title: c++ multimap equal_range found nothing
body: <p>How can I know the equal_range didn't find any match cases?</p>
  
  <p>like:</p>
  
  <pre><code>multimap&lt;string,string&gt; mapdic;
  pair&lt;multimap&lt;string,string&gt;::iterator,multimap&lt;string,string&gt;::iterator&gt; ret;
  // insert some string pairs
  
  
  ret=mapdic.equal_range(thisUpperCaseName);
  
  
      if (???)//how to test equal_range find nothing?
      {       
  }else{
  
       }
  </code></pre>
  
  <p>Anyone can help?</p>
  
  <p>Thanks</p>