Deferred Buffers

A deferred buffer is one whose value is used not at the time it is specified in a function call but at a later point in time. For example, SQLBindParameter is used to associate, or bind, a data buffer with a parameter in an SQL statement. The application specifies the number of the parameter and passes the address, byte length, and type of the buffer. The driver saves this information but does not examine the contents of the buffer. Later, when the application executes the statement, the driver retrieves the information and uses it to retrieve the parameter data and send it to the data source. Thus, the input of data in the buffer is deferred. Because deferred buffers are specified in one function and used in another, it is an application programming error to free a deferred buffer while the driver still expects it to exist; for more information, see “Allocating and Freeing Buffers,” later in this chapter.

Both input and output buffers can be deferred. The following table summarizes the uses of deferred buffers. Note that deferred buffers bound to result set columns are specified with SQLBindCol and deferred buffers bound to SQL statement parameters are specified with SQLBindParameter.

Buffer use

Type

Specified with

Used by

Sending data for input parameters	Deferred input	SQLBindParameter	SQLExecute SQLExecDirect
Sending data to update or insert a row in a result set	Deferred input	SQLBindCol	SQLSetPos
Returning data for output and input/output parameters	Deferred output	SQLBindParameter	SQLExecute SQLExecDirect
Returning result set data	Deferred output	SQLBindCol	SQLFetch SQLFetchScroll SQLSetPos