Hello Monks, I need your help!

I'm pretty new to programming and have been trying to understand (un)pack. However, the problem I have is trying to determine the templates.

Here is a small snippet of code from ChaosReader (http://chaosreader.sourceforge.net/)

        ### Unpack IP data
        ($ip_verNihl,$ip_tos,$ip_length,$ip_ident,$ip_flagNfrag,
         $ip_ttl,$ip_protocol,$ip_checksum,@ip_src[0..3],
         @ip_dest[0..3],$ip_data) = unpack('CCnnnCCa2CCCCCCCCa*',
         $ether_data);

[download]

How am I supposed to know that "CCnnnCCa2CCCCCCCCa*" is the correct template when decoding IP packets? It's network data so I would think I should be using "n" or "N" all the time, but it's only used three times in the above code.

Any help is appreciated.

In reply to Need help with (un)pack templates by Subop

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