Question

I’m building a large C++ program with a variety of different compile-time options, selected by #defines (or the -D option).

I want to have a version string that lists a number of them as tags, and ideally, to have that version string defined as a literal, not a constant.

Currently, I’m looking at three options, none of which is ideal.

1. Piles of preprocessor defines

   #ifdef AAA
   #define AAAMSG " [A]"
   #else
   #define AAAMSG ""
   #endif
   #ifdef BBB
   #define BBBMSG " [B]"
   #else
   #define BBBMSG ""
   #endif
   // ...
   #define REVISION __DATE__ " " __TIME__ AAAMSG BBBMSG CCCMSG DDDMSG
   

2. Build a constant

   const char *const REVISION=__DATE__ " " __TIME__
   #ifdef AAA
   " [A]"
   #endif
   #ifdef BBB
   " [B]"
   #endif
   // ...
   ;
   

3. Redefine the token

   #define REVISION __DATE__ " " __TIME__
   #ifdef AAA
   #define REVISION REVISION " [A]"
   #endif
   #ifdef BBB
   #define REVISION REVISION " [B]"
   #endif
   // ...
   

The first one is incredibly verbose (imagine that with half a dozen independent elements) and error-prone. The second one is far better, but it creates a constant instead of a literal, so I can’t use it as part of another string – example:

send(sock,"rev " REVISION "\n",sizeof(REVISION)+4,0);

It seems silly to use run-time string manipulation (an sprintf or somesuch) for a compile-time constant. The third example, of course, just straight-up doesn’t work, but it is pretty much what I’m trying to do.

Is there some alternative method?

Answer 1

Closing off this question with the comment that I’m sticking with option 1. There appears to be no way to do what I was hoping to do, so the imperfect remains. Thanks to those who contributed!