02
Sat, Nov
2 New Articles
  1. You are here:  
  2. Home
  3. Programming
  4. RPG
  5. Using C in RPG IV

Using C in RPG IV

RPG
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

You've heard people refer to using the C runtime library in RPG IV. In fact, I've published many articles and examples that do just that. This week, we're going to look at how and why this works, and then I'll give you several prototypes that let you call these C routines right from within good old RPG IV!

The C language has several interesting methods for evoking a procedure call. Fortunately, one of these methods allows the procedure to be called via a pointer to the procedure. Consequently, the functions for the C runtime library are stored in service programs, are callable just like any subprocedure written in RPG IV, and are exported from a service program.

Included with OS/400 is a special binding directory named QC2LE. It contains a list of modules and service programs needed to provide access to the entire C language runtime library. To use this binding directory, add the BNDDIR keyword to your H specification. I have a standard Header specification that I use in my source. Since I use conditional compiling with it, it can be used in both standalone program source as well as module source. For example:

     H   BNDDIR('QC2LE') OPTIONS(*SRCSTMT:*NODEBUGIO)
      /IF  DEFINED(*CRTBNDRPG)
     H   DFTACTGRP(*NO) 
      /ENDIF

Since the C runtime library is stored in modules and service programs, binding to them is as easy as writing an RPG IV procedure prototype. In fact, it is so easy to interface RPG IV with C that I often claim that RPG IV can now natively support every function that the C language supports. Thank you, you C bigots!

From what I have observed, the two biggest difficulties RPG IV programmers have with using the C runtime library are (1) knowing which function to use for what task and (2) writing the RPG IV version of the prototype to call the C procedure.

One function that I like to use is the system() function, which is a bit cleaner than calling QCMDEXC. Another is the memchr() function, which is a high-speed way to search for a single character within a variable.

The capability I see requested most often is the ability to convert a number that is stored in a character field into a numeric value. If the number does not contain decimal notation, (that is, it's a whole number), C has several functions to handle this capability. The one I recommend is the atoll() function. This function supports the largest number, up to 19 digits.

Knowing what the C functions do is only half the solution. The next step is to prototype the function so it can be called in RPG IV.

If you have my RPG ToolKit, you already have many of the prototypes for the C runtime library. They are included in the CPROTOS source member in the QCPYSRC source file.

For the rest of you, I am illustrating many of the C runtime library prototypes in RPG IV syntax in Figure 1 below. Copy these prototypes to a source member and /COPY them into the source when you want to call any of them. Please remember to use the BNDDIR('QC2LE') directive (and be sure to specify 'QC2LE' in uppercase, or you'll have a learning experience).

      /IF NOT   DEFINED(C_RUNTIME)
      /DEFINE  C_RUNTIME
     
      ** © Copyright 2001 by Robert Cozzi, Jr.
.....D*ame+++++++++++EUDS.......Length+TDc.Functions+++++++++++++++
     D errno           PR              *   ExtProc('__errno') 
      ***********************************************
      ** Error variable for the system() call interface.
      ***********************************************
     D RTK_C_ERRMSGID  S              7A   Import( '_EXCP_MSGID' )

.....D*ame+++++++++++EUDS.......Length+TDc.Functions+++++++++++++++
     D BSearch         PR              *   ExtProc('bsearch')
     D  pSearchData                    *   VALUE
     D  pStartOfArray                  *   VALUE
     D  nElemCount                   10U 0 VALUE
     D  nElemSize                    10U 0 VALUE
     D  CompFunc                       *   VALUE ProcPtr

     D qsort           PR              *   ExtProc('qsort')
     D  pArrayData                     *   VALUE
     D  nElemCount                   10U 0 VALUE
     D  nElemSize                    10U 0 VALUE
     D  CompFunc                       *   VALUE ProcPtr

     D strerror        PR              *   ExtProc('strerror')
     D  errno                        10I 0 VALUE 

