UDP多播

D类地址不区分网络地址和主机地址，它的第一个字节的前四位固定为1110 。所以D类地址范围：224.0.0.0到239.255.255.255

#include <sys/types.h>#include <sys/socket.h>#include <arpa/inet.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#define BUFLEN 255int main(int argc, char **argv){  struct sockaddr_in peeraddr, myaddr;  int sockfd;  char recmsg[BUFLEN + 1];  unsigned int socklen;  /* 创建 socket 用于UDP通讯 */  sockfd = socket(AF_INET, SOCK_DGRAM, 0);  if (sockfd < 0) {    printf("socket creating error\n");    exit(1);  }  socklen = sizeof(struct sockaddr_in);  /* 设置对方的端口和IP信息 */  memset(&peeraddr, 0, socklen);  peeraddr.sin_family = AF_INET;  if (argv[2])    peeraddr.sin_port = htons(atoi(argv[2]));  else    peeraddr.sin_port = htons(7838);  if (argv[1]) {    /* 注意这里设置的对方地址是指组播地址，而不是对方的实际IP地址 */    if (inet_pton(AF_INET, argv[1], &peeraddr.sin_addr) <= 0) {      printf("wrong group address!\n");      exit(0);    }  } else {    printf("no group address!\n");    exit(0);  }  /* 设置自己的端口和IP信息 */  memset(&myaddr, 0, socklen);  myaddr.sin_family = AF_INET;  if (argv[4])    myaddr.sin_port = htons(atoi(argv[4]));  else    myaddr.sin_port = htons(23456);  if (argv[3]) {    if (inet_pton(AF_INET, argv[3], &myaddr.sin_addr) <= 0) {      printf("self ip address error!\n");      exit(0);    }  } else    myaddr.sin_addr.s_addr = INADDR_ANY;  /* 绑定自己的端口和IP信息到socket上 */  if (bind      (sockfd, (struct sockaddr *) &myaddr,       sizeof(struct sockaddr_in)) == -1) {    printf("Bind error\n");    exit(0);  }  /* 循环接受用户输入的消息发送组播消息 */  for (;;) {    /* 接受用户输入 */    bzero(recmsg, BUFLEN + 1);    if (fgets(recmsg, BUFLEN, stdin) == (char *) EOF)      exit(0);    /* 发送消息 */    if (sendto(sockfd, recmsg, strlen(recmsg), 0, (struct sockaddr *) &peeraddr, sizeof(struct sockaddr_in)) < 0) {      printf("sendto error!\n");      exit(3);    }    printf("'%s' send ok\n", recmsg);  }}

#include <sys/types.h>#include <sys/socket.h>#include <arpa/inet.h>#include <stdio.h>#include <stdlib.h>#include <string.h>#include <netdb.h>#include <errno.h>#define BUFLEN 255int main(int argc, char **argv){  struct sockaddr_in peeraddr;  struct in_addr ia;  int sockfd;  char recmsg[BUFLEN + 1];  unsigned int socklen, n;  struct hostent *group;  struct ip_mreq mreq;  /* 创建 socket 用于UDP通讯 */  sockfd = socket(AF_INET, SOCK_DGRAM, 0);  if (sockfd < 0) {    printf("socket creating err in udptalk\n");    exit(1);  }  /* 设置要加入组播的地址 */  bzero(&mreq, sizeof(struct ip_mreq));  if (argv[1]) {    if ((group = gethostbyname(argv[1])) == (struct hostent *) 0) {      perror("gethostbyname");      exit(errno);    }  } else {    printf      ("you should give me a group address, 224.0.0.0-239.255.255.255\n");    exit(errno);  }  bcopy((void *) group->h_addr, (void *) &ia, group->h_length);  /* 设置组地址 */  bcopy(&ia, &mreq.imr_multiaddr.s_addr, sizeof(struct in_addr));  /* 设置发送组播消息的源主机的地址信息 */  mreq.imr_interface.s_addr = htonl(INADDR_ANY);  /* 把本机加入组播地址，即本机网卡作为组播成员，只有加入组才能收到组播消息 */  if (setsockopt      (sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq,       sizeof(struct ip_mreq)) == -1) {    perror("setsockopt");    exit(-1);  }  socklen = sizeof(struct sockaddr_in);  memset(&peeraddr, 0, socklen);  peeraddr.sin_family = AF_INET;  if (argv[2])    peeraddr.sin_port = htons(atoi(argv[2]));  else    peeraddr.sin_port = htons(7838);  if (argv[1]) {    if (inet_pton(AF_INET, argv[1], &peeraddr.sin_addr) <= 0) {      printf("Wrong dest IP address!\n");      exit(0);    }  } else {    printf("no group address given, 224.0.0.0-239.255.255.255\n");    exit(errno);  }  /* 绑定自己的端口和IP信息到socket上 */  if (bind      (sockfd, (struct sockaddr *) &peeraddr,       sizeof(struct sockaddr_in)) == -1) {    printf("Bind error\n");    exit(0);  }  /* 循环接收网络上来的组播消息 */  for (;;) {    bzero(recmsg, BUFLEN + 1);    n = recvfrom(sockfd, recmsg, BUFLEN, 0, (struct sockaddr *) &peeraddr, &socklen);    if (n < 0) {      printf("recvfrom err in udptalk!\n");      exit(4);    } else {      /* 成功接收到数据报 */      recmsg[n] = 0;      printf("peer:%s", recmsg);    }  }}

运行：

./client 230.1.0.1 7838 192.168.1.109 12345

./server 230.1.0.1 7838