cpqueue.h

linux下的一款播放器

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 * Source last modified: $Id: cpqueue.h,v 1.1.1.1.50.3 2004/07/09 01:45:51 hubbe Exp $
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/*******************************************************************
 *
 *	NAME:	CPQueue.h
 *
 *	CLASS:
 *		CPtrQueue class declaration.
 *
 *	DESCRIPTION:
 *		Class declaration for a 'Queue of pointers' object.
 *		This object inherits from the CByteQueue object by
 *		overriding the GetElementSize() method, and
 *		defining it's own assignemt operator.
 *
 *	NOTES (from CByteQueue):
 *		The only time a subclass MUST provide a virtual override
 *		is for the GetElementSize() method when the subclass changes
 *		the size of queued elements.  All other virtual methods
 *		provide fully functional default behavior that will ramain
 *		functional even when the ElementSize changes.
 *
 *		The assignment operator is one of the few cases where a
 *		subclass will need to provide new functionality by virtue of
 *		inheriting from the base.  Subclasses should use the base
 *		method for assigning the bits of the base class prior to
 *		performing their own assignment related operations.
 *
 *******************************************************************/
 
#if !defined( _CPQUEUE_H )
#define _CPQUEUE_H

#include "cbqueue.h"

class CPtrQueue : public CByteQueue
{
public:
   /*
    *	These are the functions we NEED to implement to get the
	*	desired functionality out of our base class CByteQueue.
	*/

   /*
	** CPtrQueue( nMaxPtrs )
	*
	*  PARAMETERS:
	*	nMaxPtrs		The maximum number of pointers we want to be able
	*					to enqueue.
	*
	*  DESCRIPTION:
	*	Parameterized constructor.
	*	This is the primary means of constructing a Pointer Queue.
	*
	*  RETURNS:
	*	void
	*/
	CPtrQueue( UINT16 nMaxPtrs ) :
	 CByteQueue( nMaxPtrs * sizeof( void * ), sizeof( void * ) )
	{
		//	Deliberately empty
	}
	
	/*
	** UINT16 GetElementSize()
	*
	*  PARAMETERS:
	*	void
	*
	*  DESCRIPTION:
	*	Returns the size of one of our queue elements.
	*	In this case it's the size of a pointer.
	*
	*  RETURNS:
	*	The size of a queue element.
	*/
	virtual UINT16 GetElementSize() const
	{
		return( sizeof( void * ) );
	}

	/*
	** CPtrQueue &operator=( rReferent )
	*
	*  PARAMETERS:
	*	Constant reference to a queue we want to copy.
	*
	*  DESCRIPTION:
	*	Custom assignment operator allows us to assign Queues.
	*
	*  RETURNS:
	*	A reference to the queue we've assigned into.
	*/
	CPtrQueue &operator=( const CPtrQueue &rReferent )
	{
		// return( CByteQueue::operator=( rReferent ) );
		this->CByteQueue::operator=( rReferent );
		return( *this );
	}

   /*
    *	These are the functions we've added to provide
	*	some of the semantics that are in the problem
	*	domain of a queue of pointers.
	*/
	/*
	** UINT16 EnQueuePtr( pPtr )
	*
	*  PARAMETERS:
	*	A pointer we want to enqueue.
	*
	*  DESCRIPTION:
	*	Takes the value assigned to pPtr and enqueues it.
	*	
	*  RETURNS:
	*	The number of bytes we put into the queue.
	*/
	UINT16 EnQueuePtr( void *pPtr )
	{
		return( Base_EnQueueBytes( &pPtr, sizeof( pPtr ) ) );
	}

	/*
	** void *DeQueuePtr( BOOL &bIsValid )
	*
	*  PARAMETERS:
	*	A reference to a boolean flag indicating if the return is valid.
	*
	*  DESCRIPTION:
	*	Dequeues the head pointer element in the queue.
	*
	*  RETURNS:
	*	The value of the head pointer element we've dequeue'd.
	*/
	void *DeQueuePtr( BOOL &bIsValid )
	{
		UINT16		iWrote;
		void	*pPtr;

		iWrote = Base_DeQueueBytes( &pPtr, sizeof( pPtr ) );
		if (iWrote)
		{
			bIsValid = TRUE;
			return( pPtr );
		}
		else
		{
			bIsValid = FALSE;
			return( NULL );
		}
	}

	/*
	** void *PeekPtrAt( nIndex, BOOL &bIsValid )
	*
	*  PARAMETERS:
	*	nIndex		The index of the element off of the head
	*				queue element we want to peek at.
	*
	*  DESCRIPTION:
	*	Peeks at an element offset from the queue head.
	*
	*  RETURNS:
	*	The value of the pointer element we're peeking at
	*	(if it's a valid element).
	*	bIsValid is set to true or false to indicate the
	*	validity of the return value.
	*	(since a NULL pointer might be a valid queue entry.
	*/
	void *PeekPtrAt( UINT16 nIndex, BOOL &bIsValid )
	{
		UINT16		iCount;
		void	*pPtr;

		iCount = PeekAt( nIndex, &pPtr );
		if (iCount)
		{
			bIsValid = TRUE;
			return( pPtr );
		}
		else
		{
			bIsValid = FALSE;
			return( NULL );
		}
	}
};

#endif	//	!defined( _CPQUEUE_H )