title: String conversion from System::String ^ to const wchar_t *
body: <p>I'm trying to open a file using a string parameter, however I'm getting the following error:</p>
  
  <pre><code>error C2664: 'void std::basic_ifstream&lt;_Elem,_Traits&gt;::open(const wchar_t *,std::ios_base::openmode,int)' : cannot convert parameter 1 from 'System::String ^' to 'const wchar_t *'
  </code></pre>
  
  <p>How do you convert <code>System::String ^</code> to <code>const wchar_t *</code>?</p>