Add coding standards for String constants.

CODING.md

@@ -32,12 +32,27 @@ Type names use camel case with the first letter upper case:
 
 `#define` constants should be all caps with `_` separators.
 ```c
-#DEFINE MY_CONSTANT "STRING"
+#define MY_CONSTANT                                                 "STRING"
 ```
 The value should be aligned at column 69 whenever possible.
 
 This type of constant should mostly be used for strings. Use enums whenever possible for integer constants.
 
+**String Constants**
+
+String constants can be declared using the `STRING_STATIC()` macro for local strings and `STRING_EXTERN()` for strings that will be extern'd for use in other modules.
+
+Extern'd strings should be declared in the header file as:
+```c
+#define SAMPLE_VALUE                                                "STRING"
+    STRING_DECLARE(SAMPLE_VALUE_STR);
+```
+And in the C file as:
+```c
+STRING_EXTERN(SAMPLE_VALUE_STR,                                     SAMPLE_VALUE);
+```
+Static strings declared in the C file are not required to have a `#define` if the `#define` version is not used. Extern'd strings must always have the `#define` in the header file.
+
 **Enum Constants**
 
 Enum elements follow the same case rules as variables. They are strongly typed so this shouldn't present any confusion.

doc/xml/coding.xml

@@ -46,13 +46,32 @@
                 <p><code>#define</code> constants should be all caps with <id>_</id> separators.</p>
 
                 <code-block type="c">
-#DEFINE MY_CONSTANT "STRING"
+#define MY_CONSTANT                                                 "STRING"
                 </code-block>
 
                 <p>The value should be aligned at column 69 whenever possible.</p>
 
                 <p>This type of constant should mostly be used for strings.  Use enums whenever possible for integer constants.</p>
 
+                <p><b>String Constants</b></p>
+
+                <p>String constants can be declared using the <code>STRING_STATIC()</code> macro for local strings and <code>STRING_EXTERN()</code> for strings that will be extern'd for use in other modules.</p>
+
+                <p>Extern'd strings should be declared in the header file as:</p>
+
+                <code-block type="c">
+#define SAMPLE_VALUE                                                "STRING"
+    STRING_DECLARE(SAMPLE_VALUE_STR);
+                </code-block>
+
+                <p>And in the C file as:</p>
+
+                <code-block type="c">
+STRING_EXTERN(SAMPLE_VALUE_STR,                                     SAMPLE_VALUE);
+                </code-block>
+
+                <p>Static strings declared in the C file are not required to have a <code>#define</code> if the <code>#define</code> version is not used.  Extern'd strings must always have the <code>#define</code> in the header file.</p>
+
                 <p><b>Enum Constants</b></p>
 
                 <p>Enum elements follow the same case rules as variables. They are strongly typed so this shouldn't present any confusion.</p>

doc/xml/release.xml

@@ -121,6 +121,10 @@
                         <p>Return <code>IoFilterGroup *</code> from <code>ioFilterGroupAdd()</code>.</p>
                     </release-item>
 
+                    <release-item>
+                        <p>Add coding standards for <code>String</code> constants.</p>
+                    </release-item>
+
                     <release-item>
                         <p>Add missing <code>LOG_DEBUG()</code> macro.</p>
                     </release-item>