title: Checking if input is standard input - istream
body: <p>given the following simple function declaration:</p>
  
  <pre><code>void foo (std::istream&amp; is);
  </code></pre>
  
  <p>I can call foo in several ways, for example:</p>
  
  <pre><code>fstream f;
  
  foo(std::cin);
  foo(f);
  </code></pre>
  
  <p>is there any way I can check if the given istream&amp; is standard input ? (STD::CIN)</p>
  
  <p>thanks in advance</p>