CGAL users discussion list

[Benoît Presles <>]

Le 5 oct. 10 à 22:53, Laurent Rineau (GeometryFactory) a écrit :

> Le mardi 05 octobre 2010 22:42:07, Benoît Presles a écrit :
> > Le 5 oct. 10 à 15:14, Laurent Rineau (GeometryFactory) a écrit :
> > > On Tuesday 05 October 2010 14:59:23 Benoît Presles wrote:
> > > > Hello everybody,
> > > >
> > > > I am looking for a nice way to copy my data: double* X, double* Y
> > > > to a
> > > > list of Point_2.
> > > > Here is my code:
> > > > //My data (example)
> > > > double X[]={1,2,3,5,6};
> > > > double Y[]={-10,7,5,9,5};
> > > > //My output:
> > > > std::list<Point_2> points;
> > > > //for loop
> > > > for(int i=0; i<5; ++i)
> > > > {
> > > >
> > > >         //std::cout << X[i] << " " << Y[i] << std::endl;
> > > >         points.push_back(Point_2(X[i], Y[i]));
> > > >
> > > > }
> > > >
> > > > As one can notice, I do a "for loop" to copy my data. It works but
> > > > I am
> > > > looking for a better way. Indeed, when my array X (or Y) is very  
> > > > big,
> > > > the code is a bit slow.
> > >
> > > You should use std::vector instead of std::list, and reserve the
> > >
> > > memory:
> > > points.reserve(n);
> > >
> > > where n is the size of your arrays.
> >
> > I am going to try but in fact I was wondering if there is a way to do
> > it without "for loop".
> > Maybe with the "std::copy" function ?
>
> You can use boost::zip_iterator to transform X and Y to an iterator  
> whose
> value type is a boost::tuple<double, double>, and then use a transform
> iterator to transform that iterator to an iterator whose value type is
> Point_2. Then you could use std::copy.
>
> But... well, in your case a "for loop" is the most efficient way, as  
> soon as
> you allocate the memory before the loop.

Ok, so I am going to do the "for loop" with allocated memory.

Thank you very much for your replies,
Best Regards,
Benoît