Mex results different from linux to windows!

Hello everyone.

I have a mex routine written in C++ that I use on a Windows computer compiled through Visual Studio. Now I need the same routine running on a Linux computer and I'm using gcc to compile it. I always compile the routine with a simple mex filename.cpp, but the results that I get on Windows are completely different from those on the Linux machine.

How can this be possible?

This is the structure of the code:

#include "mex.h"
#include <matrix.h>
#include <vector>
#include <math.h>
#include <iostream>
#include <algorithm>

const double pi = 3.141592653589793;

double median(double *x, const int NN);

void mexFunction(int nlhs, mxArray *plhs[], /* Output variables */
        int nrhs, const mxArray *prhs[]) /* Input variables */
{
    double *xc = mxGetPr(prhs[0]);
  // [Read variables]

  // [Output]
    plhs[0] = mxCreateDoubleMatrix(N_ws,1,mxREAL);
    double *norm = mxGetPr(plhs[0]);

  // [Declare dynamic variables]
  double *var = new double[N];

      // [Simple for cycle with calculations]

      // [Delete dynamic variables]
    delete[] var;

      return;
  }

double median(double *x, const int NN) {
    double med;
    // Even number of samples
    if (NN % 2 == 0) {
    double x1, x2;
        std::nth_element(&x[0], &x[NN/2-1], &x[NN]); // I have to put x[NN] and not x[NN-1] because the last is not sorted!
    x1 = x[NN/2-1];
    std::nth_element(&x[0], &x[NN/2], &x[NN]); // I have to put x[NN] and not x[NN-1] because the last is not sorted!
    x2 = x[NN/2];
    med = (x2 + x1)/2;
  // Odd number of samples
  } else {
    std::nth_element(&x[0], &x[0] + (NN-1)/2, &x[NN]);
    med = x[(NN-1)/2];
    }

      return med;
  }

Answer 1

[Alessandro Masullo]

I answer myself. The problem was related to the function abs. In gcc, math.h has a C version of abs that works on integers, so gcc abs was rounding all my values to integers!