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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.
Obtain argument valuesTo obtain the argument value with a C UDR, access the parameter that you have specified in the C declaration of the function. The parameter declaration indicates the appropriate passing mechanism for the UDR parameters.
Handling NULL argumentsBy default, a C UDR does not handle SQL NULL values. When you call a UDR with an SQL NULL as the argument, the routine manager does not invoke the UDR. It returns a value of SQL NULL for the UDR.

Handling NULL arguments

By default, a C UDR does not handle SQL NULL values. When you call a UDR with an SQL NULL as the argument, the routine manager does not invoke the UDR. It returns a value of SQL NULL for the UDR.

To have the UDR invoked when it is called with SQL NULL arguments, register the UDR with the HANDLESNULLS routine modifier and code the UDR to take special steps when it receives a NULL argument.

To determine whether an argument is SQL NULL, declare the MI_FPARAM structure as the last argument in the UDR and use the mi_fp_argisnull() function to check for NULL argument values. Do not just compare the argument with a NULL-valued pointer. For more information, see Handling NULL arguments with MI_FPARAM.

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