IBM AS/400 manual Main Procedure Considerations, Subprocedure Considerations, Program Creation

Coding Considerations

Program Creation

¹ If you specify that a

module

does

not

have

a

main

procedure

the

use

the

CRTBNDRPG

command

to

create

the program.

(A module

does

not

have a main procedure if the NOMAIN keyword is

specified on

a

con

cation.)

This

is

because

the CRTBNDRPG command requires that the

modu

contain a program entry procedure and only a

main

procedure

can

be

program entry

procedure.

¹ Similarly, when using CRTPGM

to

create

the

program,

keep

in

mind

that

NOMAIN module cannot be an

entry

module

since it does

not

have a pr

entry

procedure.

¹ A program that is created

to

run

in

the

default OPM

activation

grou

fying

DFTACTGRP(*YES)

on the

CRTBNDRPG command)

cannot

contain

bound

procedure

calls.

Main Procedure Considerations

¹Because the main procedure is the only procedure with a complete ifications available (except the P specification), it should be use

environment of all procedures in the module.

¹ A main procedure is	always exported, which	means	that	other proced
the program can call	the main procedure by	using	bound	calls.

¹ The call interface of a main procedure can be defined in one of

1. Using a prototype and procedure interface

2. Using an *ENTRY PLIST without a prototype

¹The functionality of an *ENTRY PLIST is similar to a prototyped call i However, a prototyped call interface is much more robust since it

parameter

checking

at

compile time.

If

you prototype

the

main

proc

you

specify how

it is

to

be

called

by specifying either the EX

EXTPGM keyword on the prototype definition. If EXTPGM is specified,

external program call is used; if EXTPROC is specified or if neithe

specified,

it

will be

called

by using

a

procedure call.

¹ You

cannot

define

return

values

for

a

main

procedure,

nor

can

you

its

parameters

be

passed

by

value.

Subprocedure Considerations

¹ Any	of	the calculation operations	may	be	coded	in	a	subprocedure.
all files must be defined globally, so all input						and	output specific
defined		in the main source section. Similarly, all				data		areas must b
the	main	procedure, although they	can	be	used	in	a	subprocedure.

¹The control specification can only be coded in the main source sec

controls the entire module.

¹A subprocedure can be called recursively. Each recursive call cause

invocation of the procedure to be placed on the call stack. The n

has new storage for all data items in automatic storage, and					that
unavailable	to	other invocations because it	is local.	(A data	item
in a subprocedure uses automatic storage			unless the	STATIC keyword
fied for	the	definition.)

46 ILE RPG for AS/400 Programmer's Guide