How to marshaling with C#

[DllImport("DK_V2.dll", CharSet = CharSet.Ansi, CallingConvention = CallingConvention.Cdecl)]

//C++
      int GetUs(void* con, uint32_t devId, char** ubjs, uint32_t* nid);

I convert above function to c# code as follow :

 extern public static int GetUs(IntPtr con,out int devId,[MarshalAs(UnmanagedType.AnsiBStr), In] ref string ubjs, out int nid);

but that's wrong.

What I have tried:

I changed function variable datatypes but confront an error.