CODEWITHSUNDEEP
c++macrosc-preprocessor
kagali-san
kagali-san

Reputation: 3082

Preprocessor macros: how to insert arguments?

The code has a number of following sections:

int filter;
#ifdef INPUTFILTER_FOO
 LOG4CXX_DEBUG(log, "FOO filter used");
         filter = F_FOO;
#endif

They are used multiple times in the code (used to provide I/O, threading support etc for all testing configurations), Circa they are essential for debugging but make the code look harsh, want to replace them with macros, one for each category_type namespace.

So, want to expand the following:

MACROSTUFFBAZ(log2, stuff, "BAZ") <- the text part is unique for each class, so it needs to be included in macro too.

to:

#ifdef INPUTSTUFF_BAZ
  LOG4CXX_DEBUG(log2, "BAZ stuff used");
  stuff = S_BAZ;
#endif

To define macros, plan to use this:

debug.hpp:

   #ifdef INPUTSTUFF_BAZ
    #define MACROSTUFFBAZ ...
   #else
   #define MACROSTUFFBAZ
    .. no code!
   #endif
  #endif

(at least this will give a clear overview of the things currently undergoing probation, without seeing them around the code)

Upvotes: 1

Views: 1868

Answers (1)

Timo
Timo

Reputation: 5176

Here's my try, although i'm not 100% sure if it works cause i'm unable to test it right now, and also different compilers handle preprocessor macros a little bit differently. But I think something like this works at least in visual studio.

Basically, you have to use a helper macro to convert the parameter into a string. And secondly, you can use ## to concatenate identifiers:

#define PRMTOSTR_HLPR(x) #x
#define PRMTOSTR(x) PRMTOSTR_HLPR(x)

#ifdef INPUTSTUFF_BAZ
  #define MACROSTUFFBAZ(A,B,C) \
  LOG4CXX_DEBUG(A, PRMTOSTR(C)" stuff used"); \
  B = S_##C;
#else
  #define MACROSTUFFBAZ(A,B,C)
#endif

//used like this:
MACROSTUFFBAZ(log2, stuff, BAZ)

edit: The helper macro is actually not needed here, so you can just put #C directly in the definition of MACROSTUFFBAZ.

Upvotes: 3

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