ILE COBOL Programmer's Guide

I-O-FEEDBACK Area

The system updates the I-O-FEEDBACK area each time a block transfers between the operating system and the program. A block can contain one or more records.

The I-O-FEEDBACK area is not updated after each read or write operation for files in which multiple records are blocked and unblocked by COBOL. If the I-O-FEEDBACK information is needed after each read or write operation in the program, the user can do either of the following:

Preventing the compiler from generating blocking and unblocking code is more efficient than specifying SEQONLY(*NO).

Even when the compiler generates blocking and unblocking code, certain OS/400 restrictions can cause blocking and unblocking to not be processed. In these cases, a performance improvement will not be realized. However, the I-O-FEEDBACK area will be updated after each read or write operation.

The I-O-FEEDBACK area contains information about the last successful I-O operation, such as: device name, device type, AID character, and error information for some devices. This area consists of a common area and a device-dependent area. The device-dependent area varies in length and content depending on the device type to which the file is associated. This area follows the I-O-FEEDBACK common area and can be obtained by specifying the receiving identifier large enough to include the common area and the appropriate device-dependent area.

For a layout and description of the data areas contained in the OPEN-FEEDBACK and I-O-FEEDBACK areas, refer to the DB2 Universal Database for AS/400 section of the Database and File Systems category in the iSeries 400 Information Center at this Web site - http://publib.boulder.ibm.com/pubs/html/as400/infocenter.htm.


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