Cygwin 1.5.18: Problem using setsockopt() for multicast

[Alessandro Saffiotti <asaffio at aass dot oru dot se>]

Hi there,

I ran into the following problem when using setsockopt to create a
multicast receiver in my own application.  Here is the relevant part
of the code:

----------------------------------------------------------------------
  .
  .
  .
  tcp_broadcast_receiver = socket(PF_INET,SOCK_DGRAM,IPPROTO_IP);

  memset(&imreq, 0, sizeof(struct ip_mreq));
  imreq.imr_multiaddr.s_addr = inet_addr("227.1.3.5");
  imreq.imr_interface.s_addr = INADDR_ANY;

  if(setsockopt(tcp_broadcast_receiver, IPPROTO_IP, IP_ADD_MEMBERSHIP, 
		(const void *)&imreq, sizeof(struct ip_mreq)) != 0)
    perror("Error joining multicast group");
  .
  .
  .
----------------------------------------------------------------------

It compiles ok, but when I run it setsockopt fails producing the
following report:

  Error joining multicast group: Invalid argument

I have noted that a similar problem was reported long time ago, when
support for multicast was not implemented, but I understand that this
support is not available.

I have also read the discussion about the conflicting values for
constants between winsock1 and winsock2.  I have tried to replace
IP_ADD_MEMBERSHIP by hardcoding either 5 (winsock1) or 12 (winsok2),
but I get the same behavior.

I run Cygwin 1.5.18 on Windows XP pro SP2.

Any hints?
Thanks!

  Alessandro Saffiotti


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