A.2.4 Cell Arrays with Mex-Files

One can perform exactly the same operations on Cell arrays in mex-files as in oct-files. An example that duplicates the function of the celldemo.cc oct-file in a mex-file is given by mycell.c as shown below.

#include "mex.h"

void
mexFunction (int nlhs, mxArray *plhs[],
             int nrhs, const mxArray *prhs[])
{
  mwSize n;
  mwIndex i;

  if (nrhs != 1 || ! mxIsCell (prhs[0]))
    mexErrMsgTxt ("ARG1 must be a cell");

  n = mxGetNumberOfElements (prhs[0]);
  n = (n > nlhs ? nlhs : n);

  for (i = 0; i < n; i++)
    plhs[i] = mxDuplicateArray (mxGetCell (prhs[0], i));
}

The output is identical to the oct-file version as well.

[b1, b2, b3] = mycell ({1, [1, 2], "test"})
⇒
b1 =  1
b2 =

   1   2

b3 = test

Note in the example the use of the mxDuplicateArray function. This is needed as the mxArray pointer returned by mxGetCell might be deallocated. The inverse function to mxGetCell, used for setting Cell values, is mxSetCell and is defined as

void mxSetCell (mxArray *ptr, int idx, mxArray *val);

Finally, to create a cell array or matrix, the appropriate functions are

mxArray *mxCreateCellArray (int ndims, const int *dims);
mxArray *mxCreateCellMatrix (int m, int n);