How to pass string from labview to c#

Hi
I have used .net assembly to use a dll in c#.
The communication part is fine and I can pass the parameters from c# to labview but one of the functions should read back a string from labview

WriteSingle(string in, out string);

And I see nothing goes back to c# . Could you please help me with this . How should I pass the string in LabVIEW that can be recognised in c#

Thanks