Re: [boost] Re: String Algo bug.

From: Pavol Droba (droba_at_[hidden])
Date: 2004-07-29 09:35:04

On Mon, Jul 19, 2004 at 11:50:57AM +0200, Stefan Slapeta wrote:
> Stefan Slapeta wrote:
> >David Abrahams wrote:
> >
> >>If STLPort is complaining about that, it's because what you're doing
> >>is illegal.  A default constructed standard container iterator is
> >>"singular", and no operations on it (including comparison) are legal
> >>other than assigning a non-singular iterator value into it.  Although
> >>a few specialized iterators in std:: work differently
> >>(e.g. istream_iterator), in general you have to make the same
> >>assumption for any other iterator.
> >
> 
> Very strange: the behaviour that the default constructor equals the 
> past-the-end value is used for the example but it's not even documented 
> for the find iterator!
> 
> See the example: http://tinyurl.com/4vzlm
> 
>     typedef find_iterator<string::iterator> string_find_iterator;
>     for(string_find_iterator It=
>             make_find_iterator(str1, first_finder("abc", is_iequal()));
>         It!=string_find_iterator();
>         ++It)
>     ...
> 
> 
> See the find iterator documentation: http://tinyurl.com/53j5x
> 
> >>
>     find_iterator();
>     Default constructor.
> 
>     Construct null iterator. All null iterators are equal.
> 
>     Postconditions: eof()==true
> <<
> 
> The example above implies that a find iterator which points to the last 
> element will become a 'null iterator' after incrementation. (However, I 
> didn't find this statement anywhere in the documentation)
> 
> Thus, fixing this bug would not only mean to provide a second function 
> like 'make_find_iterator_end(collection)' that returns a proper end 
> iterator but also to change the behaviour of iterators for 
> incrementation to the past-the-end value etc.!
> 
> I would really like to hear what Pavol says about that...
> 

As I said in the other post, you are right. There is no need for an extra
make_find_iterator_end(...) functions. Current logic is correct, unfortunately,
there was a bug in the equal function that caused the problems.
Singular iterators should realy not be compared.

In addtions, I owe to explicitly say in the documentation, that null iterator
acts as the end-of-iteration tag.

Best regards,

Pavol