IBM AS/400 manual EXFMT Operation, READ Operation, WRITE Operation, Multiple-Device Files

Multiple-Device Files

EXFMT Operation

The EXFMT operation is a					combination of a WRITE followed by a READ to
same	record		format	(it	corresponds to			a data management WRITE-READ ope
tion). If you define a WORKSTN file on the file description specifica
procedural		(F	in position		18)	combined file			(C in	position 17) that use
externally-described				data	(E	in	position	22) the EXFMT (execute format)
code	can	be	used	to write		and	read	from	the	display.

READ Operation

The

READ operation

is

valid for a

full-procedural

combined

file

or a

f

input file that uses externally-described data or program-described da

operation

retrieves

a

record from the display. However, a format must

device

before

any

input

operations

can

occur.

This

requirement

can

be

a display

device

by

conditioning

an

output

record

with

the 1P

indicat

the

first

format

to

the

device

from another program, or, if the rea

format

name, by

using

the

keyword

INZRCD

on

the

record

description

in

WRITE Operation

The	WRITE		operation	writes a new record to a					display and is valid f
file	or	an	output	file.	Output		specifications and the EXCEPT operation
used	to	write to		a WORKSTN		fileILE. SeeRPG		forthe AS/400	Referencefor a
complete		description		of	each	of	these	operation	codes.

Multiple-Device Files

Any RPG WORKSTN file with at least one of the keywords DEVID, SAVEIND, MAXDEV(*FILE) or SAVEDS specified on the file description specification is multiple-device file. Through a multiple-device file, your program may ac than one device.

The RPG program accesses devices through program devices, which are s

mechanisms for directing operations to an						actual device. When you crea
(using	the		DDS and	commands	such as the	create file	commands),	you	con
such	things		as which device is associated with a program device,						whe
file	has	a	requesting program device, which record formats will be						us
devices		to	respond	to a	READ-by-file-name	operation, and	how long	this	R

operation will wait for a response. For detailed information on the opt

requirements for	creating	a multiple-device file, see the		chapter	on d
Data Management manual, and information on ICFICFfilesProgramming
manual, and the manuals you		are referred to in these	two	publications.
With multiple-device files,		you make particular use of	the	following	ope
¹ In addition to opening		a file, the OPEN operation implicitly acquires
you specify	when you	create the file.

¹The ACQ (acquire) operation acquires any other devices for a multip file.

¹ The REL (release) operation releases a device from the file.

¹The WRITE operation, when used with the DDS keyword INVITE, invites program device to respond to subsequent read-from-invited- program-devi

342 ILE RPG for AS/400 Programmer's Guide