Using GRAMPC in C++

The C++ interface provides a single class for managing the grampc struct and all related functions as outlined in Using GRAMPC in C. The main difference is the probfct handling which is described below.

Interface from C++ to C

The constructor of the class Grampc takes a pointer to a specific problem description. This problem description is of type ProblemDescription and holds all methods which are needed to implement the OCP. The constructor of Grampc now passes the ProblemDescription* as userparam to grampc_init. Whenever GRAMPC calls a problem specific function like ffct, the userparam pointer gets dereferenced as a ProblemDescription* which calls the corresponding method.

Listing 7 Example how the bridge between C -> C++ is made.

void ffct(typeRNum *out, ctypeRNum t, ctypeRNum *x, ctypeRNum *u, ctypeRNum *p, const typeGRAMPCparam *param, typeUSERPARAM *userparam)
{
    ((grampc::ProblemDescription*)userparam)->ffct(out, t, x, u, p, param);
}

Handling of Problem Descriptions

The C++ interface provides a virtual base class ProblemDescription under the namespace grampc. It provides virtual methods which map the functions from probfct.h.

Note

userparam is not needed, because problem specific quantities can be defined as class fields.

For an example please see the folder <grampc_root>/cpp/examples/MassSpringDamper with an implementation of the mass spring damper example. Additionally, compare with the C implementation in <grampc_root>/examples/MassSpringDamper.