Re: [Boost-users] Multi_array: A "proper" iterator over a N>1 Multi_array?

From: Greg Link (link_at_[hidden])
Date: 2006-04-25 22:11:26

I would agree with you there - a 'foreach' would do what I need as  
well, but as I'm not 100% familiar with the way libraries such as  
boost are implemented, I worry that making your own control structure  
is much more difficult than making an accessor/modifier pair. I can't  
even imagine the syntax needed to convert the following into a  
theoretical boost-defined 'foreach'

double previous =  0;
double accumulator = 0;
for(iterator_t myIterator = m_array.data(); myIterator != m_array.end 
(); myIterator++)
{
        accumulator += (*myIterator);
        (*myIterator) *= previous
        accumulator = (previous > 7) ? (do_function(accumulator)) : (0);
}

Sure, it's a contrived example, but I just don't know how a primarily  
header library such as boost (or any library for that matter) would  
be able to define a

foreach(m_array) {

}

in a syntactically and compiler-friendly manner.  That doesn't mean,  
however, that I'm still not interested in the possibility of  
using .data() and iterating, I'm just concerned that if the data in  
the container isn't sequential, I'm violating some law. I know (from  
testing) that making an iterator

myIterator = m_array.begin();

and incrementing it only goes as high as the size of the highest  
dimension before it hits m_array.end(), so I'm concerned that doing

myIterator = m_array.data();

will end at the same point (or just walk off into nowheresville).  
Don't have my test code in front of me until tomorrow, where I'll  
test for sure.

  - Greg

On Apr 25, 2006, at 9:02 PM, Bruno Martínez wrote:

> On Tue, 25 Apr 2006 20:15:37 -0300, Antonio Piccolboni
> <piccolbo_at_[hidden]> wrote:
>
>> I guess what you want is origin(). Iterate from origin() to
>> origin+num_elements
>
> I think you meant data().  I also think that does not work if you  
> have a
> multiarray that is a subset of another, because the elements are not
> contiguous.
>
> I also would like to iterate easily over all elements of a multiarray.
> Maybe a foreach-like function is easier to write than a general  
> iterator.
>
> Bruno
>
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