Xref: utzoo comp.lang.c:25339 comp.unix.wizards:20311
Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!unido!gmdzi!wittig
From: wittig@gmdzi.UUCP (Georg Wittig)
Newsgroups: comp.lang.c,comp.unix.wizards
Subject: Re: Argument validity checking (addresses)
Keywords: address probing
Message-ID: <1891@gmdzi.UUCP>
Date: 22 Jan 90 13:40:44 GMT
References: <1990Jan18.175540.12131@wolves.uucp>
Organization: GMD - The German National Research Centre for Computer Science
Lines: 37

ggw@wolves.uucp (Gregory G. Woodbury) writes:
>When a subroutine depends on the user to pass addresses (strings, structures,
>or functions) that the subroutine is going to use, and the subroutine wants
>to be robust about not killing the process if the user makes a mistake,
>validity checking the aruments passed is one of the front line defenses.

>The problem, however, is that UN*X environments (at least Sys5 and related
>ones) do not provide a general means of determining if a given address is
>going to generate a memory fault of some kind.

My solution is the following one:

	#define MIN_NON_NIL_PTR ((unsigned long) 1L)
	#define MAX_NON_NIL_PTR ((unsigned long) 0x00ffffffL)

	if ( ! ( ((unsigned long) ptr_in_question) >= MIN_NON_NIL_PTR   &&
		 ((unsigned long) ptr_in_question) <= MAX_NON_NIL_PTR ) )
	{	... get_angry_or_whatever () ...
	}
or, if you allow a nil ptr:

	if (ptr_in_question != 0   &&   (...see above...))

I know, that's not a perfect solution. The values MIN_NON_NIL_PTR and
MAX_NON_NIL_PTR may vary from machine to machine. You know how to use #ifdef :-)
The condition ``MIN <= ptr <= MAX'' may be more complicated, and so on, and so
on ...

BUT it works on surprising number of machines.

Does someone know if there exists a portable ANSI C conforming solution for that
problem?
-- 
Georg Wittig   GMD-Z1.BI   P.O. Box 1240   D-5205 St. Augustin 1 (West Germany)
email: wittig@gmdzi.uucp   phone: (+49 2241) 14-2294
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