CODEWITHSUNDEEP
c++qtqsort
user3879361
user3879361

Reputation: 1

Problems with qSort

I got a little problem with qSort. I just want to sort my list after adding a vertex to my QList m_acceptedVertices.

bool Vertex::greaterThan(Vertex * v1, Vertex *v2){

    return this->computeDistanceTo(v1) > this->computeDistanceTo(v2);
}

void Vertex::acceptVertex(Vertex* vert)
{

    m_acceptedVertices.append(vert);

    qSort(m_acceptedVertices.begin(), m_acceptedVertices.end(), greaterThan);

}

But I still getting these Errors:

Fehler: C3867: 'Vertex::greaterThan': function call missing argument list; use '&Vertex::greaterThan' to create a pointer to member

Fehler: C2780: 'void qSort(Container &)' : expects 1 arguments - 3 provided

Fehler: C2780: 'void qSort(RandomAccessIterator,RandomAccessIterator)' : expects 2 > arguments - 3 provided

What am I doing wrong? Can sombody help me? Thanks!

Upvotes: 0

Views: 445

Answers (2)

Marek R
Marek R

Reputation: 37607

If you are using C++11 then probably you need something like that:

void Vertex::acceptVertex(Vertex* vert)
{
    m_acceptedVertices.append(vert);

    qSort(hallo.begin(), hallo.end(), 
          [this](Vertex* v1, Vertex* v2) {
               return this->computeDistanceTo(v1) > this->computeDistanceTo(v2);
          });
}

If you use older C++ you have to define functor object which will store pointer reference Vertex, or use lambda expression from boost.

Upvotes: 2

quantdev
quantdev

Reputation: 23793

1) You have a design issue, your comparator is supposed to be a free function (or a functor) comparing 2 Vertex, your implementation should probably look something like :

bool greaterThan(Vertex * v1, Vertex *v2){

    return v1.computeDistanceTo(v2) > 0;
}

2) Use the standard library : std::sort (it is most likely to perform a quicksort internally in most cases, but if you really want to use qSort, it will work as well)

Minimal working example with a free function comparator :

class Vertex {
    public:
     int i;
};

bool greaterThan(Vertex * v1, Vertex *v2)
{
    return v1->i > v2->i;
}

int main()
{
    std::vector<Vertex*> v;
    v.push_back(new Vertex { 5 });
    v.push_back(new Vertex { 1 });
    v.push_back(new Vertex { 3 });
    v.push_back(new Vertex { 6 });
    v.push_back(new Vertex { 2 });

    std::sort(v.begin(), v.end(), &greaterThan);

    for(auto& ve : v)
       std::cout << ve->i << " ";
}

Note:

For simple comparison functions, lambdas are a good alternative:

std::sort(v.begin(), v.end(), [] (Vertex * v1, Vertex *v2) {return v1->i > v2->i;} );

Upvotes: 2

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