在C ++中使用Comparator和构造函数上的参数的自定义类的优先级队列

Question

I want to create a priority_queue of the class Edge in C++.

For that, I created the edgeCompare comparator class as follows:

class edgeCompare{
public:
    map<int, glm::mat4x4> * Qmap;

    edgeCompare(const map<int, glm::mat4x4> & Qm){
        * Qmap = Qm;
    }

    bool operator() (const Edge & e1, const Edge & e2) const{
        // code that compares and returns corresponding bool
        // OBS: in this function I use *Qmap
    }
}

The thing is, as you can see, that I need an external variable to do the comparison.

A priority_queue is usually declared as:

priority_queue<Edge, vector<Edge>, edgeCompare> pq;

But in my case, I need to construct the edgeComparator with my variable Qmap .

How should I proceed?

Thanks a lot!

Answer 1

The template parameter is the type of the comparator. You still need to pass an instance of the comparator to the priority_queue constructor, and that is when you can construct the comparator instance with whatever parameters you like.

For instance:

map<int, glm::mat4x4> m;
edgeCompare comp(m);
priority_queue<Edge, vector<Edge>, edgeCompare> pq(comp);

You can also create the edgeCompare object inline but extra parentheses are needed for disambiguation:

priority_queue<Edge, vector<Edge>, edgeCompare> pq((edgeCompare(m)));

Answer 2

Overload operator== , operator!= , operator> and operator< in the Edge class so that you can just compare them e1 == e2 in your comparator.

Also don't derive from std::map . It does not have a virtual destructor, which makes it a bad idea to derive from it.

Just have your map as a private member to your class.

Answer 3

根据此链接 ，有一个重载允许您在priority_queue的构造函数中传入谓词。