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;
}   