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Client APIs and tools
You can use the HCL Informix® implementation of client APIs to develop applications for Informix database servers.
ESQL/C Guide
The Informix® ESQL/C Programmer's Manual explains how to use Informix ESQL/C, the Informix implementation of Embedded Structured Query Language (SQL) for C (ESQL/C), to create client applications with database-management capabilities.
Database server communication
Informix® libraries
These topics describe how to link the static, shared, and thread-safe HCL Informix® general libraries with your Informix ESQL/C application.
Create thread-safe ESQL/C applications
Program a thread-safe ESQL/C application
This section provides useful hints for how to create thread-safe Informix® ESQL/C applications.
Message file descriptors

Client APIs and tools
You can use the HCL Informix® implementation of client APIs to develop applications for Informix database servers.
- Change Data Capture API Programmer's Guide
  The Informix® Change Data Capture API Programmer's Guide describes how to program applications to process changed data from HCL Informix databases using the Informix Change Data Capture API.
- Embedded SQLJ for HCL Informix®
  The Informix® Embedded SQLJ User's Guide contains information about using Informix Embedded SQLJ.
- ESQL/C Guide
  The Informix® ESQL/C Programmer's Manual explains how to use Informix ESQL/C, the Informix implementation of Embedded Structured Query Language (SQL) for C (ESQL/C), to create client applications with database-management capabilities.
  - What is Informix® ESQL/C?
  - Database server communication
    - Exception handling
    - Working with the database server
      These topics explain how the Informix® ESQL/C program can interact with a database server.
    - Informix® libraries
      These topics describe how to link the static, shared, and thread-safe HCL Informix® general libraries with your Informix ESQL/C application.
      - Choose a version of the Informix® general libraries
      - Compatibility of preexisting ESQL/C applications with current library versions
      - Create thread-safe ESQL/C applications
        Characteristics of thread-safe ESQL/C code
        Program a thread-safe ESQL/C application
        This section provides useful hints for how to create thread-safe Informix® ESQL/C applications.
        Concurrent active connections
        Connections across threads
        The DISCONNECT ALL Statement
        The DISCONNECT ALL statement serially disconnects all connections in an application.
        Prepared statements across threads
        Cursors across threads
        Environment variables across threads
        Environment variables are not thread-scoped in a thread-safe Informix® ESQL/C application. That is, if a thread changes the value of a particular environment variable, this change is visible in all other threads as well.
        Message file descriptors
        Decimal functions
        The dececvt() and decfcvt() functions of the Informix® ESQL/C library return a character string that can be overwritten if two threads simultaneously call these functions. For this reason, use the thread-safe versions of these two functions, ifx_dececvt() and ifx_decfcvt().
        DCE restrictions (UNIX™)
        Link thread-safe libraries
        The esql command links the thread-safe versions of the static or shared HCL Informix® general libraries when you specify the -thread command-line option.
      - ESQL/C thread-safe decimal functions
      - Context threaded optimization
      - A sample thread-safe program
      - Create a dynamic thread library on UNIX™ operating systems
  - Dynamic SQL
  - Appendixes
    This section contains additional reference information.
- GLS User's Guide
  The Informix® GLS User's Guide describes the Global Language Support (GLS) feature available in Informix products.
- API
  The Informix® GLS API Programmer's Guide describes the global language support (GLS) application programming interface (API) available in Informix ESQL/C and HCL Informix DataBlade® modules.
- Informix® Object Interface for C++ Guide
  The Informix® Object Interface for C++ Programmer's Guide describes how to develop HCL Informix client applications by using the object-oriented C++ programming language.
- Informix® ODBC Driver Guide
  The Informix® ODBC Driver Programmer's Manual serves as a user guide and reference for Informix ODBC Driver, which is the Informix implementation of the Microsoft™ Open Database Connectivity (ODBC) interface, Version 3.0.
- .NET provider options
  The Data Server Provider for .NET DB2® provider option is the preferred Informix® provider for developing new applications.
- Informix® JDBC Driver Guide
  The Informix® JDBC Driver Programmer's Guide describes how to install, load, and use Informix JDBC Driver to connect to the Informix database from within a Java™ application or applet.
- Informix International Language Supplement (ILS) User Guide
  These topics include information about the translated user interface files for Informix® UNIX™ products, locales, and code set conversion tables
- Informix® OLE DB Provider Guide
  The Informix® OLE DB Provider Programmer's Guide describes the software requirements for using Informix OLE DB Provider, show how to install and configure the provider for your use, and explain how to use Informix OLE DB Provider to enable client applications, such as ActiveX Data Object (ADO) applications and web pages, to access data on the Informix server.

Message file descriptors

By default ESQL/C frees all file descriptors for a message file when it closes the message file. As a performance optimization, however, you can set the environment variable IFX_FREE_FD to cause Informix® ESQL/C to not free the file descriptor if the message file being closed is open for another thread. If you set IFX_FREE_FD to 1, Informix® ESQL/C frees the message file descriptor only for the thread that closes the file.