Re: System header structs vs custom struct

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

On Jan 13, 2006, at 6:37 PM, SPYRIDON PAPADOPOULOS wrote:

> i am creating a packet capture tool on a FreeBSD 5.4 - RELEASE for  
> my dissertation using pcap. I am using the system headers in /usr/ 
> include/net/ and /usr/include/netinet/ directories to start  
> decoding EN10MB, ip, tcp, udp, icmp etc packets.
> I am not working too long on it am i am not an experienced C  
> programmer.
> However i lately tried to test the thing on slackware (the OS my  
> project supervisor preferes) and i had many errors mostly about  
> values in system header structures.

And now you know one of the reasons why tcpdump has its own headers  
for packet data structures.

> I was thinking since the beginning that it doesn't worth it to copy  
> more or less the structs from tcpdump to describe protocol headers  
> since i have them already, so i kept staying with the system's  
> headers.
> Now i am realising that maybe this is a very good reason for  
> changing to custom structures.
> Any advice

I'd advise you to go to custom structures, so your program isn't as  
dependent on what the headers on a particular OS define - that's why  
tcpdump uses *its* own header files.
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