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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.
Perform input and outputBecause 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 to operating-system filesThe DataBlade® API provides file-access functions for access to operating-system files from within a C UDR. These functions provide file management that is similar to what operating-system file-access functions provide.
Open a fileThe mi_file_open() function is the constructor function for a file descriptor. Through the file descriptor, you access an operating-system file.
Share open filesAll UDRs that execute under the same connection can share a file (because they have the same connection descriptor).

Share open files

All UDRs that execute under the same connection can share a file (because they have the same connection descriptor).

For example, if UDR1 opens a file, UDR2 can read, write to, or close this file, as long as these two UDRs execute under the same connection. However, UDRs that do not execute under the same connection cannot share a file.

The DataBlade® API generates an error if your UDR attempts any of the following file I/O tasks:

To access a file that a UDR outside the session opened
To access a file that was not opened at all
To access a file that was opened and was closed

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