Re: Advancing Through std::vector

From:
"Fred Zwarts \(KVI\)" <F.Zwarts@KVI.nl>
Newsgroups:
comp.lang.c++
Date:
Thu, 12 Sep 2013 11:07:09 +0200
Message-ID:
<l0s07t$da8$1@news.albasani.net>
"Jorgen Grahn" wrote in message
news:slrnl31m36.2m9.grahn+nntp@frailea.sa.invalid...

On Wed, 2013-09-11, Mike Copeland wrote:

   I have a std::vector of some size (I know I can get the size with =

the

.size() function, but that doesn't help my question here). I have =

logic

which processes "chunks" of this data, 20 at a time. Let's say that =

I

have 32 objects in the container, and my first "page" of data is =

1-20.

   The next "chunk" can't be 20, and I obviously have to protect =

against

trying to access object(s) that don't exist. Normal incrementing of =

the

iterator (e.g. advance) or direct indexing don't seem to offer ways =

to

avoid accessing beyond the data set. That is, I can't find any STL
functions that give me ways to avoid problems here.
   Yes, I could do some convoluted math that works with .size(), but =

if

I'm using an iterator and advance, the work seems messy and ugly. =

8<{{

   So I asking here if there is some way to use/convert the iterator
position and apply it to see if it's "gone beyond" the container's =

data

set. Perhaps there's a function that returns an indicator, or maybe
someone who's dealt with this problems has a good solution. TIA


No worries. I'd just do something like this:

   vector<Foo> v;
   vector<Foo>::iterator a = v.begin();

   while(a!=v.end()) {
       vector<Foo>::iterator b = v.size()>20 ? a+20 : v.end();


Shouldn't that be something like
            vector<Foo>::iterator b = v.end()-a >20 ? a+20 : v.end();

       process(a, b);
       a = b;
   }

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