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ILE RPG IV Best Practices

Jim Diephuis (diephuis@us.ibm.com)

Where credit is due: RPG IV Style, Standards, and Best Practices By Bryan Meyershttp://www.bmeyers.net/resources/rpgivstyle.php

Barbara MorrisIBM Toronto LabRPG Compiler Development

Use Free Format

Use Free Format Easier to read

Easier to document

Easier to maintain

Many new features supported only in free-format

But don’t abandon using column alignment

/FreeTotalPay = (RegHours * Rate) +

(OvtHours * Rate * 1.5) +(DblHours * Rate * 2);

/End-free

Use Free FormatStructured Format Free Format

KEY SETLL DBFILE setll key dbfile;IF %EQUAL if %equal;

KEY READE DBFILE reade key dbfile;DOW NOT %EOF(DBFILE) dow not %eof(dbfile);

KEY2 CHAIN FILE2 chain key2 file2;IF %FOUND(FILE2) if %found(file2); EVAL P1DESC=DBDESC p1desc=dbdesc;ELSE else;EVAL P1DESC=*BLANK p1desc=*blank;ENDIF endif;WRITE Detail write detail;

KEY READE DBFILE reade key dbfile;ENDDO enddo;ELSE else;WRITE ErrorMsg write ErrorMsg;ENDIF endif;

/END-FREE

Use Free Format If writing new code, use free format

If changing existing code, use free format to

Replace entire subroutines

Replace large sections of code

Embrace ILE

Embrace ILE USE PROCEDURES

Modular approach to programming

• Way to organize an application

• Facilitates program maintenance

• Hides complex logic

• Efficient reuse of code – NO DUPLICATE CODE

• Smaller, more efficient, single function units

Embrace ILE Use Binding Directories

Organize the pieces required to create a program

• Refer to directory instead of explicitly listing components

Use consistent strategy

• Generic binding directory for reusable code across applications

• Application specific binding directory

Embrace ILE Use Service Programs

Procedure will be in more than one or two programs? Package it into a service program.

Use ACTGRP(*CALLER) CRTSRVPGM SRVPGM(PCIIBMLIB/MASKPRC) EXPORT(*SRCFILE) + SRCFILE(QSRVSRC) SRCMBR(*SRVPGM) ACTGRP(*CALLER)

Embrace ILE Use binder language

Don’t use EXPORT(*ALL)

CRTsrvpgm SRVPGM(ctyfrnlib/TCPCODE) MODULE(*SRVPGM) +

SRCFILE(CTYFRNLIB/QSRVSRC) TEXT('TCP/IP + procedures') BNDDIR(QZRDSAPI/QZRDSAPI)

Controls service program signatureSTRPGMEXP PGMLVL(*CURRENT) EXPORT SYMBOL(openSocket) EXPORT SYMBOL(sendBuffer) EXPORT SYMBOL(receiveBufGE) EXPORT SYMBOL(closeSocket) ENDPGMEXP

Embrace ILE Use Prototypes

Defines parameters and interfaces

Avoids run time errors

Allows coding literals and expressions

Declare parameter lists in D-specs

Pass by value and read only reference

Store prototypes in /COPY members

Save typing the prototype each time

Embrace ILED*--------------------------------------------------D* Procedure name: centuryD* Purpose: Take a 6 digit date and add theD* centry to it.D* Parameter: indate => 6 digit dateD* Returns: eight digit dateD*--------------------------------------------------* Takes a 6 digit date and adds the century to it.

D century pr 8 0D indate 6 0 const

D*--------------------------------------------------D* Procedure name: getTimeD* Purpose: Get the current time and return it as 6 numericD* Returns: numeric 6 time value.D*--------------------------------------------------D getTime PR 6S 0

D*--------------------------------------------------D* Procedure name: getDateD* Purpose: Get the current date as numeric 6D* Returns: numeric 6 date valueD*--------------------------------------------------D getDate PR 6S 0

* prototypes/copy tcpcodep TCP/IP prototypes/copy dateutilp Date utility prototypes

Embrace ILE Include constant declarations in prototype

“globalize” the constant

Use IMPORT/EXPORT only for global data

“Hidden interface”

Limit to values set once and not changed

Use CONST instead of VALUE for large parameters and data structures

Centralize Declarations

Organize all variables (and constants)

Use predictable orderPrototype definitions (/COPY)

Internal prototype definitions

Named Constants

Data Structures

Standalone variables

• And alphabetize!

