🚀 go-pugleaf

   From: ctoomey@ccvax.ucd.ie
   Newsgroups: comp.windows.open-look
   Date: 22 Jan 93 13:27:48 GMT
   Organization: University College Dublin

   Hi All,
	   came across a weird problem with XView 3.0 today. I created a canvas as
   a child of a frame and attached 11 items to it's paint window using
   XV_KEY_DATA. This worked fine with XView 2.0 but crashed under version 3.0.
   The cause seemed was an xv_get(window,XV_KEY_DATA,5) instruction which should
   have returned NULL because that item had not yet been set. I tried setting the 
   item in advance - now the thing crashed just after the start of the xv main
   loop. After many hours poring over manuals and wracking my brains for possible 
   causes I tried changing the 5 to a 23. It worked!

	   What I'd like to know is why? Is it a mistake in my code (there are 
   definitely no other items with this number) or is there an instruction in XView
   3.0 like "if key==5 then crash" :-) If anyone has any ideas I'd like to know...


can somebody FAQize this?

anyway, the deal is that the XView library itself uses
XV_KEY_DATA extensively, so you must be certain that the
key you use is unique.  the methodology for doing this is
to obtain the key from the function xv_unique_key(void).

if you just pick arbitrary numbers, especially low numbers,
your likelyhood of collision is quite high, as is your likelyhood
of trampling something that the library depends on.

<<tank

--

*********************************************************************

	Richard M. "Tank" Goldstein		rickg@Eng.Sun.COM
	Window Developer Environment
	SunSoft, Inc.

	"I'm a scientist.  I don't think, I observe."
			-Dr. Clayton Forrester

*********************************************************************

In article <RICKG.93Jan25125945@irondude.eng.sun.com>, rickg@eng.sun.com (The Tankster) writes:
|> 
|> anyway, the deal is that the XView library itself uses
|> XV_KEY_DATA extensively, so you must be certain that the
|> key you use is unique.  the methodology for doing this is
|> to obtain the key from the function xv_unique_key(void).
|> 
Another approach, one that I often use, is to use a pointer to some application
datum.  This is extremely unlikely to match any key used internally by the library.

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