chris wrote:

>
>
> Problem fixed:
>
>     packet += sizeof(struct ether_header);
>     iphdr = (struct ip *) packet;
>     printf("%02X packet captured; %d bytes\n", iphdr->ip_p, size);
>
> I guess it had something to do with precedence?
>


No, it does have to do with C basic pointer arithmetics.

If you have pointer to a type, adding a size to it WOULD NOT shift
that pointer to this many bytes:

struct ip *packet;
packet += 1;

In fact, the difference between the packet pointer and its previous
value will be the size of an (struct ip).

So, this code is invalid:

=== cut ===
iphdr = (struct ip *) packet + sizeof(struct ether_header);
=== cut ===

And must be rewritten as:


=== cut ===
iphdr = (struct ip *)(packet + sizeof(struct ether_header));
=== cut ===


--
Lev Walkin
vlm@lionet.info

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