IBM AS/400 manual Recursive Calls, Program/Procedure Call Overview

Program/Procedure Call Overview

Recursive Calls

Recursive calls are only allowed

for

subproceduresrecursive call

.is A one where

procedure

A

calls

itself or

calls

procedure B which then calls proced

Each

recursive call

causes

a

new

invocation

of

the

procedure

to

be

call stack. The new invocation has

new storage for all data items in a

storage, and that storage is unavailable

to

other

invocations

because

data

item

that

is

defined

in

a

subprocedure

uses automatic

storage

STATIC keyword is specified for

the definition.) Note also that the au

storage

that

is

associated

with

earlier

invocations

is

unaffected

by

A main procedure that is on the

call stack cannot be called until it

caller.

Therefore,

be careful

not to

call

a

procedure

that

might

call

main

procedure.

Try to avoid situations that might inadvertently lead to recursive calls suppose there are three modules, as shown in Figure 59.

MODULE X

main proc. X

PRC_A

CALLP prc_B

MODULE Y

main proc. Y

PRC_B

CALLP prc_C

MODULE Z

NOMAIN

PRC_C

CALLP prc_A

PRC_D

Figure	59. Three Modules, each with subprocedures
You are		running	a	program where procedure A in		module	X calls	procedu
module	Y.	You	are not aware of what procedure B does except that
some	fields. Procedure B in turn calls procedure C, which in turn calls
Once	procedure C calls procedure A, a recursive call has been made.
stack	sequence		is	shown	in Figure 60 on page 131.	Note	that the	most r
stack	entry is		at	the	bottom.

130 ILE RPG for AS/400 Programmer's Guide