Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!tekbspa!optilink!cramer
From: cramer@optilink.UUCP (Clayton Cramer)
Newsgroups: comp.sys.ibm.pc
Subject: Re: null pointer assignment?
Keywords: null pointer, R6001, run-time error
Message-ID: <977@optilink.UUCP>
Date: 21 Feb 89 23:06:13 GMT
References: <1413@cod.NOSC.MIL>
Organization: Optilink Corporation, Petaluma, CA
Lines: 31

In article <1413@cod.NOSC.MIL>, murphys@cod.NOSC.MIL (Steven P. Murphy) writes:
> 	How do you track down a run time null pointer assignment?
> 
> 	I have written a assembly language subroutine for QuickC, the 
> routine works ok, but when the program is over I get:
> 
> 
> 			run-time error  R6001
> 			- null pointer assignment
> 
> 	I have tried tracing through it with CodeView, but no luck.  So
> does any one have any suggestions for locating the problem.
> 
> 				Murph,

What this message means is that when the program got ready to exit,
it found that someone had altered the Microsoft copyright message
at DS:0.  The slowest but easiest way to find this program with 
CodeView is to set up a tracepoint like this:

    TPB DS:0 l20

Keep in mind that this will only work once you have reached main,
and the DS register is established.  Then start the program running,
and go get a cup of coffee -- and maybe dinner, and maybe leave it
running over night, but eventually it will find the bad function 
that is overwriting DS:0.
-- 
Clayton E. Cramer
{pyramid,pixar,tekbspa}!optilink!cramer
Disclaimer?  You must be kidding!  No company would hold opinions like mine!