MIDL2165
The documentation lists this name without a value.
Documented in Win32
use of field deriving from a void pointer needs /c_ext The type void * and other types and type qualifiers that are not supported by DCE IDL are allowed in the IDL file only when you use the MIDL default compiler settings. Using the /osf switch overrides this default. If you must compile in osf-compatibility mode, you will need to redefine the pointer type.