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In computer science, a double-ended queue (abbreviated to deque, / d ɛ k / DEK [1]) is an abstract data type that generalizes a queue, for which elements can be added to or removed from either the front (head) or back (tail). [2]
Such data structures may have not specified a fixed capacity limit besides memory constraints. Queue overflow results from trying to add an element onto a full queue and queue underflow happens when trying to remove an element from an empty queue. A bounded queue is a queue limited to a fixed number of items. [1]
In computer science, the word dequeue can be used as: A verb meaning "to remove from a queue" An abbreviation for double-ended queue (more commonly, deque
Container classes are expected to implement CRUD-like methods to do the following: create an empty container (constructor); insert objects into the container; delete objects from the container; delete all the objects in the container (clear); access the objects in the container; access the number of objects in the container (count).
The start and end indexes alone are not enough to distinguish between buffer full or empty state while also utilizing all buffer slots, [5] but can be if the buffer only has a maximum in-use size of Length − 1. [6] In this case, the buffer is empty if the start and end indexes are equal and full when the in-use size is Length − 1.
Most buffer overflows overwrite memory from lower to higher memory addresses, so in order to overwrite the return pointer (and thus take control of the process) the canary value must also be overwritten. This value is checked to make sure it has not changed before a routine uses the return pointer on the stack. [2]
is_empty: check whether the queue has no elements. insert_with_priority: add an element to the queue with an associated priority. pull_highest_priority_element: remove the element from the queue that has the highest priority, and return it. This is also known as "pop_element(Off)", "get_maximum_element" or "get_front(most)_element".
Canaries or canary words or stack cookies are known values that are placed between a buffer and control data on the stack to monitor buffer overflows. When the buffer overflows, the first data to be corrupted will usually be the canary, and a failed verification of the canary data will therefore alert of an overflow, which can then be handled, for example, by invalidating the corrupted data.