似乎终于有点看懂select了

从只会用WSAxxxx到看懂select，还真是一个飞跃，赶快记下来。
select一般用于单线程、并发服务器

SOCKET msock;
fd_set rfds, afds;

msock = passiveTCP( service, QLEN );
FD_ZERO( &afds );
FD_SET( msock, &afds );

while( 1 )
{
   memcpy( &rfds, &afds, sizeof( rfds ) );
   if( select( FD_SETSIZE, &rfds, (fd_set*)0, (fd_set*)0, (struct timeval *)0 ) == SOCKET_ERROR ) )
      errexit;
   if( FD_ISSET( msock, &rfds )) 
   {
      SOCKET ssock;
      alen = sizeof( fsin );
      ssock = accept( msock, (struct sockaddr *)&fsin,&alen );
      if( ssock == INVALID_SOCKET )
        errexit;
      FD_SET( ssock, &afds );
   }

   for( fdndx=0; fdndx < rfds.fd_count; ++ fdndx )
   {
      SOCKET fd=rfds.fd_array[fdndx];
      if( fd != msock && FD_ISSET( fd, &rfds )) 
      if( echo(fd) == 0 ) // DO Echo Process
      {
       closesocket( fd );
       FD_CLR( fd, &afds );
      }
   }
}