Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!jarthur!uunet!mcsun!ukc!stl!stc!root44!gwc
From: gwc@root.co.uk (Geoff Clare)
Newsgroups: comp.lang.c
Subject: Re: C obfuscator (Obfuscator code attached)
Message-ID: <2219@root44.co.uk>
Date: 31 May 90 14:23:12 GMT
References: <19858@duke.cs.duke.edu>
Organization: UniSoft Ltd., London, England
Lines: 42

In <19858@duke.cs.duke.edu> drh@romeo.cs.duke.edu (D. Richard Hipp) writes:

>The program below reads a C program from standard input, strips away all
>unnecessary white space and writes the results to standard output.  The
>result is a program which has been obfuscated.

BEWARE!!  Removing white space can alter C code!!

In fact, this is what happened when I compiled Richard's program:

line 22: warning: ambiguous assignment: assignment op taken
line 22: warning: old-fashioned assignment operator
line 22: operands of *= have incompatible types
line 22: warning: old-fashioned assignment operator
line 22: operands of *= have incompatible types
....
line 34: warning: ambiguous assignment: assignment op taken
line 34: warning: old-fashioned assignment operator
line 34: operands of *= have incompatible types

This wouldn't happen with most modern compilers, but serves to demonstrate
the problem.  After inserting a space in all the '=*'s, the program seemed
to run OK, but how do I know it's running correctly?  Subtle alterations
which may never be noticed are possible, e.g. the expression

	x = y + ++z;

after processing becomes:

	x=y+++z;

which actually parses as:

	x = y++ + z;

This silently changes the behaviour of the code, such that it produces
incorrect results and the user is none the wiser.

You have been warned!
-- 
Geoff Clare, UniSoft Limited, Saunderson House, Hayne Street, London EC1A 9HH
gwc@root.co.uk (Dumb mailers: ...!uunet!root.co.uk!gwc)  Tel: +44-71-315-6600