Re: Moving data into dynamic storage

[Hans Boldt <boldt@xxxxxxxxxx>]

Rich Duzenbury wrote:
> Hello,
>
> I've ALLOC'd some variable amount of storage, and now I want to move some
> data into it.  I currently use the following idiom to base a character
> variable onto a pointer:
>
> D pentry          s               *
> D entry           s            100    based(pentry)
>
> Now, I can MOVEL some data into entry (up to 100 bytes), and it goes where
> the pointer is pointing to quite nicely.
>
> My problem is that since the amount of storage is variable, I don't want to
> have to declare a fixed length for the 'entry' variable.
>
> How can I copy data into the contents of pentry while avoiding a fixed
> length restriction?
Clearly, MOVEL is inappropriate since you don't often really know
how much storage is actually allocated.

First, as someone else mentioned, declare your based variable with
some large length, such as 65535. Since no static storage is
allocated, the length doesn't really matter. Then, *only* work with
the data using %SUBST. If the length is maintained in variable
ENTRY_LEN, then use the based variable as %SUBST(ENTRY:1:ENTRY_LEN).
This works on both left-hand side and right-hand side of an EVAL
statement.

Of course, you're still limited to a maximum of 65535 characters. If
you want to work with more data than that, then you need to manage
the bits and bytes yourself at an even lower level.

On the other hand, I'd recommend keeping things simple and just use
a normal statically allocated, varying length character variable,
even if it takes up a lot of storage. It's a lot easier than having
to mess around with pointers and the extra complexity of remembering
the actual allocated size. I'm sure you can handle these issues
fine, but what about the next programmer who has to maintain this
code? You just have to forget the %SUBST once to get into
potentially very tricky debugging problems.

Cheers!  Hans