title: C++ character replace
body: <p>What is the best way to replace characters in a string?</p>
  
  <p>Specifically:</p>
  
  <pre><code>"This,Is A|Test" ----&gt; "This_Is_A_Test"
  </code></pre>
  
  <p>I want to replace all commas, spaces, and "|" with underscores.</p>
  
  <p>(I have access to Boost.)</p>