some description

receiver.c

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

struct sockaddr_in localSock;
struct ip_mreq group;
int sd;
char buf[2048];

int main(int argc, char *argv[])
{
  sd = socket(AF_INET, SOCK_DGRAM, 0);
  if(sd < 0) {
    exit(1);
  }

  {
    int reuse = 1;
    if(setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse)) < 0) {
      close(sd);
      exit(1);
    }
  }

  memset((char *) &localSock, 0, sizeof(localSock));
  localSock.sin_family = AF_INET;
  localSock.sin_port = htons(atoi(argv[1]));
  localSock.sin_addr.s_addr = INADDR_ANY;

  if(bind(sd, (struct sockaddr*)&localSock, sizeof(localSock))) {
    close(sd);
    exit(1);
  }

  group.imr_multiaddr.s_addr = inet_addr("224.0.0.1");
  group.imr_interface.s_addr = inet_addr("127.0.0.1");
  if(setsockopt(sd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char *)&group, sizeof(group)) < 0) {
    close(sd);
    exit(1);
  }

  while (1) {
  fflush(stdout);
  if(read(sd, buf, sizeof(buf)) < 0) {
    close(sd);
    exit(1);
  } else {