core.stdc.stdlib._compare_fp_t and qsort

[Joe via Digitalmars-d-learn]

I'm getting a compiler error in a qsort() call as follows:
    qsort(recs, num_recs, (Record *).sizeof, compar);

Record is a struct, recs is a fixed array of pointers to Record's 
and num_recs is a size_t that holds the number of valid records.

compar is this:

int compar(const void *p1, const void *p2)
{
    import core.stdc.string : strcmp;
    const Record **rp1 = cast(Record **)p1;
    const Record **rp2 = cast(Record **)p2;

    return strcmp((*rp1).name.ptr, (*rp2).name.ptr);
}

The error is: Error: function testd.compar (const(void*) p1, 
const(void*) p2) is not callable using argument types ()

I don't quite understand what those parentheses mean: is it 
implying "no arguments" and if so, where would one provide 
arguments?

Joe