Using C++ lib with functions with default parameters from Objective C

Starts with prototype in header:

void* _CalcImageBlobParam(
		void *pBlob,
		PERFECTLYCLEARCALLBACK callbackfn = NULL, 
		void *pUserData = NULL
);

Modified for use in Objective-C:

void* _CalcImageBlobParam(
		void *pBlob,
		PERFECTLYCLEARCALLBACK callbackfn
#ifndef __OBJC__
                = NULL
#endif
                , 
		void *pUserData
#ifndef __OBJC__
                = NULL
#endif
		);

Then, when you call this in Objective-C, you just have to explicitly pass NULL to the optional parameters.