Re: [Qemu-devel] [PATCH V2 2/6] libqblock type and structure defines

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2012-9-12 20:59, Eric Blake 写道:
> On 09/11/2012 09:05 PM, Wenchao Xia wrote:
>>> Seriously?  We require a C99-compliant compiler, which is required to
>>> treat the more compact version identically (all undefined names evaluate
>>> to 0 in the preprocessor), and HACKING doesn't mandate that we spell out
>>> a defined-ness check first.  Okay, so configure adds -Wundef to the set
>>> of CFLAGS, but I fail to see why we want -Wundef (that's an
>>> anachronistic warning, only there to help you if you are writing code
>>> portable to K&R).
>>>
>>    So if the preprocessor replaced __GNUC__ to 0, is there difference
>> between these two kinds of macoros?
>> #if __GNUC__ >= 4
>> #if defined(__GNUC__) && __GNUC__ >=4
>
> The only difference is whether -Wundef will warn, and I'm trying to
> argue that qemu's current use of -Wundef is pointless, as that warning
> exists solely for K&R compatibility, not for modern standard-compliant
> code correctness.
>
  OK ,then I think
#if __GNUC__ >= 4
....
#else
   [warn name space pollution may happen]
#endif
would be better.
-- 
Best Regards

Wenchao Xia