std optional: No such file or directory
<p>I tried to compile the following program with different compilers (including gcc 6.1) :</p>

<pre><code>#include &lt;optional&gt;
int main()
{
    std::optional&lt;int&gt; o1;
}
</code></pre>

<p>Output is</p>

<blockquote>
  <p>main.cpp:1:20: fatal error: optional: No such file or directory #include optional</p>
</blockquote>

<p>This is even true for the examples given here:
<a href="http://en.cppreference.com/w/cpp/utility/optional/optional" rel="noreferrer">http://en.cppreference.com/w/cpp/utility/optional/optional</a></p>

<p>Any clues why?</p>