C++ Comparator Not Working

Question

I'm trying to sort a set of OpenSG points by their x coord within a set, but it doesn't seem to be working.

My comparator:

struct less_than_x {
    inline bool operator() (const OSG::Pnt3f& p1, const OSG::Pnt3f& p2) {
        return (p1.x() < p2.x());
    }
};

My code:

std::set<OSG::Pnt3f, less_than_x> positions3D; 

OSG::GeoPnt3fPropertyRefPtr pos = OSG::GeoPnt3fProperty::create();

pos->addValue(OSG::Pnt3f(1,2,3));
pos->addValue(OSG::Pnt3f(5,2,1));
pos->addValue(OSG::Pnt3f(4,4,2));
pos->addValue(OSG::Pnt3f(6,4,0));
pos->addValue(OSG::Pnt3f(3,5,1));

// Remove the Z Axis from all of the points
for(OSG::UInt32 i = 0; i < pos->size(); i++)    {        
    OSG::Pnt3f p;              
    pos->getValue(p,i);
    OSG::Pnt3f p2 = OSG::Pnt3f(p.x(), p.y(), 0);
    positions3D.insert(p2);
}

for (std::set<OSG::Pnt3f>::iterator it = positions3D.begin(); it != positions3D.end(); it++) {
    std::cout << *it << std::endl;
}

When printing out the set of points, they are still not in order.

Any help would be greatly appreciated.

Edit:

vershov answer seems to work somwhat for me, but when changing it to double and using this set of points it fails.

positions3D.insert(Pnt3f(-1, 0, 0));
positions3D.insert(Pnt3f(-0.850651, -0.309017, 0));
positions3D.insert(Pnt3f(-0.850651, 0, 0));
positions3D.insert(Pnt3f(-0.525731, 0, 0));
positions3D.insert(Pnt3f(-0.525731, 0.809017, 0));
positions3D.insert(Pnt3f(-0.525731, 0.5, 0));
positions3D.insert(Pnt3f(-0.447214, 0.525731, 0));
positions3D.insert(Pnt3f(-0.447214, 0.850651, 0));
positions3D.insert(Pnt3f(-0.447214, 0, 0));
positions3D.insert(Pnt3f(-1.05104e-007, 0.309017, 0));
positions3D.insert(Pnt3f(-7.00695e-008, 0.809017, 0));
positions3D.insert(Pnt3f(0, 1, 0));
positions3D.insert(Pnt3f(7.00695e-008, 0.809017, 0));
positions3D.insert(Pnt3f(1.05104e-007, -0.309017, 0));
positions3D.insert(Pnt3f(0.447214, 0, 0));
positions3D.insert(Pnt3f(0.447214, 0.850651, 0));
positions3D.insert(Pnt3f(0.447214, 0.525731, 0));
positions3D.insert(Pnt3f(0.525731, 0.5, 0));
positions3D.insert(Pnt3f(0.525731, 0.809017, 0));
positions3D.insert(Pnt3f(0.525731, 0, 0));
positions3D.insert(Pnt3f(0.850651, 0, 0));
positions3D.insert(Pnt3f(0.850651, 0.5, 0));
positions3D.insert(Pnt3f(1, 0, 0));

These are sorted in this order:

-1, 0, 0
-0.850651, -0.309017, 0
-0.850651, 0, 0
-0.525731, 0, 0
-0.525731, 0.809017, 0
-0.525731, 0.5, 0
-0.447214, 0.525731, 0
-0.447214, 0.850651, 0
-0.447214, 0, 0
-1.05104e-007, 0.309017, 0
-7.00695e-008, 0.809017, 0
0, 1, 0
7.00695e-008, 0.809017, 0
1.05104e-007, -0.309017, 0
0.447214, 0, 0
0.447214, 0.850651, 0
0.447214, 0.525731, 0
0.525731, 0.5, 0
0.525731, 0.809017, 0
0.525731, 0, 0
0.850651, 0, 0
0.850651, 0.5, 0
1, 0, 0

Have you tried printing out the elements before you insert them into the set? — juanchopanza, Jan 03 '14 at 13:06
[OT]: Note that with you comparator, if you have 2 entries with same `x`, the second one will be discarded as `std::set` will consider `{x, 2, 3}` and `{x, 42, 42}` equivalent. — Jarod42, Jan 03 '14 at 13:37

score 1 · Accepted Answer · answered Jan 03 '14 at 13:22

Please check the following code:

#include <set>
#include <iostream>

struct Pnt3f {
        Pnt3f(int x, int y, int z) : m_x(x), m_y(y), m_z(z) {}
        int x() const { return m_x; }
        int y() const { return m_y; }
        int z() const { return m_z; }
private:
        int m_x;
        int m_y;
        int m_z;
};

struct less_than_x {
    inline bool operator() (const Pnt3f& p1, const Pnt3f& p2) {
        return (p1.x() < p2.x());
    }
};

int main() {

        std::set<Pnt3f, less_than_x> positions3D;

        positions3D.insert(Pnt3f(1,2,0));
        positions3D.insert(Pnt3f(5,2,0));
        positions3D.insert(Pnt3f(4,4,0));
        positions3D.insert(Pnt3f(6,4,0));
        positions3D.insert(Pnt3f(3,5,0));

        for (std::set<Pnt3f>::iterator it = positions3D.begin(); it != positions3D.end(); ++it) {
                std::cout << "(" << it->x() << ", " << it->y() << ", " << it->z() << ")" << std::endl;
        }
        return 0;
}

The output is as following:

./a.out 
(1, 2, 0)
(3, 5, 0)
(4, 4, 0)
(5, 2, 0)
(6, 4, 0)

So, comparator works as expected and do sort. You need to print out values before line to understand what is going wrong.

positions3D.insert(p2);

Thanks for the response. That has fixed it for those test points, but once I try it with large doubles it starts to fail, for example I've changed the struct to use double rather than int and inserted these points (edited original question) — jmahony, Jan 03 '14 at 15:43
@jmahony: I don't see where the result order (with `double`) is incorrect. (I'm surprised that the 'duplicated' x are still present thought). — Jarod42, Jan 03 '14 at 23:34
Could you please provide with sample of "large doubles" that brakes the order? — vershov, Jan 04 '14 at 05:51

C++ Comparator Not Working

1 Answers1