HFPage Class Reference

#include <HFPage.h>

List of all members.

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Detailed Description

Heap file page.

This is a wrapper around a traditional Page that adds the appropriate struture to it.

Author:

Dave Musicant, with considerable material reused from the UW-Madison Minibase project

Public Member Functions
	HFPage (Page *page)
	Creates a heap file page object by wrapping around a page object already provided.
void	init ()
	Initializes values on the heap file page as necessary.
void	setPageId (int pageId)
	Sets the page id.
int	getPageId ()
	Gets the page id.
void	setNextPageId (int pageId)
	Sets the next page id.
int	getNextPageId ()
	Gets the next page id.
void	setPrevPageId (int pageId)
	Sets the previous page id.
int	getPrevPageId ()
	Gets the previous page id.
int	getAvailableSpace ()
	Determines how much space is actually available on the page, which depends on whether or not a new slot in the slot array is needed.
void	dumpPage ()
	Dumps out to the screen the id for this page, as well as the ids for the next and previous pages.
RID	insertRecord (char record[], int recLen)
	Inserts a new record onto the page.
bool	deleteRecord (RID rid)
	Deletes the record with the given RID from the page, compacting the hole created.
RID	firstRecord ()
	Returns RID of first record on page.
RID	nextRecord (RID curRid)
	Returns RID of next record on the page, where "next on the page" means "next in the slot array.
void	getRecord (RID rid, char record[], int &recLen)
	Returns the record associated with an RID.
bool	empty ()
	Whether or not the page is empty.
Static Public Attributes
static const int	INVALID_PAGE = -1
	Value to use for an invalid page id.
static const int	INVALID_SLOT = -1
	Value to use for an invalid slot.

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Constructor & Destructor Documentation

HFPage::HFPage

(

Page *

page

)

Creates a heap file page object by wrapping around a page object already provided.

Parameters:

page

pointer to the page to be wrapped.

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Member Function Documentation

bool HFPage::deleteRecord

(

RID

rid

)

Deletes the record with the given RID from the page, compacting the hole created.

Compacting the hole, in turn, requires that all the offsets (in the slot array) of all records after the hole be adjusted by the size of the hole, because you are moving these records to "fill" the hole. You should leave a "hole" in the slot array for the slot which pointed to the deleted record, if necessary, to make sure that the rids of the remaining records do not change. The slot array should be compacted only if the record corresponding to the last slot is being deleted. (memmove, not memcpy, is used underneath since the space may overlap.)

Parameters:

rid

the RID to be deleted.

Returns:

true if successful, false if the rid is actually not found on the page.

void HFPage::dumpPage

(

)

Dumps out to the screen the id for this page, as well as the ids for the next and previous pages.

It also displays the slot array to the screen in a readable dashion. (This method merely exists for debugging and testing purposes.

bool HFPage::empty

(

)

Whether or not the page is empty.

Returns:

true if the page is empty, false otherwise.

RID HFPage::firstRecord

(

)

Returns RID of first record on page.

Returns:

the RID of the first record on the page. Returns an RID with pageId == INVALID_PAGE if the file is empty.

int HFPage::getAvailableSpace

(

)

Determines how much space is actually available on the page, which depends on whether or not a new slot in the slot array is needed.

If a new spot in the slot array is needed, then the amount of available space has to take this into consideration.

Returns:

the amount of available space in bytes

int HFPage::getNextPageId

(

)

Gets the next page id.

Returns:

the next page id.

int HFPage::getPageId

(

)

Gets the page id.

Returns:

the page id.

int HFPage::getPrevPageId

(

)

Gets the previous page id.

Returns:

the previous page id.

void HFPage::getRecord	(	RID	rid,
		char	record[],
		int &	recLen
	)

Returns the record associated with an RID.

Parameters:

	rid	the rid of interest
	record	a pre-existing array for the record to be copied into
	recLen	where the length of the record is copied into

Exceptions:

	BadPageIdException	if the page id within curRid is invalid
	BadSlotIdException	if the slot id within curRid is invalid

void HFPage::init

(

)

Initializes values on the heap file page as necessary.

This is separated out from the constructor since it actually modifies the page at hand, where as the constructor simply sets up the mechanism.

RID HFPage::insertRecord	(	char	record[],
		int	recLen
	)

Inserts a new record onto the page.

Parameters:

	record	the record to be inserted. A copy of the data is placed on the page.
	recLen	the length of the record to be inserted

Returns:

the RID of the new record

Exceptions:

PageFullException

if there is not enough room for the record on the page.

RID HFPage::nextRecord

(

RID

curRid

)

Returns RID of next record on the page, where "next on the page" means "next in the slot array.

" Remember that some slots may be empty, so you should skip over these.

Parameters:

curRid

an RID

Returns:

the RID immediately following curRid. Returns an RID with pageId == INVALID_PAGE if no next record exists.

Exceptions:

	BadPageIdException	if the page id within curRid is invalid
	BadSlotIdException	if the slot id within curRid is invalid

void HFPage::setNextPageId

(

int

pageId

)

Sets the next page id.

Parameters:

pageId

the next page id.

void HFPage::setPageId

(

int

pageId

)

Sets the page id.

Parameters:

pageId

the new page id.

void HFPage::setPrevPageId

(

int

pageId

)

Sets the previous page id.

Parameters:

pageId

the previous page id.

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