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/*** UDP。协议无关，调用 getaddrinfo 和 udp_client**/#include	"unp.h"intudp_client(const char *host, const char *serv, SA **saptr, socklen_t *lenp){	int				sockfd, n;	struct addrinfo	hints, *res, *ressave;	//1.调用 getaddrinfo	//协议地址族为 AF_UNSPEC ，套接字类型为 SOCK_DGRAM	bzero(&hints, sizeof(struct addrinfo));	hints.ai_family = AF_UNSPEC;	hints.ai_socktype = SOCK_DGRAM;	if ( (n = getaddrinfo(host, serv, &hints, &res)) != 0)		err_quit("udp_client error for %s, %s: %s",				 host, serv, gai_strerror(n));	ressave = res;	//2.尝试每一个 addrinfo 结构直到成功或到达链表尾	do {	    // 创建套接字		sockfd = socket(res->ai_family, res->ai_socktype, res->ai_protocol);		if (sockfd >= 0)			break;		/* success */	} while ( (res = res->ai_next) != NULL);	//3.假设 getaddrinfo 失败或创建套接字不成功。本函数将终止	if (res == NULL)	/* errno set from final socket() */		err_sys("udp_client error for %s, %s", host, serv);	//4.保存server套接字地址结构		*saptr = Malloc(res->ai_addrlen);	memcpy(*saptr, res->ai_addr, res->ai_addrlen);	*lenp = res->ai_addrlen;	//5.调用 freeaddrinfo 清理由 getaddrinfo 返回的动态存储空间	freeaddrinfo(ressave);	//6.返回套接字	return(sockfd);}/* end udp_client */intUdp_client(const char *host, const char *serv, SA **saptr, socklen_t *lenptr){	return(udp_client(host, serv, saptr, lenptr));}

/*** UDP，协议无关。调用 getaddrinfo 和 udp_client**/#include	"unp.h"intmain(int argc, char **argv){	int				sockfd, n;	char			recvline[MAXLINE + 1];	socklen_t		salen;	struct sockaddr	*sa;	if (argc != 3)		err_quit("usage: daytimeudpcli1 
      
      
       ");	//1.利用 Udp_client 获得 UDP 套接字和server套接字地址结构	sockfd = Udp_client(argv[1], argv[2], (void **) &sa, &salen);	//2.显示server地址	printf("sending to %s\n", Sock_ntop_host(sa, salen));	//3.发送1字节的数据报	Sendto(sockfd, "", 1, 0, sa, salen);	/* send 1-byte datagram */	//4.读取并显示应答数据报	n = Recvfrom(sockfd, recvline, MAXLINE, 0, NULL, NULL);	recvline[n] = '\0';	/* null terminate */	Fputs(recvline, stdout);	exit(0);}