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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.
Default behaviorIf no callback is registered for a particular event, the DataBlade® API uses its default behavior when this event occurs. The default event handling depends on whether the event occurs in a C UDR or in a client LIBMI application.
Default behavior in client LIBMI applications

Default behavior in client LIBMI applications

If an exception occurs during the execution of a client LIBMI application and the application does not register any callback to handle the exception, the client LIBMI takes one of the following default actions.


Exception type	Default behavior
MI_Exception	The client LIBMI executes the system-default callback. The mi_default_callback() function implements this system-default callback. An unhandled MI_MESSAGE does not halt execution of the current statement. The DataBlade® API passes the warning to the client LIBMI application, and processing continues at the next statement of this client application. An unhandled MI_EXCEPTION aborts execution of the current statement in the client LIBMI application. The DataBlade API passes the error to the client LIBMI application and returns control to this client application.
MI_Xact_State_Change	An unhandled MI_Xact_State_Change does not halt execution of the current statement. Processing continues at the next statement of the client LIBMI application.
MI_Client_Library_Error	The client LIBMI executes the system-default callback. The mi_default_callback() function implements this system-default callback.

On UNIX™ or Linux™, the system-default callback causes the client LIBMI application to send an error or warning message to stderr in response to an unhandled exception.

On Windows™, the system-default callback causes the client LIBMI to display an error or warning message in a Windows message box in response to an unhandled exception.

To prevent the execution of the system-default callback, use the mi_register_callback() function to register callbacks in the client LIBMI application.

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