Writing S-Functions

An Example Involving a Pointer Work Vector

This example opens a file and stores the FILE pointer in the pointer-work vector.

The statement below, included in the mdlInititalizeSizes function, indicates that the pointer-work vector is to contain one element.

ssSetNumPWork(S, 1)   /* pointer-work vector */

The code below uses the pointer-work vector to store a FILE pointer, returned from the standard I/O function, fopen.

#define MDL_START  /* Change to #undef to remove function. */
#if defined(MDL_START)
static void mdlStart(real_T *x0, SimStruct *S)
{
  FILE *fPtr;
  void **PWork = ssGetPWork(S);
  fPtr = fopen("file.data", "r");
  PWork[0] = fPtr;
}
#endif /*  MDL_START */

This code retrieves the FILE pointer from the pointer-work vector and passes it to fclose to close the file.

static void mdlTerminate(SimStruct *S)
{
  if (ssGetPWork(S) != NULL) {
    FILE *fPtr;
    fPtr = (FILE *) ssGetPWorkValue(S,0);
    if (fPtr != NULL) {
      fclose(fPtr);
    }
    ssSetPWorkValue(S,0,NULL);
  }
}

Note    If you are using mdlSetWorkWidths, then any work vectors you use in your S-function should be set to DYNAMICALLY_SIZED in mdlInitializeSizes, even if the exact value is known before mdlIntializeSizes is called. The size to be used by the S-function should be specified in mdlSetWorkWidths.

The synopsis is

#define MDL_SET_WORK_WIDTHS   /* Change to #undef to remove function. */
#if defined(MDL_SET_WORK_WIDTHS) && defined(MATLAB_MEX_FILE)
static void mdlSetWorkWidths(SimStruct *S)
{
}
#endif /* MDL_SET_WORK_WIDTHS */

For an example, see matlabroot/simulink/src/sfun_dynsize.c.

Work Vectors and Zero Crossings

Memory Allocation