Marshal a string from managed to unmanaged

I need to pass a string from C++/CLI managed to C++ unmanaged code.
The unmanaged function takes a LPCTSTR as parameter and I want to pass a String^. How do I do that?

The answer here:
http://msdn2.microsoft.com/en-gb/library/ms235282(VS.80).aspx

And a function to do it easily:

    LPCTSTR MarshalString(String^ managedString)

    {

        return (LPCTSTR)Marshal::StringToHGlobalUni (managedString).ToPointer();

    }

and back:

    String^  DiagramContainer::MarshalString(LPCTSTR nativeString)

    {

        return Marshal::PtrToStringAuto(IntPtr((void *)nativeString));

    }