Using C++20 __VA_OPT__ in a macro gives an error

[Edward Diener]

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.