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 12:24:55 -0700
On Thu, Aug 21, 2008 at 12:16 PM, Clark Cox <email@hidden> wrote:
> 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;).
Arg, that example of a non-pointer context that GCC can warn about
should have been (int i = NULL;)
--
Clark S. Cox III
email@hidden
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