File Management - IBM

Table 1. File Types and Their Main Operations
programs processing files for output, the last buffer of data is written.
For those programs processing files for input, an end-of-file condition is
forced for the next input operation.
RELEASE
Detaches a device or a communications session from an open file. I/O
operations can no longer be performed for this device or session.
CLOSE
Detaches a file from a program, ending I/O operations. Any remaining
data in the output buffer that has not been written will be written prior
to the completion of the close.
The operations listed above have certain restrictions based on file type and
language support. For example, a program may not write to a file that has been
opened for read only. Similarly, a read-by-key may not be issued for an ICF file.
Since file overrides can occur during processing, an operation may not be allowed
for the type of file that is ultimately being processed. See Chapter 3. Using
overrides, for additional information.
Table 1 on page 4 lists the file types and the main operations that are allowed.
There are additional functions supported for some file types that are accomplished
by additional operations or changes to these operations. For information on these
additional functions and how the operations given here apply to display, tape, and
diskette files, refer to either the Application Display Programming, SC41-5715-00 book
or the Tape and Diskette Device Programming, SC41-5716-01 book. For equivalent
information for database, ICF, DDM, printer, and save files, refer to the 5701 book,
the 5442 book, the 5307 book, the 5713 book, and the 5304 book, respectively.
Table 2 on page 6 and Table 3 on page 7 map the OS/400-supported operations
given in Table 1 to the high-level language operations (BASIC, ILE C, ILE COBOL,
PASCAL, PL/I, and ILE RPG programming languages) supported on the system.
For additional information on each operation and how it correlates to the file
declaration in the program, see the appropriate language information. Note that
not all OS/400 operations are supported in all languages.
File Types
Operation
OPEN
Database Diskette Tape Printer Display ICF DDM Save
Read X X X - X X X X
Write X X X X X X X X
Update X - - - X 1
- X -
Delete X - - - X 1
- X -
READ
By relative
record
number
X - - - X 1
- X -
By key X - - - - - X -
Sequential X X X - X X X X
Previous X - X - - - X -
4 File Management V4R5