Export C++ to VB.NET

BSTR __stdcall expfun(void)
{
   char* cp_test = "Hi World!";

   CString cs_test;
   cs_test.AppendFormat(L"%s", cp_test);

   return cs_test.AllocSysString();
}

Imports System.Runtime.InteropServices
.
.
.
<DllImport("dll_path", CallingConvention:=CallingConvention.StdCall, CharSet:=CharSet.None)> _
Public Shared Function expfun() As String
End Function