Writing S-Functions

Handling Errors

When working with S-functions, it is important to handle unexpected events such as invalid parameter values correctly.

If your S-function has parameters whose contents you need to validate, use the following technique to report errors encountered.

• ssSetErrorStatus(S,"error encountered due to ...");
  return;
  

Note that the second argument to ssSetErrorStatus must be persistent memory. It cannot be a local variable in your procedure. For example, the following causes unpredictable errors.

• mdlOutputs()
  {
      char msg[256]; /* ILLEGAL: should be "static char msg[256];" */
      sprintf(msg,"Error due to %s", string);
      ssSetErrorStatus(S,msg);
      return;
  }
  

The ssSetErrorStatus error-handling approach is the suggested alternative to using the mexErrMsgTxt function. The function mexErrMsgTxt uses exception handling to immediately terminate S-function execution and return control to Simulink. In order to support exception handling inside S-functions, Simulink must set up exception handlers prior to each S-function invocation. This introduces overhead into simulation.

Function-Call Subsystems

Exception Free Code