Re: CGFloat and 64 Bit
Re: CGFloat and 64 Bit
- Subject: Re: CGFloat and 64 Bit
- From: Clark Cox <email@hidden>
- Date: Mon, 9 Feb 2009 18:48:04 -0800
On Mon, Feb 9, 2009 at 3:17 PM, Steve Sisak <email@hidden> wrote:
> At 12:52 PM -0800 2/9/09, Clark Cox wrote:
>>
>> On Mon, Feb 9, 2009 at 12:10 PM, Sean McBride <email@hidden>
>> wrote:
>> > On 2/9/09 11:24 AM, Clark Cox said:
>> >>That is, the preprocessor treats any undefined identifier in an '#if'
>>>>
>>>> or '#elif" as if it were defined to be zero.
>>>
>> > I'm not a language lawyer, but I believe the latter is not guaranteed
>> to
>>>
>>> evaluate to 0 if the macro is not defined. However, I imagine 99% of
>>> compilers will evaluate it to 0. gcc certainly does.
>>
>> I am 100% positive that this is guaranteed by the standard:
>>
>>> From 6.10.1.3:
>>
>> "After all replacements due to macro expansion and the defined unary
>> operator have been performed, all remaining identifiers are replaced
>> with the pp-number 0"
>
> Just to be pedantic, which standard?
>
> You are definitely describing the behavior of the C++ preprocessor.
>
> IIRC, in ANSI C, #if of an undefined symbol is an error, and I'm not sure
> about C99.
It was the C99 standard that I was quoting above. The equivalent
passage from the C89/C90 standard:
"After all replacements are finished, the resulting preprocessing
tokens are converted into tokens, and then all remaining identifiers
are replaced with 0"
and the equivalent passage from the C++ standard:
"After all replacements due to macro expansion and thedefinedunary operator
have been performed, all remaining identifiers and keywords, except
for true and false, are
replaced with the pp-number 0"
> So, I belive #if defined(x) && (x) is good defensive programming.
Nope, it's still redundant. And I am 100% sure of that.
--
Clark S. Cox III
email@hidden
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