Proper way to print different debug messages in C?

Question

I need to print msg1 and msg2 for the same error when compiled with and without DEBUG flag. E.g.

      fprintf( stderr,
#ifdef DEBUG
                      "error msg1 %s",__FILE__
#else
                      "error msg2"
#endif
              );

or other way might be to pass these msg1 and msg2 to a function and print it using vfprintf(). Probably, The second method would have run time overhead. So, I am just wondering what could be better way of doing this?

E.g. A use case might be that the code need to be compiled with info and debug flags. info might be user related messages and debug for debugging purpose. Any suggestions?

Answer 1

Usualy the traces are used in the code to help debug it, so for example in your NULL pointer tests you can add smth like if (ptr==NULL) DEBUG("Entering Null pointer");. I'am just telling you that because i don't udrestand why you want use both msg1 and msg2.

For me i usually use a macro DEBUG and a global variable verbose :

#define DEBUG(...)\
if(verbose && SHOW_ERROR) {\
printf("Error : %s, %d",__FUNCTION__, __LINE__);\
printf(__VA_ARGS__);\
}\
else if (verbose && SHOW_WARNING) {\
printf("Warning : %s, %d",__FUNCTION__, __LINE__);\
printf(__VA_ARGS__);\
}

Example :

#include <stdio.h>

#define SHOW_ERROR 1
#define SHOW_WARNING 2

int verbose = 1; 
int main()
{
  DEBUG("THIS WILL SHOW ERROR MSG");
  verbose = 2;
  DEBUG("THIS WILL SHOW WARNING MSG");
}

Hope i help.