     D stricmp         PR            10I 0 ExtProc('stricmp')
     D  pVal1                          *   Value OPTIONS(*STRING)
     D  pVal2                          *   Value OPTIONS(*STRING)

     D strlen          PR            10I 0 ExtProc('strlen')
     D  pVal1                          *   Value OPTIONS(*STRING)

     D ultoa           PR              *   ExtProc('__ultoa')
     D  nUINT                        10U 0 VALUE
     D  szRtnBuffer                    *   Value
     D  nRadix                       10I 0 Value 

     D  ltoa           PR              *   ExtProc('__ltoa')
     D  nUINT                        10I 0 VALUE
     D  szRtnBuffer                    *   Value
     D  nRadix                       10I 0 Value 

     D itoa            PR              *   ExtProc('__itoa')
     D  nUINT                        10I 0 VALUE
     D  szRtnBuffer                    *   Value
     D  nRadix                       10I 0 Value

     D atoi            PR            10I 0 ExtProc('atoi')
     D  szCharIn                       *   Value Options(*STRING)

     D atoll           PR            20I 0 ExtProc('atoll')
     D  szCharIn                       *   Value Options(*STRING)

     D atol            PR            10I 0 ExtProc('atol')
     D  szCharIn                       *   Value Options(*STRING)

     D strtol          PR            10I 0 ExtProc('strtol')
     D  szInString                     *   value options(*string)
     D  ppStop                         *   value
     D  base                         10i 0 value

     D strtoll         PR            20i 0 ExtProc('strtoll')
     D  szInString                     *   value options(*string)
     D  ppStop                         *   value
     D  base                         10I 0 value             

     D system          PR            10I 0 ExtProc( 'system' )
     D  szCmd                          *   Value Options( *String )

     D sleep           PR            10U 0 ExtProc('sleep')
     D   seconds                     10U 0 value

     D memset          PR                  ExtProc('__memset')
     D  pTarget                        *   Value
     D  nChar                        10I 0 Value
     D  nBufLen                      10U 0 Value

     D memcpy          PR                  ExtProc('__memcpy')
     D  pTarget                        *   Value
     D  pSource                        *   Value
     D  nLength                      10U 0 Value       

     D memchr          PR              *   ExtProc('_MEMCHR')
     D  pBuffer                        *   Value
     D  nChar                        10I 0 Value
     D  nBufLen                      10U 0 Value

     D memcmp          PR            10I 0 ExtProc('__memcmp')
     D  pVal1                          *   Value 
     D  pVal2                          *   Value 
     D  nBufLen                      10U 0 Value

     D memicmp         PR            10I 0 ExtProc('__memicmp')
     D  pVal1                          *   Value 
     D  pVal2                          *   Value 
     D  nBufLen                      10U 0 Value

Figure 1: These are the C language runtime library prototypes in RPG IV.

Bob Cozzi has been programming in RPG since 1978. Since then, he has written many articles and several books, including The Modern RPG Language--the most widely used RPG reference manual in the world. Bob is also a very popular speaker at industry events such as RPG World and is the author of his own Web site and of the RPG ToolKit, an add-on library for RPG IV programmers.

BOB COZZI

Bob Cozzi is a programmer/consultant, writer/author, and software developer. His popular RPG xTools add-on subprocedure library for RPG IV is fast becoming a standard with RPG developers. His book The Modern RPG Language has been the most widely used RPG programming book for more than a decade. He, along with others, speaks at and produces the highly popular RPG World conference for RPG programmers.

MC Press books written by Robert Cozzi available now on the MC Press Bookstore.

RPG TnT RPG TnT
Get this jam-packed resource of quick, easy-to-implement RPG tips!
List Price $65.00

Now On Sale

The Modern RPG IV Language The Modern RPG IV Language
 Cozzi on everything RPG! What more could you want?
List Price $99.95

Now On Sale
BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: