Re: [MI400] Space pointers

[Scott Klement <klemscot@xxxxxxxxxxxx>]

On Mon, 8 Apr 2002, John Taylor wrote:

> Group,
>
> I'm building a service program (in RPG) with the intent of simplying the use
> of dynamic heap storage. One of the first things I've come across is the
> need to determine the amount of storage already allocated to a basing
> pointer. Since there is nothing in RPG, or the C runtime, that provides this
> information, I'm hoping that MI may provide a solution.
>
> I would appreciate it someone could point me in the right direction. RTFM
> will work, but which manual? And is there a specific instruction that I
> should look for?

I don't know of a way to ask the system how much memory is allocated (I
imagine you could do it in MI, but I'm still learning MI)

However, if you're doing all the memory management yourself in a service
program, you could consider just allocating some extra memory for a
variable that contains the allocated size:

I mean, something like this:

     P my_alloc        B
     D my_alloc        PI              *
     D   space                       10I 0 value

     D p_memory        S               *
     D curr_size       S             10I 0 based(p_memory)

     c                   eval      space = space + 4
     c                   alloc(e)  space         p_memory

     c                   if        %error
     c                   return    *NULL
     c                   endif

     c                   eval      curr_size = space - 4
     c                   eval      p_data = p_memory + 4

     c                   return    p_data
     P                 E


So, p_data would be what the caller would actually use...
When the caller called my_dealloc, you'd take the pointer that got
passed in, subtract 4 from it, and that would be the area to dealloc.

If the caller called my_realloc, you'd do the same thing, subtract 4,
get the size from the integer stored there, and use that size when
realloc-ing the memory...

If you need to mix & match with callers that use the RPG alloc & dealloc
op-codes, though, you're going to have problems no matter what you do :)