Hi Edward, On Thu, Oct 31, 2019 at 12:42:54PM -0400, Edward Diener wrote: > Given: > > #define NO_DATA > #define TRY_VA_OPT(...) __VA_OPT__ (0) 1 > > TRY_VA_OPT() -> expands to 1 as expected > TRY_VA_OPT(NO_DATA) -> expands to 0 1 which is not expected > > when compiled with gcc-9.2 with -std=c++2a. Why is that not expected? The variadic macro TRY_VA_OPT does get tokens in its variable argument (namely, NO_DATA), so __VA_OPT__ expands to its argument (which is 0). https://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html Segher
