80 lines
3.3 KiB
C
80 lines
3.3 KiB
C
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/************************************************************************
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* *
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* file: queue.c *
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* *
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* Module implementing queue manipulation functions. The module can *
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* hold structs of any type as long as the user of the module *
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* does the appropriate casting -- all it assumes is that the first *
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* member of the struct is a pointer, 'next', to a struct. *
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* *
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************************************************************************/
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#include "queue.h"
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#include <stdio.h>
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/************************************************************************
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* queue_init() *
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* *
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* Initialise a Queue struct. *
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* We assume this will never fail - so always return 1 for success. *
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************************************************************************/
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int
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queue_init(Queue* q)
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{
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q->front = q->back = (Qitem*)0;
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return 1;
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}
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/************************************************************************
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* queue_empty() *
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* *
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* Return TRUE (i.e. non-zero) iff queue is empty; else FALSE (i.e. 0). *
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************************************************************************/
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int
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queue_empty(Queue* q)
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{
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return q->front == (Qitem*)0;
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}
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/************************************************************************
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* queue_put() *
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* *
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* Add a new Qitem to the back of the specified queue. *
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* Make sure the next pointer of the new Qitem is 0! *
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* We assume the given Qitem can be used directly by us and does not *
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* need to be copied. *
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************************************************************************/
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void
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queue_put(Queue* q, Qitem* new_item)
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{
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new_item->next = (Qitem*)0;
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if (queue_empty(q))
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q->front = new_item;
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else
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q->back->next = new_item;
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q->back = new_item;
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}
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/************************************************************************
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* queue_get() *
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* *
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* Remove the front Qitem struct from the specified queue and return *
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* a pointer to it. When we remove and return the struct we pass all *
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* future responsibility for it to our caller. Return (Qitem *)0 if *
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* queue is empty. *
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************************************************************************/
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Qitem*
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queue_get(Queue* q)
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{
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Qitem* p = q->front;
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if (!queue_empty(q)) {
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q->front = q->front->next;
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if (q->front == (Qitem*)0) q->back = (Qitem*)0;
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}
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return p;
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}
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/* end file: queue.c */
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