Question

So I can write code like this:

#ifdef [whatever]
   // do stuff that will never show up in the production version
#endif

Answer 1

If you can assume that debug builds always use gcc -O0 (this is normally the case, but there may be odd exceptions where someone has changed the optimisation level for debug builds) then you can do this:

#if __OPTIMIZE__
  // ... non-debug stuff ... 
#else
  // ... debug stuff ...
#endif