Re: Help with pointer to unions

[Guy Harris <guy () alum mit edu>]

On Apr 18, 2011, at 7:27 PM, Alex Lindberg wrote:

> The protocol.  It is a custom protocol used for some of my companies control equipment.
>
> The structure of the protocol packet varies with the release version of the system.  While there are may similarities 
> between versions, the  structures are different enough to have different sizes and makeup etc.
>
> I could create separate dissectors for each version, but that seems like a lot of duplicate effort.  By using an over 
> loaded pointer, the coding would be much easier.  I cannot create different complied version of the protocol, one for 
> each version.
>
> Or is it possible to delay the typing of a variable to runtime?  In that case the type could be control by changing 
> the "version" variable via the preferences during dissector initialization.

Many Wireshark dissectors don't use structures to dissect the packet - they just pull each field out with a 
proto_tree_add_item() call and/or fetch the value with tvb_get_ calls and put them into the tree with other 
proto_tree_add_ calls.  A dissector written in that fashion could use common code for the common parts and use an if 
statement or a switch, and different code, for the parts that differ.

If I were writing the dissector, that's how I'd do it.
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