C++ Queue Library - priority_queue() Function

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Description

The C++ default constructor std::priority_queue::priority_queue() constructs an empty priority_queue, with zero elements. Size of this priority_queue is always zero.

Declaration

Following is the declaration for std::priority_queue::priority_queue() constructor form std::queue header.

C++98

explicit priority_queue(const Compare& compare = Compare(),
                        const Container& cnt = Container());

C++11

priority_queue(const Compare& compare, const Container& cnt );

Parameters

• compare − Comparison object to be used to order the priority_queue.

  This may be a function pointer or function object that can compare its two arguments.

• cnt − Container object.

  This is type of the underlying container for the priority_queue and it's default values is vector.

Return value

Constructor never returns value.

Exceptions

This member function never throws exception.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::priority_queue::priority_queue() constructor.

#include <iostream>
#include <queue>

using namespace std;

int main(void) {
   priority_queue<int> q;

   q.push(3);
   q.push(1);
   q.push(5);
   q.push(2);
   q.push(4);

   cout << "Queue contents are" << endl;
   while (!q.empty()) {
      cout << q.top() << endl;
      q.pop();
   }

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Queue contents are
5
4
3
2
1