Thread: Programming style: #ifdef vs regular if

Except for the often-frowned-upon way of including #ifdef's in a .c file, there are two ways to include debug code in a program:
1. In xxx.h:

Code:

#ifdef DEBUG
  void debugprint(const char *s);
#else
  static inline debugprint(const char *dummy) {}
#endif

And in xxx.c:

Code:

int somefunction(...)
{
   ...
   debugprint("...debug info...");
   ...
}

2. In xxx.c:

Code:

int somefunction(...)
{
   ...
   if (DEBUG) 
     debugprint("...debug info...");
   ...
}

The second method can test all possible execution paths of a program during compile time but the code is littered with "if (DEBUG)". DEBUG is defined in a command-line compiler option (-D). What one is better? Thank you.

you don't want to do as in the 2d example because that is executable code in release-mode programs too. In the 1st example, function debugprint() only appears in the program when DEBUG is defined. If it is not defined then a good optimizing compiler will toss out the function because it does nothing.

In the first example, any non-retarded, non-optimizing compiler will remove the call because that's what the preprocessing language tells it to do.

Originally Posted by laserlight

hmm... but wouldnt a "good optimizing compiler" also ignore the debugprint() call in the 2nd example if DEBUG is 0?

No. I was incorrect in my oritinal post. DEBUG is defined only for debug builds, and the compiler will generate an error on release builds because DEBUG is undefined.

I guess my second method needs to set DEBUG to a logical value, not just define or not define it. So, for the second method, the compilation command would be:
cc -DDEBUG=true myprog.c
or
cc -DDEBUG=false myprog.c