想实现一个程序 UDP例程的。 实现2个客户端通信， 而不是客户端于服务器的通信，大家帮忙想下怎么写啊。下面是我写的客户端和服务器的通信。 服务器作为中转数据
/* server.c*/

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

#define LISTENQ 5
#define MAXLINE 512
#define max(x,y) (((x)>(y))?(x):(y))

int main()
{
  int sockfd;
  int size;
  int nbytes;
  struct sockaddr_in servaddr;
  char message[MAXLINE];
  char sndbuff[MAXLINE];
  fd_set infds;
  int maxfd;

  /*创建套接字*/
  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (sockfd < 0){
  printf("Socket created failed\n");
  return -1;
  }

  /*填充socket_in 结构*/
  servaddr.sin_family = AF_INET;
  servaddr.sin_port=htons(6666);
  servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
  if (bind(sockfd, (struct sockaddr*)&servaddr, sizeof(servaddr)) < 0){
  printf("bind failed\n");
  return -1;
  }

  size = sizeof(servaddr);

  while(1){
  FD_ZERO(&infds);
  FD_SET(fileno(stdin),&infds);
  FD_SET(sockfd,&infds);
  maxfd=max(fileno(stdin),sockfd)+1;

  if (select(maxfd,&infds,NULL,NULL,NULL)==-1){
  printf("select io error\n");
  return -1;
  }

  /*如果scoket io 准备好了*/
  if (FD_ISSET(sockfd,&infds)){
  nbytes = recvfrom(sockfd, message, MAXLINE, 0, (struct sockaddr*)&servaddr, &size); 
  if (nbytes < 0){
  printf("recvfrom(server) failed.\n");
  return -1;
  }
  else{
  message[nbytes]=0;
  printf("receive message from %s %s", inet_ntoa(servaddr.sin_addr.s_addr), message);
  }
  }

  /*如果是输入IO 准备好了*/
  if (FD_ISSET(fileno(stdin),&infds)){
  if (fgets(sndbuff, MAXLINE, stdin) == NULL){
  return -1;
  }
  nbytes = sendto(sockfd, sndbuff, sizeof(sndbuff), 0, (struct sockaddr*)&servaddr, size);
  if (nbytes < 0){
  printf("sendto(server) failed.\n");
  return -1;
  }
  }

  }

  close(sockfd);

  return 0;
}

/*client.c*/

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

#define LISTENQ 5
#define MAXLINE 512
#define max(x,y) (((x)>(y))?(x):(y))

int main()
{
  int sockfd;
  int nbytes;
  struct sockaddr_in servaddr;
  char message[MAXLINE];
  char sndbuff[MAXLINE];
  fd_set infds;
  int maxfd;

  /*创建套接字*/
  sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (sockfd < 0){
  printf("Socket