Re: !foo vs foo == nil
Re: !foo vs foo == nil
- Subject: Re: !foo vs foo == nil
- From: "Clark Cox" <email@hidden>
- Date: Thu, 21 Aug 2008 12:16:54 -0700
On Thu, Aug 21, 2008 at 11:56 AM, Scott Ribe <email@hidden> wrote:
>>> Could you tell me which part of the standard states that NULL is 0.
>
>
>> NULL *can* be 0, it isn't *necessarily* 0
>
>
> It follows from the rules re conversions that it must be either 0, or 0 cast
> to a pointer type.
Or an "implementation defined null pointer constant". That is, this is
perfectly legal:
#define NULL __builtin_special_null_keyword_that_is_specific_to_my_compiler
as long as, when
__builtin_special_null_keyword_that_is_specific_to_my_compiler is
converted to a pointer type, it becomes a null pointer.
GCC uses such an implementation defined constant to allow additional
warnings when NULL is used in a non-pointer context (i.e. int i = 0;).
> No value other than 0 is guaranteed to cast to the
> machine's actual null address (whatever bit pattern that might actually be).
>
> 6.3.2.3 which you quoted, does not provide for any value other than 0.
--
Clark S. Cox III
email@hidden
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