Re: Why you shouldn't be afraid to use VARCHAR in RPGLE

On 2025-12-10 12:25 p.m., James H. H. Lampert via RPG400-L wrote:
> On 12/10/25 4:06 AM, Infodorado InfoDorado via RPG400-L wrote:
>> The RPG compiler is a single-pass compiler
> 
> No, it can't be pure single-pass. If it were, then a program in which a 
> variable is NOT defined in a D-spec, nor in the first C-spec in which it 
> appears, would not compile, much less run. And it's trivially simple to 
> construct an example of this (it took me about 2 minutes), and it 
> compiles and runs just fine. I'd quote the source here, but it would 
> likely be mangled beyond recognition.
> 

It's a single pass through the source but it gathers information that it 
can use multiple times.

The compiler usually allows forward-referencing, so you can code LIKE(x) 
where x is defined later.

But for free-form definitions, the compiler requires the parameter for 
the data-type keywords to be defined before the keyword is seen.

    dcl-s x char(con1);  // bad, con1 not defined yet
    dcl-c con1 5;
    dcl-s y char(con1);  // ok, con1 is defined

Where it becomes extra fun is when you have a data structure that LOOKS 
defined.

    dcl-ds ds1;
       subf char(10);
    end-ds;
    dcl-s x char(%size(ds1));  // %size(ds1) is not defined. WHAT???

RPG allows you to define the length of a data structure later, either 
due to being on an I spec, possible an externally-described I spec, or 
on a C spec.

      C            MOVE    *blanks       ds1        50

Almost certainly wrong columns, but you get what I mean. I'm defining 
DS1 to have a length of 50 here, not the length of 10 that it looked 
like it should have. Shenanigans? Yep, but upward-compatible R Us.

We have a H-spec/CTL-OPT keyword for that: DLCOPT(*NOCHGDSLEN). With 
that keyword, the compiler doesn't allow you to change the length of the 
data structure like that, so it's considered defined as soon as all the 
subfields are defined.

-- 
Barbara

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