title: Find the first character that is not whitespace in a std::string
body: <p>Lets say I have</p>
  
  <pre><code>std::wstring str(L"   abc");
  </code></pre>
  
  <p>The contents of the string could be arbitrary.</p>
  
  <p>How can I find the first character that is not whitespace in that string, i.e. in this case the position of the 'a'?</p>