RE: Opinions Wanted: List API loop logic

Hi Joe,

> Unless I miss my guess, with a MODS or an array of structures, I have to
> predefine the number of entries.  I use the technique shown whenever the
> size of the structure is known but the number of entries is not; it
> allows me to avoid having to specify the maximum number of entries the
> API can handle.

Unless I'm missing something, you had a predefined maximum number of
entries in your code sample.  You called it "MAX" and told me to set it to
a suitably high number.

Here's the code you posted:

> d Entry         e ds                  extname(myEntry)
> d                                     based(p_Entry)
> d Entries         s                   like(Entry) dim(MAX)
> d                                     based(p_Entries)

> c                   eval      pEntries = p_ListHeader + DataOff
> c                   for       EntryNo = 1 to NumEntries
> c                   eval      pEntry = %addr(Entries(EntryNo))
>    (process entry)
> c                   endfor
>
> Set MAX to some reasonable maximum value, and voila, you should have no
> problems.  (Famous last words!)


My response was, why not just replace the array that you called "Entries"
with an array of data structures (or a MODS if you're on V5R1 or earlier)

For example:

 d Entries       e ds                  extname(myEntry)
 d                                     based(pEntries)
 d                                     occurs(MAX)

 c                   eval      pEntries = p_ListHeader + DataOff
 c                   for       EntryNo = 1 to NumEntries
 c                   eval      %occur(Entries) = EntryNo
    (process entry)
 c                   endfor

It has the same limitation as your code... the MAX variable.


> I can write the called procedure to handle any arbitrary number of
> entries, but the actual number allocated depends on the calling
> application.  It's a personal preference based on being bitten one too
> many times by fixed array sizes, while at the same time not wanting to
> create arrays with an arbitrarily large size.

For that, you should eliminate arrays altogether (including the "Entries"
array from your sample code) and do it purely with pointer logic, like I
did in the original code samples I posted when I started this thread.

> Well, I did say pretty specifically that the entries need to be a
> predefined size based on an external data structure.  I couldn't tell
> from your example whether EntrySize was a variable or a constant.

Yeah, sorry... I should've been more explicit.  I figured saying "List
APIs" was enough that you'd know that the entry size needs to be
soft-coded.  I should've explained it better.


> If it were based on a data structure, it would be a pretty simple
> recompile for each release.  But if you don't like that, well, do simple
> pointer arithmetic: pointer = header + offset + (entry-1) * size.

That logic was one of the samples that I posted.


> Or, if your size changes every time, then do this:
>
>    EntrySize = 0;
>    Pointer = header + offset;
>    For x = 1 to numEntries
>      Pointer = Pointer + EntrySize;
>      (...)
>      EntrySize = SizeOfCurrentEntry;
>    Endfor
>
> There are several ways to do it without the nested if logic.  Like I
> said, I just showed my little array magic as an example.

That's an interesting way to do it...  set the entry size to 0 the first
time through, then set it to the real value at the end of the loop.
That's another good suggestion.

Thanks!