Character Strings in Mex-Files - Untitled
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#### A.2.3 Character Strings in Mex-Files

As mex-files do not make the distinction between single and double quoted strings within Octave, there is perhaps less complexity in the use of strings and character matrices in mex-files. An example of their use, that parallels the demo in `stringdemo.cc`, is given in the file `mystring.c`, as seen 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 <string.h>
         #include "mex.h"

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

           if (nrhs != 1 || ! mxIsChar (prhs[0]) ||
               mxGetNumberOfDimensions (prhs[0]) > 2)
             mexErrMsgTxt ("expecting char matrix");

           m = mxGetM (prhs[0]);
           n = mxGetN (prhs[0]);
           pi = mxGetChars (prhs[0]);
           plhs[0] = mxCreateNumericMatrix (m, n, mxCHAR_CLASS,
         				   mxREAL);
           po = mxGetChars (plhs[0]);

           for (j = 0; j < n; j++)
             for (i = 0; i < m; i++)
               po [j*m + m - 1 - i] = pi [j*m + i];
         }

An example of its expected output is

         mystring(["First String"; "Second String"])
          s1 = Second String
                 First String

Other functions in the mex interface for handling character strings are `mxCreateString`, `mxArrayToString`, and `mxCreateCharMatrixFromStrings`. In a mex-file, a character string is considered to be a vector rather than a matrix. This is perhaps an arbitrary distinction as the data in the mxArray for the matrix is consecutive in any case.