CODEWITHSUNDEEP
matlabintmex
user1270155
user1270155

Reputation: 81

Array of int at the output of a mex file

I am trying to create a mex function whose entry is an integer and whose output is an array of integer. So the function looks like: int *myFunction(unsigned int N). In the mexFunction, I declare a variable *variab of type int and then

N = mxGetScalar(prhs[0]);

  /* assign a pointer to the output */
  siz= 2*ceil(log(1.0*N)/log(2.0)-0.5)+1;
  plhs[0] = mxCreateDoubleMatrix(1,siz, mxREAL);
  vari = (int*) mxGetPr(plhs[0]); */
  /* Call the subroutine. */
  vari = myFunction(N);
  mexPrintf("The first value is %d\n", vari[0]);

The thing is the first value is the correct one (and the other ones were checked and were correct as well) but when I call the routine mxFunction(16), I get only 0's as output. I guess it is because my output is an array of int but I don't know how to solve the problem. Any hint? Cheers.

Upvotes: 4

Views: 2945

Answers (1)

learnvst
learnvst

Reputation: 16193

Matlab deals with doubles by default. You can easily cast them in your mex function like the following example based on your code snippet. I have made a myFunction that performs a demo algorithm. Rather than return a data type, I make it a void function and pass it a pointer to the output so that it can populate it . . .

/*************************************************************************/
/* Header(s)                                                             */
/*************************************************************************/
#include "mex.h"
#include "math.h"


/*************************************************************************/
/*the fabled myFunction                                                  */
/*************************************************************************/
void myFunction(unsigned int N, unsigned int siz, double* output)
{
    int sign = 1;
    for(int ii=0; ii<siz; ++ii)
    {
        output[ii] = (double)(ii * sign + N);
        sign *= -1;
    }

}


/*************************************************************************/
/* Gateway function and error checking                                   */
/*************************************************************************/
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
  /* variable declarations */
  unsigned int siz;
  double N;

  /*  check the number of input and output parameters  */  
    if(nrhs!=1)
        mexErrMsgTxt("One input arg expected");
    if(nlhs > 1)
        mexErrMsgTxt("Too many outputs");

  N = mxGetScalar(prhs[0]);

  /* assign a pointer to the output */  
  siz= 2*ceil(log(1.0*N)/log(2.0)-0.5)+1;
  plhs[0] = mxCreateDoubleMatrix(1,siz, mxREAL);
  myFunction(N, siz, mxGetPr( plhs[0]) );
}

Upvotes: 3

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