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A.2.4 Cell Arrays with Mex-Files

We can perform exactly the same operations in Cell arrays in mex-files as we can in oct-files. An example that reduplicates the functional of the celldemo.cc oct-file in a mex-file is given by mycell.c as below

     /*
     
     Copyright (C) 2006, 2007 John W. Eaton
     
     This file is part of Octave.
     
     Octave is free software; you can redistribute it and/or 
     modify it under the terms of the GNU General Public License 
     as published by the Free Software Foundation; either
     version 3  of the License, or (at your option) any later 
     version.
     
     Octave is distributed in the hope that it will be useful, 
     but WITHOUT ANY WARRANTY; without even the implied warranty
     of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
     See the GNU General Public License for more details.
     
     You should have received a copy of the GNU General Public 
     License along with Octave; see the file COPYING.  If not,
     see <http://www.gnu.org/licenses/>.
     
     */
     
     #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 ("expects cell");
     
       n = mxGetNumberOfElements (prhs[0]);
       n = (n > nlhs ? nlhs : n);
       
       for (i = 0; i < n; i++)
         plhs[i] = mxDuplicateArray (mxGetCell (prhs[0], i));
     }

which as can be seen below has exactly the same behavior as the oct-file version.

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

Note in the example the use of the mxDuplicateArry function. This is needed as the mxArray pointer returned by mxGetCell might be deallocated. The inverse function to mxGetCell is mcSetCell 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);