Perhaps this helps:
From:
http://support.sas.com/documentation/cdl/en/proc/61895/HTML/default/viewer.htm#a002975833.htm
All functions must be declared externally in your load module so that SAS can find them. For most platforms, external declaration is the default behavior for the compiler. However, many C compilers do not export function names by default. The following examples show how to declare your functions for external loading for most PC compilers:
_declspec(dllexport) int myfunc(int, double);
_declspec(dllexport) int price2(int a, double foo);
Best,
-Matt