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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
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.
Code a C UDR
When 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 parameters
When 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 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.

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.
      - 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.
        Code a C UDR
        When 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 parameters
        When 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.
        Routines with no arguments
        Routine parameters are optional. If your UDR does not need parameters, follow your C-compiler conventions for the syntax to use when declaring the C function.
        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.
        Pass-arguments by-reference
        When an argument has a value that cannot fit into an MI_DATUM structure, the routine manager passes the argument by reference. For each of these pass-by-reference arguments, you declare a parameter that is a pointer to a value of the parameter data type, in the C-function declaration.
        Pass-by-value parameters
        When an argument has a data type that can fit into an MI_DATUM structure, the routine manager passes the argument by value. For these pass-by-value arguments, you declare a parameter as the actual parameter data type in the C-function declaration.
        The MI_FPARAM argument
        The routine manager passes an MI_FPARAM structure into every UDR that it executes. This structure contains routine-state information about the UDR, such as information about arguments and return values. Because the routine manager automatically passes an MI_FPARAM structure to a UDR, you do not need to explicitly declare this structure in most C-function declarations.
        Obtain argument values
        To 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.
        Define a return value
        Code the routine body
        The actual work of the C UDR is done with C-language statements in the routine body.
        Virtual processors
        To service multiple client-application SQL requests, the database server uses virtual processors (VPs). The database server breaks the SQL request into distinct tasks, based on the resource that the task requires. Different VP types, called virtual-processor classes (VP classes), service the different kinds of tasks.
        Control the VP environment
        The routine manager executes your C UDR in a virtual-processor (VP) environment.
        Perform input and output
        Because a C UDR executes in the context of the database server, it must not use the standard input/output (I/O) calls such as scanf() and printf(). The DataBlade® API provides support for I/O on a generic stream and I/O on an operating-system file from a UDR.
        Access the UDR execution environment
      - 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.

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.