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I understand how you use alloc to get more space assigned to the
variable than the d-spec definition would normally allow. Since I prefer
the user space method, how would I set that up?

The only difference between the user space and alloc method is the way you allocate the space. Instead of calling %alloc() to get the space, you call QUSCRTUS and QUSPTRUS (and maybe QUSCUSAT, if you want it to auto-extend)


Let's say my user space pointer is USP_Ptr.
I'll need to define a variable based on that.
So,

D MyVar         ??????A  Based(USP_Ptr).

How big do I make the variable. I kept thinking that if I make it the
largest I could define on the D-spec (32767) that's all the API would
return for me.

The API doesn't know how big your variable is. It doesn't have any way to read your source code and check that. All it knows is

a) The spot in memory where it's stored (since that's what gets passed when you pass a parameter)

b) The length that you pass in the "length of receiver variable".

Or - is the 'length of receiver variable' (staying with the QMHRDQM API example) the key? Will the API use however much space I tell it to in that variable, regardless of the definition of MyVar.

Correct, it'll use as much space as you the "length of receiver variable". (Unless of course, it needs less space than that... but it'll never use more)


 Example.

D MyVar             1A   Based(USP_Ptr).
D MyVarLen         10I 0 Inz(1048544)                      *-or whatever
size I want-*

Then when the API is called, it will start putting data into MyVar but
continue as far as the MyVarLen lets it go? If this is the case, I can
run with that.

That's correct. (Assuming that you actually pass these as parameters to the API, rather than just declaring them on the D-spec)


I think that's a little obscure myself, but I'll agree that it's a little more clear than my weird pointer structure I'd forced to work before.

You have to accept the notion that the ONLY thing that gets passed when you pass a parameter is the memory address.

(And this isn't an attribute of APIs -- it's just how parameters work on the iSeries. It's the same notion that's used when you pass parameters from program or program or from the command line to a program.)

As long as you've accepted that fact, then it makes perfect sense why passing a parameter and a separate length for that parameter, will allow the API to deal with any size field.

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