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From: djimenez@ringer.cs.utsa.edu (Daniel Jimenez)
Newsgroups: comp.lang.c
Subject: Re: argv[] terminated by a NULL pointer?
Message-ID: <1991Jun28.052339.14611@ringer.cs.utsa.edu>
Date: 28 Jun 91 05:23:39 GMT
References: <12187@hub.ucsb.edu> <14603@dog.ee.lbl.gov>
Organization: University of Texas at San Antonio, San Antonio, Texas
Lines: 25

In article <14603@dog.ee.lbl.gov> torek@elf.ee.lbl.gov (Chris Torek) writes:
>In article <12187@hub.ucsb.edu> angst@cs.ucsb.edu
>(Hopelessly in love w/Donna Reed) writes:
>>I'm porting some code that assumes that the argv[] array is terminated
>>by a NULL pointer....  am I right in my belief that argv[] is not
>>*guaranteed* to be terminated by a NULL pointer?  
>
>Under Version 6 Unix, argv[argc] is (char *)-1.  This violates the
>following wording from X3.159-1989 (`ANSI C'):
>
>    argv[argc] shall be a null pointer.  (2.1.1.2, p. 7)
>

Who said the null pointer couldn't be -1?
On a system where the null pointer is represented by all bits one,
the following statement:
((char *)0) == ((char *)-1) 
would be true, since 0 in a pointer context is defined to be
the null pointer, and -1 is also the null pointer.
They would have the same bit pattern.
-- 
*    Daniel A. Jimenez			*  Please excuse my longwindedness.
*    djimenez@ringer.cs.utsa.edu	*  This Sun terminal makes everything
*    dajim@lonestar.utsa.edu		*  I write seem important.
* Opinions expressed here are mine only, and not those of UTSA.