On Sun, 29 Sep 2019 at 05:08, Edward Diener <eldlistmailingz@xxxxxxxxxxxxxx> wrote: > > On 9/26/2019 3:25 PM, Edward Diener wrote: > > I have a macro which uses the C++20 construct of __VA_OPT__. During a > > compilation with og gcc-9.2 with the '-std=c++11' option the macro is > > encountered in a header file, but it is never actually invoked in the > > code. And yet gcc-9.2 gives an error of: > > > > error: __VA_OPT__ is not available until C++2a > > > > Why would this be happening ? > > > > I realize I can surround the macro with > > > > # if defined(__cplusplus) && __cplusplus > 201703L > > #endif > > > > but my understanding is that macro code is not checked until it is > > actually invoked during the preprocessing stage. > > > > > > > > I know I saw this message but since I can not reproduce the occurrence > in my code the OP should be ignored. You were probably using an option like -pedantic-errors when you saw the error. The token __VA_OPT__ is a reserved name, so in older standards that don't define __VA_OPT__ the compiler is free to decide what it means. If it wants to issue an error if that token is encountered, it can do so. If you think there's a good reason to allow it and delay errors until it is used please file it in bugzilla (although it might not be feasible to change the preprocessor that way).
