Step Previous Extended (39)

Step Previous Extended (39)

The Step Previous Extended operation (B_STEP_PREVIOUS_EXT) examines one or more records, starting at the previous physical position and proceeding toward the beginning of the file. It checks to see if the examined record or records satisfy a filtering condition, and it retrieves the ones that do. The filtering condition is a logic expression and is not limited to key fields only.

Step Previous Extended can also extract specified fields from existing records and return a new set of records that contain only the extracted fields.


	Op Code	Pos Block	Data Buf	Data Buf Len	Key Buffer	Key Number
Sent
Returned

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The file must be open.

•

You must have established a previous physical position. (For example, a Step Previous Extended operation cannot follow a Delete operation.)

1

Set the Operation Code to 39. Optionally, you can include a lock bias:

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+100—Single wait record lock.

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+200—Single no-wait record lock.

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+300—Multiple wait record lock.

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+400—Multiple no-wait record lock.

For more information about locking, refer to the Pervasive PSQL Programmer's Guide.

2

Pass the Position Block for the file.

3

Specify a Data Buffer large enough to accommodate either the input data buffer or the returned data buffer. Initialize the Data Buffer according to the structure shown in Table 21.

4

Specify the Data Buffer Length from the preceding step.

The transactional interface sets up a buffer as a workspace for extended operations. You configure the size of this buffer using the Extended Operation Buffer Size option. The sum of the Data Buffer structure, plus the longest record to be retrieved, plus 355 bytes of requester overhead, cannot exceed the configured buffer size. (Requester overhead is not applicable in DOS workstation engines.)

This operation uses the same input and returned Data Buffers as the Get Next Extended operation. Refer to Details for more information.

This operation returns the same results as the Step Next Extended operation. Refer to Result for more information.

The Step Previous Extended operation does not establish logical currency, but the last record examined (not necessarily retrieved) becomes the current physical record. This record can be either a record that satisfies the filtering condition and is retrieved, or a record that does not satisfy the filtering condition and is rejected.

Note: The transactional interface does not allow Delete or Update operations after a Step Previous Extended operation. Because the current record is the last record examined, there is no way to ensure that your application would delete or update the intended record.