Call Level Interface Guide and Reference

Using Descriptors

DB2 CLI stores information (data types, size, pointers, and so on) about columns in a result set, and parameters in an SQL statement. The bindings of application buffers to columns and parameters must also be stored. Descriptors are a logical view of this information, and provide a way for applications to query and update this information.

Many CLI functions make use of descriptors, but the application itself does not need to manipulate them directly.

For instance:

• When an application binds column data using SQLBindCol() descriptor fields are set that completely describe the binding.

• A number of statement attributes correspond to the header fields of a descriptor. In this case you can achieve the same effect calling SQLSetStmtAttr() as calling the corresponding function SQLSetDescField() that sets the values in the descriptor directly.

Although no database operations require direct access to descriptors, there are situations where working directly with the descriptors will be more efficient or result in simpler code. For instance, a descriptor that describes a row fetched from a table can then be used to describe a row inserted back into the table.

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