#ifndef DATA_H

 #define DATA_H

 #include <stdio.h>

 #include <string.h>

 #include <sys/types.h>

 #include <sys/stat.h>

 #include <sys/socket.h>

 #include <stdlib.h>

 #include <unistd.h>

 #include <netinet/in.h>

 #include <arpa/inet.h>

 #include <netdb.h>

 #include <errno.h>

 #define PORT 4578

 #define maxn 100

 #endif

 #include "data.h"

 int main()

 {

     int sockfd;

     struct sockaddr_in server;

     struct sockaddr_in client;

     socklen_t len;

     int num;

     char buf[maxn];

     if((sockfd = socket(AF_INET,SOCK_DGRAM,)) == -)

     {

         fprintf(stderr,"socket fail,error:%s\n",strerror(errno));

         return -;

     }

     bzero(&server,sizeof(server));

     server.sin_family = AF_INET;

     server.sin_port = htons(PORT);

     server.sin_addr.s_addr = htonl(INADDR_ANY);

     if(bind(sockfd,(struct sockaddr*)&server,sizeof(server)) == -)

     {

         fprintf(stderr,"bind fail,error:%s\n",strerror(errno));

         return -;

     }

     len = sizeof(client);

     bzero(&buf,sizeof(buf));

     while()

     {

         num = recvfrom(sockfd,buf,maxn,,(struct sockaddr*)&client,&len);

         if(num < )

         {

             perror("recvfrom() error!\n");

             exit();

         }

         num--;

         buf[num] = '\0';

         printf("You got a message <%s> from client.\n",buf);

         printf("It is ip is %s,port is %d.\n",

             inet_ntoa(client.sin_addr), htons(client.sin_port));

         sendto(sockfd,buf,strlen(buf),,(struct sockaddr*)&client,len);

         if(!strcmp(buf,"bye"))

             break;

     }

     close(sockfd);

 }

#include "data.h"

int main()

{

    int sockfd,num;

    char sendbuf[maxn];

    char recvbuf[maxn];

    struct sockaddr_in server;

    struct sockaddr_in peer;

    if((sockfd = socket(AF_INET,SOCK_DGRAM,)) == -)

    {

        fprintf(stderr,"socket fail,error %s\n",strerror(errno));

        exit();

    }

    bzero(&server,sizeof(server));

    server.sin_family = AF_INET;

    server.sin_port = htons(PORT);

    server.sin_addr.s_addr = inet_addr("127.0.0.1");

    bzero(&sendbuf,sizeof(sendbuf));

    bzero(&recvbuf,sizeof(recvbuf));

    while(fgets(sendbuf,sizeof(sendbuf),stdin) != NULL)

    {

        int tt = strlen(sendbuf);

        sendto(sockfd,sendbuf,tt,,(struct sockaddr*)&server,sizeof(server));

        socklen_t len;

        recvfrom(sockfd,recvbuf,maxn,,NULL,NULL);

        printf("receive message is :");

        fputs(recvbuf,stdout);

        printf("\n");

        bzero(&sendbuf,sizeof(sendbuf));

        bzero(&recvbuf,sizeof(recvbuf));

    }

    close(sockfd);

    return ;

}