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.

you don't want to do as in the 2d example because that is executable code in release-mode programs too.

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

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.

DEBUG is defined only for debug builds, and the compiler will generate an error on release builds because DEBUG is undefined.

I think that's only the first example, since the OP did say "DEBUG is defined in a command-line compiler option (-D)" for the second example, though he/she was rather vague about it.

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