udp协议的获取时间的客户端

#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <string.h>

const int maxline=4096;

void dg_cli(FILE *fp, int sockfd, struct sockaddr * pservaddr, socklen_t servlen) {
	int n;
	char sendline[maxline], recvline[maxline+1];
	char errbuff[maxline];
	struct sockaddr_in localaddr;
	socklen_t len=sizeof(localaddr);

	while(fgets(sendline, maxline, fp) != NULL) {
		memset(recvline, 0, sizeof(recvline));
		if(sendto(sockfd, sendline, strlen(sendline), 0, pservaddr, servlen)<0) {
			strerror_r(errno, errbuff, maxline);
			fprintf(stderr, "sendto error: %s\n", errbuff);
			exit(-1);
		}

		if((n=recvfrom(sockfd, recvline, maxline, 0, pservaddr, &servlen)) < 0) {
			strerror_r(errno, errbuff, maxline);
			fprintf(stderr, "read error: %s\n", errbuff);
			exit(-1);
		}
		if(getsockname(sockfd, (struct sockaddr *)&localaddr, &len)<0) {
			strerror_r(errno, errbuff, maxline);
			fprintf(stderr, "getsockname error: %s\n", errbuff);
			exit(-1);
		}
		recvline[n]=0;
		printf("%s", recvline);
		printf("local ip: %s, local port: %d\n", inet_ntop(AF_INET, &localaddr.sin_addr, errbuff, sizeof(errbuff)), ntohs(localaddr.sin_port));
	}
}

int main(int argc, char **argv) {
	int sockfd;
	struct sockaddr_in servaddr;
	char errbuff[maxline];

	if(argc != 2) {
		fprintf(stderr, "usage: udpcli <IPaddress>\n");
		exit(-1);
	}

	if((sockfd=socket(AF_INET, SOCK_DGRAM, 0))<0) {
		strerror_r(errno, errbuff, maxline);
		fprintf(stderr, "socket error: %s\n", errbuff);
		exit(-1);
	}
	
	memset(&servaddr, 0, sizeof(servaddr));
	servaddr.sin_family = AF_INET;
	servaddr.sin_port = htons(13);
	inet_pton(AF_INET, argv[1], &servaddr.sin_addr);

	dg_cli(stdin, sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
	
	return 0;
}