Re: Problems with libpcap and C++

[Ury Segal <ury_segal () yahoo com>]

The buttom of the problem is this:

You excpect libpcap to call X::dumper in
the context of an instance of class X.
(The "real" first parameter of "X::dumper"
is a variable named "this" of the type "X*".)

But the libpcap API is not defining a 

> `void (X::)(u_char*,  const pcap_pkthdr*, const
> u_char*)'

Just a

> void (*)(u_char*, const pcap_pkthdr*, const
> u_char*)

Which is what the compiler is telling you.


Therefore, you cannot pass a non-static member
function to libpcap. You can make dumper() a 
static member.


--- David Rosal <david.rosal () upf edu> wrote:

> Hello.
>
> I'm writing a packet sniffer in C++ using
> libpcap-0.9.4.
>
> I've tried to use a class function member as a
> callback for 
> pcap_loop(), but the compiler complains that
> arguments don't 
> match. The code is something like this (I have
> simplified it):
>
> 8<-----------------------------
>
> class X
> {
>       public:
>       // This is the callback, defined below
>       void dumper(u_char *u, const struct
> pcap_pkthdr *h,
>               const u_char *p);
> };
>
>
> void X::dumper(u_char *u, const struct
> pcap_pkthdr *h, const
>       u_char *p)
> {
>       // stuff...
>       pcap_dump(blah, blah, blah);
> }
>
>
> int main()
> {
>       X x;
>       
>       // Open pcap, etc...
>       
>       pcap_loop(p, -1, x.dumper, 0);
> }
>
> ----------------------------->8
>
> And g++ says this:
>
> In function `int main()':
> sniffer.cc:645: error: argument of type `void
> (X::)(u_char*, 
> const pcap_pkthdr*, const u_char*)' does not
> match `void 
> (*)(u_char*, const pcap_pkthdr*, const
> u_char*)'
>
> This is not a warning but an error, so I cannot
> compile the program.
>
> Is there any trick to fix this? Am I missing
> something?
>
> Should I avoid C++ and use C instead (don't say
> that please...)
>
>
> Thanks.
>
>
> __david
> -
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--ury
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