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

[Kari Hurtta]

-- Start of PGP signed section.
> 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
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