Ok, wenn Sie sich einige meiner vorherigen Fragen ansehen, habe ich daran gearbeitet, eine einfache Verbindung mit C-Sockets zum Laufen zu bringen (der gesamte Netzwerkaspekt eines Programms ist noch ziemlich neu, aber jeder muss irgendwo anfangen , Recht?). Ich habe den Code unten eingefügt, den ich bisher habe, und wenn ich ihn ausführe, erhalte ich keine Fehler, aber gleichzeitig erhalte ich das Paket am anderen Ende nicht. Übrigens programmiere ich Multicast-Sockets in Objective-C und "msgStatus" ist nur eine Bezeichnung in meiner GUI (es ist korrekt angeschlossen, daher gibt es dort kein Problem). Ich sehe nur nicht, wo ich falsch liege. Könnte mir jemand helfen oder mich in die richtige Richtung weisen? Vielen Dank!

#define MAX_LEN  1024    /* maximum string size to send */
#define MIN_PORT 1024    /* minimum port allowed */
#define MAX_PORT 65535   /* maximum port allowed */
#define MYPORT 5673      /* port we will be using for our multicast socket */

    -(void)broadcastMessage {//(NSString*)msg {
        NSLog(@"broadcastMessage - Stage 1");
        NSString *msg = @"From Master";
        mc_ttl = 3; // number of node hops the message is allowed to travel across the network

        // define the port we will be using
        mc_port = MYPORT;

        /* create a socket for sending to the multicast address  */
    if ((sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        NSLog(@"ERROR: broadcastMessage - socket() failed");
        return;
    }

    mc_addr.sin_family      = AF_INET;
    mc_addr.sin_addr.s_addr = inet_addr("225.0.0.37");
    mc_addr.sin_port        = htons(mc_port);

    if (bind(sock, (struct sockaddr *) &mc_addr, sizeof(struct sockaddr_in)) < 0) {
        NSLog(@"ERROR: bind not successful");
        return;
    }

    NSLog(@"broadcastMessage - Stage 2");
    /* set the TTL (time to live/hop count) for the send */
    if ((setsockopt(sock, IPPROTO_IP, IP_MULTICAST_TTL, (void*) &mc_ttl, sizeof(mc_ttl))) < 0) {
        NSLog(@"ERROR: broadcastMessage - setsockopt() failed");
        return;
    }

    NSLog(@"broadcastMessage - Stage 3");
    /* construct a multicast address structure - erase everything in the structure first*/
    memset(&mc_addr, 0, sizeof(mc_addr));

    // prepare the message to be sent
    char send_str[MAX_LEN];

    /* clear send buffer */
    memset(send_str, 0, sizeof(send_str));

    // convert the message to a C string to send
    [msg getCString:send_str maxLength:MAX_LEN encoding:NSASCIIStringEncoding];

    //while (fgets(send_str, MAX_LEN, stdin)) {
        NSLog(@"broadcastMessage - Stage 4");
    //  send_len = strlen(send_str);

    /* send string to multicast address */
    if ((sendto(sock, send_str, sizeof(send_str), 0, (struct sockaddr *) &mc_addr, sizeof(mc_addr))) != sizeof(send_str)) {
        NSLog(@"ERROR: broadcastMessage - sendto() sent incorrect number of bytes");
        return;
    }

    NSLog(@"broadcastMessage - Stage 5");


    /* clear send buffer */
    memset(send_str, 0, sizeof(send_str));

    NSLog(@"broadcastMessage - Stage 6");
    close(sock);
}


-(void)listenForPackets {
    listeningFlag_on = 1;

    NSLog(@"listenForPackets - Stage 1");
    if ((listeningSock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP)) < 0) {
        NSLog(@"ERROR: listenForPackets - socket() failed");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    // set reuse port to on to allow multiple binds per host
    if ((setsockopt(listeningSock, SOL_SOCKET, SO_REUSEADDR, &listeningFlag_on, sizeof(listeningFlag_on))) < 0) {
        NSLog(@"ERROR: listenForPackets - setsockopt() failed");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    NSLog(@"listenForPackets - Stage 2");
    // construct a multicast address structure after erasing anything in the listeningmc_addr structure
    memset(&listeningmc_addr, 0, sizeof(listeningmc_addr));
    listeningmc_addr.sin_family      = AF_INET;
    listeningmc_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    listeningmc_addr.sin_port        = htons(mc_port);

