// in the header file...

class MyClass {
   public:
      MyClass();
      ~MyClass();
      MyClass operator << ( const string& );
      MyClass operator >> ( const string& );
}

// in the .cpp file...
MyClass::MyClass() {}
MyClass::~MyClass() {}

MyClass operator << ( const string& ) {
   // this causes an error: 'MyClass operator<<(const std::string&)' must take exactly two arguments
}

MyClass operator >> ( const string& ) {
   // same error
}