On Sat, Jul 15, 2017 at 07:43:09AM +0900, Mike Hommey wrote: > > - There were occasional cases where we wished if variable-length > > arrays, flexible array members and variadic macros were available > > in our codebase during the course of this project. We would > > probably want to add a similar test baloon patch for each of > > them to this series that is currently two-patch long. > > FWIW, variadic macros have subtle implementation differences that can > cause problems. > For instance, MSVC only supports ##__VA_ARGS__ by way of > ignoring ## somehow, but has the default behavior of dropping the comma > when __VA_ARGS__ is empty, which means , __VA_ARGS__ *without* ## has a > different behavior. > See also https://connect.microsoft.com/VisualStudio/feedback/details/380090/variadic-macro-replacement When there's any other non-optional argument, you can work around this by just lumping that argument in with the varargs. So don't do: #define FOO(fmt, ...) printf(fmt, __VA_ARGS__) which fails when the format has no placeholders. Instead do: #define FOO(...) printf(__VA_ARGS__) That limits your interface for variadic macros, but in practice it doesn't usually come up (there are also disgusting macro tricks you can do to cover the true 0-arg case portably, but we haven't had to turn to them yet). -Peff
