#include <stdio.h>#include <stdlib.h>#include <string.h>#include <netdb.h>#include <errno.h>#include <unistd.h>#include <sys/types.h>#include <sys/socket.h>#include <arpa/inet.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;	/* 創(chuàng)建 socket 用于UDP通訊 */	sockfd = socket(AF_INET, SOCK_DGRAM, 0);	if (sockfd < 0) {		printf("socket creating err in udptalk\n");		exit(1);	}	/* 設(shè)置要加入組播的地址 */	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);	/* 設(shè)置組地址 */	bcopy(&ia, &mreq.imr_multiaddr.s_addr, sizeof(struct in_addr));	/* 設(shè)置發(fā)送組播消息的源主機(jī)的地址信息 */	mreq.imr_interface.s_addr = htonl(INADDR_ANY);	/* 把本機(jī)加入組播地址，即本機(jī)網(wǎng)卡作為組播成員，只有加入組才能收到組播消息 */	if (setsockopt(sockfd, IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq,sizeof(struct ip_mreq)) == -1) {		perror("setsockopt");		exit(-1);	}	/**重要：共享UDP組播端口**/	int one = 1;	setsockopt(sockfd, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one));	/****/	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);	}	/* 綁定自己的端口和IP信息到socket上 */	if (bind(sockfd, (struct sockaddr *) &peeraddr,sizeof(struct sockaddr_in)) == -1) {		printf("Bind error\n");		exit(0);	}	/* 循環(huán)接收網(wǎng)絡(luò)上來的組播消息 */	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 {			/* 成功接收到數(shù)據(jù)報 */			recmsg[n] = 0;			printf("peer:%s\n", recmsg);			/* 判斷退出 */			if (strcmp(recmsg,"exit\n")==0)  {				close(sockfd);				exit(1);			}		}	}}