Implementing a personal to-do list using std::priority_queue

The std::priority_queue is another container adapter class, such as std::stack. It is a wrapper around another data structure (std::vector by default) and provides a queue-like interface for it. This means that items can stepwise be pushed into it, and stepwise be popped out of it again. What is pushed into it first, will be popped out of it first. This is usually also abbreviated as a first in, first out (FIFO) queue. This is the opposite of a stack, where the last item pushed onto it is popped out of it first.

While we just described the behavior of std::queue, this section shows how std::priority_queue works. That adapter is special, as it does not only take FIFO characteristics into account but also mixes it with priorities. This means that the FIFO principle is kind of broken down into sub-FIFO queues, which are ordered by the priorities their items have.