What are the functions of the queue library in C++?

The queue library in C++ provides the following functionalities:

1. A queue is a type of data structure that follows the first-in, first-out (FIFO) principle, and this library provides operations for manipulating queues.
2. push() method: insert an element at the end of the queue.
3. The pop() function: removes the first element of the queue.
4. The front() function: returns the first element of the queue.
5. The back() function returns the last element of the queue.
6. empty() function: checks if the queue is empty.
7. size() function: returns the number of elements in the queue.
8. swap() function: exchange elements between two queues.
9. == and != operators: used for comparing whether two queues are equal.
10. The time complexity of push() and pop() is constant, while the time complexity of front() and back() is constant.

These features make the queue library a useful tool for handling queue data, playing an important role in a wide range of application scenarios.