IBM AS/400 manual Defining Externally Described Files

Defining Externally Described Files

.2/

An externally described file (that is, a file with field-lev

description) is used as a program-described file

in

the

pro

program-described file is identified by an F in position 22

description specifications. This entry tells the compiler not

external field-level descriptions. This file

does

not

have

to

lation

time.

.3/

A file is described only at the record

level

to

the

opera

fields

in

the

record

are

described

within

the program;

the

22

of

the

file description

specifications

must

contain

an F.

not

have

to

exist

at

compilation

time.

.4/

A file

name

can be specified at compilation

time

(that

is,

RPG

source

member),

and

a

different

file

name

can

be

speci

time. The

E

in

position

22

of

the

file

description

specifica

that

the

external

description

of

the

file

is

to

be

copied

time. At run time, a file override command

can

be

used

so

ferent

file

is accessed by the program.

To

override

a

fil

must

make

sure

that

record

names

in

both

files

are

the

same

program

uses

the record-format name on the

input/output

operat

such as a READ operation where it specifies what record t

expected. See “Overriding and Redirecting

File

Input

and

Out

page 273

for

more

information.

Defining Externally Described		Files
You	can	use DDS to describe files to the OS/400 system. Each recor
file	is	identified by a unique record-format name.

An E entry in position 22 of the file description specifications i externally described file. The E entry indicates to the compiler th the external description of the file from the system when the prog

The information in this external description includes:

¹ File	information, such	as file	type,	and file attributes, such as
(by	key or relative	record	number)

¹Record-format description, which includes the record format name a descriptions (names, locations, and attributes).

The	information	the	compiler	retrieves from	the external description i
the compiler listing as long				as OPTION(*EXPDDS)	is	specified on either
CRTRPGMOD or CRTBNDRPG			command	when compiling the source member.
(The	default	for	both of	these commands	is	OPTION(*EXPDDS).)

The following section describes how to use a file description speci rename or ignore record formats and how to use input and output spe modify external descriptions. Remember that input and output specific externally described files are optional.

Chapter 14. Defining Files265