Re: Ada compiler differences

[Mark H Johnson <mark_h_johnson@raytheon.com>]

Magnus wrote:
> Hello,
> 
> Could someone please point me to a list of things that may be
> implementation dependent in different ADA compilers and/or on
> different platforms?
> 
I would start with chapter 13 of the Ada Reference Manual. Simple things 
like Integer'Size (e.g., 32) might not equal Natural'Size (e.g., 31) can 
trip you up in a variety of different ways. I also had problems with 
some code assuming 'Size of the object was the same as 'Size of the 
corresponding type.

I would also suggest a review of the Annotated ARM as well. The 
annotations are quite enlightening when trying to determine the possible 
implementation details of the language.

> I know that things like 'access and structures without repspec may
> differ. But what else?
> 
See above.

> Or rather: how can I write code that really is platform (and compiler)
> independent in Ada?
> 
To do that fully would require an extensive list of issues and is often 
constrained by the types of platforms you expect to run on. For a simple 
example, network order (for TCP/IP) is "big endian". If you are on a 
little endian machine, several values need to go through htonl, htons, 
and similar functions to be converted. If you "know" you will always on 
a big endian machine (same as network order), you might get away without 
them, but that isn't portable.

That particular issue has nothing to do with Ada; you have the same 
problem with C or other languages.

   --Mark