title: printf format parameter contain undefined escape character
body: <pre><code>#include &lt;stdio.h&gt;
  
  int main()
  {
     printf("Hello\c!\n");
     return 0;
  }
  </code></pre>
  
  <p>Output : <code>Helloc!</code></p>
  
  <p>So , when <code>\[some_undifined_symbol]</code>  appeared in <code>printf</code> 's format string, it just ignore the <code>\</code> ?</p>