simply empties it — so there's definitely no dangling pointer.

Even if you tried to get rid of the array (like in the following example), you wouldn't get a dangling. The reference would keep it alive until you got rid of the reference too. 

my $ref;
{
   my @array = 'element';
   $ref = \@array;
}              # Because the array is lexically scoped (my),
               # the array would normally be freed here*,
               # but the reference is keeping it alive.

print "$ref->[0]\n";  # Prints 'element'

$ref = undef;  # The scalar stops referencing the array,
               # so it's freed here.

[download]

Think of my as new. 

my @outer;
for (1..2) {
   my @inner = "pass $_";
   push @outer, \@inner;
}

print "@{ $outer[0] }\n";  # pass 1
print "@{ $outer[1] }\n";  # pass 2

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But realize that Perl will get rid of something automatically as soon as noone needs it anymore. For example, if that entire piece of code was in a sub, @outer and the two @inner would get freed by the subroutine exit code*.

One catch: Perl sometimes doesn't realize nothing needs a value anymore. It occurs when you have a reference cycle like the following: 

for (1..10) {
    my $r1;
    my $r2 = \$r1;
    my $r3 = \$r2;
       $r1 = \$r3;
}

# You have just leaked 30 variables.

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* — Aside from optimisations that would only confuse the issue.

In reply to Re: Dangling Pointer::perl referrence by ikegami
in thread Dangling Pointer::perl referrence by Anonymous Monk

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