Matlab and Visual Sudio

Can anyone suggest me why this code is not able to do the plotting?

#include <engine.h>

#include <stdio.h>

#include <math.h>

#include <string.h>

#pragma comment  ( lib, "libmat.lib")

#pragma comment  ( lib, "libmx.lib")

#pragma comment  ( lib, "libmex.lib")

#pragma comment  ( lib, "libeng.lib")

#define EBRANGE 12

int main () {
  
int i, j;

mxArray *DiscreteRangeOfEB = NULL;

DiscreteRangeOfEB = mxCreateDoubleMatrix(1, EBRANGE, mxREAL);

int *RangePoints = (int *)calloc(EBRANGE, sizeof(int));

for(i = 0; i < EBRANGE; i++){
    RangePoints[i] = i;
  }

for(i = 0; i < EBRANGE; i++){
    printf("RangePoints[%d] = %d.\n", i, RangePoints[i]);
  }

  memcpy((void *) mxGetPr(DiscreteRangeOfEB), (void *) RangePoints, EBRANGE*sizeof(int));

  float MyArray[EBRANGE];

  for(j=0; j < EBRANGE; j++)
      MyArray[j] = (float)(j);

  mxArray *EBDistributionValue = NULL;

  EBDistributionValue = mxCreateDoubleMatrix(1, EBRANGE, mxREAL);

  memcpy((void *) mxGetPr(EBDistributionValue), (void *) MyArray, EBRANGE*1*sizeof(float));

  Engine *MyEngine;

  MyEngine = engOpen("null");

  engPutVariable(MyEngine, "RangePoints", DiscreteRangeOfEB);

  engPutVariable(MyEngine, "RangeValues", EBDistributionValue);

  engEvalString(MyEngine, "plot(RangePoints, RangeValues)");

  mxDestroyArray(DiscreteRangeOfEB);

  mxDestroyArray(EBDistributionValue);

  engClose(MyEngine);

  system("pause");

  return 0;
}

Answer 1

[James Tursa]

Haven't looked at the code in detail, but for sure you don't want to close the engine before you do the pause because that will wipe out the plot (the plot is tied to the running engine). I would swap the order of those lines as a first try:

system("pause");
engClose(MyEngine);

In fact, it is not necessary at all that you close the engine prior to your program exiting so you could get rid of these two lines entirely. Your program will exit, but the engine will still be running and your plot will still be visible on the screen. You will simply have to close the engine manually later on.

[Debjit Pal]

Hi James,

Can you kindly look into the code please? I have made the Visual Studio Project available at the following link. I think I am missing some basic stuffs which I am not able point out. Because when I type " >> RangePoints" in the opened Matlab command line, I see completely different set of values than I intend to pass.

Link is : http://web.engr.illinois.edu/~dpal2/Text/MyProject.zip

Please suggest. That will help me a lot in one of my implementation.

Thanks for your kind support.

Debjit.

[James Tursa]

These two lines are in error:

memcpy((void *) mxGetPr(DiscreteRangeOfEB), (void *) RangePoints, EBRANGE*sizeof(int));

memcpy((void *) mxGetPr(EBDistributionValue), (void *) MyArray, EBRANGE*1*sizeof(float));

You can't just copy memory from one array to another unless the underlying data is the same type. E.g., you can copy a double array (8-byte floating point) to a double array using memcpy, but you CAN'T copy an int array (4-byte integer) or a float array (4-byte floating point) to a double array this way. To copy these data you need to do it in a loop so the compiler can do the type conversion. E.g.,

double *dp;
:
dp = mxGetPr(DiscreteRangeOfEB);
for(i = 0; i < EBRANGE; i++){ dp[i] = RangePoints[i]; }
dp = mxGetPr(EBDistributionValue);
for(i = 0; i < EBRANGE; i++){ dp[i] = MyArray[i]; }