pilot error; memset OK

[cr...@goingware.com]

This is most embarrassing.

It turns out that the _real_ problem I've been having all along is that 
I did something with a GUI toolkit I'm using in my application that 
the toolkit author didn't envision.

The author did in fact tell me he did things a certain way, but he 
thought it would be OK if I did it my way.  But what happened when 
I did it my way was that disposing of a pane that was populated 
with subpanes would delete all the subpanes twice, corrupting 
memory horribly.

Of course what I did in my case, was to add a pane to my app that 
would read in an XML file to get stuff to display in the pane.  I would 
delete the pane that was previously in that place.  Up until that 
point I had only been putting panes into the app that stayed in 
place, so it seemed OK to do what I was doing.

So I quite coincidentally wrote code that addled the heap and then 
created a DOM_Parser and parsed a file, which does a lot of 
allocation and so would crash.

Why did it seem to help to roll my own memcpy?  One possible 
reason is that the memcpy provided by codewarrior is a compiler 
intrinsic rather than a library function.  Another possibility is that 
simply by writing new code I changed the conditions just a little bit 
to delay a crash.

But what happened is that after rolling my own memset last night I 
was able to read in a whole XML file and walk the tree.  But I 
couldn't do that again today, and after investigating further all kinds 
of chaos occurred.

I had to be very careful about my testing because testing twice with 
apparently the same initial conditions wouldn't get the same 
results.  For most of my work the last couple weeks, stepping 
through things with the source debugger would make crashes not 
occur.  On the other hand, simply recompiling source that hadn't 
changed would turn a non-crash into a crash, probably because I 
wrote lots of nice garbage into memory.

I guess I've been suitably punished for my error.

The GUI library I'm using is a very nice cross-platform library that a 
friend wrote, that he's used for some successful products of his 
own.  But he's never been willing to release it, feeling that it wasn't 
ready yet.  I'm the first person besides himself to get to use it, and 
part of the deal is that I'm to give him feedback on getting it ready 
for release, and also I'm going to write documentation for it.

I'm not sure what he should do about my problem if anything; it's 
nicer to write my code the way I did than the way he 
recommended, but it would be a lot of work for him to rearchitect 
his code to work the way I want it to.

Anyway, thanks for all your help.

What I'd like to do, once I get my fabled build to my client, is do a 
fresh check out of the latest xerces sources, apply my patches to 
the clean source, and submit my changes after making sure it all 
works right.  In the course of debugging I've put all kinds of 
diagnostic code into everywhere and there's probably lots of 
footprints left.

So, should this merit some kind of award?  Porting to a new 
platform with a corrupted heap?

Mike Crawford
GoingWare - Sometimes Confused Software Development and 
Consulting
http://www.goingware.com
crawford@goingware.com