MPI::Intercomm comm; comm = MPI::COMM_NULL; // assign with COMM_NULL if (comm == MPI::COMM_NULL) // true cout << "comm is NULL" << endl; if (MPI::COMM_NULL == comm) // note -- a different function! cout << "comm is still NULL" << endl;
Dup() is not defined as a member function of MPI::Comm, but it is defined for the derived classes of MPI::Comm. Dup() is not virtual and it returns its OUT/ parameter by value.
MPI-Standard for MARMOT