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

Page 152 Page 154
Page 153
Image 153
IBM AS/400 manual Call Stack, Call stack
Page 152 Page 154

AS/400 specifications

The IBM AS/400, now known as the IBM iSeries, is a midrange computer system that has been a cornerstone of enterprise computing since its introduction in 1988. Designed to provide a robust platform for business applications, the AS/400 is celebrated for its reliability, scalability, and integrated database capabilities.

One of the key features of the AS/400 is its Integrated Operating Environment, which blends hardware and software resources seamlessly. This integration allows businesses to execute diverse workloads, ranging from traditional applications to modern web-based services, all on a single platform. The operating system, OS/400 (now IBM i), offers a rich set of APIs and tools for developers, simplifying application development and management.

Another standout characteristic of the AS/400 is its built-in database, DB2 for i. This powerful relational database management system allows for efficient data handling and provides advanced features such as support for SQL, XML, and JSON, making it easier for businesses to manage their data and integrate it with other systems. The database's tight integration with the operating system enables high performance and security.

In terms of scalability, the AS/400 can accommodate small businesses as well as large enterprises, with the ability to support hundreds of users simultaneously. Its architecture allows for easy upgrades in hardware, meaning that organizations can scale their systems without replacing the entire infrastructure.

Security is another critical attribute of the AS/400. With a sophisticated security model, it offers built-in user authentication, access control, encryption, and auditing capabilities to protect data and applications from unauthorized access.

The AS/400 also supports multiple programming languages, including RPG, COBOL, Java, and PHP, giving organizations the flexibility to choose the development tools that best fit their needs. This diversity helps maintain legacy applications while also developing new ones that leverage modern technologies.

Moreover, the platform supports both traditional green-screen interfaces and modern graphical user interfaces, allowing organizations to transition smoothly into contemporary user experience paradigms.

Overall, the IBM AS/400 stands out as a resilient, flexible, and secure computing platform that enables organizations to effectively manage their business operations, streamline processes, and adapt to changing market demands. Its unique combination of integrated features and capabilities ensures that it remains relevant in today's fast-paced technology landscape.
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