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A queue may be implemented as circular buffers and linked lists, or by using both the stack pointer and the base pointer. Queues provide services in computer science , transport , and operations research where various entities such as data, objects, persons, or events are stored and held to be processed later.
When only insert, find-min and extract-min are needed and in case of integer priorities, a bucket queue can be constructed as an array of C linked lists plus a pointer top, initially C. Inserting an item with key k appends the item to the k 'th list, and updates top ← min(top, k ) , both in constant time.
With a circular list, a pointer to the last node gives easy access also to the first node, by following one link. Thus, in applications that require access to both ends of the list (e.g., in the implementation of a queue), a circular structure allows one to handle the structure by a single pointer, instead of two.
Conversely, one may use either a leaky bucket approach or pointer arithmetic to generate flags in synchronous FIFO implementations. A hardware FIFO is used for synchronization purposes. It is often implemented as a circular queue, and thus has two pointers: Read pointer / read address register; Write pointer / write address register
Circular buffering makes a good implementation strategy for a queue that has fixed maximum size. Should a maximum size be adopted for a queue, then a circular buffer is a completely ideal implementation; all queue operations are constant time. However, expanding a circular buffer requires shifting memory, which is comparatively costly.
The Link fields in the records contain the XOR of the left and right successor addresses, say L⊕R. XOR of R2 (C⊕P) with the current link field (L⊕R) yields C⊕P⊕L⊕R. If the predecessor was L, the P(=L) and L cancel out leaving C⊕R. If the predecessor had been R, the P(=R) and R cancel, leaving C⊕L.
The void pointer, or void*, is supported in ANSI C and C++ as a generic pointer type. A pointer to void can store the address of any object (not function), [a] and, in C, is implicitly converted to any other object pointer type on assignment, but it must be explicitly cast if dereferenced. K&R C used char* for the “type-agnostic pointer ...
The queap keeps a pointer to the minimum element stored in the list. To add element x to list l , the element x is added to the end of the list and a bit variable in element x is set to one. This operation is done to determine if the element is either in the list or in a 2–4 tree.