pcap_dump fucntion is not getting called when used with pcap_loop and pcap_dispatch always return 0

Question

I am simply trying to capture the packets on dev.str() interface and store it in a file which can later be used for analysis.

case 1: pcap_loop- when i used pcap_loop, it called pcap_dump function and printed this line "inside pcap_dump()" infinite times and finally crashed.

case 2: pcap_dispatch - when i used this pcap_dispatch, it always returned with 0 and never entered pcap_dump function.

what does this mean? I have no pcap_setfilter.

Please suggest on how can i solve this problem.

 int main()
    {
         pthread_t thread;
         pthread_create(&thread, NULL,(void* (*)(void*))capture, NULL);

    return 0;
    }    

    void classname::capture()
    {
        pcapDeviceHandle = pcap_open_live(dev.c_str(), SNAP_LEN, 0, 1000, errbuf);

           pd = pcap_dump_open(pcapDeviceHandle, "filename.pcap");

        //returnvalue=pcap_dispatch(pcapDeviceHandle, 4, pcap_dump, (unsigned char *) pd);
        returnvalue=pcap_loop(pcapDeviceHandle, 4, pcap_dump, (unsigned char *) pd);

    pcap_dump_close(pd);
    pcap_close(pcapDeviceHandle);

    }

    void classname::pcap_dump(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
    {
          cout<<"inside pcapdump()"<<endl;
          pcap_dump(args, header, packet);
          cout<<"after pcapdump()"<<endl;
    }

Answer 1

In the first case, pcap_dump is called recursively until the stack overflows:

void classname::pcap_dump(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{
    cout<<"inside pcapdump()"<<endl;
    pcap_dump(args, header, packet); // <-- here classname::pcap_dump() calls itself
    cout<<"after pcapdump()"<<endl;
}

In order to dump the packet somewhere, you must call the proper pcap_dump function. To do this add the correct scope, e.g.

void classname::pcap_dump(u_char *args, const struct pcap_pkthdr *header, const u_char *packet)
{
    cout<<"inside pcapdump()"<<endl;
    ::pcap_dump(args, header, packet);
    cout<<"after pcapdump()"<<endl;
}