Private member have illegal prefix
Currently private member variables in couplingadapter.hh
and dumuxpreciceindexmapper.hh
start with an underscore _
. This is illegal as variables starting with an underscore are reserved
the identifiers with a double underscore anywhere are reserved;
the identifiers that begin with an underscore followed by an uppercase letter are reserved;
the identifiers that begin with an underscore are reserved in the global namespace.