It is relatively easy to take advantage of some of the useful procedures provided to you for free. The procedures I'm talking about are the routines in the C language runtime library available to RPG IV programmers.
There are only two things you need to do to call any C language procedure.
1. Specify BNDDIR('QC2LE') on the header specification of the source member that will be calling the C language procedure.
2. Prototype the C language procedure.
The more difficult part is, of course, correctly prototyping the procedure. To illustrate how this is done, I've prototyped and illustrated two C language procedures for you.
The first is atoll(). This is the ASCII to long, long procedure. The term "long, long" is the C language's way of saying an 8-byte binary value (20I0 in RPG IV-speak). The "ASCII" isn't really ASCII, but rather character. The procedure converts a numeric value that happens to be stored in a character variable to a numeric value.
While this capability is built into RPG IV in OS/400 V5R2 in the %DEC and %INT built-in functions, few people are currently running that release.
Below is the RPG IV prototype needed to call the atoll() procedure. Simply cut/paste this code into your RPG source member, and you have access to its functionality. It works on all releases of OS/400 V3R7 and later.
D szCharIn * Value Options(*STRING)
To use this procedure, just specify it on an eval statement, as illustrated below:
D szPastDue S 15A inz('65')
D nDaysOverDue 5P 0
C eval nDaysOverDue = atoll(szPastDue)
The downside to this procedure is that it only works with whole numbers. Decimal values aren't supported. Note that this procedure works with up-to-19-digit numbers.
The second C language procedure that is nice to have access to is the system() procedure. This procedure essentially replaces QCMDEXC in that it runs OS/400 CL commands. But unlike QCMDEXC, system() does not require you to know the length of the command string being passed to it. It figures that out on its own, making for much nicer syntax.
Below is the RPG IV prototype needed to call the system() procedure. Simply cut/paste this code into your RPG source member, and you have access to its functionality. It works on all releases of OS/400 V3R7 and later.
D szCmd * Value Options( *String )
The system() is used by calling it with the CALLP opcode. For example:
C callp system('ADDLIBLE TOOLKIT')
You can also call it with the eval opcode, as follows:
D nRtnCode S 10I 0
C eval nRtnCode = system('ADDLIBLE TOOLKIT')
When eval is used, the system() procedure returns a return code that can be tested for a value of something other than zero. If it is not zero, an error occurred. To make it compatible with OS/400 errors, IBM also provides an exported field for you to view the CPF error message. To access this field, declare it as an import value, as follows:
D CPFMSGID S 7A Import( '_EXCP_MSGID' )
Now, the field CPFMSGID contains the CPF message ID (if any) that is produced when an error is generated by the command processed by the system() function.
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.
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