title: How to check if a std::string is set or not?
body: <p>If using a <code>char*</code>, I can initialize it to <code>NULL</code> and later check if it is set by doing a comparison. How to do the same thing for a <code>std::string</code>? How to check if the string is set or not?</p>
  
  <p>EDIT:
      What if the string I set to is also empty? Do I have to use an additional flag to check if the <code>std::string</code> is set or not?</p>