Re: [boost] RFC: interest in Unicode codecs?

Subject: Re: [boost] RFC: interest in Unicode codecs?
From: Edward Grace (ej.grace_at_[hidden])
Date: 2009-07-20 13:50:14

>> These are assumptions that I would probably be
>> happy to accept in my own internal-use code, but you are right to say
>> that they are probably not appropriate for library code.  For library
>> code you would need to wrap the container with something that  
>> guarantees
>> this behaviour in a more solid way.  Out of interest, does anyone  
>> know
>> if a std::vector that has been reserve()d guarantees anything about
>> dereferencing beyond-the-end iterators?  It would be great if they  
>> were
>> allowed to be undefined yet certain not to segfault.
>
> Undefined behavior. Don't do it.
>

I'm having precisely this problem with a home brewed strided_iterator

Given a std::vector<int> 'a' containing

   [3,8,2,1,0,9,4,6,5,7]

I would like to sort the sub range defined by every second element  
starting at index 1.

Conceptually something like:

ejg::striding_iterator<std::vector<int>::iterator> begin(a.begin()+1,2);

std::sort(begin,begin+5);

so that I obtain

   [3,1,2,6,0,7,4,8,5,9]

While it works fine under g++, on MSVC it throws a segfault when  
applying the prefix ++ operator since it attempts to dereference the  
location one past one past the end.

Irritating beyond belief!  As far as I can see there's no way around  
this with bare iterators.   Any suggestions?

-ed

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