use of the DWORD_PTR

Question

What is the use of the DWORD_PTR in the following function

/*static*/ int FRCPACKAGE::ByHash(FRCPACKAGE* frcpackage1, FRCPACKAGE* frcpackage2, DWORD_PTR)
{return _tcsicmp(frcpackage2->Hash(), frcpackage1->Hash());}

Answer 1

It's an extra parameter of type DWORD_PTR (probably a typedef to an unsigned long * or something similar), but because it's not used in the function, it's not given a name. That way, most compilers won't issue an "unused parameter" warning.