On 05/10/2011 09:29 AM, Eric Blake wrote: >> ##__VA_ARGS__ is a GNU extension; it does not work on all C99 compilers. >> >> I'm worried that this is not portable. > > But, we CAN do: > > #ifdef __GNUC__ > # define high_level(fmt, ...) low_level(fmt, ##__VA_ARGS__) > #else > > suitably expanded (and we can also place a cap on the maximum number of > arguments we ever expect to see in VIR_DEBUG, rather than going all the > way to the C99 limit of 63).
Even simpler, using ideas from https://gustedt.wordpress.com/2010/06/08/detect-empty-macro-arguments/ (and actually tested this time): #define ARG_8(_0, _1, _2, _3, _4, _5, _6, _7, ...) _7 #define HAS_COMMA(...) ARG_8(__VA_ARGS__, 1, 1, 1, 1, 1, 1, 0) # define f(...) f_(f, HAS_COMMA(__VA_ARGS__), __VA_ARGS__) # define f_(a, b, ...) f__(a, b, __VA_ARGS__) # define f__(a, b, ...) a##b(__VA_ARGS__) # define f0(x) printf("%s", x) # define f1(x, ...) printf(x, __VA_ARGS__) I'll work up a followup patch along these lines; it doesn't seem too impossible to guarantee C99 portability for the four macros. > Yeah, it's gross, but we limit the grossness to one header, and the rest > of the code is more maintainable as a result. -- Eric Blake ebl...@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org
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