title: Eclipse Mars: Symbol 'unique_ptr' could not be resolved
body: <p>Using Eclipse Mars, I am getting the <code>Symbol 'unique_ptr' could not be resolved</code> error. I tried adding <code>-std=c++11</code> to CDT GCC Built-in Compiler Settings, but this didn't help. The error goes away when I reopen Eclipse, but if I make a modification to the code, the error comes back. </p>
  
  <p>One simple code sample: </p>
  
  <pre><code>std::unique_ptr&lt;String&gt; p1;
  </code></pre>