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From: dbrooks@osf.osf.org (David Brooks)
Newsgroups: comp.lang.c
Subject: Re: Uninitialized externals and statics
Message-ID: <609@paperboy.OSF.ORG>
Date: 26 Aug 89 04:38:37 GMT
References: <2128@infmx.UUCP> <4700042@m.cs.uiuc.edu> <1989Aug25.185428.3511@utzoo.uucp>
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Reply-To: dbrooks@osf.org (David Brooks)
Organization: Open Software Foundation
Lines: 28

In article <1989Aug25.185428.3511@utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
[...]
> There is one, repeat one, special
>case:  an integer constant expression of value zero -- repeat, an
>integer CONSTANT expression of value ZERO -- gets turned into a NULL
>pointer of the appropriate type when compared to a pointer.  Note that
>it is the integer, not the pointer, that is converted.  Note that no
>such conversion is done on integer variables, integer constant expressions
>with non-zero values, or general integer expressions.

I was about to make the same point myself.  This can be determined by
careful reading of K&R II: try section A6.6, page 198.  The constant 0
may be converted by a cast, by assignment, or by comparison, to a
pointer.  This legitimizes "if (p == 0)".  Requiring an actual
conversion step removes any implicatino that the pointer is zero-valued.

Anyway, I had a question: what is this assumption about "all bits
zero" for the common case of initializing ints?  I wonder if there's
any machine out there that represents int 0 with some other bit
pattern...

Those of us old enough to remember when ones-complement seemed like a
good idea can begin to break into a sweat at this point :-)
-- 
David Brooks			dbrooks@osf.org
Open Software Foundation	uunet!osf.org!dbrooks
11 Cambridge Center		Personal views, not necessarily those
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