Is this OK? "fmt..." #define high_level_api(fmt...) low_level_api(fmt) On 05/10/2011 11:29 PM, Eric Blake wrote: > On 05/10/2011 08:52 AM, Eric Blake wrote: >> On 05/09/2011 03:24 AM, Lai Jiangshan wrote: >>> These VIR_XXXX0 APIs make us confused, use the non-0-suffix APIs instead. >>> >>> How these coversions works? The magic is using ##. >>> #define high_levle_api(fmt, ...) low_levle_api(fmt, ##__VA_ARGS__) >>> When __VA_ARGS__ is empty, "##" will swallow the "," in "fmt," to avoid compile error. >> >> ##__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 > # define PP_NARG(...) \ > PP_NARG_(__VA_ARGS__,PP_RSEQ_N()) > # define PP_NARG_(...) \ > PP_ARG_N(__VA_ARGS__) > # define PP_ARG_N( \ > _1, _2, _3, _4, _5, _6, _7, _8, _9,_10, \ > _11,_12,_13,_14,_15,_16,_17,_18,_19,_20, \ > _21,_22,_23,_24,_25,_26,_27,_28,_29,_30, \ > _31,_32,_33,_34,_35,_36,_37,_38,_39,_40, \ > _41,_42,_43,_44,_45,_46,_47,_48,_49,_50, \ > _51,_52,_53,_54,_55,_56,_57,_58,_59,_60, \ > _61,_62,_63,N,...) N > # define PP_RSEQ_N() \ > 63,62,61,60, \ > 59,58,57,56,55,54,53,52,51,50, \ > 49,48,47,46,45,44,43,42,41,40, \ > 39,38,37,36,35,34,33,32,31,30, \ > 29,28,27,26,25,24,23,22,21,20, \ > 19,18,17,16,15,14,13,12,11,10, \ > 9,8,7,6,5,4,3,2,1,0 > # define VIR_DEBUG(...) VIR_DEBUG ## PP_NARG(__VA_ARGS__) (__VA_ARGS__) > # define VIR_DEBUG1(xxx) xxx > # define VIR_DEBUG2(xxx, xxx) xxx > ... > # define VIR_DEBUG63(xxx, ..., xxx) xxx > #endif > > 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). > > Thanks to: > https://groups.google.com/group/comp.std.c/browse_thread/thread/77ee8c8f92e4a3fb/346fc464319b1ee5 > for the idea. > > Yeah, it's gross, but we limit the grossness to one header, and the rest > of the code is more maintainable as a result. > -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list