Array of int at the output of a mex file - matlab

Question

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.

Answer 1

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]) );
}