CGAL users discussion list

[Alessandro Attanasi <>]

Ok, but why that procedure was working using all convex_hull functions?

I started from the cgal example

http://doc.cgal.org/latest/Convex_hull_2/Convex_hull_2_2array_convex_hull_2_8cpp-example.html

I freed the malloc at the end :)

On 15 January 2014 23:31, Philipp Moeller <> wrote:

Alessandro Attanasi <> writes:

> Sorry, really stupid error :P. It works as expected!
>
> Just last question about this problem: if I want to use C pointers instead
> of stl iterators, why this code is wrong? It gives to me zero points on the
> lower hull (I tried to use the same logic of the example for convex hull
> computation)
>
> K::Point_2 *ptr2;
>
>   K::Point_2 *result2 = NULL;
>
>   result2 = (K::Point_2*)malloc(totPoints * sizeof(K::Point_2));
>
>   ptr2 = CGAL::lower_hull_points_2( points, points+totPoints, result2 );

Why would you ever call malloc instead of new in such a situation? It is
exactly where your problem comes from. You cannot simply use raw
uninitialized memory as an OutputIterator. You should wrap the pointer
into a raw_storage_iterator provided by the standard header memory. [1]

You also need to take special care when releasing the memory (call the
destructor explicitly).

>
>
>   ch_points = (ptr2 - result2);
>
>   std::cout << "6) Points on the lower hull = " << ch_points << std::endl;
>
>   for(int i =0;i<ch_points;i++)
>
>   {
>
>     std::cout << result2[i] << std::endl;
>
>   }

Footnotes:
[1]  http://en.cppreference.com/w/cpp/memory/raw_storage_iterator

--

http://giovanninoperdigiorno.blogspot.it/

http://giovanninocartoons.blogspot.it/

https://gist.github.com/alecsphys