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 ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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