some portable vararg debug macros based on an old example I saw

debug.h

/* a complicated set of macros to support empty __VA_ARGS__ macros.
 * example:
 * pr_dbg("Check\n");
 * pr_dbg("Check %d\n", 12);
 * pr_dbg("Check %d %s %d\n", 42, "Hello", 99);
 *
 * pr_info() and pr_err() macros don't use __func__ and __LINE__
 */
#ifndef DEBUG_H
#define DEBUG_H
#include <stdio.h>
#define CONCAT(x, y) CONCAT_(x, y)
#define CONCAT_(x, y) x##y

#define ID(...) __VA_ARGS__

#define IFMULTIARG(if,then,else) \
	CONCAT(IFMULTIARG_, IFMULTIARG_(if, \
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
	1, 1, 1, 1, 1, 1, 1, 1, 1, 1, \
	1, 1, 0, ))(then,else)
#define IFMULTIARG_(_0, _1, _2, _3, _4, _5, _6, _7, _8, _9, \
_10, _11, _12, _13, _14, _15, _16, _17, _18, _19, \
_20, _21, _22, _23, _24, _25, _26, _27, _28, _29, \
_30, _31, _32, _33, _34, _35, _36, _37, _38, _39, \
_40, _41, _42, _43, _44, _45, _46, _47, _48, _49, \
_50, _51, _52, _53, _54, _55, _56, _57, _58, _59, \
_60, _61, _62, _63, ...) _63
#define IFMULTIARG_0(then, else) else
#define IFMULTIARG_1(then, else) then

#define PROVIDE_SECOND_ARGUMENT(x, y, ...) \
CONCAT(IFMULTIARG(ID(__VA_ARGS__), INSERT_, ADD_), \
SECOND_ARGUMENT) (x, y, __VA_ARGS__)

#define ADD_SECOND_ARGUMENT(x, y, z) z, x, y
#define INSERT_SECOND_ARGUMENT(x, y, z, ...) z, x, y, __VA_ARGS__

#define pr_err(...) fprintf(stderr, "Error:" __VA_ARGS__)
#define pr_info(...) fprintf(stderr, "Info:"  __VA_ARGS__)
#define pr_dbg(...) fprintf(stderr, "Debug:%s():%d:" PROVIDE_SECOND_ARGUMENT(__func__, __LINE__, __VA_ARGS__))
#endif