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Extending Informix®Beyond standard relational database objects, HCL Informix® can be extended to handle specialized data types, access methods, routines, and other objects. Informix® includes many built-in extensions that are fully integrated in the database server. Informix® also provides DataBlade® modules, which are packages of extended database objects for a particular purpose and that are installed separately from the database server. Alternatively, you can create your own user-defined objects for Informix®.
Creating extensionsYou can create user-defined data types, routines, access methods, and other database objects to suit your needs. You can use application programming interfaces to write user-defined routines and applications that access data in Informix® databases.
DataBlade® API Programmer's GuideThe Informix® DataBlade® API Programmer's Guide describes information about the DataBlade® API, the C-language application programming interface (API) provided with HCL Informix®.
Database access
Exceptions and eventsThis section describes exceptions and events, and explains how to handle them in DataBlade® API modules.
Event-handling mechanismsAn event-handling mechanism provides a way for one DataBlade® API module to inform another module (or another part of the same module) that an event has occurred during execution of a function.
Invoke a callbackA callback function (or just callback) is a function that you write to handle a particular event.
Register a callbackFor a callback to execute when its associated event occurs, you must register it with the mi_register_callback() function.
Callback handleThe mi_register_callback() function returns a callback handle, which accesses a registered callback within a DataBlade® API module. A callback handle has the MI_CALLBACK_HANDLE data type.

Callback handle

The mi_register_callback() function returns a callback handle, which accesses a registered callback within a DataBlade® API module. A callback handle has the MI_CALLBACK_HANDLE data type.

Use a callback handle to identify a callback for the following tasks.


Callback task	DataBlade API function
Enable a callback	mi_enable_callback()
Disable a callback	mi_disable_callback()
Retrieve a pointer to a callback function	mi_retrieve_callback()
Unregister a callback	mi_unregister_callback()

Tip: The last argument of the mi_register_callback() function is also a callback handle, but this argument is reserved for future use and must currently be a NULL-valued pointer.

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