rlh2@ukc.ac.uk (Richard Hesketh) (11/14/89)
I have a window id. obtained via various means, in most cases from a property on the root window and I wish to check whether that window still exists in the server. Looking at the Xlib manual in Chapter 4 I find: 4.1 Obtaining Window Information [ ... ] Because they are most frequently used by window managers, these functions all return a status to indicate whether the window still exists. -- Ah, ha. Just what I need!? The manual does not explicity say that the following requests can generate BadWindow errors (I want my program to be informed of any bad windows synchronously): XQueryTree() and XGetGeometry(). I would like the status to be set to indicate the window doesn't exist. Unforturnately all these still generate BadWindow errors. From my reading of section 4.1 if a bad Window is passed then it should return a Status of 0 (failure). Should this be happening? Is it dependent on the Server I am connecting to? Do I have to trap the error using an error handler? If I do have to install an error handler how can I re-install the previous error handler if one had been installed (*I* cannot know about previous handlers that may have been installed)? Thanks, Richard Richard Hesketh : rlh2@ukc.ac.uk ..!mcvax!ukc!rlh2 : @nsfnet-relay.ac.uk:rlh2@ukc.ac.uk --- Computing Lab., University of Kent at Canterbury, Canterbury, Kent, CT2 7NF, United Kingdom. Tel: (0227) 764000 ext. 3682
rws@EXPO.LCS.MIT.EDU (Bob Scheifler) (11/15/89)
From my reading
of section 4.1 if a bad Window is passed then it should return a Status
of 0 (failure). Should this be happening?
Yes, if your error handler returns.
Do I have to trap the error using an error handler?
Yes.
If I do have to install an error handler how can I re-install the
previous error handler if one had been installed (*I* cannot know about
previous handlers that may have been installed)?
In R4, XSetErrorHandler and XSetIOErrorHandler return the old handler.