how to do UDP multicast with netos 7.4.1?


I have an application, it sent a UDP multicast massage to network.
It work with netos 6.3, but don’t work with netos 7.4.1.

My code is as follows:

sockFd = socket (AF_INET, SOCK_DGRAM, 0);
opt = 1;
result = setsockopt(sockFd, SOL_SOCKET, SO_BROADCAST, (char *)&opt, sizeof(int));

sendDataSize = sendto(sockFd, UDP_dat_pkt, UDP_dat_pkt_size, 0, (struct sockaddr *) &sendAddr, sizeof sendAddr);

What I should do to make UDP multicast work?
Have someone an example for a UDP Multicast on netos 7.4.1?