title: Returning char * instead of string
body: <p>How may I correct the following code in C++11:</p>
  <pre><code>    const char *what() const noexcept override {
          return &quot;Mtm matrix error: Dimension mismatch: (&quot; + std::to_string(mat1_height) + &quot;,&quot; +
                 std::to_string(mat1_width)
                 + &quot;) (&quot; + std::to_string(mat2_height) + &quot;,&quot; + std::to_string(mat2_width) + &quot;)&quot;;
      }
  </code></pre>
  <p>As you can see I'm returning <code>string</code> instead of <code>const char*</code> but won't that be converrted automatically? and how to fix that?</p>
  <p><strong>Note:</strong> I want something to look like c++ code and not c using <code>sprintf</code> for example</p>