BSizeField
class BSizeField : public BField
BSizeField(off_t size);
BSizeField *sizeField = (BSizeField*)row->GetField(4);
SetField(new BSizeField(fResData->GetLength()), 4);
BSizeField::BSizeField(off_t size)
BSizeField::SetSize(off_t size)
BSizeField::Size()
double value = ((BSizeField*)_field)->Size();
off_t diff = ((BSizeField*)field1)->Size() - ((BSizeField*)field2)->Size();