Copying 2-D C++ array into mxArrays

If I have a pointer *ptr that is pointing to a 2-D array of UINT16 type in C++, what code in a CMEX file will convert that data to a mxArray that can be output to MATLAB? Ultimately what I want is a myfunction.mexw64 file where Z = myfunction executed in MATLAB provides the original 2-D array that I have right now in C++.

Answer 1

[James Tursa]

If the array elements are in column order in the C++ file, then a simple copy will suffice. E.g.,

#include "mex.h"
void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[])
{
  unsigned short *pr;
  unsigned short ptr[] = {1,2,3,4,5,6};
  mwSize i, m = 2, n = 3, mn = m*n;
  plhs[0] = mxCreateNumericMatrix(m,n,mxUINT16_CLASS,mxREAL);
  pr = mxGetPr(plhs[0]);
  for( i=0; i<mn; i++ ) {
    pr[i] = ptr[i];
  }
}

In the above code I have used an array for ptr for simplicity, but a pointer to a block of memory will work just as well.

If the elements are in row order instead of column order, a transpose will be involved. If that is the case, let me know and I will post that code. (Or you can just transpose it at the MATLAB level)

[Robert Hinkey]

Thanks James. One small adjustment is needed, the line:

pr = mxGetPr(plhs[0]);

should read:

pr = (unsigned short*)mxGetData(plhs[0]);

since the mxGetPr is for type double only. The original line maybe works for some people, but my Visual C++ 2008 compiler doesn't like it.

[James Tursa]

Correct. I had modified some double code that I already had and missed that. Thanks.