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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.
What is Informix® ESQL/C?
Informix® ESQL/C programming
Declaring and using host variables
Indicator variables

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?
    - Informix® ESQL/C programming
      - What is Informix® ESQL/C?
        Informix® ESQL/C is an SQL application programming interface (API) that enables you to embed Structured Query Language (SQL) statements directly into a C program.
      - Embed SQL statements
        The Informix® ESQL/C program can use SQL statements to communicate with the database server. The program can use both static and dynamic SQL statements.
      - Declaring and using host variables
        Declare a host variable
        You must define the data storage that a host variable needs before you can use that variable in Informix® ESQL/C programs. To assign an identifier to the variable and associate it with a data type, you declare the variable.
        Host variable information
        Host variables in data structures
        Host variables in Windows™ environments
        Indicator variables
        Declare indicator variables
        Associate an indicator variable with a host variable
        Indicate null values
        Indicate truncated values
        An example of using indicator variables
      - ESQL/C header files
      - ESQL/C preprocessor directives
      - Set and retrieve environment variables in Windows™ environments
        You might change the settings of environment variables or create new variables to increase the flexibility of an application. Instead of assuming a particular environment configuration, you can define the environment at run time.
      - Global ESQL/C variables in a Windows™ environment
      - A sample Informix® ESQL/C program
    - Compile programs
    - Informix® ESQL/C data types
      These topics contain information about the correspondence between SQL and C data types and how to handle data types in the Informix® ESQL/C program.
    - Character and string data types
      These topics explain how to use character data types in the Informix® ESQL/C program.
    - Numeric data types
    - Time data types
      These topics explain how to use date, datetime, and interval data types in the Informix® ESQL/C program.
    - Simple large objects
      A simple large object is a large object that is stored in a blobspace on disk and is not recoverable.
    - Smart large objects
      A smart large object is a data type that stores large, non-relational data objects such as images, sound clips, documents, graphics, maps and other large objects, and allows you to perform read, write, and seek operations on those objects.
    - Complex data types
      These topics explain how to use collection and row data types in the Informix® ESQL/C program.
    - Opaque data types
      These topics explain how to use the lvarchar, fixed binary, and var binary data types to access an opaque data type from the Informix® ESQL/C program. Use these Informix ESQL/C data types to represent an opaque data type as it is transferred to and from Informix.
  - Database server communication
  - 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.

Indicator variables

When an SQL statement returns a value, it returns it in the host variable for the specified column. In some cases, you can associate an indicator variable with the host variable to obtain additional information about the value that is returned. If you specify an indicator variable, Informix® ESQL/C sets it in addition to returning the value to the host variable.

The indicator variable provides additional information in the following situations:

If the host variable is associated with a database column or an aggregate function that allows null values, the indicator variable can specify whether the value is null.
If the host variable is a character array and the column value is truncated by the transfer, the indicator variable can specify the size of the returned value.

The following topics describe how to declare an indicator variable and associate it with a host variable, and also how Informix® ESQL/C sets an indicator variable to specify the two preceding conditions.