> -----Original Message----- > From: [EMAIL PROTECTED] > Sent: Thu, 15 Mar 2007 10:31:07 -0600 > To: [EMAIL PROTECTED] > Subject: Re: question on select & FD_ISSET > > Junior <[EMAIL PROTECTED]> wrote: >> Hi all, >> When I do an FD_ISSET, does it clear that fd bit in the set or it leaves >> = >> it as it is (set or not)? >> If it leaves it then I'll have to do an FD_CLR and an FD_SET the next >> time = >> around, correct? (if it is set) >> >> It would seem the FD_ISSET would/should take care of this, no? > > The fdsets that you pass in to select are modified by select so that only > the fds that need attention are set. FD_ISSET only tests the specified > fd, it does not modify the fdset. > > The usual way to use select is in a loop. At the top you set all the > fds in your fdsets, call select, the check which ones are still set > using FD_ISSET(), then go back up to the top.
True, but it seems to me that if I FD_SET them at the top of the loop without FD_CLR first, I will be expanding the set unnecessarily which would waste memory (eventually run out). Since FD_SET adds the set and FD_CLR clears it from the list, FD_SET without FD_CLR would duplicate fds in the set. Not so? --Jr. > See the select_tut(2) man page for examples. > > See W. Richard Stevens' "Advanced Programming in the Unix Environment" > for a detailed description of what's happening. > > > -- > Sebastian Kuzminsky > The universal acid of the true knowledge had burned away a world of > words, > and exposed a universe of things. Things we could use. -- Ken MacLeod ____________________________________________________________ FREE 3D MARINE AQUARIUM SCREENSAVER - Watch dolphins, sharks & orcas on your desktop! Check it out at http://www.inbox.com/marineaquarium
