//for predefined types, so in_use = 0.
Datatype::Datatype(char* name, int size,MPI_Aint lb, MPI_Aint ub, int flags) : name_(name), size_(size), lb_(lb), ub_(ub), flags_(flags), refcount_(0){
//for predefined types, so in_use = 0.
Datatype::Datatype(char* name, int size,MPI_Aint lb, MPI_Aint ub, int flags) : name_(name), size_(size), lb_(lb), ub_(ub), flags_(flags), refcount_(0){