How do I print a queue?

Question

I am trying to print a queue below. I have tried the idea of creating a temp queue and writing into it then writing it back.

But it's not working.

Or what am I missing here?

for(int i = 1; i<myQueue.size(); i++)
{
    queue<int> tempQueue;

    cout << myQueue.front() << endl;
    MytempQueue.push(myQueue.front());
    myQueue.pop();

    myQueue.push(myTempQueue.back());
}

My queue is queue<int> myQueue;

Essentially, I want to print this queue without emptying it. But I am stuck here.

Answer 1

There is no efficient way to do this^*. But you can do the following:

1. Make a copy of the queue.
2. Iterate over the copy, printing the front, then popping it.

For example:

#include <queue>
#include <iostream>
    
void print_queue(std::queue<int> q)
{
  while (!q.empty())
  {
    std::cout << q.front() << " ";
    q.pop();
  }
  std::cout << std::endl;
}

int main()
{
  std::queue<int> q;
  for (auto i : {1,2,3,7,4,9,7,2,4}) q.push(i);
  print_queue(q);
}

^{* There's a hack using inheritance. std::queue has a protected member C which is the underlying container holding the data. You could inherit from std::queue and add methods to do the printing using C. But you have to be fully aware of the implications of inheriting from a type that is not necessarily designed for that.}

Answer 2

for(int i = 1; i<myQueue.size(); i++)

Loop should start with 0, or check condition should be <=

queue<int> myQueue;
myQueue.push(1);
myQueue.push(2);
myQueue.push(3);
myQueue.push(4);
myQueue.push(5);

for (size_t i = 0; i < myQueue.size(); i++)
{
    cout << myQueue.front() << endl;
    myQueue.push(myQueue.front());
    myQueue.pop();
}