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* Mike Wahler:
> But I believe the type is 'std:trdiff_t'

Typo, thanks.

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wrote:
> thanks for the replies, they were all helpful.
>
> I've a question about iterator behaviour. if I have
>
> difference_type res = iter1 - iter2
>
> the SGI website says that the precondition is that iter1 is "reachable
> from iter2 or vice-versa, or both".
> that includes past-the-end iterators too, doesn't it, for either iter1
> or iter2. I mean if there are 10 iterms in a vector and I have iter1
> and iter2 such that iter1 points to vector[3] and iter2 points to
> past-the-end , then iter2-iter1 is still valid, isn't it? it's going to
> return an iterator thats pointing to element[7] in the vector. yes?

This is clearly a mental block so I'll say it loud.

THE RETURN VALUE WHEN YOU SUBTRACT TWO ITERATORS IS AN

***INTEGER***

Got that? Once you have everything else will fall into place.

john

wrote:
> one other thing... I have the iterators setup and I can now perform
> things like;
>
> myIter i1 = wrapper.begin();
> myIter i2 = wrapper.end();
>
> std::swap(i1, i2 );
>
> I can also call std::sort(i1 , i2);
>
> the above swap works fine and when I output the container contents, its
> contents are correctly ordered.
>
> however if I try to do something like;;
>
> std::sort(i1, i2 -1 );
>
> the (borland) compiler complains that;
>
> [C++ Error] iterator.cpp(285): E2285 Could not find a match for
> 'swap<_Tp,_Alloc>(myIter,myIter)'

Can't see what the problem is there, how about posting line 285 from
iterator.cpp

>
> I have defined operator- as
>
> // difference
> int operator-(const contIter& rhs) const
> {
> return abs(m_index - rhs.m_index);
> }

Are you sure that's right? Surely should be

int operator-(const contIter& rhs) const
{
return m_index - rhs.m_index;
}

Your code will always return a positive value, what if rhs is further
advanced than *this?

>
> contIter operator-(int i) const
> {
> return contIter(m_container, m_index-i);
> }
>
>
>
>
> I\m obviously missing something but can't see what. any ideas?
>
>
> thanks much again
>
> GrahamO
>

john

thanks Clarke/John,

I've cleared up the operator- business now (combination of typos and
errors on my behalf), thanks for your help.

I have painted "THE RETURN VALUE WHEN YOU SUBTRACT TWO ITERATORS IS AN
***INTEGER*** " onto the ceiling of my bedroom wall .. well not quite
but I've commited it to memory at least

Likewise the abs problem is corrected.

Everything is working nicely now, I can std::swap, std::sort, etc.
using my custom iterators.

thanks for the replies. G