C Debug Print Macros

Question

in C, what is the proper way to define a printf like macro that will print only when DEBUG symbol is defined?

#ifdef DEBUG
#define DEBUG_PRINT(???) ???
#else
#define DEBUG_PRINT(???) ???
#endif

where ??? is where I am not sure what to fill in

Answer 1

Something like:

#ifdef DEBUG
#define DEBUG_PRINT(fmt, args...)    fprintf(stderr, fmt, ## args)
#else
#define DEBUG_PRINT(fmt, args...)    /* Don't do anything in release builds */
#endif

Answer 2

#ifdef DEBUG
#define DEBUG_PRINT(...) do{ fprintf( stderr, __VA_ARGS__ ); } while( false )
#else
#define DEBUG_PRINT(...) do{ } while ( false )
#endif

Answer 3

I've seen this idiom a fair amount:

#ifdef DEBUG
# define DEBUG_PRINT(x) printf x
#else
# define DEBUG_PRINT(x) do {} while (0)
#endif

Use it like:

DEBUG_PRINT(("var1: %d; var2: %d; str: %s\n", var1, var2, str));

The extra parentheses are necessary, because some older C compilers don't support var-args in macros.