Binding-Handle Types

MIDL provides several types of handles. In this way, you can select the handle type that is best suited for your application. (See Encoding Services for additional information on using a primitive handle as a serializing handle.)

Handle characteristics:

Handles can be parameters that are passed to the remote procedure, or they can be global data structures that do not appear in the remote function prototype.
You can declare handles of the primitive handle type handle_t, or you can declare a handle type packaged in structures with other data.
Some handles are invisible to the client application and are completely managed by the stubs while others are declared, defined, and managed by the application.
A special type of handle, the context handle, allows you to maintain state information on the server in addition to acting as a binding handle.

The following table summarizes MIDL handle types:

Handle type	Characteristics
Primitive	A handle of the predefined type handle_t. Note that serializing handles (which are not binding handles) are also of the type handle_t. See Serialization Handles for more information.
Explicit	A handle used as a parameter to the remote procedure. The explicit handle usually appears as the first parameter for compatibility with DCE.
Implicit	A handle defined in the generated header file as a global variable that is available to the stubs. The developer defines the handle in the ACF only and does not include the handle as a parameter to the remote procedure call.
User-defined	A handle of the primitive type handle_t that is created by a user-supplied function that converts the user-defined data to the handle.
Auto	A handle that is automatically generated by the MIDL compiler and managed by the client run-time library. The client stub manages the binding and the handle; the client application does not require any explicit code to manage the binding or the handle.
Context	A handle that includes information about the state of the server. The context handle is automatically associated with specific user-defined functions on the server.

Handle characteristics can be combined in several ways to produce such types as explicit primitive, explicit user-defined, implicit primitive, and implicit user-defined handles, depending upon your application needs.