Re: [PATCH] Use NULL instead of integer 0 in security/selinux/

[Richard B. Johnson]

On Thu, 8 Jul 2004, P. Benie wrote:

> On Thu, 8 Jul 2004, Richard B. Johnson wrote:
> > On Thu, 8 Jul 2004, Herbert Xu wrote:
> > > What's wrong with using 0 as the NULL pointer?
> >
> > Because NULL is a valid pointer value. 0 is not. If you were
> > to make 0 valid, you would use "(void *)0", which is what
> > NULL just happens to be in all known architectures so far,
> > although that could change in an alternate universe.
>
> False. "An integer constant expressions with the value 0, or such an
> expression cast to type void *, is called a null pointer constant. If a
> null pointer constant is assigned to or compared for equality with a
> pointer, the constant is converted to a pointer of that type", and "Any
> two null pointers shall compare equal."
>
> In other words, when you use 0 as a null pointer, you really do get a null
> pointer. If you are working on an architecture where the bit pattern of
> the integer 0 and null pointers are not the same, the compiler will
> perform the appropriate conversion for you, so it is always correct to
> define NULL as (void *)0.

That's NOT what is says. It states that a NULL pointer is converted to
the appropriate type before any comparison is made. It does NOT say
that 0 is a valid null-pointer.

>
> Personally, I always use 0 and NULL for integers and null pointers
> respectively, but that's because of long estalished conventions that make
> the code readabile, rather than anything to do with validity of the code.
>
> Peter
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Cheers,
Dick Johnson
Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips).
            Note 96.31% of all statistics are fiction.


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