title: How to broadcast Message using UDP sockets locally?
body: <p>I want to broadcast messages locally to many application. For that I thought UDP sockets is the best IPC, correct me if I am worng.</p>
  
  <p>For this I am using the following codes:</p>
  
  <p>For broadcast:</p>
  
  <pre><code>/*
  ** broadcaster.c -- a datagram "client" that can broadcast
  */
  
  #include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;unistd.h&gt;
  #include &lt;errno.h&gt;
  #include &lt;string.h&gt;
  #include &lt;sys/types.h&gt;
  #include &lt;sys/socket.h&gt;
  #include &lt;netinet/in.h&gt;
  #include &lt;arpa/inet.h&gt;
  #include &lt;netdb.h&gt;
  
  #define SERVERPORT 4950    // the port users will be connecting to
  
  int main(int argc, char *argv[])
  {
      int sockfd;
      struct sockaddr_in their_addr; // connector's address information
      struct hostent *he;
      int numbytes;
      int broadcast = 1;
      //char broadcast = '1'; // if that doesn't work, try this
  
      if (argc != 3) {
          fprintf(stderr,"usage: broadcaster hostname message\n");
          exit(1);
      }
  
      if ((he=gethostbyname(argv[1])) == NULL) {  // get the host info
          perror("gethostbyname");
          exit(1);
      }
  
      if ((sockfd = socket(AF_UNIX, SOCK_DGRAM, 0)) == -1) {
          perror("socket");
          exit(1);
      }
  
      // this call is what allows broadcast packets to be sent:
      if (setsockopt(sockfd, SOL_SOCKET, SO_BROADCAST, &amp;broadcast,
          sizeof broadcast) == -1) {
          perror("setsockopt (SO_BROADCAST)");
          exit(1);
      }
  
      their_addr.sin_family = AF_UNIX;     // host byte order
      their_addr.sin_port = htons(SERVERPORT); // short, network byte order
      their_addr.sin_addr = *((struct in_addr *)he-&gt;h_addr);
      memset(their_addr.sin_zero, '\0', sizeof their_addr.sin_zero);
  
      if ((numbytes=sendto(sockfd, argv[2], strlen(argv[2]), 0,
               (struct sockaddr *)&amp;their_addr, sizeof their_addr)) == -1) {
          perror("sendto");
          exit(1);
      }
  
      printf("sent %d bytes to %s\n", numbytes,
          inet_ntoa(their_addr.sin_addr));
  
      close(sockfd);
  
      return 0;
  }
  </code></pre>
  
  <p>And to listen :</p>
  
  <pre><code>/*
  ** listener.c -- a datagram sockets "server" demo
  */
  
  #include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;unistd.h&gt;
  #include &lt;errno.h&gt;
  #include &lt;string.h&gt;
  #include &lt;sys/types.h&gt;
  #include &lt;sys/socket.h&gt;
  #include &lt;netinet/in.h&gt;
  #include &lt;arpa/inet.h&gt;
  #include &lt;netdb.h&gt;
  
  #define MYPORT "4950"    // the port users will be connecting to
  
  #define MAXBUFLEN 100
  
  // get sockaddr, IPv4 or IPv6:
  void *get_in_addr(struct sockaddr *sa)
  {
      if (sa-&gt;sa_family == AF_INET) {
          return &amp;(((struct sockaddr_in*)sa)-&gt;sin_addr);
      }
  
      return &amp;(((struct sockaddr_in6*)sa)-&gt;sin6_addr);
  }
  
  int main(void)
  {
      int sockfd;
      struct addrinfo hints, *servinfo, *p;
      int rv;
      int numbytes;
      struct sockaddr_storage their_addr;
      char buf[MAXBUFLEN];
      socklen_t addr_len;
      char s[INET6_ADDRSTRLEN];
      int optval = 1;
  
      memset(&amp;hints, 0, sizeof hints);
      hints.ai_family = AF_UNSPEC; // set to AF_INET to force IPv4
      hints.ai_socktype = SOCK_DGRAM;
      hints.ai_flags = AI_PASSIVE; // use my IP
  
      if ((rv = getaddrinfo(NULL, MYPORT, &amp;hints, &amp;servinfo)) != 0) {
          fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
          return 1;
      }
  
      // loop through all the results and bind to the first we can
      for(p = servinfo; p != NULL; p = p-&gt;ai_next) {
          if ((sockfd = socket(p-&gt;ai_family, p-&gt;ai_socktype,
                  p-&gt;ai_protocol)) == -1) {
              perror("listener: socket");
              continue;
          }
  
          if(setsockopt(sockfd, SOL_SOCKET,SO_REUSEADDR, &amp;optval, sizeof optval) != 0)
          {
              perror("listener: setsockopt");
              continue;   
          }   
  
          if (bind(sockfd, p-&gt;ai_addr, p-&gt;ai_addrlen) == -1) {
              close(sockfd);
              perror("listener: bind");
              continue;
          }
  
          break;
      }
  
      if (p == NULL) {
          fprintf(stderr, "listener: failed to bind socket\n");
          return 2;
      }
  
      freeaddrinfo(servinfo);
  
      printf("listener: waiting to recvfrom...\n");
  
      addr_len = sizeof their_addr;
      if ((numbytes = recvfrom(sockfd, buf, MAXBUFLEN-1 , 0,
          (struct sockaddr *)&amp;their_addr, &amp;addr_len)) == -1) {
          perror("recvfrom");
          exit(1);
      }
  
      printf("listener: got packet from %s\n",
          inet_ntop(their_addr.ss_family,
              get_in_addr((struct sockaddr *)&amp;their_addr),
              s, sizeof s));
      printf("listener: packet is %d bytes long\n", numbytes);
      buf[numbytes] = '\0';
      printf("listener: packet contains \"%s\"\n", buf);
  
      close(sockfd);
  
      return 0;
  }
  </code></pre>
  
  <p>The problem is that I have to pass IP like this 192.168.1.255 but in the real scenario there may not be eth0 interface, there will be only loopback. Then how can I achieve this?</p>