Eric Niebler actually asked this on StackOverflow a few years ago: https://stackoverflow.com/q/48045470/2069064The accepted answer there is:#define PP_THIRD_ARG(a,b,c,...) c #define VA_OPT_SUPPORTED_I(...) PP_THIRD_ARG(__VA_OPT__(,),true,false,) #define VA_OPT_SUPPORTED VA_OPT_SUPPORTED_I(?)