What did you expect when you used --with-clanguage=C++ for your buid? Or
were you misunderstanding what this options means wrt PETSc build?

I understand what it was trying to do but it is necessary for sieve (especially with certain mesh generators). Why does all of PETSc need to be compiled with C++ in order to use sieve is the real question?

.c -> compiled with mpicc

.cxx -> compiled with mpicxx

Is there something else missing? (Perhaps linking?)

Sean