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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.
DataBlade® API overview
Access SQL data types
This section provides an overview of the data types that the DataBlade® API supports.
Character data types
The mi_lvarchar data type
The SQL LVARCHAR data type
The LVARCHAR data type of SQL stores variable-length character strings whose length can be up to 32,739 bytes. LVARCHAR is a built-in opaque data type that is valid in distributed queries of tables, views, and synonyms of databases outside the local server.

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
      - The DataBlade® API
        The HCL Informix® DataBlade® API is the application programming interface (API) for HCL Informix. You can use DataBlade API functions in DataBlade modules to access data stored in the Informix database.
      - Access SQL data types
        This section provides an overview of the data types that the DataBlade® API supports.
        Type identifiers
        A type identifier, MI_TYPEID, is a DataBlade® API data type structure that identifies a data type uniquely. For extended data types, the type identifier is database-dependent; that is, the same type identifier might identify different data types for different databases.
        Type descriptors
        A type descriptor, MI_TYPE_DESC, is a DataBlade® API data type structure that contains information about an SQL data type. For built-in data types, this information comes from the syscolumns table. For extended data types, it contains the information in the sysxtdtypes table.
        Character data types
        The mi_char1 and mi_unsigned_char1 data types
        The mi_char1 and mi_unsigned_char1 data types hold a single-byte character. These data types can also hold an integer quantity within C code so you can also use mi_unsigned_char1 to hold unsigned one-byte integer values.
        The mi_char and mi_string data types
        The mi_char and mi_string data types are the DataBlade® API equivalents of the char C-language data type. These two data types are exactly the same in both storage and functionality. Use them to declare character strings in your DataBlade API module.
        The mi_lvarchar data type
        The SQL LVARCHAR data type
        The LVARCHAR data type of SQL stores variable-length character strings whose length can be up to 32,739 bytes. LVARCHAR is a built-in opaque data type that is valid in distributed queries of tables, views, and synonyms of databases outside the local server.
        Character data in binary mode of a query
        Character data in C UDRs (Server)
        External representation of an opaque data type (Server)
        The database server stores the external representation of an opaque data type in an mi_lvarchar varying-length structure. The external representation is a text representation of the opaque-type data. Therefore, the input and output support functions of an opaque type handle the external representation as an mi_lvarchar.
        Character data in a smart large object
        You can use a smart large object to store very large amounts of character data. The MI_LO_HANDLE data type has a structure, called an LO handle, that identifies the location of smart-large-object data in a separate database partition, called an sbspace.
        Character processing
        The DataBlade® API library provides the transfer, conversion, and operation functions to process character data.
        Varying-length data type structures
        A varying-length data type structure can hold data whose length varies from one instance to the next. The database server uses varying-length structures extensively to manage data transfer for DataBlade® API modules.
        Byte data types
        Boolean data types
        Boolean data holds values to indicate two states: true and false. The DataBlade® API provides support for boolean values in both their text and binary representations.
        Simple large objects
        The DataBlade® API does not provide direct support for simple large objects. Therefore, it cannot directly access TEXT and BYTE columns. However, the database server provides the following cast functions between simple and smart large objects.
        The MI_DATUM data type
        The DataBlade® API handles a generic data value as an MI_DATUM value, also called a datum. A datum is stored in a chunk of memory that can fit into a computer register.
        The NULL constant
        The DataBlade® API supports two different uses of a NULL constant: the SQL NULL value and the NULL-valued pointer. The DataBlade API NULL-valued pointer is not the same as the SQL NULL value.
    - Data manipulation
    - Database access
    - Create user-defined routines
    - 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 SQL LVARCHAR data type

The LVARCHAR data type of SQL stores variable-length character strings whose length can be up to 32,739 bytes. LVARCHAR is a built-in opaque data type that is valid in distributed queries of tables, views, and synonyms of databases outside the local server.

The DataBlade® API supports the LVARCHAR data type with the mi_lvarchar data type, which is implemented in the DataBlade® API as a varying-length structure.

Tip: The SQL data type LVARCHAR and the DataBlade® API data type mi_lvarchar are not the same. Although you use mi_lvarchar to hold LVARCHAR data, mi_lvarchar is also used for other purposes.

If you declare no maximum size for an LVARCHAR column, the default size is 2 KB. The maximum valid size is 32,739 bytes, but the maximum row size in a database table is limited to 32 KB. (In addition, no more than 195 columns in the same database table can be of varying-length data types, named or unnamed ROW data types, collection data types, or simple large object data types, regardless of the declared size of individual columns.)

If you attempt to insert more than the declared maximum size into an LVARCHAR column, the result depends on the data type of the data:

If the value comes from a built-in type (such as CHAR or VARCHAR), the database server truncates the data to the declared column size.
The database server does not truncate data strings that come from an mi_lvarchar structure, but the database server does return an error.

Tip: If you need to store more than 32,739 bytes of text data in a database of the local database server, use the CLOB data type. With the CLOB data type, you can store the text data outside the database table, in an sbspace.