Re: [OT] NULL versus 0 (Re: [PATCH] Use NULL instead of integer 0 in security/selinux/)

[Michael Buesch]

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That's all OK, fine and correct, but
#define NULL 0
would work for both, C and C++ as far as I can see.
Am I missing some special case?


Quoting Kari Hurtta <hurtta+zz1@xxxxxxxxxxxxxxx>:
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> > Quoting Martin Zwickel <martin.zwickel@xxxxxxxxxxxxxx>:
> > > include/linux/stddef.h:
> > >
> > > #undef NULL
> > > #if defined(__cplusplus)
> > > #define NULL 0
> > > #else
> > > #define NULL ((void *)0)
> > > #endif
> >
> > Yes, I never understood the reason for this ugly
> > #if defined(__cplusplus) here.
> > It works, but is IMHO unneccessary.
> >
>
> (This is is off topic, because kernel is not C++, but C).
>
> Some quotations from  Bjarne Stroustrup: The C++ Programming Language
> (Third Edition),
>
>    p. 843:    Note that a pointer to function or a pointer to member
>               cannot be implicity converted to a void *.
>
>    p. 844:    A constant expression (§C.5) that evaluates to 0 can
>               be implicitly converted to any pointer or pointer
>               to member type (§5.1.1.).
>
>
>    p. 88:     In C, it has been popular to define a macro NULL to
>               represent the zero pointer. Because of C++'s tighter
>               type checking, the use of plain 0, rather than any
>               suggested NULL macro, leads to fewer problems. If you
>               feel you must define NULL, use
>
>                   const int NULL = 0;
>
> (typos mine.)
>
> / Kari Hurtta
>
>

- --
Regards Michael Buesch  [ http://www.tuxsoft.de.vu ]


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