C/C++ #define Macro inside macro?

Question

I would like something like:

#define C_OR_CPP(C__, CPP__) #ifdef __cplusplus\\
CPP__\\
#else\\
C__\\
#endif

Is it possible? Maybe some dirt

Answer 1

My English is poor, and I'm sorry for language mistakes and typos if any.

If #ifdef must not wrap the macro invocation, there is a solution not so graceful.

g++ only: You may try this in selective occasions. But if there are commas in a or b, workarounds are still needed. It's simply based on the fact that __cplusplus is defined to "1" when in a C++ environment and remains itself while not.

#define SELECT1(a, b) a
#define SELECT__cplusplus(a, b) b
#define xcat(a,b)  a##b
#define concat(...) xcat(__VA_ARGS__)
#define C_OR_CPP(C, CPP) concat(SELECT, __cplusplus)(C, CPP)

C_OR_CPP(1, 2)

Other Environments Check the __cplusplus macro, a compiler that comforming to standard C++ should generate

 #define __cplusplus value 

and value should >= 199711L