title: How to optionally pass variable arguments in C
body: <p>Consider below function:</p>
  
  <pre><code>void foo(int n,...);
  </code></pre>
  
  <p>I need to call this function, "optionally" passing variable arguments. </p>
  
  <p>Is it possible?</p>
  
  <p>Something like this:</p>
  
  <pre><code>foo(10, (bIsJobDone ? "OK" : xxx) );
  </code></pre>
  
  <p>I am not able to figure out what to put in place of xxx (xxx should convert to nothing) and also how to avoid "," after 10, if I don't have to pass any variable arg to foo?</p>
  
  <p>Note: i can't change signature of "foo".</p>