How do you create a debug only function that takes a variable argument list? Like printf()

Question

I\'d like to make a debug logging function with the same parameters as printf. But one that can be removed by the pre-processor during optimized builds.

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Answer 1

@CodingTheWheel:

There is one slight problem with your approach. Consider a call such as

XTRACE("x=%d", x);

This works fine in the debug build, but in the release build it will expand to:

("x=%d", x);

Which is perfectly legitimate C and will compile and usually run without side-effects but generates unnecessary code. The approach I usually use to eliminate that problem is:

1. Make the XTrace function return an int (just return 0, the return value doesn't matter)

2. Change the #define in the #else clause to:

   0 && XTrace
   

Now the release version will expand to:

0 && XTrace("x=%d", x);

and any decent optimizer will throw away the whole thing since short-circuit evaluation would have prevented anything after the && from ever being executed.

Of course, just as I wrote that last sentence, I realized that perhaps the original form might be optimized away too and in the case of side effects, such as function calls passed as parameters to XTrace, it might be a better solution since it will make sure that debug and release versions will behave the same.