C++ Queue Library - swap() Function

Description

The C++ function std::priority_queue::swap() exchanges the contents of two priority_queues.

Declaration

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

C++11

template <class T, class Container, class Compare>
void swap (queue<T,Container,Compare>& q1, 
   queue <T,Container,Compare>& q2) noexcept;

Parameters

• q1 − First priority_queue object.

• q2 − Second priority_queue object.

Return value

None.

Exceptions

This member function never throws exception.

Time complexity

Linear i.e. O(n)

Example

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

#include <iostream>
#include <queue>

using namespace std;

int main(void) {
   auto it1 = {3, 1, 5, 2, 4};
   auto it2 = {2, 4};
   priority_queue<int> q1(less<int>(), it1);
   priority_queue<int> q2(less<int>(), it2);

   swap(q1, q2);

   cout << "Content of q1" << endl;
   while (!q1.empty()) {
      cout << q1.top() << endl;
      q1.pop();
   }

   cout << "Content of q2" << endl;
   while (!q2.empty()) {
      cout << q2.top() << endl;
      q2.pop();
   }

   return 0;
}

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

Content of q1
4
2
Content of q2
5
4
3
2
1