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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®.
Create user-defined routines
Write a user-defined routineThis section outlines some implementation issues for C user-defined routines (UDRs). This section also describes the specific features and tasks of a C UDR.
Code a C UDRWhen you code a C UDR, you define routine parameters, obtain argument values, define a return value, and code the routine body to write a C function.
Define a return value
Return a value
Return a NULL valueTo return an SQL NULL value from a user-defined function, pass the MI_FPARAM structure as the last argument in the UDR and use the mi_fp_setreturnisnull() function to set the NULL value in this MI_FPARAM structure.

Return a NULL value

To return an SQL NULL value from a user-defined function, pass the MI_FPARAM structure as the last argument in the UDR and use the mi_fp_setreturnisnull() function to set the NULL value in this MI_FPARAM structure.

You must call the mi_fp_setreturnisnull() function with MI_TRUE before your UDR completes. If you do not, you might receive an incorrect result from the UDR. Do not just return a NULL-valued pointer. For more information, see Return a NULL value.

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