13-16 旧APIでのマルチキャスト受信プログラム

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

int
main()
{
  int sock;
  struct sockaddr_in addr;
  struct ip_mreq mreq;
  char buf[2048];

  sock = socket(AF_INET, SOCK_DGRAM, 0);

  addr.sin_family = AF_INET;
  addr.sin_port = htons(12345);
  addr.sin_addr.s_addr = INADDR_ANY;

  bind(sock, (struct sockaddr *)&addr, sizeof(addr));

  /* setsockoptは、bind以降で行う必要あり */
  memset(&mreq, 0, sizeof(mreq));
  mreq.imr_interface.s_addr = INADDR_ANY;
  inet_pton(AF_INET, "239.192.1.2", &mreq.imr_multiaddr.s_addr);

  if (setsockopt(sock,
                IPPROTO_IP,
                IP_ADD_MEMBERSHIP,
                (char *)&mreq, sizeof(mreq)) != 0) {
    perror("setsockopt");
    return 1;
  }

  memset(buf, 0, sizeof(buf));
  recv(sock, buf, sizeof(buf), 0);

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

  if (setsockopt(sock,
                IPPROTO_IP,
                IP_DROP_MEMBERSHIP,
                (char *)&mreq, sizeof(mreq)) != 0) {
    perror("setsockopt");
    return 1;
  }

  close(sock);

  return 0;
}

拙著「Linuxネットワークプログラミング」の紹介