Declare literals as constants * Constants for base message option value

d APPROVAL c 'A'

d CREDIT c 'C'

Indent data item namesD ErrMsgDS DS

D ErrPrefix 3D ErrMsgID 4D ErrMajor 2 OVERLAY(ErrMsgID:1)D ErrMinor 2 OVERLAY(ErrMsgID:3)

Leave column 7 blank (on H-specs too!) Use length notation instead of positionalAvoid multiple occurrence data structures Use array data structures instead

Centralize Declarations Avoid compile-time arrays

D DaysCTData DSD 9 Inz('Sunday')D 9 Inz('Monday')D 9 Inz('Tuesday')D 9 Inz('Wednesday')D 9 Inz('Thursday')D 9 Inz('Friday')D 9 Inz('Saturday')D Days 9 Dim(7)D Overlay(DaysCTData)

Centralize Declarations Use qualified data structures

Good documentation Allows same name in different data structures

d Customer ds Qualified d Name 20a overlay(customer)d YTDSls 11s 2 overlay(customer:*next)/freeCustomer.YTDSls = 0;

/end-free

Expand Naming Conventions

Standardize

Go beyond six! (but don’t get carried away)

Describe the item

Avoid special characters

Use mixed caseD messagePtr s *D messageLength s 10I 0d messageBuffer s 1000 based(messagePtr)

Maintain dictionary of names (Have a naming convention)

Write Indicatorless Code

Eliminate numbered indicators

Indicator data structure (INDDS)fWrkCustD cf e k workstn indds(indicators)

d indicators dsd Exit n overlay(indicators:3) d Cancel n overlay(indicators:12)

/freeif Exit or Cancel;*inlr=*on;

endif;/end-free

Assign meaningful namesd indicators dsd Exit n overlay(indicators:3) d Cancel n overlay(indicators:12)d PatNbrErr n overlay(indicators:50)d PatNamErr n overlay(indicators:51)d PatAdrErr n overlay(indicators:52)

Use Built-in Functions (BIFs)

Use file exception conditions

• %eof, %found, %error

Include description of ones you do use

Level break indicators or U1-U8

Use the Boolean data type

Use Structured Programming Techniques

DO use: IF, DOU, DOW, WHEN, FOR

end them with ENDIF, ENDDO, ENDSL

Multi-path compares use SELECT

DON’T use: GOTO, CABxx, COMP, CASxx

DO use ITER, LEAVE, LEAVESR

Manipulate Character Strings

Avoid arrays and data structures for string manipulation

Use string manipulation op codes and BIFs

/FREEFull = %TRIMR(FirstName) + ‘ ‘ +

%SUBST(MidName:1:1) + ‘ ‘ +LastName;

Result = ‘It is ‘ + %CHAR(Time) +‘ on ‘ + %CHAR(Date);

Sal = ‘The annual salary is ‘+ %TRIM(%EDITC(Amt*12 : ’A’ : *CURSYM));

/END-FREE

Use free form EVAL (a = b) for string manipulation

Use %subst or %replace to not pad with blanks

Use variable-length fields to simplify string handling

D QualName S 33 VARYINGD Library S 10 VARYINGD File S 10 VARYINGD Member S 10 VARYING

/FREEQualName = Library + '/' + File + '(' + Member + ')';

/END-FREEinstead of this:

D QualName S 33D Library S 10D File S 10D Member S 10

/FREEQualName = %TRIM(Library) + '/' + %TRIM(File)

+ '(' + %TRIM(Member) + ')';/END-FREE

Use Comments Judiciously

Use // comments exclusively

// Prototypes

D DayofWeek PR 1 0D VarDate D

// Standalone variablesD DayNbr S 5 0

/Free// Calculate total pay for employeeChain(ne) EmployeeID Employees;If %Found; // If employee active, calculate total payEval(h) TotalPay = (RegHours * Rate) + (OvtHours * Rate * 1.5);

