On indicators

RPG has, since the beginning of time, supported a set of indicators — one byte characters that can be either *on or *off. These are popular but really shouldn’t be used any more. Being named *IN01 to *IN99 makes for indicators whose function is unclear and you are much better off using built in functions and explicitly defined fields.

There is an exception, of course. When dealing with display files, you have no choice but to use indicators to determine what keys have been pressed. Even here, though, it is a good idea to overlay the indicators with human readable field names.

This is how I do it:

 * Global variables
d IndicatorPtr    s               *   inz(%addr(*in))
d                 ds                  based(IndicatorPtr)
d iExit                   3      3
d iRefresh                5      5
d iAdd                    6      6
d iCancel                12     12
d iValidCmdKey           25     25
d iError                 30     30
d iPageDown              26     26
d iSflInit               80     80
d iSflEnd                81     81
d iSflEmpty              82     82
d iSflPosCursor          83     83
d iSflDeleted            84     84
d iProtectKey            90     90
d iProtectData           91     91

So *IN03 is mapped to field iExit, *IN05 is mapped to field iRefresh, and so on.

With the indicators defined in this way, I can write code like this:

p Main            b
d Main            pi
 /free

     // Identify the current program
     program = RtvProgram();

     // Main processing loop
     dou iExit = *on;
         WorkWithMessageDescriptions();
     enddo;

     return;

 /end-free
p Main            e

Note also that this Main procedure is not setting on the *LR indicator. This is because, in the header spec, I have a named main procedure:

h main(Main)

Using this tells the compiler that I am not using the RPG logic cycle and that processing should start with procedure Main. Not only does this allow me to abandon setting on *LR but also reduces a lot of the progeram’s overhead.