title: Converting C++ std::wstring to utf8 with std::codecvt_xxx
body: <p>C++11 has tools to convert wide char strings <code>std::wstring</code> from/to utf8 representation: <code>std::codecvt</code>, <code>std::codecvt_utf8</code>, <code>std::codecvt_utf8_utf16</code> etc.</p>
  
  <p>Which one is usable by Windows app to convert regular wide char Windows strings <code>std::wstring</code> to utf8 <code>std::string</code>? Is it always works without configuring locales?</p>