This is explained in section 8.21 Abstract classes and pure virtual methods of the 1800-2012 LRM. Get a copy of it, it’s free. This section was missing from earlier versions of the LRM.
This is explained in section 8.21 Abstract classes and pure virtual methods of the 1800-2012 LRM. Get a copy of it, it’s free. This section was missing from earlier versions of the LRM.