linux tcp server demo

 #include <sys/types.h>
 #include <sys/socket.h>
 #include <string.h>
 #include <netinet/in.h>
 #include <stdio.h>
 #include <stdlib.h>

 #define MAXLINE 80
 #define SERV_PORT 6970

void do_echo(int sockfd, struct sockaddr *pcliaddr, socklen_t clilen)
{
   int n;
   socklen_t len;
   char mesg[MAXLINE];

  for(;;)
  {
    len = clilen;
    /* waiting for receive data */
     n = recvfrom(sockfd, mesg, MAXLINE, 0, pcliaddr, &len);
    /* sent data back to client */
    printf("receieve: %s\n",mesg);
    fflush ( stdout ) ;
    sendto(sockfd, mesg, n, 0, pcliaddr, len);

   }
 }

 int main(void)
 {
 int sockfd;
 struct sockaddr_in servaddr, cliaddr;
 sockfd = socket(AF_INET, SOCK_DGRAM, 0); /* create a socket */

 /* init servaddr */
 bzero(&servaddr, sizeof(servaddr));
 servaddr.sin_family = AF_INET;
 servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
 servaddr.sin_port = htons(SERV_PORT);

 /* bind address and port to socket */
 if(bind(sockfd, (struct sockaddr *)&servaddr, sizeof(servaddr)) == -1)
{
 perror("bind error");
 exit(1);
 }

 do_echo(sockfd, (struct sockaddr *)&cliaddr, sizeof(cliaddr));

 return 0;
 }