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:
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).
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.