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Make C++ Objects Persistent

Your C++ callback methods might need to create persistent C++ objects, that is, objects that continue to exist after the method exits. For example, a callback method might need to access an object created during a previous invocation. Or one callback method might need to access an object created by another callback method. To create persistent C++ objects in your S-function:

  1. Create a pointer work vector to hold pointers to the persistent object between method invocations:

    static void mdlInitializeSizes(SimStruct *S)
{
    ...
		ssSetNumPWork(S, 1); // reserve element in the pointers vector
                         // to store a C++ object
    ...
 }

  2. Store a pointer to each object that you want to be persistent in the pointer work vector:

      static void mdlStart(SimStruct *S)
  {
      ssGetPWork(S)[0] = (void *) new counter; // store new C++ object in the
  }                                            // pointers vector

  3. Retrieve the pointer in any subsequent method invocation to access the object:

    static void mdlOutputs(SimStruct *S, int_T tid)
{
    counter *c = (counter *) ssGetPWork(S)[0];   // retrieve C++ object from
    real_T  *y = ssGetOutputPortRealSignal(S,0); // the pointers vector and
    y[0] = c->output();                          // use member functions of
}                                                // the object

  4. Destroy the objects when the simulation terminates:

    static void mdlTerminate(SimStruct *S)
{
    counter *c = (counter *) ssGetPWork(S)[0]; // retrieve and destroy C++
    delete c;                                  // object in the termination
}                                              // function