Mark the variadic *printf functions with __attribute__((format)).

Using __attribute__((format)) means that compilers supporting the
attribute (GCC, clang, icc, perhaps others) will automatically issue
warnings when printf arguments are incorrectly typed (i.e. inconsistent
with the type specified in the format string).

printf.h

@@ -58,6 +58,9 @@ void _putchar(char character);
  * \return The number of characters that are written into the array, not counting the terminating null character
  */
 #define printf printf_
+#ifdef __GNUC__
+__attribute__ ((format (__printf__, 1, 2)))
+#endif
 int printf_(const char* format, ...);
 
 
@@ -69,6 +72,9 @@ int printf_(const char* format, ...);
  * \return The number of characters that are WRITTEN into the buffer, not counting the terminating null character
  */
 #define sprintf sprintf_
+#ifdef __GNUC__
+__attribute__ ((format (__printf__, 2, 3)))
+#endif
 int sprintf_(char* buffer, const char* format, ...);
 
 
@@ -84,6 +90,9 @@ int sprintf_(char* buffer, const char* format, ...);
  */
 #define snprintf snprintf_
 #define vsnprintf vsnprintf_
+#ifdef __GNUC__
+__attribute__ ((format (__printf__, 3, 4)))
+#endif
 int snprintf_(char* buffer, size_t count, const char* format, ...);
 int vsnprintf_(char* buffer, size_t count, const char* format, va_list va);
 
@@ -106,6 +115,9 @@ int vprintf_(const char* format, va_list va);
  * \param format A string that specifies the format of the output
  * \return The number of characters that are sent to the output function, not counting the terminating null character
  */
+#ifdef __GNUC__
+__attribute__ ((format (__printf__, 3, 4)))
+#endif
 int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...);