MIDL2178
The documentation lists this name without a value.
Documented in Win32
attribute expression must be a variable name or a pointer dereference expression in this mode. You must specify the /ms_ext switch The DCE IDL compiler requires the size associated with the [ size_is ] attribute to be specified by a variable or pointer variable. If you want to take advantage of the Microsoft extension that allows the [ size_is ] attribute to be defined by a constant expression, you cannot use the /osf compiler switch.