title: Can you overload a global operator in a .hpp file?
body: <p>I wrote an overload for + to add two <code>vector&lt;double&gt;</code>:</p>
  
  <pre><code>vector&lt;double&gt; operator+(vector&lt;double&gt; v, vector&lt;double&gt; u)
  {
      int n = (v.size()&lt;u.size()) ? v.size() : u.size();
      vector&lt;double&gt; w;
      for (int j = 0; j&lt;n; ++j)
          w.push_back(v[j] + u[j]);
      return w;
  };
  </code></pre>
  
  <p>If I put in a .cpp file it's fine. But if I put in a .hpp file it generates a lot of errors related to "xutils" system file. Is this normal?</p>