How Can I Iterate Over a `std::queue` in C ?

Iterating Over std::queue

In C , std::queue is a first-in-first-out (FIFO) container. By default, it uses std::deque as its underlying data structure. While this makes it efficient for enqueue and dequeue operations, it presents a challenge when it comes to iterating over the queue's contents.

The documentation states that "no container class is specified for a particular queue class." This means that we cannot directly access the underlying deque and iterate over it. However, there are a few ways to work around this limitation.

Using a Range-Based For Loop

If you have C 11 support, you can use a range-based for loop to iterate over the queue's elements. This approach takes advantage of the fact that std::queue provides iterators that can be used to traverse the elements.

<code class="cpp">std::queue<int> queue;

// Populate the queue...

for (const int& element : queue) {
  std::cout << element << " ";
}</code>

Using a Standard Iterator

If you do not have C 11 support, you can still use a standard iterator to iterate over the queue. The following code demonstrates this:

<code class="cpp">std::queue<int> queue;

// Populate the queue...

std::queue<int>::iterator it;
for (it = queue.begin(); it != queue.end(); ++it) {
  std::cout << *it << " ";
}</code>

Note:

While it is possible to access the underlying deque directly, it is not recommended as it can lead to undefined behavior and data corruption. Instead, use one of the methods described above to iterate over the queue's contents.

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