On Feb 20 13:48, Corinna Vinschen wrote:
> On Feb 20 04:05, victhor_1983 wrote:
> > status= setsockopt(Descriptor, IPPROTO_IP, IP_ADD_MEMBERSHIP, &Multic,
> > sizeof(Multic));
> > if (status<0){
> > printf("Fallo al añadir el grupo de Multicast, codigo %i\n",
> > errno);
> > }
>
> I'm sorry, I can't tell you why this doesn't work. Cygwin's setsockopt
> function is basically just a shim between application and Winsock's
> setsockopt call. It only performs special actions on a very limited
> set of options, only two actually: (SOL_SOCKET, SO_REUSEADDR) and
> (IPPROTO_IP, IP_TOS). I'm also quite multicast illiterate. Is it
> possible that you have to use the IP_MULTICAST_IF option on Windows
> before you can use IP_ADD_MEMBERSHIP?!?
>Here's one idea: Is it possible that your application includes
>winsock.h? If so, don't do that, use the POSIX headers for socket and
>ip stuff. Winsock.h is the WInsock specific header file for
>applications using the old Winsock 1.x API. In that API,
>IP_ADD_MEMBERSHIP is defined as the value 5.
>However, the newer Winsock 2.x API, which is used by Cygwin under the
>hood as well, defines IP_ADD_MEMBERSHIP as the value 12. So, if there's
>any chance that you're including the winsock.h header, remove it and
>only use Cygwin's header files, not the Winsock specifc header files.
Thanks for the idea. Yes, I read something similar in a post related to
multicast in this same forum. However, I am not using windows headers, since
I migrated my code from Ubuntu. I also tried defining the value of
IP_ADD_MEMBERSHIP myself, and it checks with value 12, just as you say.
However, I still get the error.
I do the binding right after the setsockopt, but the result is the same if I
do it before. In both cases, the setsockopt() returns an errno=22, and the
binding returns an errno=125. It is a real mistery, because I know the IP
interface I associate to the multicast group exists and works, since I use
it without a problem in unicast sockets in other programs.
I have the feeling the problem is in the struct ip_mreg Multic or in
sizeof(Multic), but I cannot figure out why or how to solve it. I will keep
looking into it. Just in case, I post the whole code here:
#include <string.h>
#include <stdio.h>
#include <netinet/in.h>
#include <sys/socket.h>
#include <errno.h>
#include <sys/time.h>
#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>
#define SIGALRM 14
void salir()
{
exit(NULL);
}
int main (void)
{
int Descriptor, Descriptor2, status;
struct sockaddr_in Direccion, Direccion2;
unsigned short Puerto;
struct ip_mreq Multic;
Descriptor=socket(AF_INET,SOCK_DGRAM,0);
Puerto=12100;
Direccion.sin_family=AF_INET;
Direccion.sin_port=htons(Puerto);//Puerto->s_port;
Direccion.sin_addr.s_addr=inet_addr("224.0.22.1");//("138.4.32.34");
memset(&(Direccion.sin_zero),'\0',8);
Direccion2.sin_family=AF_INET;
Direccion2.sin_port=htons(Puerto);//Puerto->s_port;
Direccion2.sin_addr.s_addr=htonl(INADDR_ANY);//inet_addr("138.4.32.34");//("138.4.32.34");
memset(&(Direccion2.sin_zero),'\0',8);
status=bind(Descriptor,(struct sockaddr *)&Direccion, sizeof(struct
sockaddr));
if (status<0){
printf("Fallo al realizar binding, codigo %i\n", errno);
}
Multic.imr_multiaddr.s_addr=inet_addr("224.0.22.1");
Multic.imr_interface.s_addr=htonl(INADDR_ANY);//inet_addr("138.4.32.34");
status= setsockopt(Descriptor, IPPROTO_IP, IP_ADD_MEMBERSHIP, &Multic,
sizeof(Multic));
if (status<0){
printf("Fallo al añadir el grupo de Multicast, codigo %i\n",
errno);
}
signal (SIGINT, salir);
signal (SIGALRM, SIG_IGN);
return 0;
}
Maybe the error is in some other part. Thanks again for your insight and
your help.
Victor
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