[GiNaC-list] Use of STL iterators in GiNaC

Gabriel Dos Reis gdr at integrable-solutions.net
Thu Apr 16 16:32:18 CEST 2009

On Thu, Apr 16, 2009 at 8:43 AM, Michael Goffioul
<michael.goffioul at gmail.com> wrote:
> On Thu, Apr 16, 2009 at 2:04 PM, Jens Vollinga <jensv at nikhef.nl> wrote:
>>> I'm no C++ standard expert, but when I look at
>>> http://www.sgi.com/tech/stl/RandomAccessIterator.html
>>> my understanding of the precondition for "i += n" is that you cannot
>>> go after end().
>> It seems that the standard (I only have the draft. Hopefully there is no
>> difference to the final version in the areas under consideration) and the
>> SGI documentation deviate from each other. In SGI there are pre- and
>> postconditions on +, -, +=, and -=. And these conditions are violated in the
>> examples as you point out. But in the standard +, -, +=, -= have NO
>> pre-/postconditions to them! See 24.1.5. The confusing part is, that -- and
>> ++ DO have such conditions. But for the ++ operation, it is explicitly
>> allowed to go past-the-end. See 24.1.4. So no problem for the code in
>> factor.cpp. The code in utils.h seems to be against the standard, though,
>> but I am no language lawyer and so I am maybe misinterpreting the conditions
>> there. In case, this can be fixed by using reverse iterators.
> OK, I had a look in a draft C++ standard document I could find on the
> web, and when reading 24.1.3, the "pre" condition for ++r is that r must
> be dereferenceable. When r == end(), it is not dereferenceable, so you
> cannot do ++r. Don't you have the same interpretation?


-- Gaby

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