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[Sebastien Loriot <>]

If you use std::cout << std::setprecision(17) << p << " " << q << " " << 
r << "\n"; in both cases you will see that the input are different.

you will have:
0 0.29999999999999999 1 0.59999999999999998 2 0.90000000000000002
not collinear
0 0.30000000000000004 1 0.60000000000000009 2 0.89999999999999991
collinear

So the input are different, nothing specific to CGAL.

Best,

Sebastien.


On 3/12/21 1:45 PM, Aomandeyi ( via cgal-discuss 
Mailing List) wrote:
> I still couldn't understand the official explanations,the two sets of data is
> exactly the  same ,
>   why the results is different? can someone talk about his own understanding?
> the codes as follow
> -------------------------------------------------------
>
> --------------------------------------------------------------------------------
>
> #include <iostream>
> #include <CGAL/Exact_predicates_exact_constructions_kernel.h>
> #include <sstream>
> typedef CGAL::Exact_predicates_exact_constructions_kernel Kernel;
> typedef Kernel::Point_2 Point_2;
> int main()
> {
>         Point_2 p(0, 0.3), q(1, 0.6), r(2, 0.9);
>         {
>                 std::cout << (CGAL::collinear(p, q, r) ? "collinear\n" : "not
> collinear\n");
>         }
>         
>   {
>                 std::istringstream input("0 0.3   1 0.6   2 0.9");
>                 input >> p >> q >> r;
>                 std::cout << (CGAL::collinear(p, q, r) ? "collinear\n" : "not
> collinear\n");
>         }
>         
>         return 0;
> }
> -------------------------------------------------------------------
>
>
>
> --
> Sent from: http://cgal-discuss.949826.n4.nabble.com/