From: Nicola Musatti <Nicola.Musatti@gmail.com>

I believe this is an instance of the need of representing concepts both in the SQL and in the C++ world. I see indicators as conceptually a part of the SQL world, in that they are a way to access additional, detailed information about the result of a query, beyond the retrieved value itself.

Once the value is converted to a C++ type it assumes a value in the domain of that type... or not. In this case boost::optional or its moral equivalent is a reasonable representation.

Side note: a while ago I wrote a Nullable<T> type that provided implicit conversion to T and threw an exception if it held a null value. Personally I'd prefer that kind of interface, but I think it's better to stick as much as possible to what's available in the standard library or in Boost.

I've been following this thread closely, as I have a need for a database library in C++ as well (don't we all?). I wrote my own, which serves my purposes OK, but would certainly be interested in a Boosted version. On this particular point, while obviously indicator variables are the SQL way to provide information about data fields, having a separate variable is very much not in the spirit of C++. But it would be easy to define: template<class DataType, class IndicatorType> class value { private: IndicatorType indicator; DataType data; public: bool is_null() const { return indicator.is_null(); } bool is_truncated() const { return indicator.is_truncated(); } /* ... other queries ... */ }; - James Jones Administrative Data Mgmt. Webmaster 375 Raritan Center Pkwy, Suite A Data Architect Edison, NJ 08837