udp组播

 发送：

    char group_ip[20];
    int group_port = 9535;
    strcpy(group_ip,"224.1.1.2");


    int socket_fd;
    struct sockaddr_in group_addr;  //group address
    struct sockaddr_in local_addr;//local address
    struct ip_mreq mreq;
    socklen_t addr_len = sizeof(group_addr);


    socket_fd=socket(AF_INET,SOCK_DGRAM,0);
    if(socket_fd < 0)
    {
        perror("socket multicast!");
        exit(1);
    }

    /* allow multiple sockets to use the same PORT number */
    if (setsockopt(socket_fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) < 0)
    {
        perror("Reusing ADDR failed");
        exit(1);
    }

    /*set up the destination address*/
    memset(&group_addr,0,sizeof(struct sockaddr_in));
    group_addr.sin_family = AF_INET;
    group_addr.sin_port = htons(group_port);
    group_addr.sin_addr.s_addr = inet_addr("230.1.1.1");

    /*set up the local address*/
    memset(&local_addr,0,sizeof(local_addr));
    local_addr.sin_family = AF_INET;
    local_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    local_addr.sin_port = htons(group_port);              //this port must be the group port
    /*bind local address*/
    if(bind(socket_fd,(struct sockaddr *)&local_addr,sizeof(local_addr)) == -1)
    {
        perror("Binding the multicast!");
        exit(1);
    }
    /*use the setsocketopt() to request joining the multicast group*/
    mreq.imr_multiaddr.s_addr=inet_addr(group_ip);
    mreq.imr_interface.s_addr=htonl(INADDR_ANY);
    if (setsockopt(socket_fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0)
    {
        perror("setsockopt multicast!");
        exit(1);
    }
  
    //sendto  
}

接收：

    char group_ip[20];
    int group_port = 9535;
    strcpy(group_ip,"224.1.1.2");

    int socket_fd;
    struct sockaddr_in group_addr;  //group address
    struct sockaddr_in local_addr;//local address
    struct ip_mreq mreq;
    socklen_t addr_len = sizeof(group_addr);

    socket_fd=socket(AF_INET,SOCK_DGRAM,0);
    if(socket_fd < 0)
    {
        perror("socket multicast!");
        exit(1);
    }

    /* allow multiple sockets to use the same PORT number */
    if (setsockopt(socket_fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) < 0)
    {
        perror("Reusing ADDR failed");
        exit(1);
    }

    /*set up the destination address*/
    memset(&group_addr,0,sizeof(struct sockaddr_in));
    group_addr.sin_family = AF_INET;
    group_addr.sin_port = htons(group_port);
    group_addr.sin_addr.s_addr = inet_addr("230.1.1.1");

    /*set up the local address*/
    memset(&local_addr,0,sizeof(local_addr));
    local_addr.sin_family = AF_INET;
    local_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    local_addr.sin_port = htons(group_port);              //this port must be the group port
    /*bind local address*/
    if(bind(socket_fd,(struct sockaddr *)&local_addr,sizeof(local_addr)) == -1)
    {
        perror("Binding the multicast!");
        exit(1);
    }
    /*use the setsocketopt() to request joining the multicast group*/
    mreq.imr_multiaddr.s_addr=inet_addr(group_ip);
    mreq.imr_interface.s_addr=htonl(INADDR_ANY);
    if (setsockopt(socket_fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0)
    {
        perror("setsockopt multicast!");
        exit(1);
    }
   
    //recvfrom

}