class classA {
public:
  CString aString;
};
extern classA theApp;

theApp.aString = "test string";

class classA {
    public:
      CString aString;
      void set_string()
      {
          aString = "test string 2";
      }
    };
    extern classA theApp;

    //in another class function

    theApp.set_string();