    // bind multicast address to socket
    if ((bind(listeningSock, (struct sockaddr *) &listeningmc_addr, sizeof(listeningmc_addr))) < 0) {
        NSLog(@"ERROR: listenForPackets - bind() failed");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    //******************************************************************************************************************************
    //******************************************************************************************************************************
    NSString *ipAddress = [[NSString alloc] initWithString:self.getIPAddress];
    const char *tmp = [ipAddress UTF8String];
    listeningMc_addr_str = tmp;

    printf("%s\n", listeningMc_addr_str);

    listeningMc_req.imr_multiaddr.s_addr = inet_addr("225.0.0.37");
    listeningMc_req.imr_interface.s_addr = htonl(INADDR_ANY);


    // send an ADD MEMBERSHIP message via setsockopt
    if ((setsockopt(listeningSock, IPPROTO_IP, IP_ADD_MEMBERSHIP, (void*) &listeningMc_req, sizeof(listeningMc_req))) < 0) {
        NSLog(@"ERROR: listenForPackets - setsockopt() failed");
        int err = errno;
        NSLog(@"errno - %i", err);
        NSLog(@"Error = %s", strerror(err));
        perror("ERROR");
        return;                         // make the method return an int instead of void and use this statement to check for errors
    }

    NSLog(@"listenForPackets - Stage 3");
    for (;;) {          // loop forever

        // clear the receive buffers & structs
        memset(listeningRecv_str, 0, sizeof(listeningRecv_str));
        listeningFrom_len = sizeof(listeningFrom_addr);
        memset(&listeningFrom_addr, 0, listeningFrom_len);

        // block waiting to receive a packet
        if ((listeningRecv_len = recvfrom(listeningSock, listeningRecv_str, MAX_LEN, 0, (struct sockaddr*)&listeningFrom_addr, &listeningFrom_len)) < 0) {
            NSLog(@"ERROR: listenForPackets - recvfrom() failed");
            return;                     // make the method return an int instead of void and use this statement to check for errors
        }
        NSLog(@"listenForPackets - Stage 4");

        NSString *tmpy = [[NSString alloc] initWithCString:listeningRecv_str encoding:NSASCIIStringEncoding];
            msgStatus.text = tmpy;
            NSLog(@"ERROR");
        }
        // received string
        printf("Received %d bytes from %s: ", listeningRecv_len, inet_ntoa(listeningFrom_addr.sin_addr));
        printf("%s", listeningRecv_str);
    }

    // send a DROP MEMBERSHIP message via setsockopt
    if ((setsockopt(listeningSock, IPPROTO_IP, IP_DROP_MEMBERSHIP, (void*) &listeningMc_req, sizeof(listeningMc_req))) < 0) {
        NSLog(@"ERROR: listenForPackets - setsockopt() failed");
        //return 1;                         // make the method return an int instead of void and use this statement to check for errors
    }

    close(listeningSock);
    NSLog(@"listenForPackets - Stage 5 - Complete");    
}

Hier ist der Code, mit dem ich meine IP-Adresse extrahiere.

-(NSString *)getIPAddress {
    NSString *address = @"error";
    struct ifaddrs *interfaces; // = NULL;
    struct ifaddrs *temp_addr; // = NULL;
    int success = 0;

    // retrieve the current interfaces - returns 0 on success
    success = getifaddrs(&interfaces);
    if (success == 0)  
    {
        // Loop through linked list of interfaces
        temp_addr = interfaces;
        while(temp_addr != NULL)  
        {
            if(temp_addr->ifa_addr->sa_family == AF_INET)
            {
                // Check if interface is en0 which is the wifi connection on the iPhone  
                if([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"])  
                {
                    // Get NSString from C String
                    address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
                }
            }
            temp_addr = temp_addr->ifa_next;
        }
    }

    // Free memory
    freeifaddrs(interfaces); 
    return address; 
}