Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!cbmehq!cbmdeo!jsmami!jsmoller
From: jsmoller@jsmami.UUCP (Jesper Steen Moller)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Demo versions
Message-ID: <189eddd4.ARN03888@jsmami.UUCP>
Date: 2 Feb 91 19:11:00 GMT
References: <91031.112859GHGAQA4@cc1.kuleuven.ac.be> <2438@shodha.enet.dec.com>
Reply-To: cbmvax!cbmehq!cbmdeo!jsmami!jsmoller
Followup-To: comp.sys.amiga.programmer
Organization: Danish SofTech
Lines: 55

In article <2438@shodha.enet.dec.com>, Hans Ridder writes:

> In article <91031.112859GHGAQA4@cc1.kuleuven.ac.be> GHGAQA4@cc1.kuleuven.ac.be (Tyberghein Jorrit) writes:
> >It is very easy to make a demo version of an editor, simply remove the
> >'save' option and the problem is useles while you still can test the
> >power of the editor (look at the TurboText demo). But my debugger simply
> >does not have a 'save' command....
> 
> How about disabling the 'load' command (if it has one), and have a built
> in program with a bug in it (causes a Guru or some such).  Then only
> allow that program, and maybe a few other places in memory to be
> examined/modified/traced, like the task structure for the "broken" task,
> and some system structures....  When the user trys to examine an area
> outside of the boundaries, give a nice error message about buying the
> non-demo version.

Good idea...

> Of course someone could use another debugger to "fix" your debugger,
> possibly allowing full or nearly full functionality, but there's some
> level of risk you're going to have take to get the benefit of the
> publicity of the demo.

Well, not really. If you remove a command like load, which is (I guess)
is a rather longish one, nobody can replace it. If you put a kludge in
to remove load, it's not good enough. Exclude it by something like:

void load(void)
{
#ifdef DEMO
printf("Can't load - It's just a demo");
#else
....
/* stuff for loading or whatever - choose a long and hard to imitate
command... */
....
#endif

(or use a comditional assembly directive in assembler)
I used the same scheme for a commercial project of mine, and nobody
can make a save-routine work, if it isn't there.
Many good crackers can, however, remove the "5K max", or "ten minutes
only, and never of the 1st of April"-limitations. :-)

/Jesper

> >        Jorrit Tyberghein

> -hans

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