Re: [Boost-users] Iterator Range, sub range of a desired size

31 Oct 2012

      On 10/30/2012 12:50 PM, David Kimmel wrote:
...
I tried it out, yes you can get make_iterator_range with next to work.
  I like boost::next but for what I wanted it does not seem to work
appropriately.  Your example of
"make_iterator_range(boost::next(b.begin, wSize), v.end())" will only
skip the first "wSize" elements.  What I want is a range that contains
at most wSize elements (if possible) - taking them from after (and
containing) a start index.
Even my second attempt with this approach (commented out lines) does not
work because next does not check to see if it is past end.  Perhaps if
there is a "min" method I could pass the "boost::next(v.begin() +
(start-1), window)" and "v.end()".
typedef vector<int> Vector;
Vector v = { 1, 2, 3, 4, 5, 6, 7, 8 , 9, 10, 11 };
cout << "--" << endl;
for(auto i : v) { cout << i << " "; }
cout << "\n--\n" << endl;
const int start = 10;
const int window = 4;
auto r = boost::make_iterator_range(boost::next(v.begin(), start-1),
v.end());
auto r2 = boost::make_iterator_range(boost::prior(r.end(), window),
r.end());
//auto r = boost::make_iterator_range(v.begin() + (start-1),
boost::next(v.begin() + (start-1), window) );
//auto r2 = boost::make_iterator_range(boost::prior(r.end(), window),
r.end());
cout << "\n--\nr: ";
for(auto i : r) { cout << i << " "; }
cout << "\n--\nr2: ";
for(auto i : r2) { cout << i << " "; }
cout << "\n--\n" << endl;
Our application has lots of this type of index/range manipulation. So 
much in fact it was worth factoring out a open/closed integer range 
interval class(similar to boost ICL's):

class Interval
{
public:

static Interval makeInclusive(int first, int last);
static Interval makeExclusive(int begin, int  end);

static Interval makeInclusiveNormalized(int val1, int val2);
static Interval makeExclusiveNormalized(int val1, int val2);

static Interval makeSized(int begin, int size);

template<class CONTAINER>
static Interval makeSized(const CONTAINER& c)
{ return makeSized(0, c.size()); }

int indexBegin() const { return m_begin; }
int indexEnd  () const { return   m_end; }

bool       empty() const { return m_end == m_begin; }
std::size_t size() const { return m_end -  m_begin; }

...
};

Interval intersection(const Interval& lhs, const Interval& rhs);
...

This separates the index math from the final range traversal while 
providing higher level expression of the intent. Then we can construct a 
boost::adaptors::sliced using:

inline boost::adaptors::sliced slicedFrom(const Interval& i)
  { return boost::adaptors::sliced(i.indexBegin(), i.indexEnd()); }

and use it:

int main()
{
std::vector<float> v(42);

Interval vi = Interval::makeSized(v);
Interval  i = Interval::makeExclusive(37, 93);

boost::fill(v | slicedFrom(intersection(vi, i)), 123.456f);

return 0;
}

Jeff

Re: [Boost-users] Iterator Range, sub range of a desired size

Jeff Flinn