RE: Dynamic 'callp'

Just an gotcha to make note of with this.

Assuming LIB1 and LIB2 both contain a version of the THISPGM program and initially only LIB1 is in the
library list then in the following code:

D Prototype Pr ExtPgm(PgmVar)
D ParmDefn 5A

D PgmVar S 21A

D Variable S 5A

/Free

PgmVar = '*LIBL/THISPGM';
CallP Prototype(Variable);

AddLibListEntry('LIB2':'*FIRST');

CallP Prototype(Variable);

*InLR = *On;

/End-Free

Contrary to what you may expect, the second CALLP will call LIB1/THISPGM and not the LIB2/THISPGM that
can now be found higher in the *LIBL.

RPG only resolves a pointer to an external program when needed. Since the contents of the PgmVar
hasn't changed it doesn't re-resolve the program.

This code, works as you'd expect:
D Prototype Pr ExtPgm(PgmVar)
D ParmDefn 5A

D PgmVar S 21A

D Variable S 5A

/Free

PgmVar = 'LIB1/THISPGM';
CallP Prototype(Variable);

AddLibListEntry('LIB2':'*FIRST');

PgmVar = 'LIB2/THISPGM';
CallP Prototype(Variable);

*InLR = *On;

/End-Free

First LIB1/THISPGM is called, then LIB2/THISPGM is called.

If you want to call multiple versions of a program from different libraries, you either need to hard
code the libraries (probably not a great idea :) or handle the name resolution yourself like so:

D Prototype Pr ExtPgm(PgmVar)
D ParmDefn 5A

D PgmVar S 21A

D Variable S 5A

/Free

PgmVar = FindObjectInLibraryList('THISPGM':'*PGM')
CallP Prototype(Variable);

AddLibListEntry('LIB2':'*FIRST');

PgmVar = FindObjectInLibraryList('THISPGM':'*PGM')
CallP Prototype(Variable);

*InLR = *On;

/End-Free

Where the FindObjectInLibraryList() procedure returns the qualified name of an object given the
current library list.

HTH,
Charles

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Brian Parkins
Sent: Tuesday, August 07, 2007 6:28 AM
To: RPG programming on the AS400 / iSeries
Subject: Re: Dynamic 'callp'

The program I need to call through the 'callp' statement needs to be

dynamic.

Program calls - by their very definition - _are_ Dynamic.
See code below:


D Prototype Pr ExtPgm(PgmVar)
D ParmDefn 5A

D PgmVar S 21A Inz('*LIBL/THISPGM')

D Variable S 5A

/Free

PgmVar = '*CURLIB/THATPGM';

CallP Prototype(Variable);

*InLR = *On;

/End-Free

(However, dynamic calls using a variable for the program name have a
performance overhead. Hence most dynamic calls employ a
constant/literal
for the name.)

Brian Parkins





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