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From: Tanmoy Bhattacharya <tanmoy@qcd.lanl.gov>
Subject: Re: Ada to C/C++ translator needed
Date: 1996/10/07
Message-ID: <y8afty6cgh.fsf@qcd.lanl.gov>#1/1
X-Deja-AN: 187332181
references: <32499FA0.4B5E@magic.fr> <52feul$os2@goanna.cs.rmit.edu.au>
organization: Los Alamos National Laboratory
newsgroups: comp.lang.c,comp.lang.ada
Date: 1996-10-07T00:00:00+00:00
List-Id: <comp.lang.ada>


fred@genesis.demon.co.uk (Lawrence Kirby) writes:

> 
> In article <y8rancyr0n.fsf@qcd.lanl.gov>
>            tanmoy@qcd.lanl.gov "Tanmoy Bhattacharya" writes:
> 
> >Not quite. It is still not allowed to violate constraints (This came
> >up in the discussion about `char a[1?1:(0,0)]' or some such
> >meaningless example in comp.std.c). j++ in a constant expression is a
> >violation of a constraint and must be diagnosed. 
> 
> I'm sure you're right but which constraint does it violate?
> 

6.4 Constraint: 

"Constant expressions shall not contain assignment, increment,
 decrement, function-call, or comma operators, except when they are
 contained within the operand of a sizeof operator.

 Each constant expression shall evaluate to a constant that is in the
 range of representable values of its type."

Note that it does not forbid use of contents of objects (that is in
the semantics section), but it does forbid operators that change the
values of objects, operators that invoke separate body of code, and
the comma operator. Incidentally, assignment operators include
(6.3.16) both the simple assignment operator =, and also the compound
forms like += etc.; and hence all of these are forbidden.

The semantics section forbids a lot more (e.g. using floating point
arithmetic if the final answer is integral, using pointers except
within sizeof if the final answer is arithmetic, accessing the value
of an object etc.)

Cheers
Tanmoy
-- 
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