IBM AS/400 manual The Call Stack, Program/Procedure Call Overview, The call stack

Program/Procedure Call Overview

ples of using procedure pointers, see the section on the procedure type ILEin RPG for AS/400 Reference.

You use the CALLP or	both	the	CALLB	and	PARM	operations		to	make a	pro
call. You can also call a prototyped procedure							with	an expression			i
returns a value. If	you	use	the	CALLB	and	PARM	operations,		then	the
cannot perform type checking on the parameters,							which	may	result	in	r
errors.

The Call Stack

The call stack

is

a list

of

call

stack

entries,

in

a last-incall-first-out

(L

stack

entry

is

a call to a program

or

procedure.

There is one call s

When

an

ILE

program is

called,

the

program entry

procedure

is

first

call stack. The system then automatically performs

a procedure

call,

ciated

user's

procedure

(the

main

procedure)

is

added.

When

a

pr

only the user's procedure (a main procedure or subprocedure) is ad overhead of a program entry procedure.

Figure 58 shows a call stack

for

an application

consisting

of

an

OPM

pro

which calls

an

ILE

program.

The RPG

main

procedure

of

the

ILE

progra

RPG

subprocedure, which in

turn calls a C procedure. Note

that

in

t

this

book,

the

most

recent

entry

is

at

the

bottom

of

the

stack.

OPM

Program A

ILE

RPG Module

Program

Entry Proc.

Main

Procedure

Sub-

Procedure

C Module

Procedure

CALL STACK

OPM

ILE

PEP

ILE

Procedure

ILE

Procedure

ILE

Procedure

Program Call

Procedure Call (by system)

Procedure Call

Procedure Call

Figure	58. Program and Procedure Calls on the Call Stack
Note:	In a	program call, the calls to the program entry procedure an
	entry	procedure (UEP) occur together, since the call to the U
	matic.	Therefore, from now on, the two steps of	a program	call
	bined	in later diagrams involving the call stack in	this and	rema

chapters.

Chapter 10. Calling Programs and Procedures129