ILE RPG IV Best Practices - ibm.com · ILE RPG IV Best Practices ... Many new features supported only in free-format ... D-----D getDate PR 6S 0 prototypes /copy

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© 2011 IBM Corporation

ILE RPG IV Best Practices

Jim Diephuis ([email protected])

© 2011 IBM Corporation22 IBM STG Lab Services and Training05/01/12

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

/FREE

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


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


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


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ILE RPG IV Best Practices - ibm.com · ILE RPG IV Best Practices ... Many new features supported only in free-format ... D*-----D getDate PR 6S 0 * prototypes /copy

ILE RPG IV Best Practices - ibm.com · ILE RPG IV Best Practices ... Many new features supported only in free-format ... D-----D getDate PR 6S 0 prototypes /copy