Sequential files can be read from the following device types:
- TAPEFILE
- DISKETTE
- DISK
- DATABASE
Sequential files can only be read in sequential access mode.
The record that is made available by the READ statement is determined as
follows:
- If the file position indicator was set by the processing of an OPEN statement,
the record pointed to is made available.
- If the file position indicator was set by the processing of a previous
READ statement, the pointer is updated to point to the next existing record
in the file. That record is then made available.
If SELECT OPTIONAL is specified in the file-control entry for this file
and the file is not available when this program runs, processing of the first
READ statement causes an AT END condition. Since the file is not available,
the standard system end-of-file processing is not done when the file is closed.