Writing S-Functions

Example Involving a Pointer Work Vector

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

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

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

The following code 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, 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 mdlInitializeSizes 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