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<h4 class="subsection">A.2.3 Character Strings in Mex-Files</h4>

<p>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 <samp><span class="file">stringdemo.cc</span></samp>, is given in the
file <samp><span class="file">mystring.c</span></samp>, as seen below.

<pre class="example"><pre class="verbatim">     #include &lt;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 &lt; n; j++)
         for (i = 0; i &lt; m; i++)
           po [j*m + m - 1 - i] = pi [j*m + i];
     }
</pre></pre>
   <p class="noindent">An example of its expected output is

<pre class="example">     mystring(["First String"; "Second String"])
     &rArr; s1 = Second String
             First String
</pre>
   <p>Other functions in the mex interface for handling character strings are
<code>mxCreateString</code>, <code>mxArrayToString</code>, and
<code>mxCreateCharMatrixFromStrings</code>.  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.

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