[Boost-users] Preprocessor Question

Hello all, I'm trying to come up with a solution for the following problem. I've a macro with three arguments, but if the third is not given, it should be assumed as '0'. Something on the lines of default arguments for functions. I'm using VS2005, and g++ 4.4.x so i can use Variadic macros, but I'm unable to come up with a solution. Is there any way i can achieve this using Boost.Preprocessor ? I tried using BOOST_PP_IF but unable to proceed further. Any Ideas ? Surya