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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 <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];
}
</pre></pre>
<p class="noindent">An example of its expected output is
<pre class="example"> mystring(["First String"; "Second String"])
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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