Is it possible for C preprocessor macros to contain preprocessor directives?

Question

I would like to do the equivalent of the following:

#define print_max(TYPE) \\
#  ifdef TYPE##_MAX \\
     printf(\"%lld\\n\", TYPE##_MAX); \\
#  endif

prin         


        

Answer 1

There's no easy way to do this. The closest you can come is to #define a large number of IFDEF macros such as:

#undef IFDEF_INT_MAX
#ifdef INT_MAX
#define IFDEF_INT_MAX(X)  X
#else
#define IFDEF_INT_MAX(X)
#endif

#undef IFDEF_BLAH_MAX
#ifdef BLAH_MAX
#define IFDEF_BLAH_MAX(X)  X
#else
#define IFDEF_BLAH_MAX(X)
#endif

     :

since you need a lot of them (and they might be useful multiple places), it makes a lot of sense to stick all these in their own header file 'ifdefs.h' which you can include whenever you need them. You can even write a script that regenerates ifdef.h from a list of 'macros of interest'

Then, your code becomes

#include "ifdefs.h"
#define print_max(TYPE) \
IFDEF_##TYPE##_MAX( printf("%lld\n", TYPE##_MAX); )

print_max(INT);
print_max(BLAH);