a.cpp

#include <stdio.h>

#ifdef DEBUG_PRINT
#define DebugPrintf(format, args...) fprintf(stderr, "%s this=%p " format, __PRETTY_FUNCTION__, this, ##args)
#else
#define DebugPrintf(format, args...)
#endif

class Calculator
{
public:
  int add(int a, int b)
  {
    DebugPrintf("a = %d, b = %d\n", a, b);
    return a + b;
  }
};

int main(void)
{
  Calculator c;
  printf("result: %d\n", c.add(2, 1));
  return 0;
}