Unexpected Network conversion behaviour for unpack

GrandFather has asked for the wisdom of the Perl Monks concerning the following question:

I have some code that is pulling appart a file and is using unpack with a 'n' conversion to extract what should be a 16 bit signed big endien number. I'm getting an unsigned result. Is that expected behaviour?

The following code demonstrates the issue:

use strict;
use warnings;

print "Network (16 bits) pack/unpack: ", unpack ('n', pack ('n', -1)),
+ "\n";
print "Short pack/unpack: ", unpack ('s', pack ('s', -1)), "\n";
print "Network (32 bits) pack/unpack: ", unpack ('N', pack ('N', -1)),
+ "\n";
print "Long pack/unpack: ", unpack ('l', pack ('l', -1)), "\n";
print "Network (cvt) pack/unpack: ", unpack ('s', pack ('s', unpack ('
+n', pack ('n', -1)))), "\n";
[download]

Prints:

Network (16 bits) pack/unpack: 65535
Short pack/unpack: -1
Network (32 bits) pack/unpack: 4294967295
Long pack/unpack: -1
Network (cvt) pack/unpack: -1
[download]

This is using AS Perl 5.8.7 (813) on XP.

DWIM is Perl's answer to Gödel

Comment on Unexpected Network conversion behaviour for unpack Select or Download Code

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Re: Unexpected Network conversion behaviour for unpack by Corion (Patriarch) on Feb 09, 2006 at 23:12 UTC
I think that `nNvV` return unsigned results: `n An unsigned short in "network" (big-endian) order. N An unsigned long in "network" (big-endian) order. v An unsigned short in "VAX" (little-endian) order. V An unsigned long in "VAX" (little-endian) order.` [download]	[reply] [d/l] [select]
Re^2: Unexpected Network conversion behaviour for unpack by bart (Canon) on Feb 10, 2006 at 01:16 UTC
This appears to be a fix in perlfunc, the older version on this site doesn't mention "unsigned" anywhere: `n A short in "network" (big-endian) order. N A long in "network" (big-endian) order. v A short in "VAX" (little-endian) order. V A long in "VAX" (little-endian) order. (These 'shorts' and 'longs' are _exactly_ 16 bits and _exactly_ 32 bits, respectively.)` [download]	[reply] [d/l]
Re^2: Unexpected Network conversion behaviour for unpack by GrandFather (Saint) on Feb 09, 2006 at 23:23 UTC
Damn, I think I'll throw the Camel in the bin. It and the Perl Pocket Reference just say words to the effect that: n Short in network (big endien) order. Thanks for that. I should have looked at perlfunc earlier, I'd have saved a couple of hours! DWIM is Perl's answer to Gödel	[reply]