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From: aw@jello.bae.bellcore.com (Andrew Wason)
Newsgroups: comp.windows.x,comp.windows.x.motif
Subject: Re: Wcl/Motif question  ( WcCallback seg faults )
Message-ID: <1991Apr16.222832.1956@bellcore.bellcore.com>
Date: 16 Apr 91 22:28:32 GMT
References: <14109@arctic.nprdc.navy.mil>
Sender: usenet@bellcore.bellcore.com (Poster of News)
Reply-To: aw@bae.bellcore.com
Organization: Bell Communications Research
Lines: 48

In article <14109@arctic.nprdc.navy.mil>, apple@nprdc.navy.mil (Jim Apple) writes:
> 
> 	I need some help with WcCallback,  I'm trying to use WcCallback
> and XtSetValues to update a XmList widget.   But it seg faults
> when it gets to the XtSetValues call.  Below is a short example of a
>  resource file and the main.c file.
> [...]
> *courseList.wcConstructor:	XmCreateScrolledList
> *courseList.wcCallback:		CreateCourseListCB( )
> 
> [...]
>
> /* as defined in the resource file */
> 
> Widget courseList;

You declare this global Widget variable.


> [...]
> 
> void 	CreateCourseListCB( w, ignored, unused)
>      Widget w;
>      caddr_t  ignored;
>      caddr_t  unused;
> {  
>   
>   [...]
>   
>   XtSetArg(args[argn], XmNitems, (XtArgVal) courses);  argn++;
>   XtSetArg(args[argn], XmNitemCount, (XtArgVal) 3 );  argn++;
>   
>   XtSetValues(courseList,args,argn);

And use it without ever setting it.  'courseList' is NULL at this point.
You should be using 'w' in your callback.  'w' points to the
widget this wcCallback is being called for (the widget named "courseList").

    XtSetValues(w,args,argn);


Andrew

_______________________________________________________________________________

Andrew Wason                                       Bell Communications Research
aw@bae.bellcore.com                                Piscataway, NJ
bellcore!bae!aw