File Management operations overview

File management supports many operations that high-level language programs can use to process data. These include the following, which are grouped by category:

File Preparation

OPEN
Attaches a file to a program and prepares it for I/O operations. A file may be opened for any combination of read, write, update, or delete operations.
ACQUIRE
Attaches a device or establishes a communications session for an open file in preparation for I/O operations.
Input/Output

READ
Transfers a record from the file to the program. The data is made available to the program once the read has been successfully completed.
WRITE
Transfers a record from the program to the file.
WRITE-READ
Combines the WRITE and READ operations as one operation.
UPDATE
Updates a record with changed data. The record must have been successfully read prior to the update operation.
DELETE
Deletes a record in a file. The record must have been successfully read prior to the delete operation.
Commitment Control

COMMIT
Guarantees a group of changes are made as a complete transaction across multiple records or multiple files.
ROLLBACK
Rolls back a group of changes to the point of the last commit operation.
Completion

FEOD
Positions the file at the last volume or at the end of data. For those 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 "Using overrides", for additional information.

Table 1 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 and Table 3 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.

Table 1. File Types and Their Main Operations

Operation File Types
Database Diskette Tape Printer Display ICF DDM Save
OPEN

Read X X X - X X X X
Write X X X X X X X X
Update X - - - X¹ - X -
Delete X - - - X¹ - X -

READ

By relative record number X - - - X¹ - X -
By key X - - - - - X -
Sequential X X X - X X X X
Previous X - X - - - X -
Next X X X - X X X X
Invited

Device - - - - X X - -

WRITE-READ - - - - X X - -

WRITE

By relative record number X - - - X¹ - X -
By key X - - - - - X -
Sequential X X X X X X X X

FEOD X X X X - - X X

UPDATE

By relative record number X - - - X¹ - X -
By key X - - - - - X -
DELETE

By relative record number X - - - - - X -
By key X - - - - - X -

ACQUIRE - - - - X X - -

RELEASE - - - - X X - -

COMMIT X - - - - - - -

ROLLBACK X - - - - - - -

CLOSE X X X X X X X X

Note:

¹
Operation allowed only for subfile record formats

Table 2. High-Level Languages and Their OS/400 Operations

Operation High-Level Languages
BASIC ILE C/400 Programming Language ILE COBOL/400 Programming Language
OPEN
Read OPEN INPUT fopen, _Ropen OPEN INPUT
Write OPEN OUTPUT fopen, _Ropen OPEN OUTPUT, OPEN EXTEND
Update OPEN OUTIN fopen, _Ropen OPEN I-O
Delete OPEN OUTIN fopen, _Ropen OPEN I-O

READ

By relative record number READ REC _Rreadd READ
By key READ KEY _Rreadk, _Rformat READ KEY
Sequential READ NEXT, GET fread, fgetc, fgets, _Rreadf, _Rreadl, _Rreadn, _Rreadp, _Rreads, _Rformat, _Rpgmdev READ
Previous READ PRIOR _Rreadp READ
Next READ NXT, GET fread, _Rreadn READ, READ NEXT
Invited Device _Rreadindv READ

WRITE-READ _Rwriterd, _Rformat, _Rpgmdev

WRITE

By relative record number WRITE REC _Rwrited WRITE
By key WRITE _Rwrite, _Rformat
Sequential WRITE fwrite, fputc, fputs, _Rwrite, _Rformat, _Rpgmdev WRITE

FEOD _Rfeod

UPDATE
By relative record number REWRITE REC _Rupdate REWRITE
By key REWRITE KEY _Rupdate REWRITE

DELETE
By relative record number DELETE REC _Rdelete DELETE
By key DELETE KEY _Rdelete DELETE

ACQUIRE _Racquire ACQUIRE

RELEASE _Rrelease DROP

COMMIT _Rcommit COMMIT

ROLLBACK ROLLBACK

CLOSE CLOSE, END fclose, _Rclose CLOSE, STOP RUN, CANCEL

Operation	High-Level Languages
BASIC	ILE C/400 Programming Language	ILE COBOL/400 Programming Language
OPEN
Read	OPEN INPUT	fopen, _Ropen	OPEN INPUT
Write	OPEN OUTPUT	fopen, _Ropen	OPEN OUTPUT, OPEN EXTEND
Update	OPEN OUTIN	fopen, _Ropen	OPEN I-O
Delete	OPEN OUTIN	fopen, _Ropen	OPEN I-O

