reading ASCII data in s-function from a file

Hello all,

I am interested in reading ASCII data in s-function from a file. I am trying to read the data [21;77;46;183;202;84;199;198;27;84] from the file datafile.dat. I am trying to display the data in Scope using *z = ssGetOutputPortSignal(S,0); . But when I run the corresponding Model I could see that only first 5 numbers are read i.e. 21;77;46;183;202. Following is the code:

#define S_FUNCTION_NAME  sfunread
#define S_FUNCTION_LEVEL 2
#include "simstruc.h"
#include <stdio.h>
static void mdlInitializeSizes(SimStruct *S)
{

    ssSetNumSFcnParams(S, 0); 
    if (ssGetNumSFcnParams(S) != ssGetSFcnParamsCount(S)) {
        return;
    }
    ssSetNumContStates(S, 0);
    ssSetNumDiscStates(S, 0);
    if (!ssSetNumInputPorts(S, 0)) return;
    if (!ssSetNumOutputPorts(S, 1)) return;
    ssSetOutputPortWidth(S, 0, 10);
    ssSetOutputPortDataType(S,0,SS_SINGLE);
    ssSetNumPWork(S,1);
    ssSetNumSampleTimes(S, 1);
}
static void mdlInitializeSampleTimes(SimStruct *S)
{
    ssSetSampleTime(S, 0, 1.0);
    ssSetOffsetTime(S, 0, 0.0);
}
#define MDL_START  
#if defined(MDL_START)   
  static void mdlStart(SimStruct *S)
  {
      void** pwork = ssGetPWork(S);
      FILE *datafile;
      datafile = fopen("datafile.dat","r");
      pwork[0] =  datafile;
}
#endif /*  MDL_START */
static void mdlOutputs(SimStruct *S, int_T tid)
{
  int l;
  real_T       *z = ssGetOutputPortSignal(S,0);

    void** pwork = ssGetPWork(S);
    for (l=0;l<10;l++){
         real_T temp;
         fscanf(pwork[0],"%f",&temp);
         z[l]=temp;
}
static void mdlTerminate(SimStruct *S)
{
     void** pwork = ssGetPWork(S);
      FILE *datafile;
      datafile = pwork[0];
      fclose(datafile);      
}
#ifdef  MATLAB_MEX_FILE    
#include "simulink.c"      
#else
#include "cg_sfun.h"       
#endif

Please let me know if I am using the correct way to read the ASCII data from a file.

Tushar

[Kaustubha Govind]

How is the data in your file delimited? Are there spaces between the numbers?

[Tushar]

The delimiter is next line character '\n'. Each element of the array is on the next line.

Answer 1

[Jarrod Rivituso]

Your overall approach looks good. I would suggest debugging the S-function so you can step through it. There are steps on how to do that here:

http://www.mathworks.com/support/tech-notes/1800/1819.html

Also, did you copy and paste that code directly? There seems to be a missing } to end your for loop. I was looking for something subtle in your code and noticed that (I doubt that is the problem, but it makes me suspicious of whether this code actually contains the problem).

Answer 2

[Tushar]

Hello

I tried to debug my s-function in Visual C. For simplicity I tried to read array with 5 elements [21;77;46;183;202] from a file. But the values of the elements in z array in the above code are displayed like

5.442276802756e-315#DEN

5.520634191278e-315#DEN

5.488902686835e-315#DEN

5.571469356558e-315#DEN

5.577621382930e-315#DEN

in stead of the true values [21;77;46;183;202]. Please some one comment on this.

[Walter Roberson]

That #DEN indicates that the number is a "denormalized" number.

The problem appears to be that you are using "%f" to read the numbers. In C, a %f format indicates that the result is to be stored as a single precision number. Change the format to "%lf" to read a double precision number.

[Jarrod Rivituso]

Interesting, and good catch Walter.

Tushar, I believe you could set the variables tmp and z in your code to either real32_T or real64_T explicitly to try and match the desired C data type. I notice you have set your output to single precision floating point.

[Kaustubha Govind]

Tushar: You might also want to check the output of fscanf for EOF, and assign temp to 0 in that case, so you don't attempt to read past the end.

[Tushar]

Thanks Jarrod. The code runs correctly with real32_T.

Its not clear why I had to change to real32_T from real_T. What is the difference between real_T, real32_T and real64_T? I did not find any reference for these data types in Matlab help files. real_T does not work even for integer type data in the file. Also "%lf" could not read the data from the file.

[Jarrod Rivituso]

I think for most 32-bit machines the mappings from Simulink S-function typedefs to the actual C data types goes as

real32_t - float

real64_T - double

real_T - double

So, real_T shouldn't work for integer type data.