Uninitialized externals and statics

[David Brooks]

In article <1989Aug25.185428.3511 at utzoo.uucp> henry at 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 at osf.org
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