多播包的发送与接收

Listener Program
#include 
#include 
#include 
#include 
#include 
#include 
#include 

#define HELLO_PORT 12345
#define HELLO_GROUP "225.0.0.37"
#define MSGBUFSIZE 256

main(int argc, char *argv[])
{
     struct sockaddr_in addr;
     int fd, nbytes,addrlen;
     struct ip_mreq mreq;
     char msgbuf[MSGBUFSIZE];

     u_int yes=1;

     /* create what looks like an ordinary UDP socket */
     if ((fd=socket(AF_INET,SOCK_DGRAM,0)) < 0) {
          perror("socket");
          exit(1);
     }

    /* allow multiple sockets to use the same PORT number */
    if (setsockopt(fd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(yes)) < 0) {
       perror("Reusing ADDR failed");
       exit(1);
       }

     /* set up destination address */
     memset(&addr,0,sizeof(addr));
     addr.sin_family=AF_INET;
     addr.sin_addr.s_addr=htonl(INADDR_ANY); /* N.B.: differs from sender */
     addr.sin_port=htons(HELLO_PORT);
     
     /* bind to receive address */
     if (bind(fd,(struct sockaddr *) &addr,sizeof(addr)) < 0) {
          perror("bind");
          exit(1);
     }
     
     /* use setsockopt() to request that the kernel join a multicast group */
     mreq.imr_multiaddr.s_addr=inet_addr(HELLO_GROUP);
     mreq.imr_interface.s_addr=htonl(INADDR_ANY);
     if (setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0) {
          perror("setsockopt");
          exit(1);
     }

     /* now just enter a read-print loop */
     while (1) {
          addrlen=sizeof(addr);
          if ((nbytes=recvfrom(fd,msgbuf,MSGBUFSIZE,0,
                               (struct sockaddr *) &addr,&addrlen)) < 0) {
               perror("recvfrom");
               exit(1);
          }
          puts(msgbuf);
     }
}

#include 
#include 
#include 
#include 
#include 
#include 
#include 


#define HELLO_PORT 12345
#define HELLO_GROUP "225.0.0.37"

main(int argc, char *argv[])
{
     struct sockaddr_in addr;
     int fd, cnt;
     struct ip_mreq mreq;
     char message[16]="Hello, World!";

     /* create what looks like an ordinary UDP socket */
     if ((fd=socket(AF_INET,SOCK_DGRAM,0)) < 0) {
          perror("socket");
          exit(1);
     }

     /* set up destination address */
     memset(&addr,0,sizeof(addr));
     addr.sin_family=AF_INET;
     addr.sin_addr.s_addr=inet_addr(HELLO_GROUP);
     addr.sin_port=htons(HELLO_PORT);
     
     /* now just sendto() our destination! */
     while (1) {
          if (sendto(fd,message,sizeof(message),0,(struct sockaddr *) &addr,
                     sizeof(addr)) < 0) {
               perror("sendto");
               exit(1);
          }
          sleep(1);
     }
}