added vfctprintf() support

printf.c

@@ -912,3 +912,10 @@ int fctprintf(void (*out)(char character, void* arg), void* arg, const char* for
   va_end(va);
   return ret;
 }
+
+int vfctprintf(void (*out)(char character, void* arg), void* arg, const char* format, va_list va)
+{
+  const out_fct_wrap_type out_fct_wrap = { out, arg };
+  const int ret = _vsnprintf(_out_fct, (char*)(uintptr_t)&out_fct_wrap, (size_t)-1, format, va);
+  return ret;
+}

printf.h

@@ -99,15 +99,16 @@ int vprintf_(const char* format, va_list va);
 
 
 /**
- * printf with output function
+ * printf/vprintf with output function
  * You may use this as dynamic alternative to printf() with its fixed _putchar() output
  * \param out An output function which takes one character and an argument pointer
  * \param arg An argument pointer for user data passed to output function
  * \param format A string that specifies the format of the output
+ * \param va A value identifying a variable arguments list
  * \return The number of characters that are sent to the output function, not counting the terminating null character
  */
 int fctprintf(void (*out)(char character, void* arg), void* arg, const char* format, ...);
-
+int vfctprintf(void (*out)(char character, void* arg), void* arg, const char* format, va_list va);
 
 #ifdef __cplusplus
 }