Question

I am trying to speeden up my Matlab program by writing a few functions in C++ and using the mex interface to integrate them. I got my results in a vector in c++. I want to transfer it to an array in MATLAB.
I know i should redirect

 plhs[0] to the vector 

but i am not getting how exactly should I do it.

Answer 1

When I’ve done similar things, I manually marshal the data so that it won’t be freed when the C++ routine is completed. Here’s a basic outline:

#include <vector>
#include "mex.h"

mxArray * getMexArray(const std::vector<double>& v){
    mxArray * mx = mxCreateDoubleMatrix(1,v.size(), mxREAL);
    std::copy(v.begin(), v.end(), mxGetPr(mx));
    return mx;
}

void mexFunction(int nlhs, mxArray *plhs[ ], int nrhs, const mxArray *prhs[ ]) {
    std::vector<double> v;

    v.push_back(0);
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);

    plhs[0] = getMexArray(v);

}

If I save this as test.cpp and then open matlab in that directory, I do the following:

>> mex test.cpp
>> test

ans =

      0     1     2     3

which is the expected output. Hopefully that is a good starting point – you may want to inline it, but I’m not sure of the benefit. Btw, if you haven’t checked out the matlab mex help, it is a great resource.