Add a better documented version of the div example

src/MyFirstUDRKit.cpp

@@ -65,6 +65,60 @@
 
 using namespace Firebird;
 
+
+// First, let's start with a function from the UdfBackwardCompatibility
+// library and add some additional comments.
+// We will also use self-docmenting variable names
+// //////////////////////////////////////////////////
+
+/***
+ * create function div (
+ *    anumerator integer,
+ *    adenominator integer
+ * ) returns double precision
+ *    external name 'udf_compat!UC_div!Divide param1 by param2'
+ *    engine udr;
+ ***/
+FB_UDR_BEGIN_FUNCTION(UC_div)
+
+// Divide integer param 1 by integer param2 using the stdlib
+
+FB_UDR_MESSAGE(InMessage,
+							 (FB_INTEGER, anumerator)
+							 (FB_INTEGER, adenominator)
+);
+
+FB_UDR_MESSAGE(OutMessage,
+							 (FB_DOUBLE, result)
+);
+
+FB_UDR_EXECUTE_FUNCTION
+{
+	if (in->anumeratorNull || in->adenominatorNull)
+	{
+		out->resultNull = FB_TRUE;
+		out->result = 0;
+	}
+	else
+	{
+		out->resultNull = FB_FALSE;
+		if (in->adenominator) {
+			out->result = div(in->anumerator, in->adenominator).quot;
+		}
+		else
+		{
+			out->result = std::numeric_limits<double>::infinity();
+			ISC_STATUS_ARRAY StatusVector = {isc_arg_gds, isc_arith_except,
+				isc_arg_gds, isc_exception_integer_divide_by_zero, isc_arg_end};
+				FbException::check(isc_exception_integer_divide_by_zero, status, StatusVector);
+		}
+	}
+}
+FB_UDR_END_FUNCTION
+
+
+
+
 /*** DDL
 create function flagged (
     n1 integer,