I/O Considerations for Diskette Files

A diskette unit can only be accessed with a program described file. An ILE C/C++ program can only process a diskette file sequentially.

The concept of clearing a file or opening a file using append mode does not apply to diskette files.

The diskette file label name is required when the file is opened. You specify this label name using the Override Diskette File (OVRDKTF) command.

If the diskette file is opened for input and:
  • if the lrecl parameter is not specified or is specified as zero, the record length in the data file label on the name on the diskette is used to determine the length of the records to read.
  • if the lrecl parameter is greater than the length of the records on the diskette file, the records that are read are padded with blanks.
  • if the lrecl parameter is less than the length of the records on the diskette file, the records that are read are truncated.
  • if the file type in the diskette file is a source file, a date and sequence number is appended at the beginning of each record. You must remove these when writing the record and add 12 bytes to the lrecl parameter on the open statement.
Note: Output may not always result in an I/O operation to a diskette file. The I/O buffer must contain enough data to fill an entire track on a diskette.

When opening a diskette file for output, any files existing on the diskette are deleted if the data file expiration date is less than or equal to the system date.