Output a matrix with c++ and mex

Question

I have a problem with my c++ code. I want to return a matrix of k-dimensions from my cpp program to Matlab.

The matrix I want to pass is stored in all_data

Answer 1

mxGetPr does not return a vector<vector<double> >. It returns a double *. MATLAB arrays are stored contiguously in memory, column-major. Assuming you've created plhs[0] with the correct dimensions, then all you need to do is this:

double *indexes = mxGetPr(plhs[0]);
for (int i=0; i < (npoints1+1); i++)
    for (int j=0; j < ndims1; j++)
        indexes[i + ndims1*j] = all_data[ i ][ j ];

Note the conversion of the 2 indices to a linear offset.

Answer 2

It looks like mxGetPr is returning you a pointer to an array of doubles and you are assigning it to a vector of vectors.

This should work:

double* indexes = mxGetPr(plhs[0]);