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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 extensions
You 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 Guide
The 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
Develop a user-defined routine
A C user-defined routine (UDR) is a UDR that is written in the C language and uses the server-side implementation of the DataBlade® API to communicate with the database server. C UDRs (functions and procedures) are implemented as C-language functions. DataBlade modules often include C UDRs that are made available for use by registering them in the database.
Execute a UDR
The routine manager
After the query parser has used routine resolution to determine which UDR to invoke, the query executor calls the routine manager to handle the UDR execution.
Push arguments onto the thread stack
When the routine manager pushes arguments onto the thread stack, it pushes them as MI_DATUM values.

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.
- Informix® extensions and DataBlade® modules
  These topics describe how to use built-in database extensions and separately installed DataBlade® modules.
- Creating extensions
  You 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 Guide
    The Informix® DataBlade® API Programmer's Guide describes information about the DataBlade API, the C-language application programming interface (API) provided with HCL Informix.
    - DataBlade® API overview
    - Data manipulation
    - Database access
    - Create user-defined routines
      - Develop a user-defined routine
        A C user-defined routine (UDR) is a UDR that is written in the C language and uses the server-side implementation of the DataBlade® API to communicate with the database server. C UDRs (functions and procedures) are implemented as C-language functions. DataBlade modules often include C UDRs that are made available for use by registering them in the database.
        Designing a UDR
        This section provides the following design considerations for the development of a C UDR: development tools, uses of a UDR, portability, and insert and update operations.
        Creating UDR code
        This section provides an overview of C UDR development.
        Compile a C UDR
        To compile a C UDR, use a C compiler to compile the source file (.c file extension) into an object file (.o file extension) and create a shared-object file that contains the object file.
        Register a C UDR
        The CREATE FUNCTION statement registers user-defined functions in the database. The CREATE PROCEDURE statement registers user-defined procedures in the database. These functions store information about the UDR in the sysprocedures system catalog table.
        Execute a UDR
        Routine resolution
        If more than one registered UDR has the same routine name, the routine is overloaded. Routine overloading enables several routines to share a name and each of the routines to handle arguments of different data types.
        The routine manager
        After the query parser has used routine resolution to determine which UDR to invoke, the query executor calls the routine manager to handle the UDR execution.
        Load a shared-object file
        When you compile a C UDR, you store its object code in a shared-object file.
        Create the routine sequence
        A routine sequence is the context in which the UDR executes. Generally, each routine instance (whether implicit or explicit) creates a single, independent routine sequence.
        Push arguments onto the thread stack
        When the routine manager pushes arguments onto the thread stack, it pushes them as MI_DATUM values.
        Mechanism for passing MI_DATUM values
        Argument promotion
        The C compilers that accept Kernighan--Ritchie (K&R) syntax promote all arguments to the int data type when they are passed to a routine.
        Manage UDR execution
        After the routine manager creates a routine sequence and pushes the arguments onto the stack, it invokes the UDR. It then manages the execution of the UDR associated with this routine sequence.
        Return the value
        For execution of a user-defined function, the routine manager returns any resulting value to the query executor when execution is complete. When the routine manager returns the value from a user-defined function, it passes this value as an MI_DATUM value.
        Release the routine sequence
        At the end of the routine instance, the routine manager releases the associated routine sequence. At this time, it also deallocates the MI_FPARAM structure.
        Debug a UDR
        Because a UDR runs as part of the database server process, the routine must not do anything that might negatively affect the running of the database server, such as exiting. This section provides information about how to use a C debugger to attach to a virtual processor, handle the debugging session of a C UDR, and use DataBlade® API tracing.
        Change a UDR
        This section provides information about how to alter a C UDR and how to unload a shared-object file.
      - Write a user-defined routine
        This section outlines some implementation issues for C user-defined routines (UDRs). This section also describes the specific features and tasks of a C UDR.
      - Manage memory
        A C user-defined routine (UDR) has access to shared memory for dynamic allocations and stack memory for routine arguments (including the MI_FPARAM structure), local stack variables, and return values.
      - Create special-purpose UDRs
        This section describes how to create special UDRs, such as iterator functions, user-defined aggregates, and optimization functions.
      - Extend data types
        This section describes the ways to extend data types with C user-defined routines (UDRs).
    - Appendix
      This section contains additional reference information.
  - DataBlade® API Function Reference
    The Informix® DataBlade® API Function Reference describes the DataBlade API functions and the subset of Informix ESQL/C functions that the DataBlade API supports.
  - DataBlade® Developers Kit
    The DataBlade® Developers Kit (DBDK) guides contain information about the tools you can use to develop and package DataBlade modules, which extend the functionality of HCL Informix® databases.
  - J/Foundation Developer's Guide
    The J/Foundation Developer's Guide describes how to write user-defined routines (UDRs) in the Java™ programming language for Informix®.
  - R-Tree Index User's Guide
    The Informix® R-Tree Index User's Guide describes the HCL Informix R-tree secondary access method and how to access and use its components.
  - User-Defined Routines and Data Types Developer's Guide
    The Informix® User-Defined Routines and Data Types Developer's Guide describes how to define new data types and enable user-defined routines (UDRs) to extend HCL Informix.
  - Virtual-Table Interface Guide
    The Informix® Virtual-Table Interface Programmer's Guide explains how to create a primary access method with the Virtual-Table Interface (VTI) so that users have a single SQL interface to HCL Informix tables and to data that does not conform to the storage scheme of HCL Informix.
  - Virtual-Index Interface Guide
    The Informix® Virtual-Index Interface Programmer's Guide explains how to create a secondary access method with the Virtual-Index Interface (VII) to extend the built-in indexing schemes of HCL Informix typically with a DataBlade® module.

Push arguments onto the thread stack

When the routine manager pushes arguments onto the thread stack, it pushes them as MI_DATUM values.

The routine manager takes the following factors into account:

Whether the argument is passed by value or by reference
Whether the argument needs to be promoted