Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!usc!snorkelwacker.mit.edu!bloom-beacon!dont-send-mail-to-path-lines
From: mouse@lightning.mcrcim.mcgill.EDU
Newsgroups: comp.windows.x
Subject: Re:  XSetErrorHandler and access to _XPrintDefaultError routine.
Message-ID: <9102071205.AA10739@lightning.McRCIM.McGill.EDU>
Date: 7 Feb 91 12:05:08 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 37

> I had a need to set up an error handler via XSetErrorHandler to trap
> Xerrors so that my application ([...]) could kill the parent process
> before exiting; otherwise the parent process would hang around
> indefinitely.  I really wanted to duplicate the error diagnostic
> reported by mit/lib/X/XlibInt.c/_XPrintDefaultError(), but as far as
> I know it is unadvertised, therefore unsupported.  For now, I am
> using it with compiler flags configurable in the makefile ready to
> punt if it becomes unavailable.

> Can someone at MIT advise me on this, or consider promoting it to a
> documented Xlib entry point in R5?

Well, I'm not at MIT, but perhaps I'll do :-)

You don't need a documented entry point.  Instead, save the pointer
returned by XSetErrorHandler and call through that to get what you
want.  That is, your error handler should look something like

int (*prevhand)(); /* pointer to previous handler */

errhand(disp,ev)
Display *disp;
XErrorEvent *ev;
{
 ...look at things, perhaps return if you want to ignore the error,
         perhaps kill off your other process...
 (*prevhand)(disp,ev); /* call previous handler */
}

...and in your setup code,

 prevhand = XSetErrorHandler(errhand); /* install our handler */

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu