You can use the following attributes to specify the characteristics of pointers:
| Attribute | Usage |
|---|---|
| ptr | Designates a pointer as a full pointer, with all the capabilities of a C-language pointer, including aliasing. |
| ref | Designates the simplest type of pointer in MIDL—one that simply provides the address of some data. Reference pointers can never be NULL. |
| unique | Lets a pointer be NULL, but does not support aliasing. |
| pointer_default | Applied to an interface to specify the default pointer type for all pointers in that interface, except for top-level parameter pointers, which automatically default to ref pointers |
| iid_is | Provides the interface ID of the COM interface that is the object of the pointer. |
| string | Specifies that the pointer points to a string. |