CLP

CLP is an acronym for Control Language Program.

Much of what we find in CLP programs are IBM Commands. [1] Also see CLP Coding Rules and CLP Commands.

As with many other languages, there are multiple versions in popular usage, such as CLP/400 and ILE-CLP.

In some realities, this is comparable to software that is the "glue" connecting higher level language programs like RPG; data base files and their over-rides; screen and print "files" and their over-rides; and other objects with Menus ... typically when we take a menu option, we are launching a CLP program.

CLP Unique Commands

Some 400 commands can ONLY be executed from within a CLP program, not from Command Line. In other programming languages, these might be called OP CODES.

• PGM (Program)
• ENDPGM
• DCL (Declare Variable)
• IF
• ELSE
• DO
• ENDDO
• GOTO
• MONMSG

Pointer use

As of V5R4, CL allows the use of pointers. There were some problems with uninitialised pointers, and PTFs were issued. As of 15 Feb 2008, 5722-SS1:

• SI28620
• SI28196
• SI27953

These are immediate PTFs, but you will need to re-compile any CL programs using pointers in order to get the issues fixed.

One can't compare a pointer to *NULL, but a clever idea is to create an unused pointer (which will be set to *NULL if the above PTFs are applied) and compare to that. Here is a snippet from Tom L. for a CL program that performs getenv from a thread on RPG400-L.

dcl &pNull *ptr  /* Auto-initialized to *null */
if ( &pEnvVar *eq &pNull )  do