xcode-file-redirection.md

@@ -38,16 +38,15 @@ How to do it well
 
 ### Conditional compilation
 
-"Conditional compilation" in short is what its name suggests: compile depending on a condition. There are two ways to do this:
-- Include <stdlib.h> (this is important!) and use `getenv()`. For example:
+You have seen compiler guards before in header files in the form of
 
 ```
-    if (getenv("INPUT")) {
-        freopen(getenv("INPUT"), "r", stdin);
-        freopen(getenv("OUTPUT"), "w", stdout);
-    } // if
+#ifndef VAR
+#define VAR
+...
+#endif
 ```
-- You can also use compiler guards. You may have seen this before in header guards in the form of `#ifndef PATH_TO_FILE`. You can read more about it [here](https://msdn.microsoft.com/en-us/library/ew2hz0yd.aspx). On Mac OS, the operating system macro is `__APPLE__`
+You can read more about these [here](https://msdn.microsoft.com/en-us/library/ew2hz0yd.aspx). On Mac OS, the operating system macro is `__APPLE__`.
 
 ```
 #ifdef __APPLE__
@@ -56,5 +55,15 @@ How to do it well
 #endif
  ```
 
+This will compile with `freopen()` *only* when the operating system is *Mac OS*, so when your code compiles on CAEN,  those lines are ignored.
 
 ### Using environment variables
+
+Another solution is to include \<stdlib.h\> (this is important!) and use `getenv()`, which lives in stdlib.h.
+
+```
+if (getenv("INPUT")) {
+    freopen(getenv("INPUT"), "r", stdin);
+    freopen(getenv("OUTPUT"), "w", stdout);
+} // if
+```
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