c/coding_standards.md

@@ -547,6 +547,11 @@ Better alternatives to `#defines` are discussed below
     * `#define MIN_OF (a, b) (((a) < (b)) ? (a) : (b)) // THIS IS GOOD`
 * `if` macro statements should always follow the pattern: `#if (...)`
     * Example with multiple conditions: `#if ((...) && (...))`
+* Avoid using `#ifdef MACRO` when `#if MACRO` can be used
+    * Example:
+        * `#define MACRO 0`
+        * `#if MACRO // this is clear`
+        * `#ifdef MACRO // this is not clear because it is not dependent on the actual value of MACRO`
 * Macro invocations **do not** need to be surrounded in parentheses.
     * Example:
         * `#if FEATURE_UDS // This is perfectly fine`