MATLAB: Can I pass a pointer to a matrix created in MATLAB to C via a MEX file and change the data in it

Question

In MATLAB I would like to create an 1xN array of zeros, pass it to a C routine as an input argument, have the C routine update the (type double) values in the array (matrix in MATLAB). I would like to do this instead of having the MEX routine return a matrix (as is done in the example arrayProduct.c)

Is this possible, and if so, does anyone have any examples they would be willing to share?

Answer 1

Make the second to last line in step 2 this and it will work:

workOnExistingMatrix(mxGetPr(prhs[0]));

Here's the corrected MEX file:

//This is the MEX file (written in C)
#include "mex.h"
void workOnExistingMatrix(double* aMatrixCreatedInMatlab) {
    aMatrixCreatedInMatlab[0] = 0.1234;
}
//The gateway function
void mexFunction( int nlhs, mxArray *plhs[],
                  int nrhs, const mxArray *prhs[]) {
    //This works =)
    workOnExistingMatrix(mxGetPr(prhs[0]));
}