title: How to modify key values in std::map container
body: <p>Given</p>
  
  <pre><code>std::map&lt;int,std::string&gt; myMap;
  fillMyMapWithStuff(myMap);
  
  // modify key values - I need to add a constant value to each key
  for (std::map&lt;int,std::string&gt;::iterator mi=myMap.begin(); mi != myMap.end(); ++mi)
  {
      // ...
  }
  </code></pre>
  
  <p>Whats a good way apply some re-indexing? Must I remove the old entry and add a new one with the new key and old value?</p>