Re: QWCCVTDT Weirdness, solved! -- RPG400-L

I am still interested on any thoughts about how the pointer based on a
pointer thing works (because it does), and if there is a better way.

Oh, now that I've looked it over again and read Tom's reply, I can tellyou exactly how it works.


Basically what you were doing is equivalent to doing this:

     D                 ds
     D   InVar                 1     16*
     D   DTSField              1     17A

I don't know what the name of the field containing the DTS timestamp was(since you didn't post it) so I made one up. But hopefully you understandwhat I'm saying. They occupied the same spot in memory.

Granted, you used pointer logic rather than a data structure, but it hadthe exact same effect.

It didn't matter which one you passed to the API, since they contained thesame value. As long as you made sure DTSField was set to a valid DTStimestamp (and therefore made InVar an illegal pointer value) the codewould work.


It makes no sense to do that -- but that's what you did.

For example, if you wanted to dump all the messages in a data queue intoa user space with the QMHRDQM API, and the API expects a characterargument for the output variable, how would you do it?

Well, the method you're using wouldn't help with that. But you could doit this way if you wanted to:


     D mySpace         s               *
     D InVarPtr        s               *
     D InVar           s           1024A   based(InVarPtr)
     D x               s             10I 0

      ** Ask the OS for 1mb of memory:
     C                   eval      mySpace = %alloc(1024 * %Size(InVar))

      ** set the entire space to blanks:
     c                   for       x = 0 to 1023
     c                   eval      InVarPtr = mySpace + (x * %size(InVar))
     C                   eval      InVar = *blanks
     c                   endfor
      .
      .
      ** when you're done, let the OS have it's memory back
     C                   dealloc                 mySpace

Basically, InVar views 1k of memory at a time. So in the above example,I've reserved 1 mb of memory to the MySpace pointer. And then I'vechanged InVarPtr to tell it to view different sections of that 1mb ofmemory. (In this example, I used that functionality to blank it out.)


To pass the contents of the 1mb space to the API you'd do this:

      ** Ask the OS for 1mb of memory:
     C                   eval      InVarPtr = mySpace
     C                   CALL      'SOMEAPI'
     C                   PARM                    inVar

Since the current address of InVar is the same as the address stored inmySpace, it'd be the memory that's allocated to mySpace that'd be used bythe API.

I needed a lot more than 32767 characters for a large data queue.

In this case, I've used the %alloc() BIF, which is capable of allocatingup to (approx) 16mb. That's a lot more than 32k!

You could also use QUSCRTUS and QUSPTRUS to create and get a pointer to auser space instead of allocating RAM with the %alloc() BIF. It'd requiremore code, but you'd end up with the same results (more or less).

I don't know if the data queue APIs support it, but if 16mb wasn't enough,you COULD allocate the memory in teraspace. If you did that, you'd beable to allocate as much as 1 terabyte to MySpace. So... that should beenough, eh?

By basing a pointer variable on a pointer that is the address to theuser space, and then passing that based pointer to the QMHRDQM API itworks nicely, but I've sometimes wondered if there is a better way.

It makes no sense to base a pointer on a pointer for what you're trying todo. Base a character field or data struture, or whatever you need to workwith on the pointer. Not another pointer!


Anyway, I'm glad you figured it out.