title: Reference to value of STL map element?
body: <p>Is it OK to pass to function a reference to the value of map element, and to modify it there?</p>
  
  <pre><code>foo(string &amp; s)
  {
      s = "xyz";
  }
  
  map&lt;int, string&gt; m;
  m[1] = "abc";
  foo(m[1]); // &lt;-- Is it ok? Will m[1] be "xyz" after this call?
  </code></pre>
  
  <p>Thank you.</p>