int main(int argc, char *argv)
{
    int                   i, maxi, maxfd, listenfd, connfd, sockfd;
    int                   nready, client[FD_SETSIZE];    
    ssize_t               n;
    fd_set                rest, allrest;
    char                  buf[512];
    socklen_t             clilen;
    struct sockaddr_in    cliaddr, servaddr;
    
    listenfd = socket(AF_INET, SOCK_STREAM, 0);
    
    bzero(&servaddr, sizeof(servaddr)); 
    servaddr.sin_family = AF_INET;
    servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    servaddr.sin_port = htons(SERV_PORT);    
  
    bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));
    listen(listenfd, 5);
  
    maxfd = listenfd; /* 初始化 */
    maxi = -1;        
    for (i = 0; i < FD_SETSIZE; i++)
    {
        client[i] = -1;    
    }
  
    FD_ZERO(&allrest);
    FD_SET(listenfd, &allrest); /* 告诉内核，我们需要对哪些描述字进行测试 */
  
    for (; ;)
    { 
        rest = allrest;
      
        nready = select(maxfd+1, &rest, NULL, NULL, NULL); 
      
        if (FD_ISSET(listenfd, &rest)) /* 返回后， rest结构中的内容被重写，任何未就绪的描述字被置为0 */
        {
            clilen = sizeof(cliaddr);
         connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
              
            for (i=0; i < FD_SETSIZE; i++)
         {
             if (client[i] < 0)
             {
            client[i] = connfd;
            break;    
              }    
          }
              
        if (i == FD_SETSIZE)
        return -1;
            
          FD_SET(connfd, &allrest); 
        if (connfd > maxfd)
        maxfd = connfd;
                    
        if (i > maxi)
        maxi = i;
                    
        if (--nready <= 0)
        {
        continue;
        }
                    
      }
      
      for (i = 0; i < maxi; i++)
      {
          printf("44444444\n");
          if ((sockfd = client[i]) < 0)
          continue;
              
          if (FD_ISSET(sockfd, &rest)) 
          {
          printf("55555555555\n");
          if ((n = read(sockfd, buf, 512)) == 0)
          {
              close(sockfd);
              FD_CLR(sockfd, &allrest);    
              client[i] = -1;
                }
           else
           {
                write(sockfd, buf, n);    
           }
              
           if (--nready <= 0)
               break;
           }    
        }
    }
}