title: Mat to unsigned char*
body: <p>Can anyone tell me how can I convert <code>Mat</code> to <code>unsigned char*</code> in OpenCV and also whether the  data will be an array? Also, I want to know how can the same thing be done for <code>vector&lt;vector&lt;double&gt;&gt;</code> to <code>float*</code> so as to make it a pointer of array? thanks.</p>