IBM AS/400 manual Calling Programs, Calling Procedures, Program/Procedure Call Overview, calls

Program/Procedure Call Overview

¹Recursion

¹Parameter passing considerations

Calling Programs

You

can

call

OPM

or ILE

programs by

using

program callcalls. isA

a

call that is made to a

program object (*PGM). The

called

program's

name

resolved

to

an

address

at run time, just before the calling

program

p

to

the

called program for the first time. For this reason, program ca

referred to as dynamic calls.

Calls

to

an ILE

program,

an

EPM

program,

or

an

OPM

program

are all

example

program

calls.

A

call

to

a non-bindable API

is also

an

example

of

a

pro

You

use

the

CALLP operation

or

both

the

CALL

and

PARM

operations

to

make

program

call. If you use the

CALL

and

PARM

operations,

then

the

compiler

perform

type

checking

on

the

parameters,

which

may

result

in

run-time

e

When an ILE program is called, the program entry procedure receives t parameters and is given initial control for the program. In addition, a within the program become available for procedure calls.

Calling Procedures

Unlike OPM programs, ILE programs are not limited to using program calls. programs can also use static procedure calls or procedure pointer call

procedures.

Procedure

calls are also

referred

to

as

bound

calls.

A

static

procedure

call

is

a

call to an ILE procedure where the name of

dure

is

resolved

to

an

address during binding — hence, the term stat

run-time performance using

static procedure calls is faster than run-time

ance

using program

calls. Static calls allow operational descriptors, omitt

eters,

and

they

extend

the

limit

(to

399)

on

the

number

of

parameter

passed.

Procedure

pointer

calls

provide

a

way to call a procedure dynamically. For

example,

you

can

pass

a

procedure pointer as a parameter to another

which

would

then

run the

procedure

that

is

specified

in

the

passed

can also

manipulate arrays

of

procedure

names

or

addresses

to

dynamic

a

procedure

call

to different procedures. If the called procedure

vation

group,

the

cost

of

a

procedure

pointer

call

is

almost

identical

static

procedure

call.

Using either type of procedure call, you can call:

¹A procedure in a separate module within the same ILE program or se program.

¹ A procedure in a separate ILE service program.

Any procedure that can be called by using a static procedure call c called through a procedure pointer.

For	a list of examples using	static	procedure	calls, see “Examples of
Call”	on page 135 and “Examples	of CALL	and CALLB”	on page 150. For exam-

128 ILE RPG for AS/400 Programmer's Guide