title: ostringstream gives me Implicit instantiation error
body: <p>I'm trying the elegant solution provided in <a href="https://stackoverflow.com/a/332132/768472">this answer</a> but no matter what I try, I cannot get passed the error <code>Implicit instantiation of undefined template</code> for this line:</p>
  
  <p><code>std::ostringstream strs;</code></p>
  
  <p>What I need to do? I've included the following, which I'm sure is overkill. As a second question it seems hard to track down what exactly needs to be included for ostringstream:</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;fstream&gt;
  #include &lt;iosfwd&gt;
  #include &lt;ios&gt;
  </code></pre>