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

[Eric Blake]

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.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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