Writing S-Functions

Making C++ Objects Persistent

Your C++ callback methods may need to create persistent C++ objects, that is, objects that continue to exist after the method exits. For example, a callback method may need to access an object created during a previous invocation. Or one callback method may 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 use
       y[0] = c->output();                          // 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
   

Source File Format

Building C++ S-Functions