Endif;/End-free

Use Comments Judiciously Use prolog on all programs

//******************************************************************

//// Service Program: XXXXXML//// Description:// This service program contains the procedures used to parse XML// data that is received from where ever and convert it into a// string that matches a given data structure.//// External Procedures:// XMLInit - Initialize the user index and parser.// XMLParse - Parse the XML into a given data structure.// XMLParseEnd - End parsing.//// Internal Procedures:// ProcessChars - Process characters returned from the parser// ProcessField - Process a given field// ProcessStart - Process a new tag// ProcessEnd - Process the end of a tag//// Change Information:// date Profile Reason// ---------- ---------- ----------------------------------------// 2003-03-13 IBMJIMH Initial writing////*****************************************************************

Use prolog on all procedures //*****************************************************************// Procedure: XMLInit//// Description:// Initialize the index using the entries in DSPARSE. The index is// used to define the parts of the data structures that may be// parsed.// Also initialize the parser with the procedures that will be used// on it's callbacks.// All of these things only need to be done once within a job.//// Parameters:// none//// Return value:// none////*****************************************************************

Use blank lines to group related source

Avoid right-hand comments (column 81 – 100)

Stop using sequence numbers on left

Avoid Obsolescence

Avoid Obsolescence Eliminate obsolete operation codes

If free-form doesn’t support it…

If there is a function and opcode that do same thing, use the function

Avoid program described files

Use native date data types for date operations

Work on character fields as well

Parting Shots

Parting Shots Avoid programming tricks

Or make sure they are well documented

Don’t worry about relative performance

Use whatever best fits the task at hand

Parting Shots

Make it right before you make it faster

Keep it right when you make it faster

Make it clear before you make it faster

Don’t sacrifice clarity for small gains in efficiency

Trademarks and Disclaimers© IBM Corporation 1994-2005. All rights reserved.References in this document to IBM products or services do not imply that IBM intends to make them available in every country.

The following terms are trademarks of International Business Machines Corporation in the United States, other countries, or both:

Rational is a trademark of International Business Machines Corporation and Rational Software Corporation in the United States, other countries, or both.Java and all Java-based trademarks are trademarks of Sun Microsystems, Inc. in the United States, other countries, or both.Microsoft, Windows, Windows NT, and the Windows logo are trademarks of Microsoft Corporation in the United States, other countries, or both. Intel, Intel Inside (logos), MMX and Pentium are trademarks of Intel Corporation in the United States, other countries, or both.UNIX is a registered trademark of The Open Group in the United States and other countries.SET and the SET Logo are trademarks owned by SET Secure Electronic Transaction LLC. Other company, product or service names may be trademarks or service marks of others.

Information is provided "AS IS" without warranty of any kind.

All customer examples described are presented as illustrations of how those customers have used IBM products and the results they may have achieved. Actual environmental costs and performance characteristics may vary by customer.

Information concerning non-IBM products was obtained from a supplier of these products, published announcement material, or other publicly available sources and does not constitute an endorsement of such products by IBM. Sources for non-IBM list prices and performance numbers are taken from publicly available information, including vendor announcements and vendor worldwide homepages. IBM has not tested these products and cannot confirm the accuracy of performance, capability, or any other claims related to non-IBM products. Questions on the capability of non-IBM products should be addressed to the supplier of those products.

All statements regarding IBM future direction and intent are subject to change or withdrawal without notice, and represent goals and objectives only. Contact your local IBM office or IBM authorized reseller for the full text of the specific Statement of Direction.

Some information addresses anticipated future capabilities. Such information is not intended as a definitive statement of a commitment to specific levels of performance, function or delivery schedules with respect to any future products. Such commitments are only made in IBM product announcements. The information is presented here to communicate IBM's current investment and development activities as a good faith effort to help with our customers' future planning.

Performance is based on measurements and projections using standard IBM benchmarks in a controlled environment. The actual throughput or performance that any user will experience will vary depending upon considerations such as the amount of multiprogramming in the user's job stream, the I/O configuration, the storage configuration, and the workload processed. Therefore,

no assurance can be given that an individual user will achieve throughput or performance improvements equivalent to the ratios stated here.

Photographs shown are of engineering prototypes. Changes may be incorporated in production models.

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