Pass parameter via s-function parameter field into c++ function

Hi,

i need to define a paramter globally within my s-function (c++). The problem is that I need to define this paramter without any reference to Simstruct S, so that I am able to use the paramter in my c++ functions without passing Simstruct S. This is what works:

 #define some_param(S) ssGetSFcnParam(S,0)

But I need somethink like this, without Simstruct:

 #define some_param ssGetSFcnParam(S,0)

Thank you in advance.