Using C in RPG IV

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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   DFTACTGRP(*NO) 

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).

      ** © Copyright 2001 by Robert Cozzi, Jr.
     D errno           PR              *   ExtProc('__errno') 
      ** Error variable for the system() call interface.
     D RTK_C_ERRMSGID  S              7A   Import( '_EXCP_MSGID' )

     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.

Robert 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.

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