Why arraysize is identified as zero in my mex code?

Question

I have a mex function and I'm using it in matlab with the following command (interface):

Matsize = 30555

Fv_calc(:,2) = mx_solve_quadratic(QuadraticCoefficients,MatSize);  

The gateway function is as follows:

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
    int *arraysizePtr = NULL;
    arraysizePtr = (int *)mxGetPr(prhs[1]);
    int arraysize = *arraysizePtr;
    float *inMatrix = NULL;
    inMatrix = (float *)mxGetPr(prhs[0]);
    const float a = 1; /* coefficient for x^2 is always 1*/
    plhs[0] = mxCreateNumericMatrix(arraysize, 1, mxSINGLE_CLASS, mxREAL);
    float *out = (float *)mxGetPr(plhs[0]);
    float x0; /* the smaller root */
    float x1; /* the bigger root */
    int fOutput = 0;
    int i = 0;
    for (i = 0; i < arraysize; i++)
    {
        fOutput = gsl_poly_solve_quadratic(a, inMatrix[i], inMatrix[i + arraysize], &x0, &x1);
        out[i] = (x1 > 0 ? x1 : 0);
    }
}  

Everything is true because I have run the code before and now I have just made a slight change. I really don't understand why arraysize is identified as 0 when running the mex code?

Answer 1

mxGetPr seems to return a double * from what I can find online.

(https://nl.mathworks.com/help/matlab/apiref/mxgetpr.html?s_tid=gn_loc_drop)

Casting and assigning it to int *arraysizePtr will cause the double data to be interpreted as int when accessed trough *arraysizePtr, yielding nonsense.