#! /usr/bin/perl -l

$a="fergal";
$p=\$a+0;
print $p;
$x=unpack("P9", pack 'j', $p);
print length($x);
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Anyway, this is not really what I'm getting at. You can't use this to try treat the memory for a perl array variable as a perl string variable, at most this allows you to treat the memory for a perl array variable as the C string inside a perl string variable.

Imagine you could twiddle the pointer inside a perl reference value, it still wouldn't be weakly typed. If you point the ref at a bit of memory that contains a perl string variable then it will become a string-ref if you point it at an array variable it will become an array-ref (I think this is the case although I'm not an XS whizz and I don't have time to test it as I'm going on holidays in an hour!). So for perl to be weakly typed I would have to wrong and the language would have to have this reference twiddling feature built in.

Demo? I've had this code lying around for ages:

#!/usr/bin/perl -wl

use strict;

my $target = 'IHBT';

print "target contains       : $target";

my $target_address = \$target + 0; # nummify
my $native_version    = pack 'L', $target_address;
my $pointer = pack 'P', $native_version;

print "target address        : ", sprintf('%x', $target_address);

my $sv = unpack('P4', $native_version);
print "deref'd packed (sv)   : ", sprintf('%x', unpack('L', $sv));

my $pv = unpack('P4', $sv);
print "deref'd sv (pv)       : ", sprintf('%x', unpack('L', $pv));

my $value = unpack('P' . length($target), $pv);
print "deref'd pv (value)    : ``$value''\n";
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I hope it helps. :)

--
Rocco Caputo - http://poe.perl.org/

You're just missing a few pointer dereferences. The pack("j",...) does the int->ptr conversion. The first unpack does SvANY( $p ) to find $a. The next one doesSvANY( $a ) to find its xpv struct. The next and final unpack is dereffing the xpv_pv pointer to read the C string.

$x = unpack "P9", unpack "P4", unpack "P4", pack "j", $p;

This is all *reading* addressable memory. Writing back to it is a completely different trick involving faking structs for B to convince perl that strings that you control are real perl structures. You can then fake up a perl string where the pointer goes to any arbitrary location.

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