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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.
Create a copy of an error descriptorThe DataBlade® API passes the error descriptor as an argument to the callback. Therefore, the DataBlade® API allocates memory for the error descriptor when it invokes the callback and deallocates this memory when the callback exits. To preserve the error information for the calling routine, you can create a user copy of the error descriptor within the callback.

Create a copy of an error descriptor

The DataBlade® API passes the error descriptor as an argument to the callback. Therefore, the DataBlade API allocates memory for the error descriptor when it invokes the callback and deallocates this memory when the callback exits. To preserve the error information for the calling routine, you can create a user copy of the error descriptor within the callback.

The following DataBlade API functions facilitate an error-descriptor copy.


DataBlade API function	Description
mi_error_desc_copy()	Allocates memory for a user copy of a specified error descriptor and returns a pointer to this user copy
mi_error_desc_is_copy()	Determines whether the specified error descriptor is a user copy
mi_error_desc_destroy()	Frees memory for a specified user copy of an error descriptor (which was allocated with mi_error_desc_copy())

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