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In article <315a9640.1061096@news.ultranet.com>
phalpern@truffle.ultranet.com (Pablo Halpern) writes:

|> kanze@gabi-soft.fr (J. Kanze) wrote:

|> >The error may be historically conditioned.  As I interpret the C
|> >standard, an enumerated constant has type int, and a constant integral
|> >expression which evalutates to 0 is a null pointer.  Even in the ARM,
|> >however, ``An enumeration is a distinct integral type.''

|> That begs the question, however, whether being an integral type with
|> constant value zero is sufficient to allow assignment to a pointer.

|> Is this legal? I believe all of the above is legal, though IMO it
|> shouldn't be (see below)

|>     enum ptrNil { nil3 };
|>     void *p = nil3;

|> You are claiming that this is not legal because nil3 is of type ptrNil
|> which is not compatable with the type of p. However, I fail to see how
|> nil3 is different from nil1 and nil2 in this respect. All are `integral'
|> types with value zero.

Before going any farther, several people have already pointed out my
mistake to me in private email.  Basically, I missed the fact that when
enum's were made full types, the definition of integral constant was
also extended to include them.  So the above is legal, and nil3 is a
legal null pointer.  (In C, it was definitly legal, because the type of
nil3 was expressedly int.  I mistakenly supposed that because C++
changed this type, it had also rendered the above illegal.)

I, for one, wouldn't object if the definition of a null pointer were
further restricted to limit it to only {int, unsigned int, long,
unsigned long}.
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
Conseils en informatique industrielle --
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