Re: Variable length raw-byte data

[Robert Dewar <robert_dewar@my-deja.com>]

In article
<976563484.10868.0.nnrp-01.c1ed21d4@news.demon.co.uk>,
  "Julian Morrison" <julian.morrison@virgin.net> wrote:
> I'm trying to shim to a C library that returns some data as a
length in
> bytes and a pointer to the first byte. The length is not known
at compile
> time. Is there any way I can morph this into an array of mod
2**8? I'm
> using the latest Linux GNAT.



The important thing is to NEVER use pointers to unconstrained
arrays in such a case. this is asking for non-portable, peculiar
behavior.

A good type to use in this case is what we in GNAT-land call
big arrays:

   type byte is mod 2 ** 8;

   type memory is array (natural) of byte;
   type memptr is access memory;

Now it is almost certainly safe to use address_to_access
conversions to go between address and memptr.

Of course you have to be careful not to access the array
out of bounds, but that's going to be up to the calling
program anyway if the bounds don't come built in :-)


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