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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.
Callback functionsTo catch or handle an event, you create a C function called a callback function. In your DataBlade® API module, you can register callback functions to handle recovery from events. The DataBlade® API invokes a registered (and enabled) callback when the event associated with the callback occurs.
Write a callback functionWithin the body of a callback function, you provide the code that handles a particular event or events. Only certain tasks are valid within a callback. When a callback function is invoked for an event, the DataBlade® API passes information about the event to the callback.
Event informationWhen a callback function is invoked for a particular event, the DataBlade® API passes an event-type structure as the third parameter of this function. This event-type structure contains information about the event that triggered the callback.
An error descriptorThe DataBlade® API stores information about exceptions and errors in an error descriptor. An error descriptor is an MI_ERROR_DESC structure. It holds information for the MI_Exception and MI_Client_Library_Error event types.

An error descriptor

The DataBlade® API stores information about exceptions and errors in an error descriptor. An error descriptor is an MI_ERROR_DESC structure. It holds information for the MI_Exception and MI_Client_Library_Error event types.

The following table summarizes the memory operations for an error descriptor.


Memory duration	Memory operation	Function name
Current® memory duration	Constructor	mi_error_desc_copy()
Current memory duration	Destructor	mi_error_desc_destroy()

When an MI_Exception or MI_Client_Library_Error event occurs, the DataBlade API invokes the appropriate callback. To this callback, the DataBlade API passes an initialized error descriptor as the third callback argument. The error descriptor contains information about the MI_Exception or MI_Client_Library_Error event. Within the callback, use the accessor functions in Accessor functions for an error descriptor to obtain the error information from the error descriptor.

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