Indicator Variables

Indicator variables are C variables that hold supplementary information when you are fetching or putting data. There are several distinct uses for indicator variables:

• NULL values – To enable applications to handle NULL values.
• String truncation – To enable applications to handle cases when fetched values must be truncated to fit into host variables.
• Conversion errors – To hold error information.

An indicator variable is a host variable of type a_sql_len that is placed immediately following a regular host variable in a SQL statement. For example, in the following INSERT statement, :ind_phone is an indicator variable:

EXEC SQL INSERT INTO Employees
 VALUES (:employee_number, :employee_name,
 :employee_initials, :employee_phone:ind_phone );

On a fetch or execute where no rows are received from the database server (such as when an error or end of result set occurs), then indicator values are unchanged.

• Indicator Variables: The SQL NULL Value
  Do not confuse the SQL concept of NULL with the C-language constant of the same name. In the SQL language, NULL represents either an unknown attribute or inapplicable information. The C-language constant represents a pointer value that does not point to a memory location.
• Indicator Variables: Truncated Values
  Indicator variables indicate whether any fetched values were truncated to fit into a host variable. This enables applications to handle truncation appropriately.
• Indicator Variables: Conversion Errors
  By default, the conversion_error database option is set to On, and any data type conversion failure leads to an error, with no row returned.
• Summary of Indicator Variable Values
  The following table provides a summary of indicator variable usage.