IBM AS/400 manual Order of Evaluation, Interlanguage Calls, Passing Prototyped Parameters, effect

Passing Prototyped Parameters

Figure 71		on page 146		shows the prototype for QCMDEXC, where				the	first
eter is		defined	with	OPTIONS(*VARSIZE)	meaning that	you can	pass		paramet
of	different lengths for the first				parameter. Note that		OPTIONS		*VARSI
be	specified for		a	character field, a graphic		field,	or	an	array.

*-------------------------------------------------------------

*This prototype for QCMDEXC defines three parameters. The

*first parameter can be passed character fields of

*different lengths, since it is defined with *VARSIZE.

	*-------------------------------------------------------------
D qcmdexc		PR		EXTPGM('QCMDEXC')
D	cmd		3000A	OPTIONS(*VARSIZE) CONST
D	cmdlen		15P	5 CONST
D			3A	CONST OPTIONS(*NOPASS)

Figure 71. Prototype for System API QCMDEXC with *VARSIZE Parameter

Order of Evaluation

There

is no guaranteed order for

evaluation

of

parameters

on

a protot

This

fact

may

be

important

when

using

parameters

that

cause

side

eff

results

may

not be what you would expect.

A side

effect

occurs if the processing of the

parameter

changes:

¹

The

value of a reference parameter

¹

The

value of a global variable

¹

An

external object, such as a file

or

data

area

If

a

side

effect occurs,

then,

if

the

parameter

is

used

elsewher

list,

then

the value used for the

parameter

in

one

part

of

the

list

same

as

the

value

used

in

another

part.

For

example,

consider

this

ca

CALLP

procA (fld : procB(fld) : fld)

Assume

that

procA has all value parameters, and

procB

has

a

reference

eter.

Assume

alsofldthatstarts off with

the

value

3,

and fldthato procB

modif

be

5,

and

returns 10. Depending on the order

in

which

the

parameters

ated,

procA

will

receive

either

3,

10,

and

5

or

possibly,

3,

10,

and

10,

and

3;

or

even

5,

10,

and 5.

In

short,

it

is

important

to

be

aware

of the

possibility

of

side

e

particular,

if

you

are

providing

an

application

for third-party use, wh

may

not

know

the

details

of

some

of the

procedures,

it

is

important

values

of

the

passed

parameters

are

the

expected

ones.

Interlanguage Calls

When passing or receiving data from a							program or procedure written in
language, it is important to know whether the other language supports									th
parameter passing methods and the same							data types as ILE RPG. Table
page 147		shows	the different			parameter	passing	methods allowed by	ILE
and,	where applicable,			how	they would		be coded in the other the I
The	table	also	includes	the	OPM	RPG/400	compiler	for comparison.

146 ILE RPG for AS/400 Programmer's Guide