READ
By relative record number	READ REC	_Rreadd	READ
By key	READ KEY	_Rreadk, _Rformat	READ KEY
Sequential	READ NEXT, GET	fread, fgetc, fgets, _Rreadf, _Rreadl, _Rreadn, _Rreadp, _Rreads, _Rformat, _Rpgmdev	READ
Previous	READ PRIOR	_Rreadp	READ
Next	READ NXT, GET	fread, _Rreadn	READ, READ NEXT
Invited Device		_Rreadindv	READ

WRITE-READ		_Rwriterd, _Rformat, _Rpgmdev

WRITE
By relative record number	WRITE REC	_Rwrited	WRITE
By key	WRITE	_Rwrite, _Rformat
Sequential	WRITE	fwrite, fputc, fputs, _Rwrite, _Rformat, _Rpgmdev	WRITE

FEOD		_Rfeod

UPDATE
By relative record number	REWRITE REC	_Rupdate	REWRITE
By key	REWRITE KEY	_Rupdate	REWRITE

DELETE
By relative record number	DELETE REC	_Rdelete	DELETE
By key	DELETE KEY	_Rdelete	DELETE

ACQUIRE		_Racquire	ACQUIRE

RELEASE		_Rrelease	DROP

COMMIT		_Rcommit	COMMIT

ROLLBACK			ROLLBACK

CLOSE	CLOSE, END	fclose, _Rclose	CLOSE, STOP RUN, CANCEL

Table 3. High-Level Languages and Their OS/400 Operations

Operation High-Level Languages
PASCAL PL/I ILE RPG/400 Programming Language
OPEN

Read RESET, GET, READ, READLN OPEN INPUT OPEN
Write REWRITE, WRITE, WRITELN OPEN OUTPUT OPEN
Update UPDATE OPEN UPDATE OPEN
Delete UPDATE OPEN UPDATE OPEN

READ
By relative record number GET, READ READ KEY READ, CHAIN
By key READ KEY READ, READE, CHAIN
Sequential GET, READ, READLN READ NEXT, GET READ
Previous GET, READ, READLN READ PRV READP, READPE
Next GET, READ, READLN READ NXT, GET READ, READE
Invited Device READ

WRITE-READ EXFMT

WRITE
By relative record number PUT, WRITE, WRITELN WRITE, EXCPT primary file WRITE
By key WRITE KEY WRITE, EXCEPT
Sequential PUT, WRITE, WRITELN WRITE, PUT WRITE, EXCEPT

FEOD FEOD

UPDATE
By relative record number PUT, WRITE, WRITELN REWRITE KEY UPDATE
By key REWRITE KEY UPDATE

DELETE
By relative record number DELETE DELETE
By key DELETE KEY DELETE

ACQUIRE ACQ

RELEASE REL

COMMIT use CL COMMIT PLICOMMIT subroutine COMMIT

ROLLBACK use CL ROLLBACK PLIROLLBACK subroutine ROLBK

CLOSE CLOSE, END CLOSE, STOP CLOSE, RETURN

Operation	High-Level Languages
PASCAL	PL/I	ILE RPG/400 Programming Language
OPEN

Read	RESET, GET, READ, READLN	OPEN INPUT	OPEN
Write	REWRITE, WRITE, WRITELN	OPEN OUTPUT	OPEN
Update	UPDATE	OPEN UPDATE	OPEN
Delete	UPDATE	OPEN UPDATE	OPEN

READ
By relative record number	GET, READ	READ KEY	READ, CHAIN
By key		READ KEY	READ, READE, CHAIN
Sequential	GET, READ, READLN	READ NEXT, GET	READ
Previous	GET, READ, READLN	READ PRV	READP, READPE
Next	GET, READ, READLN	READ NXT, GET	READ, READE
Invited Device			READ

WRITE-READ			EXFMT

WRITE
By relative record number	PUT, WRITE, WRITELN	WRITE, EXCPT primary file	WRITE
By key		WRITE KEY	WRITE, EXCEPT
Sequential	PUT, WRITE, WRITELN	WRITE, PUT	WRITE, EXCEPT

FEOD			FEOD

UPDATE
By relative record number	PUT, WRITE, WRITELN	REWRITE KEY	UPDATE
By key		REWRITE KEY	UPDATE

DELETE
By relative record number		DELETE	DELETE
By key		DELETE KEY	DELETE

ACQUIRE			ACQ

RELEASE			REL

COMMIT	use CL COMMIT	PLICOMMIT subroutine	COMMIT

ROLLBACK	use CL ROLLBACK	PLIROLLBACK subroutine	ROLBK

CLOSE	CLOSE, END	CLOSE, STOP	CLOSE, RETURN

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