A tiny little macro to help debug your C code.

debugf.h

// debugf.h 
// Charlton Trezevant - 2018
// MIT license

/* USAGE:
 * To use this macro, simply paste it into your source file (you may also 
 * include debugf.h if you have many source files). Doing this will define 
 * the function debugf(), which acts as a thin wrapper around fprintf() with
 * a little added pizazz.
 *
 * When DEBUG is defined, any calls made to debugf() will behave in exactly the 
 * same way as calls to printf() or fprintf() (because there's full support for variadic 
 * arguments :). Output will be sent to stderr instead of stdout to ensure that any test
 * cases relying on stdout will pass if debugging is enabled. Additionally, a call is made
 * to fflush() after each line of debugging output, so crashes and segfaults wont cause 
 * you to lose precious debugging insights to the ether.
 *
 * Enjoy!
 */

// Comment out the below to disable debug output.
#define DEBUG
#ifdef DEBUG
  #define debugf(fmt, ...) fprintf(stderr, fmt, ## __VA_ARGS__); fflush(stderr)
#else
  #define debugf(fmt, ...) ((void)0)
#endif

debugf_leveled.h

// debugf.h 

// Charlton Trezevant - 2018

// MIT license

/* USAGE:

 * This is a leveled version of debugf
 
 * Unfamiliar with leveled logging? Check out http://thejoyofcode.com/Logging_Levels_and_how_to_use_them.aspx
 * for some background. 
 
 * Example call:
 * debugf(DEBUG_LEVEL_INFO, "Hi! The magic number is %d", 5);

 * Enjoy!

 */

// You can define your own custom debug levels, or use these defaults
#define DEBUG_LEVEL_ALL 0
#define DEBUG_LEVEL_TRACE 1
#define DEBUG_LEVEL_DEBUG 2
#define DEBUG_LEVEL_INFO 3
#define DEBUG_LEVEL_WARN 4
#define DEBUG_LEVEL_ERROR 5
#define DEBUG_LEVEL_FATAL 6
#define DEBUG_LEVEL_NONE 99

// Comment out the below or set DEBUG_LEVEL_NONE to disable debug output.
// When not disabled, only calls to debugf with a level that's greater than or equal to 
// the current global debug level will produce output.
//#define DEBUG DEBUG_LEVEL_NONE

#ifdef DEBUG
#define debugf(lvl, fmt, ...) \
        ({ \
                if (DEBUG == 0 || (lvl) >= DEBUG) { \
                        fprintf(stderr, fmt, ## __VA_ARGS__); fflush(stderr); \
                } \
        })
#else
  #define debugf(lvl, fmt, ...) ((void)0)
#endif

panic.h

// Panic is called when something goes wrong
void panic(const char * fmt, ...){
        // Vargs to behave like printf (but not to make black metal)
        va_list vargs;
        va_start(vargs, fmt);
        // Print error message to stderr
        vfprintf(stderr, fmt, vargs);
        fflush(stderr);
        va_end(vargs);
        exit(1);
}