The Message Passing Interface 1.1 (MPI 1.1) standard defines a library of message-passing functions for parallel and distributed computing. We have developed a new software tool called C++2MPI, which can automatically generate MPI derived datatypes for a specified C++ class. C++2MPI can generate data types for derived classes, for partially and fully-specialized templated classes, and for classes with private data members. Given one or more user-provided classes as input, C++2MPI generates, compiles and archives a function for creating the MPI derived datatype. When the generated function is executed, it builds the derived MPI datatype if the datatype does not already exist, and returns the value of an MPI handle for referencing the datatype. PGMT (Processing Graph Method Tool) is a set of application program interfaces for porting the Processing Graph Method (PGM), a parallel programming method, to diverse networks of processors. C++2MPI was developed as a component of PGMT, but can be used as a stand-alone tool.