send and receive a broadcast udp packet in c or objective c

#include <netinet/in.h>
#include <sys/socket.h>
#include <unistd.h>
#include <arpa/inet.h>

- (void)broadCast
{
    int socketSD = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (socketSD <= 0) {
        NSLog(@"Error: Could not open socket.");
        return;
    }
    
    // set socket options enable broadcast
    int broadcastEnable = 1;
    int ret = setsockopt(socketSD, SOL_SOCKET, SO_BROADCAST, &broadcastEnable, sizeof(broadcastEnable));
    if (ret) {
        NSLog(@"Error: Could not open set socket to broadcast mode");
        close(socketSD);
        return;
    }
    
    // Configure the port and ip we want to send to
    struct sockaddr_in broadcastAddr;
    memset(&broadcastAddr, 0, sizeof(broadcastAddr));
    broadcastAddr.sin_family = AF_INET;
    inet_pton(AF_INET, "255.255.255.255", &broadcastAddr.sin_addr);
    broadcastAddr.sin_port = htons(8585);
    
    char *request = "message from ios by c";
    ret = sendto(socketSD, request, strlen(request), 0, (struct sockaddr*)&broadcastAddr, sizeof(broadcastAddr));
    if (ret < 0) {
        NSLog(@"Error: Could not open send broadcast.");
        close(socketSD);
        return;
    }
    
    close(socketSD);
    
    dispatch_async(dispatch_get_global_queue(0, 0), ^{
        [self listenForPackets];
    });
    
    [_connectionSpinner show:YES];
    [_connectionTimer invalidate];
    _connectionTimer = [NSTimer scheduledTimerWithTimeInterval:3.0f target:self selector:@selector(checkConnection) userInfo:nil repeats:NO];
}

- (void)listenForPackets
{
    int listeningSocket = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
    if (listeningSocket <= 0) {
        NSLog(@"Error: listenForPackets - socket() failed.");
        return;
    }
    
    // set timeout to 2 seconds.
    struct timeval timeV;
    timeV.tv_sec = 2;
    timeV.tv_usec = 0;
    
    if (setsockopt(listeningSocket, SOL_SOCKET, SO_RCVTIMEO, &timeV, sizeof(timeV)) == -1) {
        NSLog(@"Error: listenForPackets - setsockopt failed");
        close(listeningSocket);
        return;
    }
    
    // bind the port
    struct sockaddr_in sockaddr;
    memset(&sockaddr, 0, sizeof(sockaddr));
    
    sockaddr.sin_len = sizeof(sockaddr);
    sockaddr.sin_family = AF_INET;
    sockaddr.sin_port = htons(18686);
    sockaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    
    int status = bind(listeningSocket, (struct sockaddr *)&sockaddr, sizeof(sockaddr));
    if (status == -1) {
        close(listeningSocket);
        NSLog(@"Error: listenForPackets - bind() failed.");
        return;
    }
    
    // receive
    struct sockaddr_in receiveSockaddr;
    socklen_t receiveSockaddrLen = sizeof(receiveSockaddr);
    
    size_t bufSize = 9216;
    void *buf = malloc(bufSize);
    ssize_t result = recvfrom(listeningSocket, buf, bufSize, 0, (struct sockaddr *)&receiveSockaddr, &receiveSockaddrLen);
    
    NSData *data = nil;

    if (result > 0) {
        if ((size_t)result != bufSize) {
            buf = realloc(buf, result);
        }
        data = [NSData dataWithBytesNoCopy:buf length:result freeWhenDone:YES];
        
        char addrBuf[INET_ADDRSTRLEN];
        if (inet_ntop(AF_INET, &receiveSockaddr.sin_addr, addrBuf, (size_t)sizeof(addrBuf)) == NULL) {
            addrBuf[0] = '\0';
        }
        
        NSString *address = [NSString stringWithCString:addrBuf encoding:NSASCIIStringEncoding];
        NSString *msg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        
        dispatch_async(dispatch_get_main_queue(), ^{
            [self didReceiveMessage:msg fromAddress:address];
        });
        
    } else {
        free(buf);
    }
    
    close(listeningSocket);
}

- (void)didReceiveMessage:(NSString *)message fromAddress:(NSString *)address
{
} 

i have implemented both methods into my application. I made 2 buttons one to call broadCast method and other is to call listenForPackets method.
I do not get data into listenForPackets method each time control goes into else condition where you do free buffer. I first broadcast message from one device then i listen for it on second device. Can you please tell me what going wrong on my end?
I can not see "checkConnection" method here into download code. Can you please explain what is the use of this method.

hi changxi wu,

I see ur udp post on the github -> https://gist.github.com/chancyWu/8349411
and I use ur function for test is worked,
but I found issue the udp server send echo message back to client ,
client's recvfrom function response is -1 ,

could u please give me some hint ?

PS. the udp server in my mac is CocoaAsyncSocket UdpEchoServer Sample
https://github.com/robbiehanson/CocoaAsyncSocket

Did you manage to make it work? Anywhere to find your code?