Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!ATHENA.MIT.EDU!kit
From: kit@ATHENA.MIT.EDU (Chris D. Peterson)
Newsgroups: comp.windows.x
Subject: Re: Question on Callbacks
Message-ID: <8903102248.AA06321@DORA.MIT.EDU>
Date: 10 Mar 89 22:48:11 GMT
References: <332@salt.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 40


> I get the infamous "Segmentation fault" error and everything bombs out.
> 	What am I doing wrong ? 

Saber C to the rescue...

In your Private header file the definition for the instance record for
you widget is:

typedef struct _BaarsBoxRec
{
  CorePart	  core;
  BaarsBoxPart	  BaarsBox;
} BaarsBoxRec;

It should be:

typedef struct _BaarsBoxRec
{
  CorePart	  core;
  CompositePart   composite;
  BoxPart 	  box;
  BaarsBoxPart	  BaarsBox;
} BaarsBoxRec;

Since you are leaving out some of the fields the XtOffset() macro gets
confused and when you specify a resource (In this case a callback list with
XtAddCallback) it scribbles all over your instance record.  In your case it
was setting the number of children to some garbage value, and thus running off
the end of an array, causing a seg. fault.

						Chris D. Peterson     
						MIT X Consortium /
						Project Athena 

Net:	kit@athena.mit.edu		
Phone: (617) 253 - 1326			
USMail: MIT - Room E40-321
	77 Massachusetts Ave.		
	Cambridge, MA 02139