priority queue clear method
The priority_queue interface doesn't have a clear() method (for no good reason I've ever been able to discern). A simple way to clear it is just to assign a new, empty queue:
priority_queue <int> q;
// use it
q = priority_queue <int>(); // reset it
priority_queue
doesn't have a clear method. It may be that this is for interface simplicity, or because it there may be situations in which elements must be destroyed in priority-order, making a generic clear function unsafe.
Regardless, the following code block includes two functions to clear priority queues. The first works by building a temporary instance of a wrapper class around the priority_queue and then using this to access the underlying storage object, which is assumed to have a clear()
method. The second works by replacing the existing priority_queue with a new queue.
I use templating so that the functions can be recycled time and again.
#include <queue>
#include <iostream>
using namespace std;
template <class T, class S, class C>
void clearpq(priority_queue<T, S, C>& q) {
struct HackedQueue : private priority_queue<T, S, C> {
static S& Container(priority_queue<T, S, C>& q) {
return q.*&HackedQueue::c;
}
};
HackedQueue::Container(q).clear();
}
template <class T, class S, class C>
void clearpq2(priority_queue<T, S, C>& q){
q=priority_queue<T, S, C>();
}
int main(){
priority_queue<int> testq, testq2;
//Load priority queue
for(int i=0;i<10;++i)
testq.push(i);
testq2=testq;
//Establish it is working
cout<<testq.top()<<endl;
testq.pop();
cout<<testq.top()<<endl;
testq.pop();
//Clear it and prove that it worked
clearpq(testq);
cout<<testq.size()<<endl;
//Use the second clearing function
cout<<testq2.size()<<endl;
clearpq2(testq2);
cout<<testq2.size()<<endl;
}