ILE RPG Programmer's Guide
Figure 156. Typical Relationships between an RPG Program and Files on the i5/OS® System
- 1
- The program uses the field-level description of a file that
is defined to the operating system. An externally described file is
identified by an E in position 22 of the file description specifications.
At compilation time, the compiler copies in the external field-level
description.
- 2
- An externally described file (that is, a file with field-level
external description) is used as a program-described file in the program.
A program-described file is identified by an F in position 22 of the
file description specifications. This entry tells the compiler not
to copy in the external field-level descriptions. This file does not
have to exist at compilation time.
- 3
- A file is described only at the record level to the operating
system. The fields in the record are described within the program;
therefore, position 22 of the file description specifications must
contain an F. This file does not have to exist at compilation time.
- 4
- A file name can be specified at compilation time (that is, coded
in the RPG source member), and a different file name can be specified
at run time. The E in position 22 of the file description specifications
indicates that the external description of the file is to be copied
in at compilation time. At run time, a file override command can be
used so that a different file is accessed by the program. To override
a file at run time, you must make sure that record names in both files
are the same. The RPG program uses the record-format name on the input/output
operations, such as a READ operation where it specifies what record
type is expected. See Overriding and Redirecting File Input and Output for more information.
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