Type Attributes

Type attributes are the MIDL attributes that can be applied to type declarations:

• [handle]
• [context_handle]
• [switch_type]
• pointer type attributes

The [switch_type] attribute designates the type of a union discriminator. This attribute applies only to a nonencapsulated union.

A context handle is a pointer with a [context_handle] attribute. The [context_handle] attribute allows you to write procedures that maintain state information between remote procedure calls. A context handle with a non-null value represents saved context and serves two purposes:

• On the client side, it contains the information needed by the RPC run-time library to direct the call to the server.
• On the server side, it serves as a handle on active context.

The [handle] attribute specifies that a type can occur as a user-defined (generic) handle. This feature permits the design of handles that are meaningful to the application. The user must provide binding and unbinding routines to convert between the user-defined handle type and the RPC primitive handle type, handle_t. A primitive handle contains destination information meaningful to the RPC run-time libraries. A user-defined handle can only be defined in a type declaration, not in a function declaration. A parameter with the [handle] attribute has a double purpose. It is used to determine the binding for the call, and it is transmitted to the called procedure as a normal data parameter.