1 #include <apue.h> 2  3 #define PORT 8088 4  5 #define MULTIIP "225.0.0.1" 6  7 int main(int argc,char **argv) 8 { 9     if(argc!=2)10     {11         printf("%s <msg>\n",argv[0]);12         exit(0);13     }14 15     int sockfd;16     if((sockfd = socket(AF_INET,SOCK_DGRAM,0))<0)17         ERR("socket failed");18     19     struct sockaddr_in peer;20     CLEAR(peer);21     peer.sin_family = AF_INET;22     peer.sin_port = htons(PORT);23     inet_pton(AF_INET,MULTIIP,&peer.sin_addr);24 25     if(sendto(sockfd,argv[1],strlen(argv[1]),0,(struct sockaddr*)&peer,sizeof(peer))<0)26         ERR("send failed");27     28     close(sockfd);29     return 0;30 }

 1 #include <apue.h> 2  3 #define PORT 8088 4 #define MULTIIP "225.0.0.1" 5  6 int main(int argc,char **argv) 7 { 8     int sockfd; 9     if((sockfd = socket(AF_INET,SOCK_DGRAM,0))<0)10         ERR("socket failed");11     12     struct sockaddr_in ipv4;13     CLEAR(ipv4);14     ipv4.sin_family = AF_INET;15     ipv4.sin_port = htons(PORT);16     ipv4.sin_addr.s_addr = htonl(INADDR_ANY);17     if(bind(sockfd,(struct sockaddr*)&ipv4,sizeof(ipv4))<0)18         ERR("bind failed");19         20     //加入组21     #if 022     struct ip_mreq{    23         struct in_addr imr_multiaddr;   /* IP multicast address of group */24         struct in_addr imr_interface;   /* local IP address of interface */;25     }26     #endif27     struct ip_mreq mreq;28     inet_pton(AF_INET,MULTIIP,&mreq.imr_multiaddr);29     mreq.imr_interface.s_addr = INADDR_ANY;30     if(setsockopt(sockfd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq))<0)31         ERR("setsockopt failed");32 33     int n;34     char buf[255];35     while(1)36     {37         if((n = recvfrom(sockfd,buf,sizeof(buf),0,NULL,NULL))<0)38             ERR("recv failed");39         buf[n] = 0;40         printf("%s\n",buf);41     }42 43     //离开组44     if(setsockopt(sockfd,IPPROTO_IP,IP_DROP_MEMBERSHIP,&mreq,sizeof(mreq))<0)45         ERR("setsockopt failed");46 47     close(sockfd);48     return 0;49 }