Date: Sun, 5 Apr 1998 21:40:20 -0700 (PDT)
Message-Id: <199804060440.VAA02993@adit.ap.net>
Mime-Version: 1.0
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To: obremski AT nwrain DOT com, djgpp AT delorie DOT com
From: Nate Eldredge <eldredge AT ap DOT net>
Subject: Re: malloc errors
Precedence: bulk

At 02:01  4/5/1998 +0000, Neil & Joey Obremski wrote:
>I've had problems in some of my programs using 'new' which of course
>comes out using malloc anyway.  I found this out quickly when a lot of
>my programs kept crashing and gdb kept saying malloc did it ;)

The traceback should show that `malloc' was called by `__builtin_new', which
should have tipped you off.

>I don't know if there's a problem with malloc in djgpp or not, but it
>certainly doesn't work 100% correctly when I use it.  Some of my
>programs I spent hours debugging only to find that if I pass a
>constant added to a variable to my allocation function (Alloc I called
>it, wow pretty original =) malloc works fine, otherwise it doesn't.

99% chance, this is your bug. `malloc' maintains some fairly delicate data
structures keeping track of what's allocated, and messing them up can mean
crashes. In your case, you're lucky it crashes; makes it a lot easier to
debug than when it just corrupts some other piece of memory. Watch out for
the following:

* `free'ing a pointer not obtained from `malloc'
* `free'ing a pointer twice
* Overwriting the bounds of a `malloc'ed block

There is a package called MSS which can help catch these; look in v2tk/ on
Simtelnet.

Nate Eldredge
eldredge AT ap DOT net