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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 routine parametersWhen the routine manager invokes a C UDR, the routine manager passes to the UDR any argument values that the calling SQL statement provided. When you write a C UDR, you can define routine parameters that indicate the data types of the arguments that you expect the UDR to handle.
The MI_DATUM argumentsWhen an SQL statement invokes a UDR, the statement can specify column values or expressions to pass to the UDR. The routine manager passes these argument values to a UDR as MI_DATUM values.

The MI_DATUM arguments

When an SQL statement invokes a UDR, the statement can specify column values or expressions to pass to the UDR. The routine manager passes these argument values to a UDR as MI_DATUM values.

The data type of each argument determines the passing mechanism that the routine manager uses for the argument value, as follows:

Values of most data types cannot fit into an MI_DATUM structure. The routine manager passes these argument values by reference.
Values of a few data types can fit into an MI_DATUM structure. The routine manager passes these argument values by value.

The passing mechanism that the routine manager uses for a particular argument determines how you must declare the corresponding parameter of the UDR. For more information about how the routine manager passes argument values to a C UDR, see The MI_DATUM data type and Push arguments onto the thread stack.

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