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/* ========================================================================== **
* ubi_StackQueue.c
*
* Copyright (C) 1997 by Christopher R. Hertel
*
* Email: crh@ubiqx.mn.org
* -------------------------------------------------------------------------- **
* This module implements simple queues and stacks using a singly linked
* list.
* -------------------------------------------------------------------------- **
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with this library; if not, write to the Free
* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* -------------------------------------------------------------------------- **
* This module uses a singly-linked list to implement both a queue and a
* stack. For a queue, entries are added at the tail and removed from the
* head of the list. For a stack, the entries are entered and removed from
* the head of the list. A traversal of the list will always start at the
* head of the list and proceed toward the tail. This is all mind-numbingly
* simple, but I'm surprised by the number of programs out there which
* re-implement this a dozen or so times.
*
* Note: When the list header is initialized, the Tail pointer is set to
* point to the Head pointer. This simplifies the InsTail function
* at little or no cost to InsHead or Remove. The one problem is
* that you can't initialize a stack or queue headerby simply zeroing
* it out. One sure way to initialize the header is to call
* ubi_sqInit(). Another option would be something like this:
*
* static ubi_sqList MyList = { NULL, (ubi_sqNodePtr)&MyList, 0 };
*
* See ubi_sqInit() and the ubi_sqList structure for more info.
*
* -------------------------------------------------------------------------- **
*
* Revision 0.1 1997/10/24 02:47:52 crh
* Initial revision.
*
* ========================================================================== **
*/
#include "ubi_StackQueue.h"
/* ========================================================================== **
* Functions...
*/
ubi_sqListPtr ubi_sqInit( ubi_sqListPtr ListPtr )
/* ------------------------------------------------------------------------ **
* Initialize a stack & queue header.
*
* Input: ListPtr - A pointer to the list header that is to be
* initialized for use.
*
* Output: A pointer to the initialized list header (i.e., same as
* <ListPtr>).
*
* ------------------------------------------------------------------------ **
*/
{
ListPtr->Head = NULL;
ListPtr->Tail = (ubi_sqNodePtr)ListPtr;
ListPtr->count = 0;
return( ListPtr );
} /* ubi_sqInit */
ubi_sqNodePtr ubi_sqInsHead( ubi_sqListPtr ListPtr, ubi_sqNodePtr New )
/* ------------------------------------------------------------------------ **
* Insert a new node at the head of the list (push).
*
* Input: ListPtr - A pointer to the stack into which the node is to
* be inserted.
* New - Pointer to the node that is to be pushed onto the
* stack.
*
* Output: A pointer to the node that was added to the list (i.e., same
* same as <New>).
*
* ------------------------------------------------------------------------ **
*/
{
if( NULL == ListPtr->Head ) /* If list is empty, must change tail ptr. */
ListPtr->Tail = New;
New->Next = ListPtr->Head;
ListPtr->Head = New;
++(ListPtr->count);
return( New );
} /* ubi_sqInsHead */
ubi_sqNodePtr ubi_sqInsTail( ubi_sqListPtr ListPtr, ubi_sqNodePtr New )
/* ------------------------------------------------------------------------ **
* Add a new node to the tail of the list (enqueue).
*
* Input: ListPtr - A pointer to the queue into which the node is to
* be inserted.
* New - Pointer to the node that is to be enqueued.
*
* Output: A pointer to the node that was inserted into the queue (i.e.,
* the same as <New>).
*
* ------------------------------------------------------------------------ **
*/
{
ListPtr->Tail->Next = New;
ListPtr->Tail = New;
New->Next = NULL;
++(ListPtr->count);
return( New );
} /* ubi_sqInsTail */
ubi_sqNodePtr ubi_sqRemove( ubi_sqListPtr ListPtr )
/* ------------------------------------------------------------------------ **
* Remove the frontmost entry from the queue, or topmost entry from the
* stack.
*
* Input: ListPtr - A pointer to the list from which the node is to be
* removed.
*
* Output: A pointer to the node that was removed.
*
* ------------------------------------------------------------------------ **
*/
{
ubi_sqNodePtr Old = ListPtr->Head;
if( NULL != Old )
{
if( NULL == Old->Next )
ListPtr->Tail = (ubi_sqNodePtr)ListPtr;
ListPtr->Head = Old->Next;
--(ListPtr->count);
}
return( Old );
} /* ubi_sqRemove */
/* ================================ The End ================================= */
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