What does the hexadecimal number in a reference to an array, hash, etc. indicate?

Question

When printing a reference to an array, hash, etc, what is that hexadecimal number in brackets?

perl -e 'print []'

Gives an output like: ARRAY(0x9acb830)

What is 0x9acb830 exactly? If I print the same ref again, this number changes.

Answer 1

If you print the same ref again the number should remain the same; the number is the actual address of the SV header for the referred to thingy.

Answer 2

It's basically the memory location of the array. Perl is trying to let you know you're trying to print a reference and not a scalar value.

Try this:

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

my @foo = qw(one two three four five);
print @foo . "\n";   #Prints the array in a scalar context (five items)
print \@foo . "\n";
print $foo[1] . "\n";
print \$foo[1] . "\n";

5
two
SCALAR(0x100804ff0)
ARRAY(0x10082ae48)

Notice that when I print a reference, Perl tries to do the right thing. Instead of attempting to print some strange value, it tells you that you're trying to print a scalar or array reference.