gcc and NULL function pointers.

[Jim Patterson]

In article <ND1CKO3 at xds13.ferranti.com> peter at ficc.ferranti.com (Peter da Silva) writes:
>
>The "best" definition for "NULL" is entirely compiler/hardware dependent.

I don't agree. Any compiler should generate the SAME code whether you
define NULL to be 0 or (void*)0, provided it is coerced to the correct
pointer type where used. So, (void*)0 should always be correct if you
follow the rules, regardless of compiler/hardware, and generate equivalent
code.

On the other hand, defining NULL to be 0 allows NULL to be misused as a
non-pointer constant. For example, I've seen this code around here the
odd time:

     char x[5];
     x[4] = NULL; /* sic */

If NULL is (void*)0, these slipups will likely be caught. If only some
compilers define it this way, you only find out about it when you compile
with those compilers.

>And that's the point of *having* a standard for the language, after all.

Which is why there should be a standard definition. It avoids suprises
when porting to new environments.  Except for the substantial prior
art for #define NULL (0), I think (void*)0 is ALWAYS the best
definition.

Of course, prior art is an important consideration, so I can't fault
the X3J11 group for leaving the definition somewhat ill-defined, but
if it were designed again from scratch I think the argument for 
#define NULL (0) would be pretty weak.
-- 
Jim Patterson                              Cognos Incorporated
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