Setting ODBC version and environment attributes

After an environment space has been requested, and before any connections are established, the application has the opportunity to set some attributes that control the behavior of the ODBC environment. At least one of these attributes (the application ODBC version) must be set explicitly by the application. This is done by setting the environment attribute SQL_ATTR_ ODBC_VERSION. This attribute states whether the application will follow the ODBC 2.x or ODBC 3.5 specification when using the following items:

• SQLSTATEs. Many SQLSTATE values are different in ODBC 2.x and ODBC 3.5.

• Date, Time, and Timestamp Type Identifiers. There are important differences in the naming of these identifiers between the two versions.

• CatalogName Argument in f90SQLTables. In ODBC 2.x, the wild card characters ("%" and "_") in the CatalogName argument are treated literally. In ODBC 3.5, they are treated as wild cards. Thus, an application that follows the ODBC 2.x specification cannot use these as wild cards and does not escape them when using them as literals. An application that follows the ODBC 3.5 specification can use these as wild cards or escape them and use them as literals.

This manual always uses the ODBC ver. 3.5. You may want to review the documentation in the ODBC-SDK if your applications will make use of both versions.

To set the attribute SQL_ATTR_ ODBC_VERSION, you use the subroutine f90SQLSetEnvAttr. A typical call to f90SQLSetEnvAttr takes this form:

Where EnvHndl is an environment handle, Attribute is an integer identifying the attribute being set. f90SQL offers several constants that identify the different attributes. For example, constant SQL_ATTR_ODBC_VERSION identifies the attribute which contains the ODBC version of the application. AttributeValue is the new value for the attribute (it may be a variable). The type of AttributeValue depends on the attribute being set. If the attribute contains an integer, the AttributeValue must be an integer. If Attribute is being stored as a string, then AttributeValue must be an string.

For example the following call sets the application ODBC version to 3.5:

An important point to keep in mind is setting the application ODBC version does not change the functionality offered by a driver. When working with ODBC 2.x drivers, applications that follow the ODBC 3.5 specification must use conditional code to avoid using functionality new to ODBC 3.5. ODBC 2.x drivers will not support functionality new to ODBC 3.5 just because the application declares that it follows the ODBC 3.5 specification. Furthermore, ODBC 3.5 drivers will not cease to support functionality new to ODBC 3.5 just because the application declares that it follows the ODBC 2.x specification.

You can call f90SQLSetEnvAttr to set other environment attributes also:

• SQL_ATTR_CONNECTION_POOLING: Enables or disables connection pooling at the environment level (see the section Connection Pooling later in this chapter)

• SQL_ATTR_CP_MATCH: Determines how a connection is chosen from a connection pool. When f90SQLConnect or f90SQLDriverConnect is called, the Driver Manager determines which connection is reused from the pool. The Driver Manager attempts to match the connection options in the call and the connection attributes set by the application to the keywords and connection attributes of these connections in the pool. The value of this attribute determines the level of precision in the matching criteria.

• SQL_ATTR_OUTPUT_NTS: Determines whether the driver returns string data as null terminated strings or not. This attribute is not currently implemented.