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From: merlyn@attunix.att.com (Steve Humphrey)
Newsgroups: comp.windows.x,comp.windows.open-look
Subject: Re: OL Flat Checkbox Widget Woes
Message-ID: <1991May29.182035.26184@cbnewsm.att.com>
Date: 29 May 91 18:20:35 GMT
References: <kkirksey.910528220951@lab12.eng.auburn.edu>
Sender: mls@cbnewsm.att.com (mike.siemon)
Followup-To: comp.windows.open-look
Organization: AT&T Bell Laboratories
Lines: 65


> I'm having a terrible time using the OL flat checkbox widget.  I've
> included at the bottom the sample program I wrote to try my hand at using
> the flat checkbox.  When I run it as is, it gives me a bus error.
> I use dbx to trace it, I get the following dump:

>	warning: core file read error: address not in data space
>	`FCheckBox`DrawLabel() at 0xf7731774
>	...
>
> typedef	struct _Item
> 	{
> 		String	label;
> 	} Item;
> 
> static	Item	items[] = {
> 						{"CSE100"},
> ...
>
> 	n = 0;
> 	XtSetArg (args[n], XtNitems, items); n++;
> 	XtSetArg (args[n], XtNnumItems, NUM_ITEMS); n++;
> 
> 	rs_flat_checkbox = XtCreateManagedWidget(
> 					"rs_flat_checkbox",
> 					flatCheckBoxWidgetClass,
> 					toplevel,
> 					args, n);
> ...

I tried your code exactly as sent; it works fine on my '386 running
the OPEN LOOK 4.0 toolkit (equivalent to the OpenWindows 2.5 OLIT).
I have not tried it yet on a Sun. However, the problem MAY be in the
definition of the Item structure.  Now the ``Open Look at UNIX'' book
has exactly the same problem, and I thought John Miller tested his
examples on a Sun, so something else may be wrong.

The XtNitems resource takes an array of items, each of which is
defined by a structure of XtArgVal's. This parallels the way attributes
are passed in regular XtCreateWidget or XtSetValues calls, for exactly
the same reason: The widgets (or Intrinsics) do not know a priori
the type of each value, thus the values must be coerced to a common
type for passing from the client to the widget.

So the correct code fragment from the above should be:

> typedef	struct _Item
> 	{
> 		XtArgVal	label;
> 	} Item;
>
> static	Item	items[] = {
> 						{ (XtArgVal)"CSE100" },
> ...

XtArgVal is defined as a "long" on Suns, versus the "char*" definition
of String. Now I would think this would be OK, but I'm not familiar
with native types of a SPARC chip.

Even if it turns out this is not the problem at hand, I suggest
using the XtArgVal type in the definition of the XtNitems array's
structure. Eventually this *will* save you a core dump.

Steve Humphrey
UNIX System Laboratories