com - Passing string by ref to activex component in C# -

i'm trying activex api function pattern function(ref string returnvalue) in c#. api function modifies string.

string returnvalue = string.empty; api.func(ref returnvalue); // disp_e_typemismatch 

ok, maybe that's because strings immutable. trying stringbuilder per this:

stringbuilder returnvalue = new stringbuilder(128); api.func(returnvalue); 

this causes compile-time error type mismatch.

how call function?

i don't know if need marshal c# string bstr, , if so, don't know how pass ref api function.

if func should change returnvalue , think code should changed this:

string returnvalue = string.empty; api.func(ref returnvalue); 

you should init returnvalue before pass ref.

upd: did try call this?:

api.func(ref marshal.stringtobstr(string value));